THE INFLUENCE or GIBBERELUN on THE VEGETATIVE GROWTH RESPONSES OF CERTAIN woonv PLANTS SUBJECTED TO VARIOUS PHOTOPERIODS AND THERMOPEPJODS, WITH SPECIAL REFERENCE To CATALPA SPECIOSA Thais Ior tho Dogma of Ph. D. MICHIGAN STATE UNIVERSITY George Randall NIch 1961 This is to certify that the thesis entitled THE INFLUENCE OF GIBBERELLIN ON THE VEGETATIVE GROWTH RESPONSES. OF CERTAIN MOODY PLANTS SUBJECTED TO VARIOUS PHOTOPERIODS AND THERMOPERIODS, WITH SPECIAL REFERENCE TO CATALPA SPECIOSA presented by GEORGE R. MCVEY has been accepted towards fulfillment of the requirements for Ph.D. Horticulture degree in / r , / . " / 1'4 JLL’v' l ’ V v Majorvprofessor If "I A A Datererl/u-I’ “\ '~ '/ g. -/ I . 0-169 LIBRARY Michigan State University ABSTRACT THE INFLUENCE OF GIBBERELLIN ON THE VEGETATIVE GROWTH RESPONSES OF CERTAIN WOODY PLANTS SUEJECTED TO VARIOUS PHOTOPERIODS AND THERMOPERIODS, WITH SPECIAL REFERENCE TO CATALPA SPECIOSA by GEORGE RANDALL never Certain woody plants (Catalpa speciosa, ggriodendron Tulipifera, Viburnum Csrlesii, Acer saccharum, Pinus sylvestris, Byracantha coccinea Lalandii, gyringg vulgaris and Buonymus Fortunei vegetus) exhibiting a known photoperiodic response and a broad range of temperature adaptations were selected for this study. The objective was to determine the degree of replacement by gibberellin of the photoperiodically and/or thermo- periodically dependent vegetative responses. Shoot extension and dry weights of various plant parts, from plants subjected to photOperiods of 9 (short) and 18 (long) hours and night temperatures of 40°? (low) and 70°? (high) in the presence (50 ppm) and absence of gibberellin, were used as a criteria for determining response differences. Radio-phosphorus (P32) was applied to the roots of Catalpa speciosa held at different temperatures, or to the foliage to evaluate alterations in metabolism induced by gibberellin or photoperiod. Gibberellin simulated the shoot extension responses of long days, low, or high night temperatures in those plants which responded most favorably to these environments. The degree of the replacement was generally greatest in those species which exhibited a rapid and an extended shoot elongation response to long days or high temperatures. by GEORGE RANDALL McVEY In contrast, an inhibition in dry weight accumulation in the roots, leaves and old shoot wood, accompanied increases in shoot elongation and dry weight of shoots. In species exhibiting a moderate rate of shoot elongation, the replacement of the environmental requirements for vegetative extension by gibberellin was not exaggerated, but was comparable to that of long days or high night temperatures. In addition, the dry weight accumulation in the leaves and roots was not inhibited as extensively as in those plants that exhibited a rapid and extended response to high temperatures and long days. Dormancy of the first flush of growth was delayed by gibberellin in the presence of low night temperatures and short days in Age; saccharum while gibberellin in die presence of low night temperatures prevented dormancy of the second flush of growth in Euonymus Fortunei vegetus and Liriodendron Tulipifera. Gibberellin was also effective in breaking summer dormancy in 5525 saccharum at the high night temperatures. Alterations in the metabolism by gibberellin suggest that the principle source of carbohydrates for shoot extension is derived from reserves in the old wood. A gibberellin induced increase in leaf area in some species partially spared the carbohydrate reserves. Differential rates of uptake and distribution of phosphorus by roots of Catalpa speciosa at different temperatures suggest that the carbo- hydrates in the roots held at high temperatures were insufficient to supply the energy required for active absorption, but were adequate at the low root temperatures. There was inhibition in phosphorus uptake by the roots of Catalpa gpeciosa plants pretreated for 6 weeks to long by GEORGE RANDALL MCVEY days and gibberellin, as compared to plants exposed to long days but not treated with gibberellin. There was no inhibition of phosphate uptake after 3 weeks of pretreatment. In Catalpa plants exposed to short days and to gibberellin for 3 weeks, more phosphorus was trans- ported from the roots to the shoots. Thus, gibberellin treatment simulated the long day effect. Six weeks of pretreatment with gibber- ellin, however, had no effect. These observations, as well as many others, strongly suggest that endogenous levels of growth regulators are in a constant flux throughout the season. Thus the response to gibberellin will vary during the progressive stages of physiological deveIOpment in a given season. A control mechanism of growth and development, based on the progressively changing levels of endogenous gibberellins and inhibitors in woody plants is prOposed. In the first scheme, plants grown under low night temperatures or long days exhibit, after the initial stage of growth in the spring, an increase in the level of endogenous gibberellins accompanied by a decrease in the level of endogenous inhibitors as the season progresses from spring to fall. In scheme 2, after the initial stages of growth, an exposure of woody plants to high night temperatures or short days results in a reciprocal pattern. As the season progresses from spring to fall there is an increase in the level of endogenous inhibitors accompanied by a decrease in the quantity of endogenous gibberellins. The relative concentrations, as well as the season of the year when the gibberellin-inhibitor ratio is in balance will vary with the species. y by GEORGE RANDALL McVEY A delayed balance in the endogenous gibberellin-inhibitor ratio, accompanied by a rapid synthesis or a high concentration of endogenous gibberellins in the spring results in a rapid shoot elongation. Conse- quently, an exogenous source of gibberellin in the spring results in abnormally rapid vegetative extension accompanied by a marked inhibition of dry weight accumulation in leaves and old wood. In contrast, a slow rate of synthesis of gibberellins in the spring accompanied by either a rapid or a slow balance in the endOgenous gibberellin- inhibitor ratio results in a slow rate of vegetative extension for a short or long period of time, respectively. Thus an exogenous application of gibberellin results in a continuation of a moderate rate of vegetative extension beyond the interval of time in which growth would otherwise occur, accompanied by a slight inhibition of dry weight accumulation in leaves and old wood. THE INFLUENCE OF GIBBERELLIN ON THE VEGETATIVE GROWTH RESPONSES OF CERTAIN NOODY PLANTS SUEJECTED TO VARIOUS PHOTOPERIODS AND TRERHOPERIODS, WITH SPECIAL REFERENCE TO CATALPA SPECIOSA By GEORGE RANDALL McVEY A THESIS Submitted to the School for Advanced Graduate Studies of Michigan State University of Agriculture and Applied Science in partial fulfilhment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Horticulture 1961 TO MY WIFE ii Acknowledgements The author wishes to express his sincere appreciation to Dr. Sylvan H. Wittwer for his accurate guidance, encouragement and invaluable suggestions during the course of this investigation and preparation of the manuscript. Sincere thanks are expressed to Dre. 3. K. Ries, A. L. Kenworthy and D. H. Dewey for their interest and technical assistance during the investigation. Appriciation is also extended to the members of the guidance committee: Bra. 8. Davidson,‘H. J. Bukovac, C. M. Harrison, G. P. Steinbauer and R. C. Beeskow for their helpful advise. Grateful acknowledgement is extended to John E. Carver and C. Edward Johnson of the Michigan Department of Agriculture Seed Laboratory, East Lansing, for their c00peration in the investigation. The author gratefully appreciates the financial assistance of the Chas. Pfizer Co., Brooklyn, New York, that made this study possible. Finally the author wishes to extend his personal thanks to James A. Simona, James T. Converse, Mary Y. Chapman and Richard D. Wilson for their assistance during the preparation of the manuscript. iii TABLE OF CONTENTS Page OOOOOOOV111 OOOOOOOOOOOOOOOOOOOOOO LIST OF TABLES.... .......... . LISTorFIMSOOOOOOOOOOOODOOOOO00.. 0.0.09.0... 1x :ImmucrIONOOOOIOOOOO 00000 OOOOOOGOCOO HumorLIEMMOOOCCOOOOIOOOGGO 00.0.00... 3 I. Photoperiodism in Woody Plants................. A. Shoot DevelopuntIO0.00...OI.OOOOOOOOOODOOOOOOOOOOOOI B. Root Development....................... C. Induction and Cessation of Dormancy.................. D. Hardinea.....0.0.0.0000....0.00....OOOIOOOOOOOOOOOCO. lo 3. Leaf Size and Horphology............................. 10 P. Seed GemnationOOOOOO..0...OOOOOCOIOOOOIOOOOOIOOO... 11 II. Thermperiwiam in "My Pl‘nC'COO...IOOOOOOOOOOOOOOOOOOO 13 A. Shoot DevelwncOOOOOOOOOOO0..OOOOOOOOOOOOOOOOOOI... 13 B. Root DevelOpment..................................... 15 C. Induction and Cessation of Dormancy.................. 16 Effects of Gibberellin on Growth and DeveIOpment of III. "my PlantsOOOOOOCOOOOOCOOOOOO0.00000000CDOOOOOOOOO0.0.. l7 17 A. HistoryOCOOCOOOOOOCOOOOOOODOOI0.0... 8. Shoot DevelomnCOOO00.0.0000...OOOOOOOOOOOOOOOOOOOOO 18 C. Root DeVElopflent...OOOOOOOOOOOOOOOOOOOOOOOOOIOOIOOOOO 31 D. Induction and Cessation of Dormancy.................. 34 E. Hardine.300000000000000.0..O...OOOOOOOOOOOOOOOOOOOOOO 39 F. Le‘f Size and “orphOIOBYO...O...OOOOOOOOOOOOOOOOOOOOO 39 Go Plant cmo‘itionssssssossoosssssosssssssssososoossg. (.1 43 IOOOOOOOO 44 H. Chlorosis.............. 1. Seed Germination.......... iv STATEMENT OF THE PROBLEM ........... .................... ... .. EXPERIMENTAL............................... ..... .... ...... . . I. VEGETATIVE MODIFICATIONS BY GIBBERELLIN.... ...... . ....... A. Materials and Methods................................ 1. Plant Material and Cultural Techniques........... 2. Environmental Conditions......................... 3., Method of Treatment................ ...... ........ 4. Data Recorded.................................. . 5. Analysis of Variance............................. 6. Catalpa speciosa Seed Germination................ B. Results............................................. 1. CONTENTS CONT'D Vegetative Modifications of Shoot Growth and DevelopmntOOoo........OOOOOOOOOOOOOOOOOO00.. 8. Shoot Exten31°n000000000 b. Node ForutionCOOCOOCOOCOCCC......OOOCOOOCOOO Degree of Replacement by Gibberellin of the Environmental Factors Which Influence Shoot Elongation and Node Formation................ Modifications of the Induction and Cessation Of Dormcy00.0...0.0.......OOOOOOOCOOOOOOOOOO... a. Breaking of Dormmncy in Buds................. b. Breaking of Dormancy in Seeds................ Accumulative Vegetative Modifications by GibberellinOOOO...I...........OIOOOOOCCOOOOIOOOOO a. Shoot Extension and Dry Weight............... b. Leaf Area and Dry Weight..................... c. Root Dry "eight00......OCOOOOIOOOOO. 48 SO 57 57 59 60 61 61 61 69 74 78 78 83 83 85 88 89 CONTENTS CONT'D Page d. Total Dry weightOOOCOOOOOOOOOOIOOOOOCOOOOOO. 89 e. Degree of Replacement by Gibberellin of Environmental Factors Which Influence the Accumulative Vegetative Growth Response.OOOCOOOOIOOOOOOOOOOOOOOOOOOOOIOO... 92 II.‘ ALTERATIONS IN THE METABOLISM OF CATALPA SPECIOSA AS 103 ImUBNCED BY GlnnxnuIN....IOOOOOOOOGIOOOOO0.0.0.9.... A. C. 1. 2. 1. Modifications of the Che-deal Composition........... Materials and Methods........................... Results......................................... ‘Modifications of Poliar Absorption and Transport.... Modifications by Gibberellin and PhotOperiod.... . Materials and Methods....................... b. Re.ult.0030000.0.00...OOOOOOOOOOOOOOOOOOOOCO Modifications by Gibberellin and Leaf Position.. a. Materials and'Methods....................... b. Raaulc'OOCOOOOOODO.........OOOOOOOOOOOOOOOOO Modifications of Root Absorption and Transport...... 1. Rs by b. to of Absorption and Transport as Influenced Gibberellin............n.......o........o.... Materials and Methods....................... Result...........OOOCOOOOOI0.000.000.0000... Rate of Absorption and Transport as Influenced by a. b. Gibberellin and Root Temperature............. Materials and Methods....................... Re.u1c.0000...00............OOOCOOOOOOCOOOOO Rate of Absorption and Transport at Different Root Temperatures as Influenced by Precondi- tioning to Gibberellin and Photoperiod.......... b. mter1.h‘nd“ethodaOCOOOOO00.000.00.000... ResUIt‘OO......COOOCOOIOO0.00.00.00.00...... vi 103 103 104 107 107 107 110 112 112 113 116 116 116 118 120 120 121 125 125 129 CONTENTS CONT'D Page DISCUSSIONsOOOsessoososossesssssoooases ossssssossasssossssossss 133 I. Genet-.1 com1derat1°fla0OOIOOOOOOOOOOOOOOOOIOOOOOOOOOOOOI 133 II. Replacement or Partial Replacement of the PhotOperiodic or Thermoperiodic Requirements by Gibberellin..... ..... 134 III. Interrelationships Between Gibberellin and Endogenous erth Regul‘tor.000000000000OOOOOOOOOOOCOOOOCOOI0.00... 135 A. Modifying Influence of the PhotOperiod on Gibberellin Anti-”0.0.0.000.........OCOOOOOOOO0.0... 135 B. Modifying Influence of the Thermoperiod on Gibberellin Action....IOOOIOOOCOOOO0.0.00.00....0... 143 IV. Alterations in the Metabolism by Gibberellin............ 150 A. Modifications of Mineral Absorption and Distribution.0.0.0.0.........OOOOOOOOC....0.00.00... 150 1. Dry weight Di’tributionsosoa000.00.000.00...sees 150 2. Mineral Distribution in Catalpa speciosa........ 152 3. Absorption and Transport of Labelled Phosphorus in Catslps speciosa.................. 153 SWYIOOOOOOOIOOOO 0.. 0.00.00.00.00...OOOOOOOOOOOOOOOCOOO 156 LITERATURE CImOOOOOOOOOOOOOOOOOO o...........OOOOOOOOOOOOOOOOO 158 vii Table II III IV VI VII VIII IX XI LIST 0P TABLES Page The Photoperiodic Response, Hardiness Zone, Description at the Time of Treatment, and Early Chronology of cert‘in wowy Pl‘nt‘OI......OOOOOOIOOOOIOOOOIIOOOOIIO... “9 Duration of the First Plush of Growth of Certain Woody Plants as Modified by Gibberellin, PhotOperibd “d Tm‘r‘tureOOCC......OOCCOOOCQQOO0..........IOOOOOOO 79 Periodic and Total Germination of Cstalpa specioss Seed within Specific Time Intervals After Seeding, as Modified by Temperature and Gibberellin.......................... 84 Modifying Influence of Gibberellin, PhotOperiod and Temperature on the Distribution of Nitrogen and Ash in c‘h‘la. 'Eec1o..000000000O..........OCOOOOOOCQOQOOOO. 105 Polisr Uptake and Distribution of P32 and Vegetative Growth by Cstslpa spgciosa as Modified by Gibberellin am Photop‘rinOOIOOOO0.0000.0.0.0...IIOODOOOOOOOOOOOO. 111 Rate of Uptake and Distribution of Poliar Applied P32 by Catalpa specioss as Affected by Leaf Position ‘nd Gibberellin.0.00.00.........OOUOOCOOCOCIIOC0.0000... 115 Rate of Uptake and Distribution of Phosphorus by Roots of Catalpa speciosa as Modified by Gibberellin.... 119 The Effects of Root Temperature on the Uptake and Dis- tribution of Phosphorus by Roots of Cstalpa,gpeciosa as Modified by a Poliar Spray of Gibberellin............ 123 Root Temperature Coefficients for Uptake and Dis- tribution of Phosphorus by Roots of Catalpg speciosa “Madified by GibberellinOOOOOI...0....IOOOOOOOOOOOOOOO 124 The Modifying Influence of Three and Six.Weeks of Preconditioning to Gibberellin and PhotOperiod on the Percent of Phosphorus Translocated to the Shoots from the Roots of Catalpa speciosa Exposed to Different Root Temperatures........................................13l The Modifying Influence of Six Weeks of Preconditioning to Gibberellin and Photoperiod on the Uptake and Dis- tribution of Phosphorus by Roots of Catalpa gpeciosa.... 132 viii Figure 10 11 12 13 LIST OF FIGURES Page Punt chisng AreaOOOOOOOCIDOOOOOO......IOOOOIIOIOIOOO... 51 Methods Employed in Satisfying the ThermOperiodic and Photoperiwic Requirmnt...00000.00......OIOOOOOOOOIOOI. 53 Maximum, Minimum and Hour 1y Temperatures Averaged Weekly for Eight Woody Plants Subjected to Low and High Night Tmer‘ture‘OOOOOOIIOOOOOOOOOOCOIOOOOOOI00.0.0.0... 54 Typical Air and Soil Temperatures During a Selected 24 Hour Period for Plants Exposed to Low and High Night Tmer‘turesOO......OOOOIOO...0...........OOOOOOOUOIOOOOO SS Comparative Growth Rates of Terminal Shoots of Catalpa, Acer, Pyracantha and Syrigga as Influenced by Gibberellin, Photoperiod and Temperature.............................. 62 Comparative Growth Rates of Terminal Shoots of Liriodendron, Pinus, Viburnum and Euonyggs as Influenced by Gibberellin, Photoperiod and Temperature.............. 63 The Modifying Influence of Gibberellin on the Thermo- periodic Response of Shoot Extension in Certain Woody Punt‘OOOOOCOOOOOCO00.0.00...I.0.........OOOOOOOOCOOOOOOO 68 Comparative Rates of Node Formation in Tenninal Shoots of Catalpg,.Acer, Pyracantha and Syringe as Influenced by Gibberellin, PhotOperiod and Temperature.............. 70 Comparative Rates of Node Formation in Termdnal Shoots of Viburnum” Liriodendron and Euonyggg as Influenced by Gibberellin, Photoperiod and Temperature.............. 71 The Modifying Influence of Gibberellin on.the Thermo- periodic Response of Node Formation in Viburnum” Acer, 8251538 and EumIEE‘OOOOOOIOOCICO..........OOOOOOOOOOOOOO 73 The Extent to Which Gibberellin Replaced the Photo- periodic and Then-aperiodic Response of Terminal Growth in Certain Woody Plants During the Growing Season........ 76 The Extent to Which Gibberellin Replaced the Photo- periodic and Thermoperiodic Response of Node Formation in Certain Woody Plants During the Growing Season........ 77 ‘Modifying Influence of Gibberellin, Photoperiod and Temperature on the Number of Growth Flushes, Period of Dormnncy and Shoot Extension of Acer, Buonxggg, Syrigga and Liriodendron................................. 80 ix Figure 14 15 16 17-24 25 26 27 Page Growth Differences of Certain woody Plants, that Deve10ped Between April 26 and September 15, as Influenced by Gibberellin, Photoperiod and Temperature.............................................. 86 The Modifying Influence of Gibberellin on the Photo- periodic and Thermpperiodic Responses of Various Plant Parts in Certain woody Plants............................ 91 The Extent to Which Gibberellin Replaced the Photo- periodic and Thermoperiodic Responses of Specific Vegetative Phenomena in Certain woody Plants............. 94 ‘Hodifying Influences of Gibberellin, PhotOperiod and Temperature on Root, Shoot and Leaf Development in cerc.in “my P1.nt.0000.0............IOOOOOOOOOOOOIOQOOI 95 A Refrigerated and Heated Water Bath for Exgosing Catalpa to Various Root Temperatures and P3 Solutions... l27 Catalpa speciosa Precondition to Gibberellin (100 ppm as a Foliar Spray) and Photoperiod (9 and 18 hours) During an Interval of Six‘Heeks.......................... 128 Proposed mechanism of Action Controlling the Growth and Development of the Eight woody Plants Investigated... 139 INTRODUCTION Since the beginning of time one of man's principle objectives has been to promote and regulate the growth of plants. With the advent of IAA, NAA and 2,4-D and many other chemical substances, possibilities of modifying the behavior of plants for better survival under adverse weather conditions were introduced. Many new substances have been tested to determine their growth regulatory properties. Of primary interest in both applied and basic research are the gibberellins. These compounds have challenged many former concepts held by plant physiologists, necessitating changes in many theories relating to plant growth and development. In ornamental horticulture, growth regulators offer promising avenues of approach to some of the present day problems. These include the control of flower and fruit development, increasing the rate of growth, expanding the area of adaptation, increasing the rooting and ease of grafting of stem pieces, improving the esthetic value, regulation of the time of dormancy, and as a tool to evaluate the physiology of growth and develOpment. Research in the above areas has been very limited primarily because of the small number of graduates in ornamental horticulture and the lack of funds. Within the past few years, however, there has been an increasing interest in the response of woody plants to photOperiod and plant growth substances. Findings thus far have been very stimulating for further activity. Home owners are beginning to move the center of their recreation from the playroom to the playlawn. Pride in the lawn 2. and shrubbery surrounding the home has intensified the demand for more knowledge of woody ornamental plants. There is need to solve such problems as iron chlorosis, sun scald, better methods of trans- planting, controlling flowering, reducing maintenance cost, and many others. The gibberellins, as a tool, offer the possibility of evaluating the growth and deveIOpment of woody plants. Early research reports with the gibberellins gave strong indications that these chemicals, if prOperly used, might revolutionize many of our cultural practices and also solve some of the physiological problems encountered in the field of ornamental horticulture. With interest in the gibberellins, it became increasingly evident that research was needed in the field of ornamental horticulture to evaluate these compounds. Preliminary reports presented many interesting possibilities as to how the gibber- ellins might be of value to the nurseryman. Also, their effects on growth and flowering warranted a re-evaluation of the response of woody ornamental plants to photoperiod and temperature. Consequently, a series of studies were initiated to evaluate the response of several woody plants to gibberellin, photOperiod and temperature separately and in combination. Dry matter accumulation, shoot elongation, leaf area, period of active growth, and node number were used to measure external growth responses, while uptake and distribution of radioactive phosphorus, ash content, and percent nitrogen were indicative of internal changes in plant metabolism. REVIEW OF LITERATURE I. PhotOperiodism in Woody Plants A. Shoot Development The response of woody ornamental plants to photOperiod is not a new concept, since it was reported as early as 1914 by Klebs (1914) that beech, oak, ash and hornbeam grew all winter when placed under continuous lighting. In the early twenties, Garner and Allard (1920) demonstrated conclusively the phenomenon of photOperiodism in plants. They used the term photoperiod to designate the favorable length of day for an organism, and photOperiodism‘was suggested "to designate the response of organisms to the relative length of day and night". Early interest in photOperiodism was principally concerned with the flowering response and relatively little attention was given to the vegetative response. In their survey of plant material, Garner and Allard (1923) made note of the vegetative response of Egg; 313255 and Liriodendron Tulipifera to long days. Liriodendron Tulipifera was placed in the greenhouse in September and a renewal of growth occurred following exposure to long days. Short days (10 hours) caused a cessation of upward growth. Almost 15 years elapsed before interest was again directed toward the vegetative response, since the flowering response, as altered by photoperiod, was given first priority. In the late thirties, Gustafson (1938) and Skinner (1939a) reported a vegetative response when cuttings of Leucothoe Catesbaei, Rhododendron ponticum, Rhododendron roseum elegans and Pinus resinosa seedlings were exposed to long days (16 hours of light). In the early forties, interest in this area of study was 3. 4. intensified by Wareing, Chouard, Kramer, Perlmutter and Darrow. By the late forties and early fifties the real significance of the vegetative response of woody plants to photoperiod was well realized. Nitsch, Downs, Davidson, Borthwick, Kramer, Waxman and others have devoted many hours of study to this area of research. Yet, evidence is still vague and much more work is greatly needed. According to reports to date, long days will cause shoot elongation of woody plants if the day length is longer than the critical photo- period. (Klebs, 1914; Garner and Allard, 1920, 1923; Gustafson, 1938; Skinner, 1939b; Perlmutter, 1939; Perlmutter and Darrow, 1942; Wareing, 1948; Wareing, 1950; Shanks and Link, 1951; Piringer and Stuart, 1955; Zahner, 1955; Downs and Piringer, 1958; Nitsch and Nitsch, 1959; waxman, 1959) At day length of less than the critical duration growth may be proportional to the photoperiod imposed (e.g. {£335 sylvestris) (Wareing, 1948). A number of methods have been used to prolong day lengths beyond the critical photoperiod such as with continuous electric lighting (Klebs, 1914), an interrupted dark period with one-half hour of light, (Wareing, 1948; Zahner, 1955; Waxman, 1958), or a long day of 16 hours followed by 8 hours of darkness and other degrees of variation between day and night. The optimum photOperiod for mdnimum growth and vegetative extensions, of course, varies with species, but generally is greater than 12 hours and may be as high as 24 hours in some of the pines (Downs and Piringer, 1958). A photOperiod longer than the critical day length may cause such varied responses in shoot development as increasing dry weight (Downs and Piringer, 1958; Perlmutter, 1939), increasing internode length and number of nodes (Wareing, 1950), prolonging the phase of juvenile growth. 5. (Downs and Piringer, 1958), eliminating the necessity for freezing temperatures in breaking dormancy (Gustafson 1938), inhibit the development of buds (Piringer and Stuart, 1955), or may not be effective in elongation of shoots which have a predetermined growth (Olmsted, 1942; Wareing, 1948). Excellent reviews concerning the shoot response of woody plants to photoperiod have been prepared by Nitsch (1957a) and Wareing (1956). B. Root Development Root development of woody plants as affected by photoperiod has not been as thoroughly investigated as shoot growth. Most of the reports available today are concerned with the rooting of cuttings under long or short days. For instance, (Skinner, 1939a) reported that seven hours of additional light improved the rooting of leaf bud cuttings of Rhododendron, but Snyder (1955) reported no significant effects of long days on the rooting of cuttings or growth of mature Taxus cuspidata plants. Not all plants exhibit increased rooting under long days (Lanphear and‘Meahl, 1959). Cuttings of Pieris japonica and Pyracantha costings Lglandii did not respond to photoperiodic treatment while Euonymus Fortunei coloratus, Ilex crenata convexa, Ilex Qpagg, Juniperus hgrizontalis plumosa, and Rhododendron mucronulatum cuttings rooted well under an extended photOperiod. Root development of established plants of Pinus_sylvestris is not affected by the photoperiod (Wareing, 1950). Weaver and Himmel (1929) reported earlier that growth of both taps and roots of certain herbaceous craps were greatly retarded under short days. In contrast, Roberts and Struckmeyer (1946) found that plants which blossom under long photoperiods 6. have fewer roots, indicating a correlation between flowering and limited root develOpment. The literature is far too deficient in this area to draw any conclusive evidence as to the effect of photoperiod upon root deve lopment . C. Induction and Cessation of Dormancy One of the principal areas of interest in relation to photOperiod and woody plants is the phenomen of dormancy. Dormancy will be interpreted in the same sense as reported by Doorenbos (1953). "Dormancy is applied to all cases where a living tissue predisposed to elongate does not do so." He subdivides dormancy into three categories: 1 - Imposed dormancy - dormancy imposed by external environmental conditions such as drought or cold. 2 - Summer dormancy - dormancy imposed by internal causes, namely physiological processes inside the plant, but outside the bud, thus an indirect influence of the environment. 3 - Winter dormancy - dormancy also caused by internal causes, but the inhibitor system is inside the bud, thus again an indirect influence of the environment. Short days will cause the onset of dormancy in many plants while long days delay or break dormancy. (Lammerts, 1943; Chouard, 1946; Wareing, 1948; Wareing, 1951 and 1953; Doorenbos, 1953; Vegis, 1956; Downs and Borthwick, 1956; Downs, 1957; Hellmers, 1959a; and Rawase and Nitsch, 1958) Other plants, such as Pyracantha coccinea, do not become dormant when exposed to short days (Nitsch, 1957b). 7. Plants induced into dormancy first develop leaves of darker green color, then shoot elongation ceases. (Garner and Allard, 1923; Downs, 1957; and Olmsted, 1951) The temminal bud may die and abscission occurs at the point of blackening just below the bud (e.g. 9355125), or the terminal bud mmy just stOp expanding leaves and internodes with no bud scales forming (e.g. Liriodendron and Begglg). Other species may form a terminal bud completely with bud scales (Downs, 1957). Needle and internode extension is reduced in Pinus sylvestris (Wareing, 1949). Leaf abscission generally follows under naturally induced dormancy with the youngest leaves remaining attached a few days longer (e.g. Sugar maple) (Olmsted, 1951). The degree of dormancy induced by short days varies with duration under short days, species, and many other factors. Downs (1957) reported two extremes which might exist in dormant plants. Some species develOp dormancy which is not broken by long days while in others, growth resumes immediately upon transfer to a long day. Between the two extremes lie some species which resume growth from lower buds and from the terminal bud only if the plant is defoliated and placed under long days. Catalpa when placed under short days becomes dormant but when placed under long days will initiate a new flush of growth as long as the short days imposed do not exceed 2 to 3 weeks. As the number of short days increase, a greater number of long days is required to break dormancy until long days are no longer effective. Liriodendron is not as sensitive to short day inhibition, as growth resumes readily when placed under long days regardless of the number of short days imposed (Downs, 1957). 8. In contrast Weigela does not require long days to break dormancy since removal of the uppermost fully expanded leaves will cause a resumption of growth even under short days (Downs, 1957). Kramer (1957a) reported that growth might cease and start again during the growing season several times. If conditions are favorable for the formation of an inhibitor, growth would then cease permanently. In this respect, Doorenbos (1953) reported that summer dormancy was caused by (1) a lack of a stimulus from the roots or (2) an inhibitory influence from the leaves. The second flush of growth (Lemmas shoot) may occur so rapidly as to show only a few very short internodes with small leaves which have morphological characteristics different from the first flush. Acer saccharum'will initiate a second flush of growth under long days (20 hours) (Olmsted, 1951). Olmsted (1951) also reported that long days will cause a temporary stimulation of buds which are not in deep rest. Irrespective of photOperiod, Acer saccharu! will eventually become dormant. The difference being, long days will stimulate a second flush of growth while short days will not. (Olmsted, 1942). l The duration of the short day exposure required to induce dormancy varies with species. Liriodendron will stOp growth completely after only ten 8 hour days while ELEEE requires 20 weeks of 8 hour days for the same response. Betulalpubescens is almost as sensitive to short days as Liriodendron since less than one week under 10 hour days will slow down growth and is stapped completely after 2 weeks (Rawase and Nitsch, 1958). In general, most woody plants require 4 weeks of 8 hour days before they stop growth (Downs and Borthwick, 1956). 9. The natural means of breaking dormancy in many woody plants is by chilling during the winter months. The chilling requirements of most woody plants are not known and the chemistry involved in breaking dormancy is even more obscure (Went, 1953). Went (1953) attributed the breaking of dormancy to either (1) starch hydrolysis at low temperature, (2) removal of inhibitors from the buds or branches, or (3) development of growth stimulating substances in the buds. Cool temperatures have been reported to hasten and facilitate the breaking of dormancy (Wareing, 1951) and in some species, cannot be replaced by long days (e.g. Hydrangea macrophylla) (Piringer and Stuart, 1955). In contrast, long days are effective in stimulating growth of non- chilled embryo cultured peach seedlings (Lammerts, 1943), and buds of Eggs; sylvatica which do not require a chilling period (Wareing, 1953). Eggert (1951) reported that all buds on the same tree do not require the same degree of chilling to break dormancy. Lateral leaf buds were found to require more chilling in order to break dormancy than termdnal or spur leaf buds or flower buds. Long days are more effective in breaking dormancy during the earlier part of the growing season than the latter. Wareing (1951) reported that seedlings of giggg,§ylvestris could be induced into active growth during the summer months by exposure to long days but not during the fall. In the spring, the cambial activity is sensitive to both long and short days provided there is an actively growing shoot present. Short days are only effective at the end of the growing season in inhibiting cambial activity in Pinus sylvestris (Wareing, 1949). Long days appear to be a temporary stimulus for elongation of buds not in deep rest (Olmsted, 1951). 10. D. Hardiness Long days are very effective for increasing the rate and total growth of woody plants, but often winter hardiness is reduced. Wareing (1948) found that southern species grown in more northern latitudes exhibited signs of frost damage because of the longer natural photOperiod, whereas northern species grown in the south produced less total growth. As early as 1937, Kramer (1937) found that growth of Agglig_which was stimulated by electric lights was killed by freezing temperatures. In contrast, short days will increase maturity in Hydrangea (Piringer and Stuart, 1955). Olmsted (1942) reported that long days will increase cambial activity and decrease frost resistance. Irgens-Moller, (1958) found that plants growing in northern regions of the hemisphere have a greater sensitivity to artificially induced short days. This is an important component to survival in northern latitudes. E. Leaf Size and Morphology Leaf size and morphology is markedly affected by photOperiod and intensity of light. Garner and Allard (1920) reported that reduced light intensity tended to increase the superficial area of the foliage of many species. The leaf may be less compact with a reduction in the thickness of the blade. Long days have been reported to increase the leaf area per plant in Vaccinium,(Perlmutter and Darrow, 1942) and Pinus sylvestris (Wareing, 1950). Leaf growth under long days can be reduced by the application of an anti-auxin (Lona, 1959). Short days, in contrast to long days, will cause the production of a tougher 11. textured and thicker leaf in Phaseolus multiflorus. Palisade cells were noticeably longer under short days as compared to long days (Tincker, 1928). F. Seed Germination Germination of seeds of woody plants respond in some cases to the photoperiod imposed. Undoubtedly, seeds of many woody ornamentals are photoperiodically responsive but there are very few reports available. Birch (Betula pubescens) was extensively investigated by Black and Wareing (1955) mainly because the non-chilled resting buds of dormant plants were induced to expand by long days. This indicated that possibly seed would respond similarly. Thus it was discovered that birch seed exhibited a definite response to photoperiod. Under long days, or short days followed by a short dark period, germination was greatly increased at 15° C after 8 photoperiodic cycles as compared to short days or long days followed by a long dark period. The photo- periodic effect, however, was not always critical. If the seeds were pre-chilled or germinated at a relatively high temperature (20° C), the necessity for the 8 photoperiodic cycles was negated. The pre-chilling or high temperatures (20°C), however, were not effective unless the seed had previously been exposed to light. Thus it appears that the reactions initiated by the light were promoted at the higher temperature. If a low temperature (50 C) during the light period is used, germination will respond to the photoperiod imposed if the dark period is at a higher temperature (200 C). The higher temperature imposed during the dark period should continue for several days and be imposed immediately after exposure to the photoperiod at lower temperatures for maximum Stimulation. 12. Vaartaja (1956) confirmed the results of Black and Wareing (1955) although his environmental conditions were not as well controlled. In addition, he found that germination was slightly correlated to the illumination intensity. Germdnation was reduced when the intensity was above or below 800 foot candles at 20 to 300 C irrespective of the photOperiod. At temperatures of 10 to 25° C, a higher light intensity (1000 foot candles) was more favorable. Stearns and Olson (1958) testing seeds of 132g; canadensis, found short days of 8 to 12 hours were capable of hastening germination at 22° C. Temperature above or below this Optimal range delayed or decreased genmination. The effects of high temperatures in inhibiting germination were partially overcome by exposure to long days, but short days were not effective at high temperatures. The short day-high temperature inhibition of seed germination was reversed by placing the seeds at a lower temperature (17° C). As in birch, chilling of the seed replaced the necessity for a photoperiod stimulus to induce germination. Excised embryos of B55213 and Tgygg canadensis seed gave excellent germination in the dark (Black and Wareing, 1955; Stearns and Olson, 1958). This indicates that the pericarp, endosperm or nucellus is important in seed inhibition and that the seed is able to overcome this inhibition when exposed to light. The effects of red and far red light is operative in seed genmination which is responsive to a photOperiodic stimuli. Far red completely nullified the effect of red light when given immediately after birch seeds were exposed to red light. The reversal of red light stimulation of birch seeds at 15° C by far red is no longer effective after 12 hours of exposure to the red light (Black and Wareing, 1955). 13. In limited studies conducted with woody ornamental seeds, most seem to require a long photoperiod for optimum germination. 133g; canadensis seeds held at 27° C and Betula pubescens at 150 C gave better germination under long days (16 hours) than under short days (8 hours) (Black and Wareing, 1955; Stearns and Olson, 1958). Earlier reports have shown that seeds of Pseudotsuga (Allen, 1941), Pinus sylvestris, Picea excelgg, Eggglg verrucosa and Betula pubescens (Sarvas, 1950) germinated more quickly in the light than in the dark. The final germination count of seeds germinated in the dark was reduced only with seeds of giggg_sylvestris. Vaartaja (1952) made similar observations with Betula verrucosa and Pinus sylvestris. These earlier experiments, however, were so designed that it could not be determdned if the seeds were photOperiodic or photosensitive. At any rate, germination of almost all seeds tested was improved by the addition of light during germination. II. ThermOperiodism in Woody Plants A. Shoot Deve10pment Thermoperiodism (a periodic response that can be induced by temperature cycles) has not been investigated as extensively as photo- periodism. However slight our knowledge of thermoperiodiam, its importance in regulating growth in plants should not be overlooked. Went (1959) reported that "one of the most disturbing new facts in photOperiodism is that temperature can substitute for light". According to Hellmers and Sundahl (1959), Pseudotsuga shows a dramatic response to thermoperiodism. Optimum growth occurred with a l4. diurnal variation of 10° C (7° C night to 17° C day temperature) while a diurnal variation of 16° C inhibited growth (7° C night and 23° C day temperature). In contrast, growth of Sequoia sempervirens was not altered by diurnal variations. Hellmers (1959b) also reported that Pinus Lambertiana would grow equally well when night temperature ranged from 4° C to 17° C. If the night temperatures exceeded 17° C however, (in conjunction with a 23° C day temperature) dry weight production was decreased. By increasing the night temperatures above 10° C and holding the day temperatures below 10° C, an increase in dry weight could be realized. This condition was also conducive to increasing the root/ shoot ratio while higher day temperatures decreased the ratio. Kramer (1957b) also reported a decrease in shoot growth as the night temperature increases. This was especially noticeable in Pinus Taeda whereas Quercus borealis actually showed an increase in shoot growth as the night temperatures increased up to 17° C, but further increase in the temper- ature resulted in less growth. The duration of active growth may be reduced by warm nights, while cool night temperatures will delay the onset of dormancy. Kramer, (1957b) reported that Quercus seedlings actually grew 8 weeks longer in the alternating day-night temperature regime as compared to the constant temperature. Kramer felt it was the spread between day and night temperatures which was the important factor in thermoperiodism rather than the actual temperature itself. He found that Pinus Taeda resumed growth early in the season and elongated more rapidly at a higher temperature than those grown at a lower temperature. In contrast, plants held at the lower night temperatures made more growth later in the season. This suggested that the high nights of mid and late summer may be the cause of dormancy (Kramer, 1957s). 15. B. Root Development Richardson (1957) conducted extensive studies with Acer saccharinum to determine the effect of shoot temperature in relationship to root elongation. He found that root growth will only occur after the taps have been exposed to low temperatures. Low shoot temperatures resulted in a physiologically active bud which was a prerequisite for root elongation in the spring. The stimulus for the elongation of the roots appear to be formed in the developing buds and leaves, while the root initiating factor is located in the terminal bud. Root growth in Seguoia aggpervirens is not too responsive to thermoperiodism and yet cool nights (7° C) with 23° C day temperatures favored root growth slightly. Pseudotsuga was more responsive to alternating day and night temperatures and exhibited the maximum root growth at 7° C night and 17° C day temperature (Hellmers and Sundahl, 1959). Hellmers also reported that root growth is greater than top growth if day temperatures were less than 10° C, whereas high day temperatures resulted in a shoot/root ratio approaching two (Hellmers, 1959a). Barney (1951) working with Pinus Taeda related the response of roots to a number of soil temperatures. He found that as the soil temperature increased to a maximum of 25° C, root growth increased, then decreased with further increases in soil temperature. The leaf/root ratio decreased with increasing temperatures up to 20° C, but increased at higher soil temperatures. A sudden rise in temperatures from 20° C to 35° C markedly increased root growth but subsequent growth was greatly reduced and stapped almost completely after 30 hours. By dropping the l6. soil temperature after this treatment to 20° C, growth of the roots again resumed in 6 days. Transpiration of Loblolly pine was positively correlated to the soil temperature for a short period of time, then gradually leveled off to a stable rate. Apple and peach roots do not appear to require an alternating temperature for maximum growth. Nightingale (1935) found that the ideal root temperature was 65° F, and any deviation from 65° F resulted in reduced yields of roots and aerial organs. C. Induction and Cessation of Dormancy Dormancy as influenced by photoperiod, and in some cases temperature, was discussed previously, but the two environments were not discussed in any great detail together. Downs and Borthwick (1956) working with Ulmus ggericana, Cornus florida, Légiodendron and Catalpa found in contrast to many other reports that higher temperatures delayed the onset of dormancy under eight hour days. Temperatures lower than 70° F completely inhibited growth even under long days. The resumption of growth of dormant £5521; is markedly affected by temperature and photoperiod. At 23° C long days will break dormancy in 2 to 3 weeks while the leafless shoots remain dormant under short days. In contrast, no growth occurs at 15° C irrespective of photo- period imposed, (Black and Wareing, 1955). Bud development is also affected by temperature. Went (1953) reported that buds on ygphgg_Cneorum are formed at high temperatures but require a low temperature for further develOpment. III. Effects of Gibberellin on Growth and DevelOpment of Woody Plants A. History Gibberellin symptoms were first reported by Kari (1898) on rice plants. The disease, which was known as "Bakanae," became a major problem in rice production in the Orient because yields were greatly reduced. Hori described the symptoms as follows, "The rice plant becomes taller, with longer internodes and leaf sheaths, leaves were longer, narrower and thinner and the angle the leaf formed with the culm increased. Root growth and tillering is reduced, the plant appears chlorotic. In light infestation, flowering may be 2 to 3 days early but ears are smaller and yields are reduced. Severe infestion leads to adventitious roots, stem curving at the nodes, leaf curl, foot rot and death before flowering." It wasn‘t until 1926, however, that Kurosawa (1926) successfully induced "Bakanae" symptoms in rice plants by treating them.with a culture medium in which Gibberella fujikuroi had been grown. Twelve years later Yabuta and Sumiki, (1938) successfully crystallized the active ingredient responsible for inducing the Bakanae disease and called it gibberellin A and B (019H2206). Research in this area was greatly reduced prior to and during World War II, but immediately afterwards Marth, Audia and Mitchell (1956) under the security of the United States Government began working with this compound on woody plants. Stodola at Northern Regional Laboratories in Illinois in the meantime was attempting to develop the techniques for biological synthesis. In 1956 the story of gibberellin as influencing woody plants was released by Marth, Audia and Mitchell (1956). Experimental quantities of gibberellin were made available in 1955 by Stodola who had perfected the cultural techniques and extraction. 1?. 18. Several reviews on this subject have been written, (Stowe and Yamki, 1957 and 1959; Brian, 1959; Brian, Grove and MacMillan, 1960) and a collection of more than 600 abstracts were published by Stodola (1958). Wittwer and Bukovac (1958) summarized the responses of economic plants to gibberellin. Gibberellins which have now been characterized as nine distinct chemical structures are gibberellin A1 (C19H2406), gibberellin A2 (C19H2606), gibberellin A3 (C19H2206) and gibberellin A4 (C19H2405) which are produced by the fungus Gibberellggfujikuroi; Gibberellin A5, A6 and A8 were isolated from higher plants by MacMillan, Seaton and Suter (1961). Gibberellin A7 and A9 were isolated from the fungus Gibberella fujikuroi by Cross, Galt and Halson (1960) and are closely related chemically to the other gibberellins. Phinney and West (1960) suggested that due to the close structural relationship between GA-3, GA-l and GA-S, and of GA-2 and GA-4, there may be a close metabolic inter-relationship between these compounds: +H 0 -2H gibberellin A5 1 gibberellin A] ’ gibberellin A3 EH20 +23 gibberellin A4 +°2°’ gibberellin A2 -H20 No direct evidence for the above reactions has been obtained. B. Shoot Development One of the most widely reported responses of woody plants to gibberellin is the accelerated shoot growth accompanied by an increase in internode length (Barton, 1956; Benjamin and Snyder, 1958; Bilan and l9. Kemp, 1960; Bourdeau, 1958; Bradley and Crane, 1957; Bukovac and Davidson, 1959; Chakravarti and Loshali, 1959; Chakravarti, 1958; C00per, 1957; Crane, 1957; Donoho and Walker, 1957; Ergle, 1958; Fogle, 1958; Giordano, 1959; Hull and Lewis, 1959; Hull and Klos, 1958; Iwagaki, 1958; Kearns, 1958; Renworthy and Campbell, 1959; Litvinenko, 1959; Marth, Audia and Mitchell, 1956; Martin and Wiggans, 1959; McVey and Wittwer, 1958; Murphy, 1958; Marth and Smale, 1958; Nishiura and lbs, 1958; Marc and Hirata, 1958; Nitsch, 1957b; Pelton, 1958; Powell, Cain and Lamb, 1959; Robbins, 1957; Sato and Miyajima, 1958; Shidei and Akai, 1958; Scurfield and Moore, 1958; Stuart, Cathay and Asen, 1959; Stuart, 1958; Ueda, Saito, Hashimoto and Ogasawara, 1958; Walker and Donoho, 1959; Weaver and McCune, 1959; Yukawa, 1958). Growth of physiological dwarfs may be stimulated by application of gibberellin, (Barton, 1956; Donoho and Walker, 1957). Barton, (1956) working with non-after-ripened embryos of Malus Arnoldiana, reported that gibberellin would stimulate shoot elongation. This is also true if half-ripened seeds of Elberta peach are soaked in 100 ppm of gibber- ellin (Donoho and Walker, 1957). A number of reports have made reference to the_shoot diameter of woody plants treated with gibberellin. The growth of the shoot may be spindly or sturdy, depending on the gibberellin concentration, method of application, and species treated. Foliar sprays of gibberellin 0n Juniperus chinensis pfitzeriana resulted in long spindly shoots (Benjamin and Snyder, 1958). The degree of after-ripening also alters response to gibberellin. Fogle (1958) found that seeds of sweet cherry, after-ripened for 4 months (normal requirement is 5 to 6 months), produced sturdy plants when treated with 100 ppm of gibberellin, while 20. seed after-ripened for the full term, grew weak and spindly following treatment. Bradley and Crane (1957) reported that gibberellin stimulated division in the cambial zone of Prunus Armeniaca of the spur branches only, while the main shoots were not affected. Almost all the activity was found along the xylem rays while the phloem tissue was not affected. Giordano (1959) also reported an increase in stem diameter of Eucalyptus with increased concentrations of gibberellin from 5 to 200 ppm. Scurfield and Moore (1958) reported a similar response. Hull and Klos (1958) noted an increase in shoot diameter when 1 year old Mont- morency cherry trees were sprayed with 100 ppm on.May 7, June 1, and weekly until August 7. Gibberellin caused an increase in the trunk diameter of 1 year old Montmorency cherries which had been grown in the greenhouse and then transferred to the field on May 21 for treatment (Hull and Lewis, 1959). Ergle (1958) and Sato and Miyajima (1958) re- ported that gibberellin treatment resulted in an increase in stem,diameter of cotton, and Cryptomerig and Papulus seedlings, respectively. Shoot diameter may also be reduced as reported by Kearns (1958) when Robinia Pseudoacacia was treated with gibberellin on July 24 and August 14.1 Marth, Audia and Mitchell (1956) reported that, generally, one would expect some plants to produce very thin threadlike stems while others would produce thicker stems. Apple trees sprayed with 1000 ppm, twice weekly, developed shoots of smaller diameter (Powell, Cain and Lamb, 1959). Iwagaki (1958) noted that 1000 ppm applied to the spur of pear, peach, and Malus sieboldii Rehd seedlings resulted in slender stems. Nishiura and lbs (1958) also reported a smaller stem diameter as compared to non-treated controls when orange seedlings were sprayed with 10 to 100 ppm between May 13 and August 29 with 6 applications of gibberellin. 21. The stem diameter of the new growth was initially smaller but gradually increased in thickness later in the season. Suyamm, Yamasaki and Kubota (1958) observed spindly growth following a root soaking or foliar treatment of apple seedlings with 20 to 100 ppm of gibberellin. Wareing (1958) working with one year old pot grown seedlings of Age; Psuedo-Platanus, Populus giggg, Fraxinus excelsior discovered a relationship between gibberellin and 1AA in xylem development. By applying 1AA to disbudded shoots of the above species, a narrow zone of new xylem‘with lignified vessels was produced as compared to no new wood in the control. when gibberellin was applied to the disbudded shoot, new wood with small unlignified cells with no sign of vessels was produced. If gibberellin and 1AA were applied simultaneously, a wide zone of new wood with fully lignified vessels with intervening fibrous tissue developed. This approximated normal wood. Wareing felt that normal xylem development would involve the interaction of both endogenous IAA and native gibberellin. Lateral shoot growth is markedly affected by gibberellin treatment. It may be increased or inhibited, depending on species, method of application, concentration of gibberellin, and temperature. Benjamin and Snyder (1958) and Bilan and Kemp (1960) both reported a decrease in lateral shoot growth of conifers (luniperus chinensis Pfitzeriana and Einus Taeda, respectively) when treated with gibberellin. In contrast, CoOper (1957) reported increased growth of lateral buds in the new shoots of grapefruit trees treated with a 1 percent solution of gibber- ellin. The following year, COOper and Peynado (1958) reported that elongation of Citrus shoots resulted from a series of flushes from 22. lateral buds close to the apex. Hull and Lewis (1959) also observed that gibberellin induced lateral bud growth of Hontmorency cherries in the distal region of the previous flush of growth. Marth, Audie and'Hitchell (1956) surveyed numerous woody plants and found that there was a reduction in the number of laterals developing in 25523 agapervirens, while gitggg exhibited an increase in lateral bud deve10pment as reported by COOper (1957). Eggnymus Portunei vegetus, when treated May 4th with 100 ppm and at weekly intervals until August 21, exhibited a marked reduction in the total number of shoots per plant GHcVey and Wittwer, 1958). Young apple seedlings treated twice weekly with 1000 ppm of gibberellin showed an increase in the number of growing points per tree (Powell, Cain and Lamb, 1959). Lateral shoot growth development may be dependent on concentration and temperature as reported by Donoho and Walker (1957). They found that when two year old peach trees were treated with 500 to 1000 ppm nearly all growth occurred from the terminal bud, whereas with 100 ppm of gibberellin,‘more lateral growth occurred. This was especially true when trees were held at 40° F as compared to 65° F. Nishiura and lbs (1958) found that the deleterious effect of gibberellin in stimulating axillary buds could be avoided by treating only the growing tips of orange seedlings. A temporary stimulation of spurs of persimmons by low concentrations (20 to 100 ppm) was reported by Sato and Hirose (1958). Yokosawa and Yasui (1958) found low concentrations of gibberellin (25 to 100 pme caused a permanent increase in elongation of spurs of Hasui Dauphina fig. The rate of appearance of lateral buds was increased by treating ngulus with 50 to 1000 ppm of gibberellin from.2 to 6 times (Sato and Miyajima, 1958). 23. COOper and Peynado (1958) postulated a mechanism of action of gibberellin in stimulating axillary deve10pment which was related to the IAA concentration. It is known that shoots of citrus which are actively growing, produce capious amounts of auxin. He further stated that auxins cause inhibition of lateral buds. Therefore, gibberellin may act in some way to deplete the inhibitory concentration of auxin in buds. Kato (1958) reported that gibberellin increased the bud growth of peas so greatly that the inhibition of applied auxin was nullified. Gibber- ellin also counteracted the stimulating effect of auxin in root formation. When 1AA was applied in concentrations that promoted growth, gibberellin acted additively. Fresh and dry weights of woody plants are markedly altered by gibberellin. A number of reports had shown an increase in fresh and dry weight of shoots (Benjamin and Snyder, 1958; Hull and Lewis, 1959; Scurfield and Meore, 1958; and Chakravarti, 1958). Benjamin and Snyder (1958) found that when seeds of Quercus Robur were soaked in 100 ppm for 24 hours there was a significant increase in fresh and dry weights of the seedlings. If a lower (10 ppm) or higher (1000 ppm) concentration was used no response or deleterious effects, respectively, would result. Chakravarti (1958) also reported an increase in dry weight of Sesamwm indicum seedlings from seed treated with gibberellin (1 to 100 ppm). Hull and Lewis (1959) treated one year old Hontmorency cherry trees with gibberellin (100 to 1000 ppm) on May 21, (prior to this period, the trees had been in the greenhouse and had completed their first flush of growth for the season) which resulted in a significant increase in fresh and dry weight of the t0?“- 24. Scurfield and‘Hoore (1958) attributed the increase in stem*weight to the alteration in the relative weights of stem, root and leaves. When young seedlings of Eucalyptus were treated with gibberellin there was an increase in the weight of the stem, but the leaves and roots weighed less. Ergle (1958) reported a similar redistribution of dry weight in cotton plants. At low concentration (10 and 100 micrograms per plant) gibberellin caused an increase in stemwweight with little or no effect on leaf and root dry weights. If, however, a higher concen- tration was used (1000 pmm) there was a marked reduction in leaf weight, together with the weight of the entire plant. At the higher concentrations the stem diameter was smaller than the controls but the dry weight was not altered. A few investigators have reported a decrease or no change in fresh and dry weight following gibberellin treatment. Benjamin and Snyder (1958) reported a reduction in fresh and dry weight of the taps of gggiperus chinensis pfitgeriggg. Young apple seedlings treated with 1000 ppm of gibberellin exhibited an increase in linear growth and a reduced root/tap ratio but there was no significant change in the dry weight per tree (Powell, Cain and Lamb, 1959). Bamboo shoots also failed to show an increase in shoot weight when treated with #0 to 200 ppm of gibberellin (Ueda, Saito, Hashimoto and Ogasawara, 1958). Node number may be increased or not affected by gibberellin treatment. Seed of Quercus pgluatris soaked in 100 ppm of gibberellin produced a greater number of leaves upon germination as compared to those soaked in water (Benjamin and Snyder, 1958). Litvinenko (1959) reported a similar condition if young seedlings of Ligustrum.vulgare and gyracantha coccinea were treated with .0025 percent “Ukranian 25. Gibberellin". McVey and Wittwer (1958) noted a significant increase in the node number of Eggnymus Portunei yggetus, Porsythia "Arnold Dwarf", Liggstrum obtusifoliug vicari and Phellodendron amurense following gibberellin treatment. A repeat application of 100 ppm or a single application of 1000 ppm was more effective in increasing the node number than lower concentrations of gibberellin. Nitsch (1957b) found the same to be true with Acer palmatum. Young apple seedlings (Powell, Cain and Lamb, 1959) and Eucalyptus (Scurfield and Moore, 1958) also exhibited an increase in node number. Other reports indicate that there is no increase in node number following gibberellin treatment. McVey and Wittwer (1958) reported that Magnolia Soulanggana, Berberis Thunbergi "Crimson Pygmy? and Viburnum qulus nanm! exhibited increased growth with no increase in node number following gibberellin treatment. Marth, Audia and Mitchell (1956) also observed a number of woody plants which failed to exhibit an increase in node number following gibberellin treatment. Anatomical studies following gibberellin treatment have shown a change in the rate of cell division. Prunus Armeniagg spurs sprayed with gibberellin exhibited increased cell division in the cambial zone, but there was a reduction in the size of bud development on the spur branches. (Bradley and Crane, 1960). They also reported a retardation in bud deve10pment following gibberellin treatment during full bloom or at the beginning of pit hardening. The higher the dosage, the greater the elongation, but the more retarded the bud development. Gibberellin inhibited cell division in lateral bud spices while the termdnal was relatively immune. Bud scales and leaf primordia failed to form or eventually disintegrated if formed when the gibberellin.was 26. applied (Bradley and Crane, 1957). Wareing (1958) reported a similar condition could be induced in Acer Pseudo-Plaggnus, Populus‘niggg and Fraxinus excelsior. A number of studies have been carried out on herbaceous plants which support the concept that gibberellin induces an increase in the rate of cell division (Feucht and Watson, 1958; Geulach and Haes100p, 1958; Sachs, Breta and Lang, 1959). The action of gibberellin is not long lasting. A continuous supply of gibberellin must be available to induce continuous elongation. Chakravarti and Loshali (1959), working with Hamelia.pggg§g which has two different types of growth (winter rosette leaves of the terminal shoots and normal summer elongated internodes) found that gibberellin will cause a summer type growth when applied to winter rosette leaves. The effect is not long lasting since growth will revert back to a winter type growth within a month. McVey and Wittwer (1958) reported that a continuous supply of gibberellin was required to stimulate continuous growth of Porsythia "Arnold Qggggf, Ligustrg! obtusifolium vicari and Euonymus Portunei vegetus. In contrast, a single spray application of 1000 ppm was adequate in stimulating continuous elongation in Magnolia Soulangeana. The elongation of terminal internodes of control plants tends to decrease as the plant approaches dormancy, whereas Buonymus Portunei vegetus and Magnolia Soulangeana treated with a single application of gibberellin at 1000 ppm, or a repeat treatment of 100 ppm in the case of Magnolia, exhibited an increase in the length of the internodes as the plants went into dormancy. Pujita (1958) reported an initial stimulation of hOp plants‘with 10 or 50 ppm of gibberellin but later growth was re- tarded and within 20 days there was no difference between control and 27. treated plants. Sato and Hirose (1958) reported a similar retarding effect of gibberellin on spur branches of Puyu persimmons. In contrast, a 1 percent lanolin mixture of gibberellin applied to 2 to 3 year old £25222, Acer, Catnip; and Aesculus caused continuous growth for 18 months in the greenhouse at 60 to 1000 P. Chakravarti (1958) supported the finding that repeat treatments are required for continuous internode elongation. He states that with a cessation of application of gibberellin there was a decrease in the length of the subsequently formed internodes when compared to the corresponding ones in the non-treated plants. Chakravarti felt that this may be caused by a reduction in the rate of synthesis of endogenous growth factors (Chakravarti and Loshali, 1959). Phinney (1956) also reported that a continuous supply of gibberellin was required to maintain a normal type of growth for dwarf mutant corn seedlings. Gibberellin has also been reported to affect the development of the terminal buds of woody plants. Chakravarti and Loshali (1959) reported that when Lawsonia gl§g_was treated with 100 to 200 ppm of gibberellin, elongation of the shoot terminated in death of the terminal meristmm. McVey and Wittwer (1958) also reported a similar response in Berberis Thunbergii "Crimson gym" treated with 100 ppm weekly. A number of auflhors have found that gibberellin will initiate a second flush of growth in woody plants (Hull and Lewis, 1959; Fogle, 1958; McVey and Wittwer, 1958). ‘Murphy, (1958) reported no apparent growth response to gibberellin during the growing season when poplar trees were treated with 1 to 1000 ppm. After growth had terminated in September, a fall application of 60 to 1000 ppm to the vascular system resulted in a second flush of growth. Gibberellin induced a greater number of growth 28. flushes to occur in Red Blush grapefruit tree with a reduction in the period of dormancy between the first and second flush of growth. The terminal bud of grapefruit trees which is normally abscised, remained intact following gibberellin treatment (COOper and Peynado, 1958). Nelson (1957) in contrast, reported that the terminal bud of Platanus desiccated after a substantial increase in growth rate over the control had been obtained. Juvenility has been induced in several woody ornamentals treated with gibberellin. Cooper and Peynado (1958) reported that Red Blush grapefruit trees sprayed with 1000 ppm produced unusually long shoots which bore long thorns (characteristic of juvenility). Robbins (1957) also reports a reversal to the juvenile stage of leaf development in Bedera canarienis variggata following treatment with 10 micrograms of gibberellin per plant. In contrast, Scurfield and Moore (1958) found an alternate leaf arrangement and falcate-lanceolate shaped leaves when Eucalyptus was treated with gibberellin. These characteristics are typical of the adult phase of deve10pment and appeared much earlier in the development of the plant as compared to plants not treated with gibberellin. Chakravarti and Loshali (1959) felt that a "Gibberellin- like" material might be responsible for changes in leaf arrangement. He reported that Linaria marocanna ( an annual) treated with gibberellin in the vegetative phase of development, develOped an alternate leaf arrange- ment. The non-treated plants produced a whorled leaf arrangement in the vegetative phase and an alternate arrangement in the inflorescence. An interesting report by Bull and Klos (1958) which has not been observed elsewhere in woody plants, was the response of virus yellows and ring spot stunted plants of young Montmorency cherry trees to gibber- 29. ellin. Gibberellin (100 ppm) caused stimulation of vegetative elongation to slightly offset ring spot virus and had a marked effect on overcoming stunting induced by cherry yellows virus. In contrast to the rapid elongation of deciduous woody plants to gibberellin, most conifers fail to show any striking increase in shoot elongation. Rearns reported a significant increase in height of Pippa Strobus treated with 100 to 1000 ppm at weekly intervals for 4 consecutive weeks. Pseudotsuga taxifolia, gigs; Abies, Pinus Banksiana, 21223 . sylvestris and Picea glaugg failed to respond to gibberellin concentration as high as 20,000 ppm for the latter three species and 100 to 1000 ppm in the former two species (Kearns, 1958). Nelson (1957) treated ggppg Strobus and Cupressus ariaonica with 0.1 percent lanolin paste of gibber- ellin and found no growth response. Knight (1958) reported no response of £3552 Epgelmannii or Tppgg heterophyllngith 10 to 1000 ppm of gibberellin repeated numerous times. Westing (1959) found a large number of conifers failed to respond to gibberellin. Marth, Audia and Mitchell (1956) were able to stimulate shoot elongation in Pinus virginiapp, Pinus Taeda and Picea glauca if the gibberellin was applied as a lanolin paste at a con- centration of 0.25 to 1.0 percent to a wounded area of the stem. Shidei and Akai (1958) reported that Larix gave only a slight response to gibberellin. The response of woody plants to gibberellin is dependent on a number of factors, some of which are the physiological stage of develOp- ment, degree of establishment of the plant, and method of application. Marth, Audie and Mitchell (1956) reported that the greatest response of woody plants to gibberellin occurred when it was applied to shoots that had just begun to elongate. Sato and Miyajima (1958) found that 30. Melaseguoig glypgostgpboides exhibited an increase in growth following gibberellin treatment only during the initial stage of develOpment. In contrast, MeVey and Wittwer (1958) and Murphy (1958) reported no increase in the rate of shoot extension of the first flush of growth in Buonygpg Fortunei vegetus and Poplar, respectively, but gibberellin greatly influenced the second flush of growth. Rearns (1958) reported that. 525; saccharum failed to respond to concentrations of 10 to 1000 ppm in late July and early August, but exhibited a growth response in early July following a foliar spray of 20,000 ppm of gibberellin. Nelson (1957) also reported that the oak responded to gibberellin immediately following the first flush of growth. Nelson (1957) placed 11 different species of one year old woody plants in the greenhouse in December under 16 hour photoperiods, he found that a 0.1 percent spray of gibberellin caused marked stem elongation with no spindly weakened stems such as is typical in many plants treated with gibberellin. Wilting following gibberellin treatment was observed in Ligustrum (MoVey and Wittwer, 1958) and in.gppplps (Murphy, 1958) following a foliar spray of 100 ppm.of gibberellin. Wilting, however, was only temporary, lasting 1 to 2 weeks after first observed. In contrast, Nelson (1957) reported that 11 different woody plants treated with 0.1 percent gibberellin as a lanolin paste or as a foliar spray in December exhibited less tendency to wilt under a soil moisture stress than non- treated plants. Genetically dwarfed herbaceous plants show a marked response to gibberellin. Brian (1959) reported that dwarf woody plants also respond remarkably well to gibberellin treatment. ‘McVey and Wittwer, (1958) found that dwarf forms of Barberry (Berberis Thunbeggpp "Crimson gygpyf) 31. and Forsythia (Forsythia "Appplg_2!p£§") exhibited the most dramatic responses to gibberellin. Pelton (1958) also found that a genetically controlled dwarf alpine plant (Potentilla) responded to either gibber- ellin or a transfer to lower altitudes both causing marked stimulations in growth. Shidei and Akai (1958) treated dwarf plants of Robinia Pseudggcacgp, Liguidambar formosana and Acer palmaggg gap, with gibber- ellin resulting in a noticeable response. Nor only may gibberellin stimulate shoot elongation but it may in contrast inhibit shoot develOpment. MeVey and Wittwer (1958) reported that high concentration of gibberellin (100 to 1000 ppm) caused a re- tardation of growth of Taxus cuspidata. Nickell and Tulecke (1959) exposed numerous isolated plant tissues to gibberellin. In general, the plant tissues tested showed no response. In some cases, however, there was a marked inhibition of growth by low levels of gibberellin. Pear trees treated with 100 to 1000 ppm'were inhibited in their deveIOpment with less total linear growth than controls (Powell, Cain and Lamb, 1959). Schoedle (1958) and Sato and Miyajima (1958) also reported that Pseudotsuga meneiesii was inhibited in its development when sprayed with 125, 500 or 1000 ppm of gibberellin. C. Root DevelOpment Several investigators have reported that gibberellin reduces the rate of growth and development of roots of woody plants. Rood develOp- ment of apple seedlings may be greatly retarded with a resulting de- crease in the root/top ratio following treatment with 1000 ppm of gibber- ellin (Powell, Cain and Lamb, 1959). Suyama, Yamasaki and Kubota (1958) 32. also reported that root growth was suppressed by gibberellin when apple seedlings were soaked overnight in 20 ppm or sprayed with 20 to 100 ppm. Benjamin and Snyder (1958) and Scurfield and Moore (1958) reported a reduction in fresh and dry weight of the roots following treatment of Juniperus chinensis Pfitzeriana and Eucalyptus seedlings, respectively, with gibberellin. Concentrations as low as 25 ppm of gibberellin were effective in reducing root weight of Eucalyptus. Rooting of cuttings may be affected by gibberellin. Miller (1959) treated §pl$§ cuttings, collected at monthly intervals, with .01 to 100 ppm of gibberellin. He found that gibberellin was only effective during the normal fall depression of root induction. During periods of high rooting capacity gibberellin was not effective. Sato and‘Miyajima (1958) reported that gibberellin inhibited appearance of roots and root- ing of Chamaecyparis obtuse. If, however, gibberellin and naphthalene- acetic acid (NAA) were used simultaneously, the rooting induced by BAA was increased by gibberellin. In contrast, Marth and Smale (1958) treated cuttings of Hydrangea with IAA and gibberellin and found that gibberellin reduced the ability of the cuttings to respond to IAA. Rooting of cuttings of Rosa, Juniperus, Ligustrum and Pyracantha was also reduced when treated with 10 to 100 ppm of gibberellin. Gray (1957) supported Marth and Smale's (1958) findings when studying the effects of gibberellin on cuttings of Chinese Hibiscus treated with indolebutyric acid (IBA). In contrast, he found that gibberellin stimulated rooting of intact bean and tomato plants treated with IBA. Rooting was also improved in 921225 with gibberellin. Root growth and development on intact plants may be stimulated by gibberellin depending on the concentration and species treated. Sato 33. and Miyajima (1958) found that high concentrations of gibberellin (4 to 7 applications of 400 ppmo promoted root elongation of Cryptomeria seedlings. Donoho and Walker (1957) reported an increase in root growth from‘half ripened Elberta peach seeds soaked in 20 to 200 ppm. When higher concentrations were employed, little root extension occurred. Stowe and Yamaki's review (1957) stated that Azaki bean roots were stimulated by gibberellin. An unsubstantiated report revealed that gibberellin B promotes root growth. Dry weight of roots of the Mont- morency cherry was not altered by gibberellin treatment when applied to one year old seedlings which had made their first initial flush of growth prior to treatment with 100 to 1000 ppm of gibberellin (Hull and Lewis, 1959). In contrast, when excised embryos of Pinus Lambertiana were grown in contact with agar containing 3 x 10 '7 and 3 x 10 '5 molar gibberellin there was a 45 percent increase in root growth after #5 days. Root growth however, during the remaining 16 days paralleled that of the controls (Brown and Gibbord, 1958). Size of the root and light intensity may play an important role in response of woody plants to gibberellin. Total yield and quality of roots of Derris elliptigg_were reduced if roots of treated plants were less than 6 millimeters in diameter. If however, the diameter of the roots was greater than 6 millimeters there was an increase in the diameter, quality, and yield of roots when gibberellin was applied as a root treat- ment of 100 milligrams per plant. Gibberellin decreased the fresh weight of roots and stems, but increased the root/tap ratio (Moore, 1959). Richardson (1958) also reported that the size of the root affects their response to gibberellin. Growth of roots of Douglas fir seedlings, greater than 5 millimeters in initial length were markedly affected by 34. gibberellin applied to the roots. As the initial root length increased from 5 millmeters to 10 millimeters, the Optimum concentration of gibberellin for promoting growth decreased from 10 to 5 ppm. Richardson (1958) also found that the inhibiting influence of 4000 lux of light on root growth could be completely overcome by 3 ppm of gibberellin. The initial response of roots to 8 ppm of gibberellin was much greater in the light than in the dark. In this respect, Hejnowicz (1958) reported that protochlorophyll was present in root tips of many different species and was destroyed by red and blue light. Light also inhibited growth of roots at an action spectrum similar to the spectrum of protochlorophyll destruction. D. Induction and Cessation of Dormancy Dormancy of woody plants has been studied for many years, but since the advent of gibberellin, more emphasis has been devoted to this area. It has been reported that gibberellin will delay the abortion or setting of terminal buds in woody plants. Cooper (1957) found that a 1 percent solution of gibberellin would delay the abortion of the terminal bud of grapefruit. He later reported that gibberellin delayed but failed to prevent dormancy from occurring in Red Blush grapefruit trees Cooper and Peynado, 1958). Yukawa (1958) also found this to be true in Satsuma orange seedlings. Hull and Klos (1958) reported that a foliar spray of gibberellin (100 ppm) caused a three week delay in terminal dormancy of Eggppg. Kearns (1958) found that the terminal buds of Douglas fir seedlings set 6 weeks later than the buds of the control plants following treatment with 100 to 1000 ppm of gibberellin. Forsythia flggnold Dwarf" and Phellodendron amurense also failed to initiate a 35. terminal bud until 2 or 3 weeks after the control, when treated with 100 ppm.of gibberellin.(McVey and Wittwer, 1958). Nitsch (1957) reported that abscission of the terminal bud of sumac under short days could be prevented by the addition of gibberellin. Gibberellin also induces abortion or desiccation of tenminal buds. McVey and Wittwer (1958) found that 20 to 40 percent of the terminal buds of Phellodendron amurense abscised when treated weekly with 10 to 100 ppm of gibberellin. Desiccation of the terminal buds of Eorsythia "Arnold Qyppgi, Prunus tomentosa and ggrberis Thunbergii "Crimson gygpy: occurred following treatment with 100 ppm at weekly intervals throughout the summer starting in early May. The growing points of Platapus occidentalis seedlings and Quercus were injured following 23 days of shoot elongation stimulated by 1 percent gibberellin in a lanolin paste applied to the main shoot (Nelson, 1957). He further stated that the terminal buds of Quercus did not desiccate but tended to form on a partially elongated internode. Soost (1959) also reported twig dieback on Clementine 25993212 one month after treatment with 100 or 500 ppm of gibberellin. In contrast to many reports, Weaver (1959) found that gibberellin applied in the autumn prolonged the dormancy of buds of Vitis vinifera. The higher the gibberellin concentration, the longer the deveIOpment of buds was delayed. Low temperature exposure is essential for breaking dormancy of many woody plants. Yet, gibberellin has been shown to replace the low temperature requirement of dormant epicotyls of tree peony (Barton and Chandler, 1957). oohata and Shiraki (1958) reported that the leaf buds of 252325 BEES Opened earlier in the spring when sprayed with 50 ppm of gibberellin repeated three times in late January. Barton (1956) also 36. reported that low temperature requirements needed for elongation of non-after-ripened embryos of Malus Arnoldiana could be replaced with gibberellin. Azaleas for forcing are normally stored at 400 F for 8 to 12 weeks to break the dormancy, then an additional 4 to 6 weeks at 600 P is required for forcing. Gibberellin (1000 ppm) will completely replace the cold treatment being more effective at higher temperatures (700 P) than at 60° F. Fewer applications are required inimid-winter than during late fall forcing, (Boodley and Mastalerz, 1959). The physiological stage of development influences the response of woody plants to gibberellin. Donoho and Walker (1957) reported that as the chilling requirement for Elberta peach trees decreased, the optimum concentration of gibberellin for breaking dormancy also de- creased. Pogle and MeCrory (1959) found a similar condition to be true when Lambert cherry seeds were after-ripened in the presence of gibber- ellin. Terminal buds of Quercus and Acer which had their cold require- ments satisfied, were induced to break one to two weeks earlier when treated with gibberellin (Marth, Audia and Mitchell, 1956). Prince (1958) in support of Donoho and Walker (1957), reported that eight varieties of Georgian peaches which had received 100 hours of the chilling requirements necessary to break their rest period, showed growth responses to contrations as low as 100 ppm of gibberellin. Stuart (1957), working with Hydrangea macrophylla also found that gibberellin was more effective in breaking dormancy if the plants cold requirement had already been partially satisfied. Apple trees held at 40° F for 2 or 4 weeks broke dormancy following gibberellin treatment, but only small tufts of leaves develOped (Walker and Donoho, 1959). 37. Dormancy, broken by gibberellin, may be only temporary and even- tually the plant may revert to a dormant condition. Eagle (1958) treated rosetted 252535 seedlings, with 100 ppm of gibberellin as a foliar spray 6 weeks after germination, which had develOped from non- after-ripened embryos. A lateral bud was forced into active growth but the shoot rosetted again after 3 to 4 weeks. A second application of gibberellin again broke dormancy and induced active growth for another month while some shoots grew continuously. Completely dormant plants of Hydrapgea macrophylla can have their cold requirements satisfied in at least two ways. Gibberellin and IAA (1 milligram.each per plant) if applied prior to flower initiation will enable the plant to bypass the cold requirement needed for flowering. If, however, the plant is already dormant, defoliating the plant plus the addition of gibberellin to the soil or terminal buds will break dormancy (Stuart, 1958). A number of woody plants will resume growth from dormant buds when treated with gibberellin. Bukovac and Davidson (1959) reported that photoinduced dormancy (9 hour days) of Weigela was inhibited following a single application of 50 ppm of gibberellin while the controls became dormant. Bourdeau (1958) reported a similar response for Pinus elliotti which had been induced into dormancy by short days. He found that if a 0.1 percent solution of gibberellin was applied at weekly intervals the ces- sation of photo-induced dormancy occurred within one month after the initial gibberellin treatment. Winter twigs of Eggpg sylvatica, which normally require long days to break dormancy, were induced into vegetative elongation by 50 ppm gibberellin while the controls under short days at 170 to 19° C exhibited only a slight vegetative response (Lona and Borghi, 1957). 38. Brian (1958) prOposed a mechanism of action for gibberellin in inducing a photOperiodic response with respect to flowering. The following scheme might also be applicable to vegetative response of woody plants. "In response to light, gibberellin-like hormones are formed in leaves, a physiologically inactive precursor (P) being intermediary. The hormone is converted slowly back to (P) in the dark and more rapidly in far red. C02 5 P Red ! Gibberellin-like Hormone EPar Red I Darkness , Thus in a long day plant, gibberellin-like hormones induce flowering, but flowering takes place in short day plants only at low levels of gibberellin." Apical dominance may be negated in some species and intensified in others depending on the concentration of gibberellin imposed. Marth, Audia and Mitchell (1956) reported that generally, the main stem is the first to elongate following gibberellin treatment with no apparent stimulation to the lateral buds. As the rate of elongation of the main axis decreases, there is a simultaneous increase in lateral bud elon- gation (e.g. giggpg and snapdragon). MeVey and Wittwer (1958) reported a similar condition in Hydrapgea arborescens giandiflora and Berberis Thunbergii "Crimson 2155!" following weekly application of 100 ppm of gibberellin. Walker and Donoho (1959) however, found that higher con- centrations of gibberellin (500 or 1000 ppaD would stimulate growth from the terminal bud and had little or no affect on lateral bud elongation in partially dormant peach trees. 39. E. Hardiness Frost resistance is increased in some cases, while in others there is a reduction in frost tolerance. Earth and Smale (1958) found that English boxwood was more susceptible to frost injury when subjected to out-of-door winter temperatures following gibberellin treatment. Kearns (1958) reported a similar condition for black locust sprayed with 100 or 1000 ppm of gibberellin. High concentrations of gibberellin (200 ppmo were injurious to orange seedlings with a delay in maturity resulting (Yukawa, 1958). Allsopp (1959) presented a hypothesis which might account for the variation in hardiness reported for plants following treatment with gibberellin: "The increase in growth vigor following gibberellin treatment might be expected to increase the rate of heteroblastic deveIOpment (aging) in cases where the appearance of the adult characteristic is dependent on the enlargement of the apical meristem, while an increased utilization of carbohydrates might lead to a delay in the appearance of adult characteristics when their formation is dependent on an increasing accumulation of soluble carbohydrates in the de- veloping organs." F. Leaf Size and Morphology Leaf size and weight may be markedly reduced following gibberellin treatment. Benjamin and Snyder (1958) found that leaf size of Quercus 52225 was reduced when seeds were soaked 24 hours in gibberellin before planting. unvey and wittwer (1958) reported that gggnglia Soulanggana, {hellodendron ammrense, Berberis Thunbergii "Crimson £1351", Hydrangea arborescens grandiflora, Prunus tomentosa, Thuja occidentalis Hoveyi 40. and Viburnum qulus nanum produced smaller leaves following weekly treatments of 100 ppm beginning in early May and continuing through- out the summer. Other investigations dealing with herbaceous plants have shown a decrease in leaf size and weight following gibberellin treanment (Haes100p and Greulach, 1958; Gray, 1957; and Ergle, 1958). Leaves are generally longer and narrower following treatment of woody plants with gibberellin. Bukovac and Davidson (1959) reported an increase in length but a decrease in width of Weigela leaves treated with 50 ppm irrespective of the photoperiod imposed. Chakravarti and Loshali (1959) noted a temporary change in leaf shape from ovate to lanceolate which persisted for only a month in Hameliagpatens. Cooper and Peynado,(l958), Kearns (1958),.Harth, Audie and Mitchell (1956), Nelson (1957), Scurfield and “core (1958), Stuart (1958), walker and Donoho (1959), Yakushiji, Yamaguchi and Yamanaka (1958), Hero and Hirata (1958) and Chakravarti (1958) all reported an increase in length with a subsequent decrease in width of leaves treated with gibberellin. Chakravarti and Arora (1958) noted a similarity between removal of cotyledons and response to gibberellin in Sesamum indicum. Both methods of treatment caused the pair of leaves develOping just above the coty- ledons, to exhibit prominent concavities on both sides near the apex, as compared to the ovate control leaves. Numerous reports have shown an increase in leaf size and weight but most of these reports have delt primarily with herbaceous plants (Gray, 1957; Humphries, 1958; Kuraishi and Hashimoto, 1957; Scott and Liverman, 1957; and Njoku, 1958). Tskizawa and Kano (1958) and Sawada and Yakuwa (1958) treated mulberry in late summer and apple trees at full bloom with 50 and 100 ppm of gibberellin, respectively, with a resultant 41. increase in leaf size and dry weight. Mulberry leaves were increased in size by twofold. Apple leaves exhibited an increase in area and fresh and dry weight, with no effect on the water content of the leaves. McVey and Wittwer (1958) reported that low rates of gibberellin (10 ppm in early spring) would increase the size of leaves of Magnolia Soulangeana, Hydrangea arborescens grandiflora, Euonymus Fortunei vegetus, Prunus tomentosa and Viburnum_9pulus nanumu Marth, Audia and Mitchell (1956) also observed an increase in leaf width in a number of woody plants treated with gibberellin. Leaf thickness and surface morphology may be altered following gibberellin treatment. McVey and Wittwer (1958) noted that £52223 tomentosa sprayed with 10 to 1000 ppm produced leaves that appeared thinner and less tomentose. Nitsch (1957b) also reported a reduction in leaf thickness in Age; palmatum treated with 5 micrograms of gibbere- llin. The reduction was attributed to a decrease in mesOphyll tissue. G. Plant Composition Gibberellin can significantly alter the chemical composition of woody plants. Hull and Lewis (1959) working with one year old Mont- morency cherry trees grown in sand cultures, reported a significant decrease in boron and calcium and an increase in nitrogen in the leaves. Powell, Cain and Lamb (1959) treated apple seedlings with l to 1000 ppm of gibberellin twice weekly. All concentrations of gibberellin decreased the percent nitrogen in the leaves while only high levels of gibberellin (1000 ppm) decreased the calcium and magnesium content. Potassium was increased in the leaves following treatment with 1000 ppm but all 42. other levels of gibberellin (l, 10 and 100 ppm) decreased the percent potassium in the leaf tissue. Ergle (1958) also reported a decrease in protein nitrogen, total nitrogen and percent ash in leaves, stems and petioles when cotton plants were sprayed with 1000 micrograms of gibberellin. At lower rates of gibberellin, there was an increase in total nitrogen as well as total ash in the stem plus petioles. Straus and Epp (1960) working with tissue cultures of Qupressus funebris reported a possible increase in the utilization of nitrogen when plant parts were treated with 1.0 ppm of gibberellin. He postulated that gibberellin may somehow be concerned with nitrogen metabolism since gibberellin permitted three times the amount of growth (no organic nitrogen added), as com- pared to the basal medium alone. Gibberellin may enhance the utili- zation by plants of organic and inorganic nitrogen sources. Reports on the composition of herbaceous plants as affected by gibberellin have occurred in the literature (Morgan and Mees, 1958; Wittwer, Bukovac and Grigsby, 1957), but few reports have dealt with gibberellin affects on composition of woody ornamentals. Some studies concerning the chemical composition of fruit of various citrus species have been reported (flield, Gaggins and Gerber, 1958). Numerous elements in woody plants are not changed following gibber- ellin treatment. Hull and Lewis (1959) reported no change in the phosphorus potassium, magnesium” manganese, iron and capper content of one year old {5332; plants treated with 100 to 1000 ppm.of gibberellin. Powell, Cain and Lamb (1959) also reported no change in the phosphorus content of apple leaves treated twice weekly with l to 1000 ppm of gibberellin. 43. N. Chlorosis Some degree of chlorosis often accompanies gibberellin treatment of woody plants. Conifers, though not greatly stimulated vegetatively, do exhibit some degree of chlorosis following gibberellin treaoment (Bilan and Kemp, 1960; Kearns, 1958; McVey and Wittwer, 1958). In contrast to conifers, deciduous woody plants generally exhibit an increase in vegetative extension which is accompanied by a chlorotic condition following gibberellin treatment. McVey and Wittwer (1958) reported marked chlorosis by the first of July in Prunus tomentosa sprayed weekly with 100 ppm.of gibberellin. Plants sprayed once with 100 ppm in early May, however, did not show a marked chlorosis until September. Chlorosis is temporary in Phellodendron amurense if the gibberellin treatment is not repeated. pguxus‘microphylla, in contrast to other woody ornamental plants treated, produced darker green leaves following weekly applications of 100 ppm of gibberellin. Only 10 ppm repeated weekly caused chlorosis which was not evident until late in the season (McVey and Wittwer, 1958). Weaver and McCune (1959) observed a chlorotic condition in grapes treated with gibberellin which was only temporary. The chlorotic condition became more intense as the concentration in- creased. Numerous other reports have noted a chlorotic condition accompanying gibberellin treatment (Bukovac and Davidson, 1959; Nora and Hirata, 1958; Suyama, Yamasaki and Kubota, 1958). Chlorosis may be a result of pigment dilution or reduced chlorOphyll synthesis in herbaceous craps. Ullmann and Krekule (1957) reported a 30 percent decrease in chlorOphyll content of lettuce seedlings 44. per unit dry weight. Wolf and Haber (1960) supported the above findings and attributed the chlorosis of young wheat plants entirely to a chlorOphyll dilution (synthesis of chlorOphyll failed to keep pace with the increase in cell expansion). These findings support a theory that chlorosis induced by gibberellin is in part related to nutritional deficiencies. In this respect Dancer and Dyer (1958) were able to prevent chlorosis by the application of small quantities of certain mineral elements. If chlorosis had already been induced prior to application of certain minerals it could only be reduced. They also noted that chlorosis did not ensue if the gibberellin was applied to the primary leaves of beans, yet if applied to the tri-foliate leaves, chlorosis was induced. Stowe and Yamaki (1957) reported in their review that that gibberellin actually decreases the percent chlorOphyll and chlorOplast content. They stated that the degree of chlorosis was associated with the nutritional level of the plant. 1. Seed Germination l The response of germinating seeds has probably been investigated as thoroughly as any area concerning the gibberellins. Gibberellin will stimulate the rate of germination of seeds of woody plants. Litvinenko (1959) soaked fresh seeds of apple, pear and dogwood in a 0.2 percent solution of gibberellin for 24 hours. All species treated with gibber- ellin exhibited an increase in germination of 30 to 60 percent as compared to the controls. Tod (1958) evaluated numerous herbaceous seeds and found that gibberellin (25 ppm) was effective in inducing germination. He hated that seeds which normally germinate fairly freely were inhibited A‘EI. 45, at high concentrations of gibberellin. Benjamin and Snyder (1958) soaked seeds of Quercus Robur 24 hours in gibberellin, and found a positive correlation between the concentration of gibberellin and the rate of germination. The final percent germination was not affected. Martin and Wiggans (1959) reported that pecan seeds soaked for 8 days in 5000 ppm showed an increase in the rate of emergence and the total percent germination. Many seeds require a period of chilling to induce seed germination. Gibberellin has been reported to completely or partially substitute for the chilling requirement of many seeds. Donoho and Walker (1957) stimulated germination of partially stratified peach seeds by soaking for 24 hours in 100 to 200 ppm of gibberellin. If higher concentrations of gibberellin were used, germination was inhibited. Sweet cherry seeds responded similarly when soaked in 100 ppm of gibberellin (Pogle, 1958). In contrast, Mes (1959) reported that non-stratified and partially stratified seeds of peach soaked in gibberellic acid showed no improvement in germination. Richardson (1959) working with seeds of Douglas fir reported that non-stratified seeds required a lower concentration of gibberellin for Optimum germination than stratified seed. Richardson attributed this difference to a dilution of the gibberellin in the stratified seeds. Gibberellin (3 to 10 ppmo was most effective in stimulating germination, with evidence of a depressing effect on germination at higher concentrations. The total germination was not affected. 46. STATEMENT OF THE PROBLEM That gibberellin will replace or partially replace the vegetative phases of development which are controlled by the photoperiod and/or thermoperiod was assumed. In this investigation two general areas of plant growth and development as affected by gibberellin are considered, (1) vegetative phases of plant growth and develOpment and (2) metabolic phases of growth and develOpment which are controlled by the photo- period andlor thermoperiod. The problem is to ascertain whether gibberellin will (I) replace the vegetative and metabolic phenomena which are controlled by the photOperiod and/or thermoperiod and (2) if the degree of replacement is dependent on the photoperiodic and/or thermOperiodic sensitivity of the plants investigated. The first area of investigation (vegetative modifications by gibberellin on plant responses controlled by the photoperiod and/or temperature) can be divided into three areas (1) vegetative modification of shoot growth and development (2) modification of the induction and cessation of dormancy and (3) accumulative vegetative modification by gibberellin. A logical approach for investigation of this area should include the selection of woody plants which vary in their degree of response to photOperiod and/or thermoperiod. These plants could be exposed to different photOperiods and thermoperiods in conjunction with their treatment with gibberellin. The second area of investigation (metabolic modifications by gibberellin on plant responses controlled by either photoperiod and/or temperature) can also be divided into three phases (1) modification of the chemical composition (2) modification of foliar absorption and transport of phosphorus (3) modification of root absorption and transport of phosphorus. 4?. Investigation of the metabolic modifications by gibberellin should be conducted on a woody plant which is very responsive to gibberellin, photcperiod and temperature and is also easily prOpagated. The modifying influence of gibberellin on the chemical composition should be a long term experiment (2 to 3 months) while foliar or root absorption of a radioactive mineral nutrient should be on a short term basis. An isotOpe which is readily available, actively absorbed, easily transported, and would reflect the movement of carbohydrates within the plant would be desirable. Accordingly an isotOpe of phosphorus32 and Catalpa speciosa were selected for these investigations since they closely conformed to the above specifications. A mechanism of the modifying influence of gibberellin on growth and develOpment of woody plants is proposed with certain practical implications. EXPERIMENTAL I. VEGETATIVE MODIFICATIONS BY GIBBERELLIN A. Materials and Methods 1. Plant Material and Cultural Techniques Special equipment and plant material was required to study the response of woody plants to gibberellin, photOperiod and temperature. Eight woody plants (Catalpa speciosa, Liriodendron Tulipifera, Viburnum.Carlesii, Acer sacdharum, Pinus gylvestris, Pyracantha coccinea Lalandii, Syringa vulgaris and Euonymus Portunei vegetus) were selected in accordance to their photoperiodic response as reported by Nitsch (1957a) (Table I). The physiological age, method of propagation, and zone of hardiness varied with species (Table I). All plants were locally grown except Catalpa speciosa and Syringa vulgaris which were shipped from Iowa. The plants were selected for uniformity to reduce variability of response to imposed treatments. During late March and early April all plant material was placed in 6 inch clay pots containing a well mixed 3-1-1 loam, peat, sand mixture. Following bud break, 2 buds exhibiting good vigor were allowed to deve10pe on each shrub while the trees were allowed to develOpe only one shoot per plant. The plants of Pinus sylvestris and Acer saccharum were so small that two plants were placed in each pot where only one plant of the other species was used. The plant material was all in excellent vigor at the initiation of the experiment on April 26, 1958 l at which time the variables gibberellin (O or 50 ppm), photOperiod 48. 49. . mesa use a Ou n space» uoono 3oz m wood .nau N cu a euaoum uoonu so: N wcwxoouo spam a s .mnom mdwuuao .nsuomo> .uaMJu.m:wm m~-¢ maue uso> N m omuma m .Hocsuuom as soon moauweueao uoz .HHH mcuuusu hussauom mo guano sou caun mane use» a N manna m .A.e«umuas> muauuNm ocu>oum one on name wmoa .HH mswuuoo .ommn .HHmce .Ioo haemauom oases e~-¢ mane use» g a om-m~ o .eocuuoou sensuous m use on omen uuomm .N waaaooom ou-¢ NN-¢ one» a N ma-n~ N .a.a«uuaun«uu «seam wowamoem .gmwmm nuaouw caucuuom cane naue use» H a manna m .asumeuuou nou< onnou when waoa .n vouusuu .Huaom e~-e as-a page a N we-ms e .aaauquau;aaauamam nauseoum .a.auuu«a«a=a oi-m n~-e use» a s o~-ma s aquuaquqauam wcaamoom .uo as gumbo» asosaaaoou oNuQ NN-< use» d a ou-ma e .ouo«uome a onsmo ammo wooa .m auceauo IAmmmmM.IIIquwnM cannon uses ~uaou sense when uuonm .H anus vuusauacu undone -mo~u>om gamma: -uesus susouu «0 venues. suoosm .mucalhom we ounce Heuuucu use om< III II: sen aco>oum omen wcoa .H 11. Nuofioc0uso umufiumoua Admaa Aemoa modumnu [Nwmmma nonu«2v mean» no uses on can mean usaz sauna uucoauoe useoauoaouoem sawumuuuaon coahzv scam nauseous: euooam mvoo3 nuouuoo mo hmofiooounu mauem one .ucuauaoua mo same any on newumauoson .ocou nauseouom .oncomnom caucuquOuomm sea H man< 1 $35.“...sz 232.32 5x3; 3452 343:. 38 2. 083a $25.“ mo... $3232? 592 3533 3:3. 7:3. ”(vzaonSfia 325.323 592 5.3%.. £35.32? :32 5x3; mo< 1 32% 32%.. 32% $25“. :4 m8 mmaémazm» >3 5x32. 35:; _ — b h _ p — b _ _ _ _ _ b _ _ p 3 ZHHLVH9HUV71 2 do Figure 4 Typical Air and Soil Temperatures During a Selected 24 Hour Period for Plants Exposed to Low and High Night Temperatures. 55. TEMPERATURE PLANT EXPOSED 7'0 -‘ AIR SOIL LOW NIGHT fprfRAn/RE -—o— o —- — x — x —- ”/6” MIG/IT TEMPERATURE ______ ——__ 90 ‘3 I + \ 177' DEGREE-'5‘ FARE/VHE/T 8 “~\ /"I _ / / . 1. . . ‘ \ 50 // . ‘ .,, \ \. ., 1 ‘ I - \* .... v. 40 L_. .___.—\‘ A. w 30 1 1 1 l I J 1* ‘ I l 1 i Q 6 5 IO 12 2 4 8‘A~,'° '3' 2 4' PM I AM HOURS Figure 4 56. Figure 2-C. Air circulation was sufficient to prevent temperature buildup under the long day regime. Plants held daily at the 40°F temperature from 5 pm to 8 amiwere segregated by black velveteen cloth into 6 areas, thus providing 3 long day and 3 short day locations (Figure Z-B). Plants on the outside and exposed to the high night temperatures were divided similarly to obtain the desired photoperiods. The outdoor area was covered with a black velveteen cloth followed by lamdnated black and white plastic (white side out, to reduce heat buildup in the early morning). The coverings prevented photosynthesis and screened out any light which might have come from the sun, street lights or cars (Figures 2-C and D). The variables under test in this experiment necessitated an area in close proximity to the refrigerated storage room thus allowing rapid transfer and placement of the plants receiving the 40°F night temperature. An area between two greenhouses running north and south, measuring 16 x 20 feet was selected. The area was covered with a 4 inch slab of concrete to allow Operation of a dolly for removal and return of the plants exposed daily to 40°F from 5 pm to 8 am. The entire outdoor plant growing area was covered by a luminite shading material which produced 50 percent shade and appreciably reduced the daytime temperature. The netting was suspended 6 feet above the cement to allow room for recording data (Figure 1). This location was only 70 feet from.the refrigerated storage which was located inside of the Michigan State University Horticulture Building. S7. 3. Method of Treatment Gibberellin was applied at the rate of 50 ppm as an aqueous spray to the foliage until runoff. The solution, containing 0.1 percent Tween 20, was applied between 3 and 4 pm.on April 26 and for 4 consecutive weeks thereafter. Two genera (Liriodendron and Syringa) did not receive the initial treatment until May 10 as they were not available at the earlier date of application. Four genera, Viburnum, 555;, {$235 and Pyracantha received a sixth treatment on August ll. A self-contained air pressure container delivered the spray under 100 pounds of pressure. In place of the Tween 20 wetting agent, all pine seedlings were sprayed with a 2 percent solution of Volck oil to allow greater penetration of the gibberellin. Plants which were sprayed with gibberellin or the surfactants only (controls) were removed from the plant growing area to a shaded location for treatment. After the chemicals were applied uniformly to the foliage of the plants, they were allowed to dry in the shade before returning to the growing area. Consequently the rate of drying was reduced possibly insuring better uptake. Mechanical injury of the foliage prior to treatment was avoided in so far as possible. 4. Data Recorded Shoot elongation and number of nodes were recorded at weekly intervals from April 24 through June 21, then again on July 24. The last shoot elongation measurements were taken on September 5, 1958. Final harvest and measurements occurred between the 9th and 16th of 58. September. Weekly notes as to the development of the plants were taken, with a detailed description on July 24, 1958. Shoot extension and node nuflaer were recorded from the base of the current season's shoot to its apex with stem diameter measurements taken on the shoots at the mid-point of the current season's growth. All leaf blades (petiole discarded) of the current season's shoot growth were removed and counted. This also permitted a recording of the dry weight per leaf. At the termination of the experiment the plants were dismantled into five parts - leaves, new shoot growth, new root growth, old shoot growth, and old root growth. The five parts were placed in paper bags, and dried thoroughly in a forced air drying oven at 70°C. In addition to the above data, the total dry weight per plant, dry weight per centimeter of the new shoot growth, number of flushes of growth, the dates of induction and cessation of dormancy, average internode length (2132; not included) and shoot-root ratio were analyzed. Leaf area per plant was determined for all genera except 25221. This value was obtained by determining the correlation between leaf area and dry weight. Six representative leaves, 2 each from the lower middle and upper nodes of the new shoot growth were selected from 3 replicate plants of each genera which were exposed to the different treatments. The leaf area was determined by placing the leaf in a light tight chamber which permitted the recording of the percent light trans- mitted through a clear window glass. The reduction of the light trans- mitted through the glass by the leaf was recorded, and converted to leaf area in centimeters. Subsequent dry weights of each leaf allowed a test for a correlation between leaf dry weight and area. The correlation was highly significant for all genera. By knowing the weight of the leaves per plant, the total leaf area could be readily calculated. 59. 5. Analysis of Variance A high speed computer ("The Mistic" at Michigan State University) was employed for the analysis of variance. A program tape (P-lO) prepared by Dr. W. C. Jacob at the University of Illinois was used. This facility permitted detailed calculations that would have been virtually impossible in the time available using a standard hand calculator. Each species was analyzed separately using a split plot design as no program tapes were available which could handle a 4-way inter- action (species x temperature x photoperiod x gibberellin). The photo- period was replicated three times assuring a valid test for the photo- periodic response. In contrast, the temperature was not replicated, but was adequately controlled to justify the evaluation of the effects of temperature on growth. Genera were randomized within the randomised photoperiods with the control and treated plants of each variety, adjacent to each other to reduce variation. Within each photoperiod replicate were two single pot samples containing one plant for each genera, the exception being Age; and E$22£ in which two plants comprised a sample. A total of 4 shoots were measured for the two single pot samples of all species with the exception of one shoot per sample for Catalpa and Eiriodendron. Thus either 2 or 4 shoots were averaged to give values for each replication. In the case of the old shoots, and old and new roots, only 2 samples were averaged in the values for each replication, except with 5525 and Pinus, in which 4 samples were averaged for each replication. 60. Since only two variables for each treatment (gibberellin (0 to 50 ppm), photOperiod (9 and 18 hours) and night temperature (40 and 70°F) were tested, a significant "F" test indicated significant difference resulting from treatment. Consequently a least significant difference (LSD) was not required to determine differences (Snedecor and Cochran, . (1956). 6. Catalpa speciosa Seed Germination Catalpa speciosa seed germinated at different temperatures following gibberellin treatment might give supporting evidence to the modifying influence of gibberellin on the vegetative response in woody plants. Consequently seed from pods of Catalpa speciosa were collected on September 15, 1959 from locally grown trees for germination studies. Prior to placing the seeds under test, they were soaked in aerated solutions of 0, l, 10, 100 and 1000 ppm of gibberellin for 24 hours on September 16, 1959. The seeds were dried at room temperature and placed in bottles until ready for use. On September 22, the seeds were placed in two germinators held at a constant 68°F and on an alternating day-night temperature of 86°F for 8 hours and 680 for 16 hours during the dark period. Treatments were replicated four times. Thirty seeds were placed in each 5 inch Petri dish containing a moistened filture paper for germination. The seeds were watered with tap water during the germination test. The temperature was adequately controlled in standard germination equipment furnished by the Michigan Department of Agriculture Seed Testing Laboratory. The percent germination was recorded periodically until germination was complete or no further evidence of germination was apparent. A standard analysis of variance, utilizing Duncan's multiple range test, was used to determine Significance. (Duncan, 1955). 61. B. Results 1. Vegetative Modifications of Shoot Growth and Development a. Shoot Extension Figures 5 and 6 present a summary of the modifying influence of gibberellin, photOperiod and temperature on shoot elongation during the season, for eight woody plants. A perusal of the data illustrates the degree, rapidity and duration of shoot extension resulting from.the variables imposed within and between species. A significant response to gibberellin treatment (0 or 50 ppao and night temperatures (40 or 70°F) was evident at various periods during the growing season for all species. In contrast, Acer saccharug, Pyracantha coccinea Lalandii and Euonyggg Fortunei vegetus failed to respond to the photoperiods imposed (9 and 18 hours) (Figures 20, 22 and 24). In this respect the above species generally failed to respond markedly to gibberellin treatment. This was particularly evident in Pyracanthg coccingg Lalandii and less apparent in Acer saccharum and Buonzggs Fortunei vegetus. Four species (Catalpa speciosa, Liriodendron Tulipifera, Viburnum Carlesii and Syringe vulgaris) exhibited a marked response to gibberellin throughout the growing season (Figures 17, 18, 19 and 23). The similarity in the response to the variables imposed on these species is interesting. Note that in all 4 species the same sequence of response to treatments is evident (A24-C2+'Bz+'81+'cl+'A1) although differences between treatments were not always significant. The shoot elongation for plants treated with gibberellin (50 ppm), high night temperature Figure 5 Comparative Growth Rates of Terminal Shoots of Catalpa, Acer, Pyrancantha and 82inga as Influenced by Gibberellin, Photoperiod an! Temperature. 62. ! ”r .4 . I ---, ——~-Aa ...; CATALPA .~ SPECIOSA (1) ._ ACER SACCHARUM r “ / -. Ir 'f ,. _ - ---Ce / l / . / . - _ —— "BE I / . /' a. C1 / I I 4» ,,.... " "" “m Ae . / r x ” -7 -~ -u— a ..//' r ./’ , — - - a. I /_' 'l {/4 4 L. 3 IL c-{A/ .’ /’_ -‘— A! .‘,":'.:-’ ‘ (J’— — ——7 A! .'I / l to KC’ we 8' N' 6 IE r‘ ---—J—-J.—-—~ .1-4. 4* A L w“ ' " v -‘—*m*~*fi4 ‘.3 — \ I ..Cz g I ~I PYRACANTHA . SYRINGA v k W coccmea ,x , ”LOANS § P. LALANDII .. ' g: mama", g,“ . .» a. . AL__CONTROL ,JA: ; A2_GIBBERELUN ~l ' ' ,/ . BI_SHORT DAYS §,' /. - mm,unm'mws i . C:_ LOW NIGHT TEMPERATURE q i , c, Ce_MIGH NIGHT TEMPERATURE I“ / k er. " .. ___.... 4.... ~Ad _,.-/ L ’3 . ‘p. / // I w (a. "/1 .’ ’// ,"I .. Ca 5 //(I /’ {at ‘/.;J‘h'_’ “"“—Ba I? 1' / ,1/ ‘ -s’ ‘ :5 ~ _ a" / ' .. -_ ‘ .- I../' I .I/ / E / / ill I l/'. _‘// / / '7. I r I / / 0 ,-'././ / . I“ / J .— /I y ’ 3;, / 7__________‘. __ A1 ’. I / y , _/ 5 ~ 7‘ z, 1 f" :I’ I J b I..// C i ..30 a. I o e (3' CK A' A’ C' C" A" C'C' C' B“ C' C' J FL 1 i 2 1 L L 1 #1 i 1 J i :6 5 n :7 24 34 7 .a z: (a 5 20 5 H ' -4 $4 7 .4 21 :4 5 mm mv was JUU sermasrs APRIL mv .1qu JULV smmsm (1) MULTIPLY SCALE BY 2 TO OBTAIN TRUE VALUE “OR “I SIGNIFICANT DIFFERENCE BETWEEN TREATMENTS SHOWN BY THE LETTERS (44,8 0R C) AT THE 5 OR I PERCENT LEVELS, RESPECTIVELY, AT DATE INDICATED, 0R ATALL MTES NOTED LATER IN THE SEASON. IF THE LETTER IS FOLLOWED BY A SQUARE (I). THE TREATMENT IS NO LONGER SIGNIFICANT. Figure 5 Figure 6 Comparative Growth Rates of Terminal Shoots of Liriodendron, Pinus, Viburnum and Euonms as Influenced by Gibberellin, PhotOperiod and Temperature. TERMINAL GROWTH (CEN TIME TER s/ 63. 55; ~ 35 i 1 so LIRIODENDRON TULIPIFERA ; PINUS SYLVESTRIS . ,0 2" fl/mAa I ’e 9" /.. (Jr— /-"/ CC ‘ 30 ..- ‘./'. I 5" W / I / CI 15 .n ., M" ‘__ _ ,. - .,,_ // BI 11 \_-lu"-u N“ #1.." ;-—2: ’ ,, .. " c: ,/C{’ ’TT'KL if S: .’ / ’- ” .7 /” _ — - Cl no e .- . l. " — _. [7 , » AI . 5 T ,/'.:'I r, ’I’fl I ‘ .112 ”‘ a- . 7/ 9 As A. I o,__ A" a" c' 8' A' C'A"C" c' «. C" I. l .__g_._+ . . _.. ..- ._._ _ ...}.1_ Li. ‘ __ ‘5 u g 2| II )I 4- I ... VIBURNUM CARLESII EUONVMUS .. , M FORTUNEI -—/‘ , c. VEGETUS - 7’ ' 55'— ,/' , " 1,31 ‘ 55 _.P 7 ," Bl / “A!" I so JVL—fiw’fl/T _ — — - —--Ca 1 I»; .. «' M M AI ../ x i... I ZSIf— /.:,' .;// ,/' £5 __ I I." / r L a, a I /, .. r .1: // 7, c. ‘ , / Ba /j. - .../”,L/'/ /.-.- I. 1’ TREATMENTS I 5 _ /-/ z.” ’ AL _CONTROL 5 .. -/ «(,2 , H A2- -GIBBERELLIN ‘- ‘ 2}" -- ' _- ,,-§: 41/ a. SHORT oavs ,/- ’ " , ”I?" ashtouo oavs .0- . .. ,,__/ / c: LOW NIGHT TEMPERATURE _ ,/ // / c; HIGH NIGHT TEMPERATURE .rf/ci "’V KIT «"1 I S ‘ é‘va—fllr/ IL.» 8.. ss 0L AI BsAs-Ca 8. cos Cs .4 _ CH C. 3 !L_ .____l_,, 1, _1, i _ _J... ____ _. L n __J..., ,1.——L ___4.. ..L__._. ______¢_,_ ___4 .G 5 m? a4! ('40 24 5 in 5” 52431 T 14 an 24 3 A; Rn. M... JUNE JULY SEPTEMBER APRIL MAV JUNE JULV Iii-PI F MBf R 4* OR‘I SIGNIFICANT DIFERENCE EETDVEEN TREATMENTS SHO'VN BY ”IE LE TTERS (AB MCI AT THE 5 OR I PERCENT LEVELS. RESPECTIVELY, AT DATE INUCATED. 0R ATALL M755 NOTED LATER IN THE SEASON. IF THE LETTER IS FOLLOWED BY A SQUARE (m), THE TREATMENT IS NO LONGER SIGNIFICANT. Figure 6 64. (70°F) or long days (18 hours) is very similar particularly in Viburnum.Carlesii and Eiriodendron Tulipifera. This relationship is also true for Catalpa speciosa and Syringa vulgaris, but in contrast, the response to gibberellin is more dramatic than the photoperiodic or thermoperiodic response observed (Figures 5 and 6). Acer ssccharum.and Euonxggg Fortunei vegetus exhibited the above trend for a short time during the spring. Later the sequence of shoot elongation was altered, (A2+ Cl*'Dz+ Czr A1) with gibberellin (50 ppm) low night temperature (40°F) and long days (18 hours) approximating a similar response, although the differences were not always significant between the temperature treatments. gigg; sylvestris could be grouped with the above two species, at least through July 24th. Subsequently, gibberellin caused death of the plants at the high temperatures. Pyracanthg coccingg Lalandii failed to follow the above two patterns of growth, common for all other species. In contrast, shoot extension was more evident under high night temperature (70°F) than any of the other variables imposed (Figures 5 and 22). The rapidity of response of shoot elongation to the variables imposed varied between species but again a pattern of response emerged (Figures 5 and 6). Catalpa speciosa, Syringa vulgaris, Liriodendron Tulipifera responded to gibberellin one to two weeks after the initial treatment but failed to respond to photoperiod (9 or 18 hours) until 6, 3 and 3 weeks, respectively, after the initiation of the experiment. The above species responded to the thermoperiodic treatment one week after the response to gibberellin was observed, except with Liriodendron in which the response occurred simultaneously to temperature and gibberellin (Figures 5 and 6). 6S. Viburnum Carlesii which had previously been grouped with the above species did not respond to gibberellin (50 ppm) until 4 weeks after treatment. It is of interest to note that a similarity still exists between these 4 species; a response to gibberellin was always evident prior to or during the response to the other variables (low or high night temperature, long or short days. Acer saccharum, Pyracantha coccinea Lalandii, and Pinus sylvestris were slow to respond to gibberellin treatment. This was particularly evident in Pyracantha coccinea Lalandii (Figures 5 and 6). In the latter 2 species and also Euonyggs Fortunei vegetus, the shoot responded more rapidly to the temperature treatment (40 and 70°F) than gibberellin (O and 50 ppm). (Figure 5 and 6). The duration of elongation as influenced by gibberellin (0 or 50 ppm), photOperiod (9 or 18 hours) and night temperature (40 or 70°F) are shown in figure 5 and 6. It is of interest to note that gibberellin had an influence on growth in Liriodendron Tulipifera, Viburnum Carlesii and Euonzmgs throughout the growing season which was comparable to the long day and high temperature (low temperature in the case of Euonymus). In contrast, gibberellin did not cause an increase in growth of Catalpa and Syringe after mid-July and in Age; after late June (Figure 5 and 6). The shoot elongation response to photoperiod and temperature followed a comparable pattern. Pyracantha which failed to respond to photoperiod was influenced by gibberellin during late May and early June only. It is of interest that those species which exhibited the greatest shoot elongation following gibberellin treatment could be classified in two groups (I.-l.-a. and II.) which are shown in Table 1. In 66. contrast, species in group I.-l.-b. and I.-2 were least responsive to gibberellin treatment. Euonyggg should be placed in group I.-l.-b with 5555 and giggg in this investigation. A differential response of shoot extension to gibberellin treatment at the different night temperatures is shown in Figure 7. It appears that the action of gibberellin is reduced in some manner under low night temperature in Catalpa, Eiriodendron, Viburnum and Syriggs. Note that the duration of the interaction in Catalpa and Liriodendron is apparent only until July 24, whereas Viburnum and Syringe responded differently to gibberellin under the different night temperatures until the termination of the experiment in September. The general lack of a significant interaction between gibberellin (50 ppm) and night temperature (40 or 70°F) is of interest in Aggy, Pinus, Fyracantha and Euonxggs. If compounds were present within these species to counteract the action of gibberellin or shoot elongation they were ineffective except in certain instances. Note that on May 24 there was a greater response to gibberellin at the higher than at the lower temperature in 5255. As the season progresses this interaction was no longer apparent. In contrast giggg and Pyracantha failed to respond differentially to gibberellin treatment early in the season but did so late in the summer. The action of gibberellin on Piggy under high night temperature was so intense during July that death ensued. The implication in Figure 7 is that species which respond most favorably to a low night temperature (e.g. Pinus, Euonymus and 5225‘ note Figure 5 and 6) do not respond differentially to gibberellin when 67. grown under different night temperature regimes. Apparently the inhibition by high night temperature is not very intense in these species except during specific periods of the growth cycle. In contrast, in those species responding most markedly to high night temperature (Catalpa, Liriodendron, Syrigga and yibgrggn) the inhibitory influence of low night temperatures is not completely over- come by gibberellin (50 ppm) (Figures 5, 6 and 7). In Catalpa and Liriodendron however, the inhibitory influence of the low night temperature on the shoot growth response was no longer apparent after July 24. It also appears that inhibitors accumulate in plants under high night temperatures thus reducing the action of gibberellin. In this respect, on August 12, Pyracantha, Pinus, Viburnum and 5255 were sprayed with 50 ppm in hopes of stimulating additional growth. As shown in Figure 7, only 1 species appeared to be affected (Fyracantha). Apparently the action of gibberellin was inhibited at the cool temperature while this was not apparent at the higher night temperatures. In contrast the failure of Acer, Viburnum and {£932 to respond differential to gibberellin would indicate that the endogenous inhibitors had accumulated in the shoots irrespective of the night temperature or photoperiod. There also exists the possibility that the concentration of gibberellin was insufficient to overcome the endogenous inhibitor within the plant. The inhibitory influence of short days on shoot elongation can easily be over ridden by gibberellin resulting in a similar growth response irrespective of the photoperiod imposed in all species. One exception was Syringe, in which a greater response to gibberellin was observed under long days from June 7 to 21. Figure 7 The Modifying Influence of Gibberellin on the ThermOperiodic Response of Shoot Extension in Certain woody Plants. * or ** Significant interactions at the S or 1 percent levels, respectively. 5;]007' EXTENS/O/V DIFFERENCES /N CENWMETERS-RESULT/NG FROM G/BEERELL/N TREATMENT 68. T CATALPA leooeuoaou vaeuauum ACER 60 oo 50E .— 40 40 ..L I! 20.— 10— 2 $3 3 2: q 4— 3 =— 2 a— R o) 1... 0439999 Pmus a... 15r- “maniacs lj [17!” STIMULA T/ON 1“ /;\‘*1/5/770N mam ._ GENO DATE OF TREA rMENT CODE 1 MAY 24- 2 JUNE 7 .3 JUNE 21 4 __ JULV 84 5 __ SEPT 15 L I LOW N/Lsz’ «'EMPER-lfL/K'F D HIGH N/oh‘f rEMDERA TUR: \ Figure 7 69. A greater shoot elongation to the long day regime was evident at the higher night temperatures throughout the growing season in Liriodendron and Viburnum (Figures 18 and 19). Shoot elongation of {£225 and Syringe, however, was greatest under the long day regime irrespective of the night temperatures (Figure 17, 21 and 23). Euonygus and Catalpa exhibited a greater shoot growth response to long days under the high night temperature as compared to the low night temperature regime only, on June 14 and May 24 respectively. b. Node Formation Node formation was altered by gibberellin (50 ppm) in all species at some period during the growing season as shown in Figures 8 and 9. The degree, rapidity and duration of response to gibberellin (0 or 50 ppm) as well as, photOperiod (9 or 18 hours) and night temperature (40 or 70°F) are shown. The response of node formation to the variables imposed followed a very similar pattern as found in shoot elongation. Generally, however, the differences were not as evident (Figures 5, 6, 8 and 9). In contrast to the response of shoot elongation to gibberellin, node formation generally responded more rapidly to high night temperatures (e.g. Liriodendron and Syrigga) and long days (e.g. Viburnum) than to the gibberellin treatment. Euonymms, Zyracantha, Catalpa and Age; approximated the same rapidity of response to gibberellin in both node formation and shoot elongation. The duration of response to the variable imposed follows a simdlar pattern in all species as exemplified by shoot extension. Figure 8 Comparative Rates of Node Formation in Terminal Shoots of Catalpa, Acer, firacantha and Syringa as Influenced by Gibberellin, Photoperiod and Temperature. 70. .1 _ ; q 4, lb 1-- : CATALPA SPECIOSA AC E R SACC HA RUM “ - 4L 4:4 . — + TREATMENTS .4 a r (H AI__CONTROL J g , ,,..A2 ‘4 Az_GIBBERELLIN V _,,..._._:':;;:;-“.i}>i:" 5 BI__5HORT DAYS '° ., s -‘ " /- —- " ; + ne_-Lo~G oavs ‘ - .L ./ '/ / . .. (Zn—LOW NIGHT TEMPERATURE ,4 , _ , //., 1, ca__moH man-r TEMPERATURE ; ° F . ,/ “h -... A2 . 5 ’— :/ 44 .... *__,.- _ 1:” ' _fl—_ - 7 Cl 4. . ~ .5/ «» 3;,7; ‘— -.—~ — — - f 1 4 U) 54 If ..4. ”if: _.-__. —" “ _ii‘- _ f ‘ [U 24' ‘4”/ I Q . _ g 0 AeAaa A. A. 0 Ali Bus. 4 C‘ H :'1' ll ,,J_J_LJ 3! 211—" ,fi_L__ _hi 7 ,_1_ L 4 [L 22 4F g 0 £1 ,e [I as PYRACANTHA ,c. «» SYRINGA VULoAms .. COCCINEA , ' -» 1‘ lu _. m y. LALANDII m M 4. ~ 1. Z 174»- -;J- 33 a.. _ .5 7 l 3 ° / /- A: ~~ .. :6 2 154 / ///// 41- _. "4‘ I, 21,/Ix t. .4» _1 l4 13IL— / ///:, / ,” 4.. 4 124— ,- ' .0- .. {a 11'.— «1- . _— __ __ A2 _, ..... / BI or— «+- ’./,/' ’ / ..r r— _ - C! 1 _ «~ .;;:.e< “ _— z . a - «>- /;;:# __ __ __ w in A. 4 6 7* 4 7/ 4 o _ .L //’. J 6 5 ~ «— < 4: - >— -4 4 3 ._ 41- A 3 >- -.. q 2 I w 4- c. «4 o . c'c" A"A" c' .. c’t’c’at‘c’ o 4.1 1 1 1 1 1_J_ 1 1 1 , 1 l__l 1 L 1 i 1 1 i-___] 26 5 ll 1T 24 31 7 I4 El 24 5 fi 5 II \T 66 3| 7 14 21 24 5 APRIL MAY JUNf JULY SEPIEMBER m MW JJRE JULY SEPIEMBER (1) NULTIPLY SCALE av 2 7'0 03mm TRUE VALUE . * OR if SIGNIFICANT DIFFERENCE BETWEEN TREATMENTS SHOWN BY THE LET TERS [AB (RC AT THE 5 OR 1 PERCENT LEVELS, RESPECTIVELY, AT “75 INDICATED ORATALLM S NOTED LATER IN THE SEASON. IF THE LETTER I6 FOLLOWED BY A SQUARE (I), THE TREATMENT IS NO LONGER SIGNIFICANT. ' Figure 8 Figure 8 Comparative Rates of Node Formation in Terminal Shoots of Catalpa, Acer, Pyracantha and Syringe as Influenced by Gibberellin, PhotOperiod and Temperature. 70. . A. 16 7 4,. 1° _ 4.- c CATALPA SPECIOSA W ACER SACCHARUM M e 4.. 4 -. ’ ‘ + TREATMENTS Z 4- ..L A._C°~TR°L :5 ,4 , . [mAz 4L “_GIBBERELLIN 7 I ...‘::;;_‘:T}'-’_' f’ g BI_SHORT DAYS '°*‘ -~ ;* ' ,- ; ._ as__LONG DAYS 1 L' 9 L- . / / ’ / ' T CI_LOW NIGHT TEMPERATURE 4 a L : /’_/.-. 4 C8_H|OH NIGHT TEMPERATURE A 3 o e - e 6 ./ __ A2 1— / 4» ... ’0. 1... “ :7___ CI 4 >— .17 «b- /-':_ ’ ‘J/T;:-_fl; ,: —. —- f ‘ a. «4 4 m” i ~» ,Aeefiie_im : -~—'::;" -? J LU "- . 1~/—/ 4 Q lI JD-f “ g o ACAI. A. A. {’- AI. BIGB. _, C [L Pg 1 '1. L 1 51I 1 1 z1 1 1 _1 _L_.l ’1 L__ _ +J._ __ i g 71:1 >- " I; 0 .; . - (I m PYRACANTHA s/CZ r SYRINGA VULGARIS . as m J COCCINEA ., * 4L 1 tn «L LALANDII m , - I. + ~ w z . g. 4. - b _.' J‘ A: .. _ e 2 54 ”/ / «P R ‘ Y' / .4 | )/ 1‘4. /’ r/jc, «» 4 ”4. ///’ .44- ‘4 124: ‘W' " 12 l'. 4» / ~———— —- *3? .. m- ~~ /” r - — — _ C3 « ; I)" , T — I 9» > ’ 1,6 ! a . s»- - /3"/_ ._ __ _. 7 A: - e K" o >- T %;/ .4 6 5 r— .0. .. s » '* d 4 3 +- 44- -4 2 1- 4L -4 2 4»- C. -4 o » c'c" A"A' c' 1. C't'C'N'C' o 41L“... .: 5 unsung .1. L—J 341115 H {Alva 3' 7 .1311? JULY swarms m m JUNE M" “mm“ (1) NULTIPLV SCALE BY 2 TO OBTAIN TRUE VALUE . y me LETTERS he mc FFERENCE serwsew TREA TMENTS SHOWN a . OR " ifgsécéflgnag PERCENT LEVELS, RESPEC TIVELY, 47' am: macarsa ”7.22“.“} s NOTED LATER IN rue season. 1;: THE LETTER :5 FOLLOWED av A sou ( , THE TREATMENT IS NO LONGER SIGNIFICANT. Figure 8 Figure 9 Comparative Rates of Node Formation in Terminal Shoots of Viburnum, Liriodendron and Euonms as Influenced by Gibberellin, PhotoPeriod and Teuperature. 71. VIBURNUM CARLESII TREATMENTS *CONTROL M~GIBBERELLIN BI_SHORT DAYS B¢_LONG DAYS Cl_ LOW NIGHT TEMPERATURE C¢_HIGH NIGHT TEMPERATURE Bl . Al; 8. Bot V, W s‘e‘e'c‘c c' C" d. [U \ 8 H.._.=_.|JT_L JLI 1 a: 1 1 If; 1 5 1 i 21‘ 1 L 22 -<>- 22 L léfo LIRIODENDRON TULIPIFERA w EUONYMUS /C' q, « FORTUNE! / M q a VEGETUS .5/ L1,]./// _ 8: q] __ ,/ B: E ab _‘h / // /.‘/ 3 [5 _‘F '"/ I ’ / / Al z.4 ZFLJ r‘:‘*—-**- 62 I3 4»- fiz/ // !2e w ///// :1 /Ba ” // '0 ,,/' C: 4* 9 [/2..;:Al 4V 8 ”2’. L.”- A! __ I?” /_/ 7’ . ""15” /:: fi/// 6 .1? r”-- 4 .- - S L ,57';:' A. ,_ ‘ 7F": fi- 3 1 w 3* I. r - -._ C C C | o no an an .... c' 0% do“ A” A" A' 1 A' A't' c' WED 1 1 1 1 J J_ g _ 1 t 4 L A 1 2_b 51:17:6317143 as ? usunuuvna 24 S N’RL HAY JUNE JUU SEPTEMBER Wt MY JUNE JULY SEPTEMBER . on u SIGNIFICANT DIFFERENCE :ErmsEN TREATMENTS suamv ay 71!! LErrE/zs 64,5 mc/ AT THE 5 0R 1 PERCENT LEVELS, RESPECTIVELY, IN THE SEASON. IF 7W5 LETTER NOTED LATER AT DATE INDICATED, 0R AT ALL DATES IS FOLLOWED BY A SOMRE / l / THE TREATMENT IS NO LONGER SIGNIFICANT. Figure 9 72. The significant response to the variables imposed early in the season, does not necessitate a significant response throughout the growing season. It is of interest to note that in Viburnum.and Euonxmus the response of shoot extension or node formation to night temperature (40 or 70°F) was not significant in mid-June but was significant earlier and later in the season (Figure 6). The degree, variation in duration, and rapidity of response to gibberellin, (0 or 50 ppm) photOperiod (9 and 18 hours) or night temperature (40 or 70°F) illustrates that plants are not always physiologically receptive to these variables (Figures 5, 6, 8 and 9). Interactions between gibberellin (50 ppm) and night temperature (40 or 70°F) as influencing node formation are shown in Figure 10. There is a marked similarity between Figures 7 and 10, illustrating again that the response in shoot elongation and node number to gibber- ellin (50 ppm) are very similar. The differential response of node formation to gibberellin (50 ppm) under the different temperature regimes is well illustrated in.égg£ and Viburnum and less evident in Syringa and Euonyggs. In contrast to the response of shoot elongation to gibberellin (SO ppmo at different night temperatures, node formation in.§gg£ was greater under the low night temperature regime following gibberellin treatment. Syringg exhibited a greater response to gibberellin under the high night temperature during the latter part of the season only (Figure 10). The formation of nodes of Catalpa, Liriodendron and Pzgscantha were affected similarly by gibberellin treatment irrespective of the night temperature imposed. Figure 10 The Modifying Influence of Gibberellin on the Thermo- periodic Response of Node Formation in Viburnum, Acer, Syringa and Euonyggs. * or ** Significant interactions at the 5 or 1 percent levels, respectively. 73. IITT [Hill] I m “32>ZODW on «human measewtmuxfl .233 :91 D manganese? E32 e3 I (oz—“>W m! KQQW vm \QQB R $.33 k “.933 Wm :x? ZQKQ EQNWQO KO .UIKYQ KNU( [DZKDG _> N011 IQIHNI QGIQPQV? *7 '9 N NO/J V7/7N/15‘ .4 JNE/WJVEHJ N/7'738399/9 WOb’j 9N/17/75‘5’e/ SHE’JE/V/JNB’D N/ S‘EQNgHEdj/O NO/J IVA/801 BOO/V 74. The effects of gibberellin on node formation in the various woody plants were in almost all cases completely independent of the photo- period imposed (9 or 18 hours). This is in marked contrast to the interaction observed between gibberellin (50 ppm) and night temperature (40 and 70°F) (Figure 10). This illustrates that the temperature modifies the response of plants to gibberellin to a greater extent than the photOperiod. c. Degree of Replacement by Gibberellin of the Environmental Factors Which Influence Shoot Elongation and Node Formation The effectiveness of gibberellin in replacing or partially replacing the response of shoot elongation or node formation to photoperiod (9 or 18 hours) or night temperature is (40 or 70°F) summarized in Figures 11 and 12. These figures illustrate conclusively that (l) gibberellin will replace or partially replace the effects of photOperiod or thermo- period on shoot elongation and node formation and (2) the degree of replacement varies with species. Gibberellin was more efficient in replacing the influence of long days than that of high temperatures on shoot extension, in Catalpa, Liriodendron and Viburnum. This relationship was not as apparent in Syrigga. Viburnum in contrast to Catalpa and Liriodendron exhibits only a partial replacement earlier in the season but by July 24 complete replacement of the high night temperature by gibberellin was evident. Shoot elongatiOn in 33923 and 5255 under low or high night temperatures is of interest. As shown in Figures 5 and 6, the shoot elongation of Pinus and Acer was greater under the low night temperatures 75. than the higher night temperature regime. Consequently the comparison, with the addition of gibberellin, should be between the response of high night temperature plants treated with gibberellin as compared to the low night temperature controls. As shown in Figure ll, gibberellin completely replaced the effects of low night temperatures in both 5555 and giggg. In the case of the latter species replacement was complete until June 14 at which time gibberellin became toxic. In 552;, gibberellin did not become toxic but continued to substitute for the low temperature affect throughout the season (Figures 21 and 23). Gibberellin was not effective in substituting for the high night temperature response in Fyracantha (Figure 11) except on May 31. And yet this species responds markedly to high night temperatures. This is difficult to explain since most all plants that respond to photo- period or thermoperiod respond to gibberellin. Gibberellin replaced the effects of long days or high night temperature on node formation. In contrast to the substitution of gibberellin for the control of shoot elongation by photOperiod and temperature, only a partial replacement of nodal formation was evident in Liriodendron. Viburnum and Syringe grown at low night temperatures and treated with gibberellin simulated a node formation response which was typical at high night temperatures (Figure 12). Gibberellin was effective in replacing the influence of low night temperature (which stimulated node formation, see Figure 9) in Euonxggs for a major part of the season. However, in September, gibberellin applied to plants under the high night temperature was only partially effective in replacing the low night temperature response (Figure 12.) Possibly at the higher night temperatures an inhibitor accumulates in the Figure 11 The and Hood Extent to Which Gibberellin Replaced the Photoperiodic ThermOperiodic Response of Terminal Growth in Certain y Plants During the Growing Season. Placement of the photoperiodic in at the 5 percent level. H.— ouflwwh <02_K>W <1hzm KNUd‘ $32130.) ZOEDZUDOE: it 4... m/Jfl (Q J (.5‘0 I ,. 95.. are. :1 76. 2‘ lwlufimd «i “(55 no.3!” ziquwmmmxa T a “.wa RQOIW (Edmunfims 7,. .Aan. 020.. \(WWVNVNQon a.» WQDK~o>wuosnauu .eao>oa acuuuua A can m on» us acouawwcwaa sum uaoaunouu new season co>aw n uou nosan> ||ll «8 no i .mN aaua< noumn ammo «0 ocean: acunouauu nusas> n 3 2 2 3 «N 2 uslauaoau 13 B 8 S S S «a on ten 5 in 3 13 an 32 7 us an on mm am can Hosanna> choose 2 3 3 a 1 + .. t. Eco €265 ousueusmaua voauumouocm caaauuonnqu .nnn uuoueuomaua can moduumOuonm codename HH ugm__L * =91» a z \\\\\\\\\\\\\\\\\\ , LL ~ Ill i“&\\\“\\\\\\\ “\\\“\\ 1_§_O,I_,E,§___; ‘9 0 P“\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ gigs; m g \9...\\\\\\\\\\\\ \\\\\\\\\\\\\\\\\\\§\\\\ “Lamps * . H- LLL-i ...:z: n :. m\\\\\\\\\\\\\‘ ‘ 13km ~ :\\\\\\\\\\\\\\\\\\\ EQIE — u °_E_3_<_%—§ < {T 0 TVWTL—g‘ o .2. ID \IIE "* [I :iVVV‘; ' .sl. ' [9 V > .L H .. ”.9 W Liam N Z . .Q‘ ...? p :\\\\\\\\\\‘ g \\\\\\\\\\\\\‘ m \::a\\\\\\\\\\\\\\\\\\\\\\\\\ \\\\\\ \\\\\\\\\\\\\\\\ ,_ EELJCDDJNKF1LJ£5 IIIIIIIIIIIIIIIIII§\\VNR!!!BEREQ\‘!\\‘R§§§§R§ s::“.\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ \\\\\\\ \\\\\\\\\\\\\ \\\\\\“ SthS§b lliilllllllskx“ W‘\\VRRkIR§!I§k\VR§S&§Sh. 12345678 IKCZEEFi SR§§§§QB§S is Cfi§§§3 ; 7L. JUNE 15 F 1 a9_ : aOr i 1411an s 12345678 Figure 13 81. The first flush of growth of the control plants grown under long days and low temperatures terminated in early June and produced a second flush of growth after 3 weeks of dormancy. The initial flush of the control plants under the low night temperature short day regime also terminated in early June, but failed to initiate a second flush of growth. Gibberellin applied to the long day-low temperature plants was not effective in delaying dormancy of the first flush of growth and had no effect on the duration of the dormancy period. The control plants under long day and low temperatures, terminated in late July, while dormancy of the second flush of growth of gibberellin treated plants under a comparable environment‘was delayed indefinitely. Gibber- ellin in the presence of low temperature and long days appears to be instrumental in delaying dormancy of the second flush of growth (Figure 13). Under the high night temperature regime, gibberellin did not delay dormancy in 5255 but was effective in causing a second flush of growth which terminated after 2 or 3 weeks. It is of interest that in Euonymus, gibberellin was effective in preventing dormancy of the second flush of growth which normally occurs under low night temperatures but was ineffective under the high night temperatures. A third flush of growth was initiated in the control plants growing under the low night temperature, indicating that dormancy was not very intense (Figure 13). Gibberellin was effective in breaking dormancy in buds of Syringa under the low night temperature-short day regime, but had no influence on plants under low night temperatures and long days. It would appear that in control plants grown under low night temperatures dormancy is 4!: 82. delayed, while under high night temperatures, dormancy is induced earlier in the season. The second flush of growth of the control plant under high night temperatures and short days would indicate that short days are instrumental in initiating a second flush of growth. Note that gibberellin was also more effective in initiating a second flush of growth, in the presence of the higher night temperatures and short days (Figure 13). A second flush of growth was induced by gibberellin under the high night temperature-long day regime but the period of dormancy was greater under this environment, indicating a more intense quiescence. Dormancy of the first flush of growth in Liriodendron was apparently not too intense, since gibberellin caused continuous growth under all environments except short days and high temperature. Note that plants under the long day-high night temperature regime produced a second flush of growth which grew continuously. Cessation of growth of the second flush was delayed in control plants under the low night temperatures, irrespective of the photOperiod, and hastened in the short day-high temperature plants. A low night temperature appears to be instrumental in delaying dormancy. It is of interest to note that in SyringeI although the duration of the first or second flush of growth was altered by the temperatures imposed (40 or 70°) the final hight was not altered (comparison of treatments 1, 2 and 3 with 4) (Figure 13). This growth response was also evident in Age; (comparison of treatment 1 with 2, 5 with 6) This relationship was not as evident in Euonzggg for a longer duration of growth generally resulted in an increase in length of the shoot. 83. Tenmination of shoot elongation in Liriodendron, Catalpa and {$225 occasionally was caused by desiccation of the growing tip. This was only evident at the higher night temperatures in Catalp . Gibberellin was not effective in altering the frequency of desiccation. Gibberellin was instrumental in causing desiccation of the buds in liege and Airiodendron, in all of the secondary shoots of E$22£ irrespective of the environment, and in 6 out of a possible 24 terminal buds in Liriodendron, which was most evident under the higher night temperatures. b. Breaking of Dormancy in Seeds The effects of gibberellin on dormancy in seeds of Catalpa followed a similar pattern as was evidenced in the growth of Aee; and Euonyees buds. A constant temperature of 68°F prevented germination almost com- pletely, but with the addition of gibberellin the rate and total germ- ination increased appreciably (Table III). Under the alternating day and night temperatures, the rate of germinating was also increased, but in comparison to the constant temperature regime, the total germdnation was not affected by gibberellin treatment. It would appear that the alternating day and night temperatures were instrumental in the synthesis of a growth promoting compound. Note the addition of gibberellin to seeds under the constant temperature gave a germination response between 11 and 14 days comparable to the non-treated controls under the alternating day and night temperature (Table III). 84. .~s>uuucu «lay «an» manna: nouncaahow ensue oz at .~o>ua acouuoa m use us uoouuwuwp haucnuumucwuu you own coma pagOe a he puuuuccou eu=~w> a ~.ea m.~ o.o~ o.eh _ n.o oooH o.~s n.n o.aN o.ao n.a com H.nm “.5 a.~a 5.5o _ O.“ cm a.»@ h.o “.5n o.H~ _ e.~ a m.mo «a n.» o.om a.a~ n.m o sensuousmaua u:w«21>om wcauucuuua< m one a oeo o.an _ n.n a.“ o.m~ a.- _ coca ~.m¢ o.¢ o.- o.o~ s.o oca m.o¢ u.m “.ma n.m~ c.c ea o.NH n.~ o.m n.n n.~ d ¢.n~ ~.n h." u.~ n.~ as o unsusuomaua ucsuncoo m one Aammv couuncaauou mN-~N kuma sguma «Haum OHuH ucuausuua anuoy poem cumusuoeewo weapoom wouw< when cu an>uoucm saws zoom campus acquwcuahsu accouum cuaaouoanwo was ousumuomaoa he ovumwvo: no .mcuvoom nouw< nHa>uouau saga oauuuumm casuuz poem snowosun suaauco mo couuecwahsu annoy can capsuuom HHH Mammy 85. 3. Accumulative Vegetative‘Modifications by Gibberellin a. Shoot Extension and Dry Weight of Shoots Numerous measurements of the shoot growth response to gibberellin (O or 50 ppm), photoperiod (9 or 18 hours), or night temperature (40 or 70°F) are shown in Figure 14 along with other data to be discussed later. It is apparent that the growth of shoots respond dramatically to gibberellin treatment in all species except geeee and gyracantha. Note that the shoot extension (1) shoot—root ratio (6) and the dry weight of the new shoot wood (9) increased in most of the species studied following gibberellin treatment (50 ppm). The number of nodes initiated (3) and the internode length (4) were also increased by gibberellin when a significant response occurred, but the frequency in response among species was reduced. The dry weight per centimeter of the new shoot growth (8) and the stem diameter (2) were not greatly altered by gibberellin treatment. However, when a significant response to gibberellin did occur, the dry weight per centimeter (8) was reduced in Catalpa but was increased in 25223. The stem diameter (2) was generally increased whenever a significant response to gibberellin was evident (e.g. Pinus, Liriodendron, Viburnuep except with Catalpa in which the diameter of the shoot was less (Figure 14). In all species, if a significant response to photOperiod occurred, long days resulted in an increase in shoot growth (9) were the most frequent growth responses to be affected by long days. This was particularly evident in Liriodendron, Viburnum and Syringa. Figure 14 Growth Differences of Certain woody Plants, that Developed Between April 26 and September 15, as Influenced by Gibberellin, PhotOperiod and Temperature. Lawn Shoot Extension StemlDiameter Node Number Internode Length Leaf Area Per Plant Shoot-Root Ratio of New Wood Dry Weight Per Leaf Dry Weight Per Centimeter of New Shoot Growth Dry Weight of New Shoot Growth Dry weight of Old Shoot Growth Dry Weight of New Root Growth Dry Weight of Old Root Growth Total Dry weight Per Plant GNOUDWNH . I O O O 0 . HHHH (plot-low O * Only values exhibiting significant growth differences between gibberellin (50 ppm) an d no gibberellin, short 9 ho a and long days (18 hours), a ( ur ) nd low (40°F) and hi h ni t t eratures (70 ) are included in the figure. 8 8h cup PERCENT 6R0 WTH DIFFERENCES NN—u UIOU‘O OOOO - —- N N (2‘ U1 U1 0 U1 0 m o O O u 0 o (a O O 86. M _ 500 I“ LEGENK’ .1 ‘ D esowm sr/Muur/o/v 400 _cnon T~ [NH/5mm - 300 CATALPA - PINUS < 200 A 100 25781910111215 -L 101115 F 9‘ A , L, i L , 1 - Q ~ 1;- 1 1 l l I I I l —. PYRACANTHA - '4 ZOO - 100 I)” E (93"!1 o i 50 J 4i V I . - ‘ 300 SYRINGA l | I I . «20c 8791‘) : 0 .. IIHTIZ 1 1 I i ACER EUONYMUS Ilafl l6 IaEIrl7 5 611'. — 100 man man ‘ 200 GIBBERELUN [LONG DAYS Jflofl NISNT 1‘2"me GIBBERELLIN l LONG DAYS Em TR E A TME N 7'5 Figure 14 87. High night temperatures generally altered the growth of the shoots in a greater number of species than the long day regime. The dry weight accumulation of the new shoot growth (9) was markedly affected by high night temperatures, and was significantly increased in Catalpa, Liriodendron, Viburnum and gyracantha, but was inhibited in_Aee; and 23221. Node number (3) and dry weight per centimeter of the new shoot growth (8) were not as markedly affected by high night temperature, although differences were apparent in 3 of the species studied. Dry weight of the old shoot wood was not altered to any great extent by any of the variables imposed. However, gibberellin was instrumental in inhibiting dry matter accumulation in the old shoot wood of Catalpa and {$923. In contrast, an increase was realized in Airiodendron. Long days or high night temperatures increased the dry weight accumulation in the old shoot wood of Age; and Catalpa, respectively. It became apparent that the majority of the growth phenomena affected by either gibberellin, long days or high night temperatures as compared to no gibberellin, short days and low night temperatures, are associated with the growth and development of the shoot. b. Leaf Area and Dry Weight of Leaves In contrast to the increase in growth of shoots, dry weight accumulation in leaves of all species (except Liriodendron ‘“d_§i22£) was inhibited following gibberellin treatment (Figure 14). Although dry matter accumulation of leaves was inhibited, the increase in the number of leaves initiated (3) compensated for the smaller leaves produced in Viburnum, Acer and Sy;iega (Figures 19, 20 and 23). This compensatory 88. affect was not evident in Catalpa, Fyracantha and Euonyees (Figure 17, 22 and 24). Long days or high temperature, in contrast to short days or low temperature, generally caused an increase in leaf area per plant (5) and leaf dry weight (7) in Catalpa (Figure 17), while only an increase in the leaf area per plant (5) was evident in Liriodendron and Viburnum (Figure 18 and 19). c. Root Dry Height Associated with a general inhibition of dry weight accumulation in leaves by gibberellin was an inhibition of the dry weight accumulated in the newly initiated roots of some species. This was particularly evident in Catalpa and geeee and less so in Viburnum and Zyracantha (Figure 14, 17, 21, 19 and 22). Liriodendron, Syrigga and Euonmes were not affected (Figures 18, 23 and 24). Tum species (Catalpa and Acer) exhibited an inhibition in dry weight accumulation in the old root wood following gibberellin treatment. The inhibition in Catalpa was very evident while Acer was only slightly affected. Long days, as compared to short days, had little or no influence on the dry matter accumulation in the species studied, except in Syringa in which an increase in both old and new root dry weight was realized under long days (Figure 23). High night temperatures were much more effective in altering dry matter accumulation in roots. As shown in Figure 14, the new roots accumulated a greater quantity of dry matter at the higher, as compared to the lower, temperature in Catalpa, Liriodendron, Acer and Euonymus, while the other species were not 89. affected (Figures 17, 18, 20 and 24). Dry weight of the old root wood was increased by a high night temperature as compared to a low night temperature in only Catalpa and Euonzeeg. d. Total Dry Weight The total dry weight accumulation as modified by gibberellin (O or 50 ppm), photoperiod (9 or 18 hours), or temperature (40 or 70°F) is shown in Figure 14. It is of interest that not one species treated with gibberellin exhibited an increase in total dry weight accumulation. It appears that there is an accumulation of dry weight in the shoot at the expense of the roots and leaves. ‘Airiodendron, in contrast to all other species, exhibited no inhibition in growth following gibberellin treatment, and yet there was no increase in total dry weight. In contrast to other species the total dry matter accumulation in Catalpa and £l222."' inhibited by gibberellin. Total dry weight accumulation in Viburnum and Sz;inga was increased to a greater extent under long than short days. High night temperature, as compared to low night temperature, stimulated dry weight increases in Liriodendron, Viburnum and Cstalpa. Figure 15 summarises the interaction between gibberellin and photo- period or gibberellin and temperature for the various vegetative responses. It is of interest to note that under the short day regime there was less inhibition (e.g. Catal a or a greater stimulation in the growth index (Liriodendron, Pinus and Buonymus) following gibberellin treatment. This generalisation holds true for the growth responses under low night temperatures. For example, the inhibition of growth at high night 90. temperatures by gibberellin is reduced (e.g. Catalpa) or results in a greater stimulation of growth under low night temperature in Liriodendron, Aee; (node number (3) and shoot-root ratio (6)), [Aeeg_and Euonygeg (stem diameter (2) and internode length (4) ). In Viburnum,‘Pyracantha and Sx;iega this relationship is not evident since a greater response to gibberellin is observed at the higher than under the lower night temperature regime. A perusal of Figure 15 shows a greater inhibition of growth following gibberellin treatment occurring more frequently under high temperatures or long days than under low night temperatures or short days. Conversely a greater stimulation in growth occurs, in general, under short days or low temperature as compared to long days or high temperatures. The growth stimulation of gibberellin under low night temperatures occurs most frequently when shoot extension (1) node number (3) shoot-root ratio (6) and dry weight of the new shoot growth are used as criteria for response. Under short days the growth stimulation of gibberellin occurs most frequently in number of nodes initiated (3) and leaf area per plant (5). Conversely the greatest frequency of inhibition of growth under high night temperature is with respect to stem diameter (2), dry weight of the old root growth (12), and total dry weight per plant (13). Inhibition from gibberellin treatment under long days was most frequent in the initiate of nodes (3), leaf area per plant (5), and dry weight per leaf (7). The modifying influence of low and high temperatures or long and short days on the growth responses to gibberellin is puzzling. It would appear that under short days an inhibitor is modifying the influence Figure 15 The Modifying Influence of Gibberellin on the Photo- periodic and Thermoperiodic Responses of Various Plant Parts in Certain woody Plants.* Only srwth responses exhibiting significant interactions between gibberellin (0 or 50 ppm) and photoperiod (9 or 18 hours) or 8113591311111 (0 01' 50 ppm) and night t erature 40 or 700?) are included in this figure. 3‘? ( 91. xx...» .330. mum alone: ‘36. icon 5. \tscctiouo .89... 96 no atom} 86 .2 foe to .8 o. >32 u I n3: \Ec .: $36 0&3 m thee o o k a V Foe tkiomo acct“. 96 no aroma... >3 9. .936 trot“. § xiv» 335mm Loose. em? up krone). >3 ...... \iISOr‘O kQQIh. 3AM? K0 QWkN)§.tN~$ XQQ Q 82 mubtwumqiut .392 moi I 8.. embedding .39? trod I on. \otxkgmu tum khanuk .86 a. MC 0t 1t ROOM 1.89%. o o. " Kinetqu mum (mtg .133 w «to» Ikozmu mgktwks a. 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Lam! lo Ltofi‘: >20 \0!\ 15:80 Look“. in? .10 (ML WIRZNU QWQ Ltoxmi Ltd \o¥\ 11”..» (Wt LION: Ltd Q09: \xfiz to Give LootnLooiu. ~\!.u\ L33! anx 3.3“ uwhu xiv» IL szJ NQOEtWL‘S (moi)? 33% \IX\ (UL N230 XML» «2.! 299$th Loot“. 231mmmmm5 Tk 936 Lg 23.4UQMQQRM xxx .93 Leora. 3 qqhthmhxo fin .936 9.6.x 3quthme E 5.3L «93‘th Lkoxk \SOu exqqfitmmmxm \Q 53L VKNQIWL L103 :64 zghnfiefi xi WQDL «(NQXML Lloxk 19). ~~nphokO°QENQ IIIUECII 23 qhthfl§3 \Q htbL (KWQXUL L35 to? “usfiut ”3‘5368‘) ‘0‘ ggflw hakzwzk(mtk Q0“ Q23~4 Figure 17 - 24 Modifying Influences of Gibberellin, Photoperiod and Temperature on Root, Shoot and Leaf Development in Certain Woody Plants Legend for Figures 17 through 24 Eggdy Plants Figure Catalpa s eciosa.... ....... . ........ . ...... ... ............ 17 Liriodendron Tulipifera.... ...................... ......... 13 Viburnum Carlesii.... ........... .... .............. ........ 19 Acer saccharum....... ................... ........ ........ .. 20 mail-vescrisoooooooooe oooooooooooooooo so on... o ..... o 21 P racantha coccinea Lalandii. .............. ............... 22 S rin a vulgaris................ ..... ..... ............ .... 23 WWW” ............ 24 M Night Gibberellin PhotOperiod Temperature COde __150 qul_ __(hoursl__ (OF) 1 - 9 40 2 - 18 40 3 - 9 7o 4 - 18 7o 5 + 9 40 6 + 18 40 7 + 9 7o 8 + 13 70 Leaf Arraggement Left to Right, one leaf was collected from each node of a representative plant for each treatment from the , ro i l to the distal end of the new shoot. P X "I 95. ‘ «.uu .@ “"a.“. (9 inane ' * Made" ...... Q) fl‘tA./‘C“ 4,..mou..”, v x , r _ ”Yak Figure 17. Catalpa speciosa Figure 18. Liriodendron Tulipifera 97. A r we 3., 53; w _330 «p 7. ‘ffi, I ’\ V f ‘ '- h ‘ 9t I {a .. v ._ .19 ~< 1" x \ V ,v r (1 . Y P " ;‘_ a; ' . V . \‘ . . ._ ‘. : . , _\ ‘ ,‘ . q . , \ ‘_ . ‘ .1 . V. l , e‘ . . . 1 ‘ N V. .. N . , 1‘ ‘ . 3' , _ . 1" v y’ (D ‘<.. a 0 =— Figure 19. Viburnum Carlesii 98. “* w ‘Ho?& @9639 99. lvestris Pinus s Figure 21. 100. A fiHQHuuumW» onflflnuumom.....@ fimamu “mm“w MO“. 00» 0 000mm...@ . . w Q o ...w “Max:373. ' ”..‘ffrrr:t.:z':::.~....; nag-go. ”0.0000990”an 09'0””wa 0mm...» w oummmmm Figure 22. Pyracantha coccinea Lalandii lOl. m... @ weuflmw ”“00” ® ibiflinufl ace-ac. ® Wynnwsm e333 //‘ ® é$a‘$“‘s ® I i Figure 23. Syginga vulgaris 102. ° ‘....O o 0”...“ ... .000 Winona-4'00- G) a ”....... o I OOOOCO®OO : ‘ -O..O.o:® ....... ........®.-.. "“0." an . ...... O . no ...® "... ' (D .um. ......e Figure 24. Euonzmis Fortunei vegetus II. ALTERATIONS IN THE METABOLISM OF CATALPA SPECIOSA AS INFLUENCED BY GIBBERELLIN A. Modifications of the Chemical Composition 1. Materials and Hethods In the previous study Catalpa gpeciosa exhibited a marked response to all variables imposed, consequently this species was selected for chemical analysis. Routine nitrogen and percent ash determinations were made on the various plant parts previously mentioned. Half or one gram.samples of finely ground (20 mesh) dried plant material were used. The standard Kjeldahl method was employed for nitrOgen. The per- cent ash was determined by recording the difference between weights of an oven dried sample before and after ashing in a muffle furnace at 550°C for 8 hours. 103. 104 O 2. Results The influence of gibberellin (0 or 50 ppm), photOperiod (9 or 18 hours) and night temperature (40 or 70°F) on the chemical composition (ash and nitrogen) of Catalpa is recorded in Table IV. Two obvious responses to gibberellin are evident, (1) an increase in the ash content of the old and new roots, (2) an increase in the nitrogen content of the leaves and new roots but an inhibition of nitrogen accumulation in the old shoots. The inhibition of the nitrogen content of the old shoots was more pronounced under short days, consequently simulating a long day response. In contrast, the accumulation of nitrogen in the new roots following gibberellin treatment was more evident under long days and approximated the normal accumulation under short days. Nitrogen accumulation was inhibited in the old shoots and roots to a greater ex- tent under long days than short days. High night temperatures as com- pared to low night temperatures cause a decrease in nitrogen in the new roots and increase the ash of the new roots and leaves. It is evident that the various plant parts responded differently to gibberellin treatment. The modifying influence of gibberellin on the distribution of the ash and nitrogen in Catalpa strongly suggested an alteration in the normal metabolism. The accumulation of nitrogen in the new roots following gibberellin treatment approximated a short day and/or a low temperature response. In contrast the accumulation of nitrogen in the old shoots, and possibly new shoots (not significant), resembled a long day response. This is difficult to explain. It appears that the reduction in nitrogen movement out of the roots associated with .hao>«uuomusu .uHo>oa assumed a no m any as ucmuwuuewdu one unflaunouu was uumm ueefim co>wm a you moaas> at no t mo.~ e~.a mo.a an.“ .oe.~ ee.a oe.a oo.~ atmo.a mn.~ «sacs auz ~o.o so.a mo.o am.o mw.o na.o «sme.o mm.o om.o oL.o .uoou ego «m.o mm.o No.0 mw.o om.o om.o mm.o no.o mo.o oo.o «sun.o 0L.o sam.o as.o .uooem vac am.o em.o mL.o om.o eL.o aa.o mucosa auz oo.~ oe.~ ee.~ om.~ «seL.~ -.~ use; mmumuuuz uncouom .L «o.» o.o n.L n.L ga.m a.» .uoom 3oz m Tu L.~ ad ad «36 .2 302. 3c m.~ o.~ m.~ n.~ n.~ ¢.~ e.~ n.~ «*m.~ a.~ uuooem ego e.~ o.~ L.~ n.~ s.~ o.~ .uooem soz «a~.L n.n o.o e.o n.o ~.o aqua + - + - apnea saga seems when oL as mm a + - eu< sauouom «use: ma space a a noL a see «new Awesome coauoNOerm x eaaaouonaao moduem0uosm x ouauwuomauy uuaueuumaoa noduom0uosm auaauuonnwu seawuosuoueu “aquamaauam uueuaumuua Augwamz man no moweueooumm mm pompoumxu mos~s>v encaoomu mmasuuo cu £m< was cowouuuz uo ecuunnquumun man so euausuualeh use vo«u090uo£m .ewuaouoanuu mo ooaoaawcu wewhuuvoxu >H mamu~ assumed H onu um unmoauumwum one ucuaumouu use uumm unmum eo>ww u now momum> as 13.3 m .m 0.2 «.3 238m 3; 2; 3; en; :33 no. no. am. 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Ln -.nm me.nL mn.am mo.~n on.n~ on.m~ mo.an mn.~m oa.no em nu a.o~ «.mn N. La wo.on os.en «L.oe om.L nL.o an.» an.a~ Lm.L~ so.nn we n.L ~.L N. o Ln.en oc.en n~.en ma.o no.0 oo.n oe.nn mm.na nn.nn «a m.n a.e L. e um.“ oa.m na.n o~.o Ln.o L~.o mm.m me.m as.m m n.on m.n o. a nm.n ne.~ ma.n mn.c nn.o «n.o on.n an.~ no.n 0 «.mn o.L L. as Lo.n Lu.” on.n en.o «n.o an.o nn.n «L.n «o.n m~.o an .5600 nuu>nmm no sank com on O can an o con on o can on o Negev unmounsaane nooem on nooonom deuce noosw uoom madman one now vousaslmuod monoemnonm mo mamnwonuaz Auegauaoun a on house case n ananonoaano no eonuuunnaa< nunnonv eaanuuoaaSu 50 0000000: no queues a smasnso we muoom ho manoemaoem we downpounnmuo one among: we seem HH> 00009 120. 2. Rate of Absorption and Transport as Influenced by Gibberellin and Root Temperature a. Materials and Methods The effects of root temperature on uptake and distribution as 'modified by gibberellin might partially explain the interactions between gibberellin and temperature in the previous experiments relating to vegetative modifications by gibberellin. Consequently seedlings of Catalpa speciosa, cultured and prepared for treatment as previously described, were treated with a foliar spray of gibberellin (O and 500 ppm). Four days later the plants in their first and second leaf stage were transferred to 7 inch test tubes containing an aerated solution of radio-phosphorus as previously stated. The root temperatures were controlled within t 2°C by a cooled and heated water bath. Four root temperatures (5, 10, 15 and 20°C) were maintained during the 48 hour ex- posure to the radio-phosphorus. The plants were harvested, prepared for radioactivity and dry weight determinations, as previously described. The micrograms absorbed per unit dry weight and per plant part were also determined according to procedure already mentioned in previous experiments. Temperature coefficients (Q-lO) of phosphorus absorption by the roots were readily calculated from the above information. Eight single plant replicates were incorporated in a split plot randomized block design. Root temperatures (5, 10, 15 or 20°C) were the main plot and gibberellin (0 or 500 ppm) the sub plots. Duncan's multiple range test for differences among means was employed. (Duncan, 1955). 121. b. Results In the previous experiment the implication was that gibberellin would inhibit the uptake of phosphorus on a unit basis. Consequently, a further evaluation of the effects of gibberellin on the uptake of phosphorus by roots, in conjunction with various root temperatures, should substantiate or refute this hypothesis. This phase of the in- vestigation gives strong evidence supporting the possibility that gibberellin increases plant growth at subOptimal temperatures. As shown in Table VIII, the overall efficiency of uptake is generally reduced on a per plant as well as a per unit dry weight basis by gibberellin treatment. However, the percent transported to the shoot was not altered. This relationship was, however, not consistent under the various root temperature regimes. It is of interest to note in Table VIII, that an increase in temperature results in a subsequent increase in phosphorus uptake by roots of the control plants on a unit weight basis. If, however, gibberellin treated plants are placed under similar root temperatures, the rate of uptake with increasing temperature is not as rapid. Therefore, the rate of uptake and distribution is not altered at the lower root temperatures, (5 or 10°C) but is markedly reduced at the higher root temperatures. This would imply that a mechanism associated with active absorption of phosphorus has been modified. The root temperature coefficients for data in Table VIII are shown in Table IX. The data clearly illustrate that gibberellin caused a marked reduction in the root temperature coefficients on a unit weight basis for the roots, shoots and total plant. In contrast the percent 122. phosphorus translocated to the shoot under the different root temperatures was not modified by gibberellin treatment. The reduction in the teuperature coefficients for root uptake on a plant basis was only apparent between the 5-15°C range and not influenced by the 10-20°C range . 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Rate of Absorption and Transport at Different Root Temperatures as Influenced by Preconditioning to Gibberellin and PhotOperiod a. Materials and Methods Previous findings warranted an investigation of the influence of root temperature on the uptake of P32 by plants which had been preconditioned to gibberellin and photoperiod for a longer period. Consequently, seedlings of Catalpa were transplanted to 4 inch pots containing a 50-50 muck soil mixture. Half of all the plants were treated with a foliar spray of gibberellin (100 ppm) and exposed to long (18 hours) or short (9 hours) days. The photoperiod was extended by both incandescent and fluorescent lamps which produced 50 foot candles at pot level. Short days were provided by moving the plants to a dark room at 5 pm and re- turning the plants to their day positions at 8 am. Three and six weeks after the initiation of the experiment, 80 uniform plants (20 from each environment) were gently removed from the soil in the pots and placed in a pan of tap water. These plants ‘were then transferred to aerated cultures for 4 days containing.0.5 strength Hosgland's solution. This procedure permitted callus formation where roots might have been broken in the transfer from the soil to the solution cultures. After the 4 day healing period, plants were transferred to the test tubes containing the radioactive phosphorus and 0.5 strength Hoagland's solution as previously described (Figure 25 and 26). Root temperatures in the water bath containing the test tubes were main- tained at 50 and 68°F t 2°F. The root temperature was replicated twice to assure a valid test for the temperature response and a duplicate 126. sample for each treatment was randomized within. The air temperature was maintained at 68°? t 2°? during this period. Consequently, a split plot design with temperature as the main plot and precondition treatments as the subplot was utilized. Duncan's multiple range test was employed to determine if the differences among means were significant. The first and second harvests were made 3 and 12 hours respectively after P32 treatment. The plants were segregated into two parts, roots and shoot, with the division at the cotyledonary node. This point of segregation was essential to reduce the possibility of contamination from.the radioactive root media. The plant roots were rinsed in distilled water prior to placement in 50 milliliter beakers and air dried at 70°C prior to counting, using the counting procedures and equipment previously described. Since the plants were relatively large in the above experiments, self absorption became a problem. Self absorption was corrected by determining the relationship of the activity before and after ashing of 16 different samples representing a range in weights for both the shoots and roots. The standard A. O. A. C. method for preparing plant material for phosphorus determination was followed (Horwitz, 1960). A well defined curve was obtained between dry weight of the sample and activity. This correlation precluded further ashing. Consequently, the remaining dryed samples were analyzed for activity without ashing. The self absorption was corrected by adjusting the activity of a given sample weight to fit the curve. Total micrograms per plant and per gram dry weight were determined as previously described. Figure 25 A Refrigerated and Heated Water Bath for E xposing Eggglpg_to Various Root Temperatures and P3 Solutions. 127. Figure 25 If.” Figure 26 Catalpa speciosa Seedlings Precondition to Gibberellin (100 ppm as a Foliar Spray) and PhotOperiod (9 and 18 hours) During an Interval of Six Weeks. Treatments PhotOperiod Code gibberellin (hOUIS) A - 9 B + 9 C - 18 128 . \ in“ « J \ L I ' \ A n , a Figure 26 129. b. Results The modifying influence of gibberellin on the rate of uptake at various root temperatures was indicative of young seedling as illustrated in the previous experiment. Evaluation of the effects of gibberellin, in conjunction with various photOperiods, on the uptake of phosphorus at different root temperature in older plants should confirm.or refute previous findings in addition to giving new information. The results of this investigation are shown in Tables X and XI. At least 6 weeks of preconditioning to gibberellin (O or 100 ppm) or photoperiod (9 or 18 hours) were required to alter the uptake of phosphorus by roots. As shown in Table XI the accumulation of phosphorus by roots after 12 hours in the F32 solution, on a per plant or per unit dry weight basis, was generally inhibited following a preconditioning to gibberellin under a long day regime, as compared to the long day control plants. This inhibition was not apparent in treated plants under short days as compared to the short day controls. The percent phosphorus translocated to the shoot from the root was not greatly altered after six weeks of preconditioning but was markedly affected in plants preconditioned for 3 weeks to gibberellin (100 ppmo or photOperiod (9 or 18 hours) (Table X). Two general observations are evident, (l) gibberellin temporarily inhibited the percent of phosphorus transported to the shoots which normally increases at the higher root temperature, irrespective of the photOperiod imposed, and (2) gibberellin applied to plants under short days partially substituted for the percent of phosphorus translocated to the shoots under a long 130. day regime. This was apparent at the 12 hour harvest only (Table X). It becmme evident that root temperature was only effective in altering the percent of phosphorus transported to the shoots in younger plants and that gibberellin will modify this effect. The partial substitution by gibberellin, of the long day effect on the percent transported to the shoots, is only evident in young plants also (3 weeks of pre- conditioning). As the plant matures the influence of root temperature is no longer effective in altering the uptake and distribution of phosphorus, but photoperiod (9 or 18 hours) becomes the controlling factor. Gibberellin inhibited uptake of phosphorus under long days but had no influence on the uptake of root applied P32 by plants exposed to short days. 131. .ueaouwwcmwn you one: euucuuouwum can mu vsosauaa yo: «no: muse-anIUu uoou mo uuuoumo 0:9 A .Ho>oa usuuuom m emu us noguo some Bonn ucouowqu hausnuumusmqn no: one alsaou nous :«nuua uuuuoa case one an evacuees“ eosas> ~a< s e~.¢a no.0 oo.m~ s~.m mo.n~ e~.o s~.m~ m~.m am.a~ ee.- on.HH m~.m mm.o~ ns~.oa a~.o~ e~.m NH n Na m age: hum asuu use?" pom pom asuosmeozm usuonmeosm mo namuwouuuz mo unannouuw: am.o sm.m As.n~ no.5 an.» on.m ah.nN so.» + ma ma.na sa.m An.m~ no.o~ s¢.ma mN.o au.ou an.H~ u ma A~.m sm.NAsn.h~ on.¢ n~.o s~.n now.- ao.¢ + m on.MH s~.~ mm.- Ado.m sm.na sm.~ on.- s¢.m n a s Neusonw eaaauuoaAao consumosoem ocuauwouk wo«co«u«osouuum H AoOV ousuouumaoa uoom n ucoaumuua «mm we mason ON 3 II ON 3 m Na n n Na mango: hum Esau uoaam new mom nanoseconm asuosmeosm mo mieuwouuu:_ mo namuwouoqz poauomouonm use samauuonnao ou mcucouuqmcououm mo axoea xam moduomouoem mes suaauuonauu on mcueoquavcouuum mo asses cough coususwomaoa boom aeouumuun ou monomxm mnouuumm mmfloumo mo nuoom can scan nuoosm any ou monsooamamua usuonmaosm mo ucuuuom one so modquOuonm one :«aguuonnwu ea unaccuuaocououm no exec: xum one «cash no mucosamcu mnwhuqmozhona x mamu~ unuuuum n «so as uunuo some scum ucuuuuwav aduos0uuqewun uo: one :BSHou some caeuwsvuuuuua mean use an vuusuuvaa nosam> HH< a nus.o¢~ auu.ao ne.am aua.am no.oa no.os us.qm sn.hm + as am.mms us.mm ow.nna o~.~m oo.m- am.wm au.wa am.~n - ms sm.eo paa.n~ auo.om aao.o~ um.m~ um.ms um.n~ am.os + o mm sw.nm un.ma u~.s¢ an.aa nua.~n an.om as.m~ ma.o - a 1L ~nusoem caaauuunnau magnumOuonm usuausuua newscauwoaouuum «a m «A n Na n «a n usuausuua «mm we muse: soausaaasuum boom sequedsasuu< uoom amuse Hobos uewuoz an: ammo hum ocean Mom nanoseconm mo useuwouuaz nanosmeosm we casewouuuz unauoumn suasueo wo uuoom he nanosmnosm uo :o«u=a«uun«n was assuma was ac cosuuaouoam can sandstoneso as mascoasaeaououa no axoaz.xam mo mucosamau masseuse: one ax man '1‘. ‘3 Endogenous Inhibitors .3 Spring Fall Scheme 11 Plants Under High Night Temperatures or Short Days \ r Endogenous Inhibitors Relative Concentrations Endogenous Gibberellins % Spring Fall‘ 140. or reduced rates in the summer, resulted in an inhibition of leaf expansion (HoVey and Wittwer, 1958; Scurfield and Moore, 1958; Powell, Cain and Lamb, 1959; Suyama, Yamasaki and Kubota, 1958). Gibberellin applied to plants under a short day regime generally caused an increase in leaf expansion as compared to those plants placed under a long day regime (Fig 15, 17, 18, 21, and 24). If an inhibition in leaf dry weight accumlation does occur following treat- ‘ment with gibberellin, it is generally more evident under the long day regime as compared to that found in plants under the short day regime (Figure 17). In this respect a few of the rapidly growing Catalpa plants under the long day high temperature regime were injured in late June by the heat of the incandescent bulbs used to extend the photOperiod. As shown in Figure 17, an axillary bud developed and elongated but in contrast to the treated plants under the same environment which had not been injured, the leaves which develOped closely resembled leaves of the check plants. This accident in cultural techniques would indicate that inhibitors which accumulated during the period of axillary bud develOpment moderated the subsequent action of gibberellin on the expanding leaves. The actual cause of the inhibition of leaf expansion by gibberellin is not known. It is highly probable that the high concentration of gibberellin in relation to the endogenous inhibitors cause a marked increase in the rate of respiration. In this respect Rate (1956 and Coulombe and Paquin (1959) have reported a marked increase in the rate of respiration in pea and tomato foliage following gibberellin treatment. 141. In Pyracantha, as compared to the other plants studied gibberellin caused an increase in the leaf area per plant under long days while a reduction in leaf area occurred following gibberellin treatment to plants under short days (Figure 15). In order to explain this reversal in the the trend, it would appear that the balance between the endogenous gibber- ellin and inhibitor is very delicate (Angle A greatly reduced). The increase in leaf area following gibberellin treatment under long days would indicate that an inhibitor was moderating the action of gibber- ellin, whereas under short days this was not the case. This is the reverse of other plants studies, in which short days generally moderated the action of gibberellin to a greater extent than long days. , To explain this difference we note in Figure 5 that gyracantha exhibited no photoperiod response in respect to shoot elongation. It is possible that within theplant a similar balance between gibberellin and inhibitor is maintained irrespective of the photoperiod. However, the mechanism of maintaining the balance varies. It is postulated that the synthesis of endogenous gibberellin in the leaf is dependent and the inhibitor concentration is independent of influence of long days on growth. Plants grown under the short day regime.would exhibit a re- ciprocal relationship. If this relationship does exist, the addition of gibberellin would be destroyed at a greater rate under long days than short days. The inhibitor, which is synthesized under short days, would not greatly modify the addition of an exogenous source of gibber- ellin. The end result would be a moderation of gibberellin effect on leaf expansion by long days with the reciprocal relationship evident 142. under short days. In this respect it has been suggested that the mechanism responsible for the synthesis of the endogenous gibberellin is blocked by light (Lockhart, 1959). As previously mentioned a high gibberellin-inhibitor ratio might result in an increased rate of respiration. This relationship might also explain the greater inhibition of dry weight accumulation in leaves of Euonygug treated with gibberellin under short days as compared to long days (Figure 15). Note in Figure 5 and 6 that neither Pyracantha or Buonyggs respond to photoperiod treatment. It appears that plants which exhibit little or no response to photo- period exhibit a similar response to gibberellin. If, however, there is a response to gibberellin in plants which do not exhibit a marked response to photOperiod the response is greater under long days. If gibberellin causes an inhibition in dry weight accumulation in plants which fail to respond markedly to photOperiod, the inhibition is more evident under short days than under the long day regime. (e.g. Pzracantha and Euonygug Figure 15). Leaf area per plant and dry weight per leaf of 5555 and Viburnum following gibberellin treatment were not differentially affected by the photoperiodic treatment imposed. This would indicate that the endogenous sources of gibberellin and inhibitor are relatively equal in amounts within the leaves. Consequently a similar response to an exogenous source of gibberellin results. 143. B. Modifying Influence of the ThermOperiod on Gibberellin Action In contrast to the effect of photoperiod, the response of shoot development and dry weight accumulation in various plant parts to gibberellin, was greatly modified by temperature.‘ A perusal of Figures 4, 5, 6, 7, 8, 9 and 10, strongly supported the theories previously discussed. All plants under high night temperature showed a more rapid rate of shoot elongation in the spring in contrast to those under low night temperature. As the season progresses the rate of shoot elongation of plants under high night temperatures decreased while shoot elongation of plants under low night temperatures increased. This decrease in the rate of shoot elongation under high night temperatures accompanied by an increase rate at the lower night temperature as the season prOgressed was not evident in gyracantha, Liriodendron and Viburnum. Scheme I and 11 fit into the above pattern of shoot extension evident under the low and high night temperatures. The addition of an exogenous supply of gibberellin also lends strong supporting evidence to the mechanism.controlling shoot elongation in the woody plants investigated. A differential response of shoot elongation to the thermoperiod following gibberellin treatment is evident early in the spring. As the season progresses the rate of elongation under high night temperatures decreases while the shoot extension under low night temperatures increases following gibberellin treatment. Viburnum.and Syringe exhibited greater growth at the end of the season under high as compared to low night temperatures. However, the inter— actions‘were not as evident at the end of the season as they were during ‘mid-spring (Figure 7). Employing the schemes I and II, it would appear 144. that the rate of synthesis of endogenous gibberellins under the low night temperature as compared to high night temperatures is increased as the season progresses. Therefore, the addition of gibberellin to plants under the low night temperature would result in a greater shoot elongation response than plants under the high night temperatures, thus accounting for the reduction in the interaction observed. In contrast, early in the spring the quantity of endogenous gibberellin was synthesized at a much faster rate under the high night temperature as compared to the low night temperature. This resulted in a greater increase in the rate of shoot elongation in Viburnum.and Sysigga. An exogenous source plus a relatively high endogenous sourceof gibberellin (Scheme II, angle A increased) resulted in a growth pattern of the shoots which could not be over-taken by the low temperature gibberellin treated plants. The rates of shoot elongation of Viburnum and Sygiggg under low and high temperatures during early spring and mid-summer bare out this hypothesis. Theoretically Liriodendron should have shown an interaction between gibberellin and temperature during the entire growing season, since the rate of shoot extension under high and low temperatures in 21223925 and Liriodendron is very similar (Figure 6). However, this was not the case (Figure 7). To explain this lack of conformity to the theory pr0posed is not difficult. Gibberellin caused desiccation of some terminal buds of Liriodendron at the higher night temperature. Consequently gibberellin treated plants grown under the lower night temperature rapidly over-took the elongation of shoots occurring under the higher night temperature regime. 145. The shoot elongation response of Pyracantha induced by gibberellin unler the various temperature regimes greatly challenges the schemes presented (Figure 7). The lack of a significant interaction during the first 3 months of the experiment would indicate that the endogenous gibberellins and inhibitors are closely balanced (Angle A greatly reduced). Employing the previous explanation used to explain the interaction between gibberellin and photoperiod on the growth responses of Pygacantha will suffice. That is, under high night temperatures the production of endogenous gibberellins are controlled by the temperature while the syn- thesis of the endogenous inhibitors are not. The reverse is true for the synthesis of endogenous gibberellins and inhibitors under low night tem» peratures. Consequently, the addition of gibberellin to plants under the higher night temperature results in a growth stimulation of the shoots. The exogenous source of gibberellin in combination with the endogenous source is slowly destroyed by the mechanisms which are Operative under high night temperatures, consequently a slight acceleration in shoot elongation results. In contrast plants under low night temperatures do not possess this system to destroy or make gibberellin inoperative, thus an inhibition in growth results. A failure of an interaction earlier in the season would indicate that the mechanism,for destroying an exogenous supply of gibberellin is operative in plants under both low or high night temperatures. 2332; also failed to respond markedly to gibberellin treatment early in the season, but in mideuly death of plants treated with gibberellin under high night temperatures occurred. It is difficult to explain this response. Possibly under high night temperatures, there is a rapid 146. accumulation of inhibitors as the season progresses. In this respect the shoot extension of 1192‘. in early June under high night temperatures is markedly reduced but not so under low night temeratures. This supports the above schemes. It is postulated that gibberellin increases the sensitivity of plant tissue to endogenous inhibitors. Gibberellin has been reported to induce abortion or disiccation of terminal buds in other woody plants. (McVey and Wittwer, 1958; Nelson, 1957; Soost, 1959). Clor, Currier and Stocking (1958) also reported an increase in the sen- sitivity of been plants to 2,4-D following gibberellin treatment. Weaver (1959) reported a prolonged dormancy in buds of m vinifera with increasing amounts of gibberellin. It appears that the sensitivity of some tissues to the endogenous inhibitors may be increased by the presence of gibberellin. T1: interaction of the accmlative vegetative responses to gibber- ellin and temperature can be explained amply by the schemes presented. Note in Figure 15 that under the high night temperature regime, Catalpa plants treated with gibberellin exhibited a greater inhibition in growth than those under the low night temperatures. This relationship was not evident in Viburnum and Sy_r_i_nga. Explanation of this difference by the schemes presented is as follows: In Catalpa there is a rapid increase in endogenous gibberellin synthesis in the early spring. The accmlation of an inhibitor to over balance the concentration of gibberellin is not apparent until late June or early July (Figure 5, Treatment C2). The rate of synthesis of endogenous gibberellin is as rapid in Syringe, but in contrast to Catalpa, the accumlation of the inhibitor complex occurs much more rapidly; about the first of June (Figure 5, Treatment C2). 147. The rate of inhibitor accumulation consequently controls the action of gibberellin. In one case, (Catalpa), the reduced rate of synthesis of the inhibitor in conjunction with a rapid rate of synthesis of the endogenous gibberellins results in uncontrolled growth (Figure 17). While in Syringe the growth is moderated by a rapid production of endogenous inhibitors. To explain this relationship in respect to scheme II would necessitate both a change in position of the vertex and the degree of angle A. For example, the position of the vertex would shift to the right and the angle would increase for Catalpa. In contrast,for Syringa the vertex would have to move to the left with relatively no change in the position of angle A. Viburnum, in contrast to Syrigga does not accumulate an inhibitor under high night temperatures. However, the rate of elongation of the shoot is greatly reduced, as compared to Syringe and Cstalp . This would imply that it is not essential for an inhibitor to be produced to prevent the deleterious effects following gibberellin treatment. 0n the contrary, a relatively low quantity of endogenous gibberellin will permit the addition of an exogenous source of gibberellin without resulting in the inhibition of growth. Graphically presented, the shift in the vertex would be to the right, but the angle A would be greatly reduced. Shoot elongation which was greater under higher night temperature than under lower night temperatures would suggest a greater production of endogenous gibberellin under the higher as compared to the lower night temperature. The reduction of angle A allows the addition of an exogenous source of gibberellin under either low or high temperatures without a deleterious effect resulting (Figure 27). 148. _A_c_5£, m and Euonyms generally exhibited an increased growth under low temperature, but in contrast to Viburnum, the rate of elongation under high night temperatures was inhibited later in the season. Possibly a rapid accumulation of inhibitors in Acer, Pinus and Euonymug under high night temperatures (Figures 5 and 6, Treatment CZ) reduced the action of gibberellin. In some cases gibberellin might increase the sensitivity of the cells. Consequently resulting in an inhibition in growth from.the high concentration of inhibitors present. The induction and cessation of dormancy as shown in Figure 13 strongly supports the concept presented. Note that under high night temperatures as compared to low night regime (treatment 7 and 8) gibber- ellin was much less effective in preventing induction of dormancy in 552;, Euonyggg, Sygigga and Liriodendron. In the latter species this was only evident under high night temperature-short day regime illustrating the importance of photoperiod in this overall scheme of dormancy. It would appear that the synthesis of gibberellin in shoots of plants is not as temperature dependent as that of seeds. In this respect, note in Table III that the total germination under alternating day and night temperatures was not altered following gibberellin treatment. In contrast the shoot extension of Catalpa and Syringe was greatly stimulated as compared to the check under the low night temperature regime. This would indicate that the synthesis of gibberellin in seeds is relatively high, or conversely the distruction of inhibitors are relatively rapid resulting in a total germination. However, in terminal shoots of plants there appears to be a strongly moderating influence of endogenous 149. inhibitors within the plant which prevents full expression of the endogenous gibberellin regardless of the environmental exposure. In Liriodendron and Viburnum however the ultimate achievement is similar to that of germination of Catalpa seed under Optimum conditions, that is, the total growth was similar under either long days, high night temperatures, or gibberellin treatment. This would imply that there is a complete utili- sation of the endogenous gibberellins synthesised under the long days or high night temperatures, during the shoot extension period. It would appear that a high production of gibberellin in conjunction with a reduced rate of synthesis of an inhibitor within the seed (increase in the angle A with the vertex removed to the left in scheme 1) might result in poor germination following gibberellin treatment. In this respect Tod (1958) reported that seeds which were difficult or erratic germinators exhibited an increase in germination following treatment with gibberellin. In contrast, seeds which normally germinate fairly freely were inhibited by high concentrations of gibberellin. Donaho and'wslker (1957), also reported an increase in germination with low concentrations of gibberellin applied to partially stratified seed, if however a high concentration was used, germination was inhibited. Richardson (1959)' reported a depressing effect of gibberellin on germination of Pseudotsuga taxifolia with higher concentrations in comparison to low concentration of 3 to 10 ppm of gibberellin. The concept of a gibberellin-inhibitor balance as a mechanism controlling growth has been present elsewhere (Lockhart, 1961; “arcing and Villiers, 1961; Nitsch and Nitsch, 1959). It is of interest to note that "gibberellin-like" substances were present in larger amounts in plants grown under long days than those exposed to a short day regime. 150. (Chailskhisn, 1961). In this respect Brain and Hemming, (1961) reported an increase in the response of plants to a exogenous source of gibber- ellin as the length of the previous photoperiod increased. Not only is the photoperiod effective in modifying the synthesis of an endogenous source of gibberellin but the thermoperiod might play an important role. Wareing and Villiers (1961) reported that chilling of dormant Frsxinus seeds resulted in an increase in the concentration of a growth promoter accompanied by a reduction in the inhibitor concentration. Dondho and walker, 1957; Fogle and'McCrory, 1959; Marth, Audie and Mitchell, 1956; Prince, 1958; Stuart, 1957, also reported the optimnm concentration of gibberellin for breaking dormancy decreased as the period of exposure to chilling temperatures~increased. IV. Alterations in the Metabolism by Gibberellin A. Modifications of‘Hineral Absorption and Distribution 1. Dry Weight Distribution Alterations in the distribution of the dry weight in woody plants following gibberellin treatment have been widely reported (Benjamin and Snyder, 1958; Bull and Lewis, 1959; Scurfield and‘loore, 1958; Powell, Cain and Lamb, 1959). The degree of alterations in dry weight distribution appears to be dependent on the time of application, physiological stage of development, species, and concentration of gibber- ellin (Bull and Lewis, 1959; Benjmmin and Snyder, 1958; Chakrevarti, 1958; and Ergle, 1958). ‘Hore specifically, Ergle (1958) reported an in- 151. crease in stemnweight with little or no effect on leaf and shoot dry weight with small quantities of gibberellin (10 to 100 micrograms). If a large quantity of gibberellin were used, there was a marked reduction in leaf weight together with that of the entire plant. Scurfield and Moore (1958) reported a similar condition in Eucalyptus but in contrast the shoot weight increased concurrently with a reduction in leaf and root weight. The physiological stage of deveIOpment as shown by Fogle (1958) in his studies with after-ripened Sweet cherry seeds, also greatly modifies the response of shoot growth to gibberellin. Evidence present in Figures 14 and 15 illustrate many of the varied dry weight modifications in woody plants resulting from gibberellin treatment. The marked increase in dry weight of the newly deve10ping shoot of most species studied, accompanied by an inhibition in root, leaf and occasionally old shoot growth development, would necessitate an alteration in the nonmal distribution of the plant constituents. The rapidly deve10ping shoots resulting from gibberellin treatment can obtain the carbohydrates required from.two sources, the leaf, or reserve carbohydrates in the older wood. It is of interest to note that Hayashi (1961) reported a reduction in the reducing and total sugars in the roots of rice plant treated with gibberellin with a subsequent increase in the reducing sugars in the shoots. If there is a reduction in leaf area, the carbohydrate required for shoot extension would come basically from the stored reserve. In contrast, if the leaf area is not reduced, the reserve carbohydrate would be partially spared. To illustrate this point, note in Figure 14, that a reduction in the leaf area per plant (5) in Catalpa resulted in a subsequent reduction in the dry weight of the old 152. wood. However, as shown in Figure 15, the inhibition in leaf expansion was not as evident under low night temperatures or short days. This resulted in an actual increase in the dry weight of the old shoot under a low night temperature regime, following gibberellin treatment. The dry weight of the old wood was generally spared when the leaf expansion or leaf area was greater under one environment than another, following gibberellin treatment. 2. Mineral Distribution in Catalpa speciosa Evidence presented would strongly suggest that the nitrogen metabolism within the roots of Catalpa speciosa treated with gibberellin simulates that of short days and low temperatures. In contrast, it is suggested by the data that the reciprocal relationship is true for the shoots. This relationship might partially explain the greater inhibition of growth under long days or high temperatures following gibberellin treatment. That is, a reduced rate of transport of nitrogen to the shoot following gibberellin treatment which normally occurs under long day and high temperature, would result in a nitrogen deficiency in the shoots of plants. This response, associated with an increased carbohydrate move- ment to the shoot, which was suggested by the data in Table IV, would result in an increased C/N ratio in the shoots or conversely a de- creased CIH ratio in the roots. An increased carbohydrate content in the shoot would necessitate a decrease in the ash content. This, however, was not evident, suggesting that gibberellin caused an increase in the utilisation of the carbo- hydrates translocated to the shoots. Consequently, the difference 153. between the percent ash in the leaves and new shoots was not significant. In this respect, high night temperatures caused an increase in the ash content in the leaves, suggesting that gibberellin treatment simulated the response of high night temperatures. Evidence has appeared in the literature indicating an increase in the rate of respiration following gibberellin treatment, (Nielsen and Bergquist, 1958; Paleg, 1960). 3. Absorption and Transport of Labelled Phosphorus in Catalpa speciosa Evidence is presented which strongly suggests that gibberellin or photoperiod does not alter the movement of labeled phosphorus out of the leaves of Catalpa seedlings. In contrast to the photOperiodic response, which was not apparent in the young seedlings, gibberellin greatly stimulates growth of the shoot with a subsequent reduction in root weight (Table V). This evidence would suggest that the greater quantity of photosynthate utilized in the synthesis of organic constituents, within the rapidly develOping shoot, came from the reserves accumulated in the root and old shoot wood. In this respect, Alvin (1960) reported that the inhibition of dry weight accumulation in roots of beans treated with gibberellin could be controlled by the addition of s 10 percent sucrose solution. A relationship between the metabolism of nutrient uptake and vegetative growth of Catalpa speciosa. suggests possible causes for the differential growth response to gibberellin under various thermoperiodic and photOperiodic regimes. The inhibition of nutrient uptake and distribution by roots of young seedlings following gibberellin treatment 154. might suggest that a reduction in root surface caused the inhibition observed. However, a differential rate of uptake at different root temperatures rules out this possibility. The uptake of anions, such as phosphates are generally accumulated ‘metabolically in relation to enhanced aerobic respiration. However, it is now recognized that phosphates can be absorbed by non metabolic pathways. (Steward and Sutcliffe, 1959). If we assume that the quantity of photosynthates moving to the roots are reduced as a result of gibber- ellin treatment, it is evident that at higher temperatures a greater quantity of the photosynthates would be needed to compensate for the increased rate of respiration. Consequently, a reduction in uptake at the higher temperature following gibberellin treatment would result. In contrast, at lower temperatures the rate of respiration in the root would not be greatly accelerated thus the supply of photosynthate would be sufficient to provide the energy required for active uptake. The reduced rate of uptake under high root temperatures might explain the greater inhibition of growth in Catalpa speciosa under high as compared to low night temperatures. Uptake and distribution of phosphorus, as affected by gibberellin is mediated by the photOperiod imposed on young seedlings of Catalpa (3 weeks of preconditioning to gibberellin and photoperiod). The percentage of phosphorus translocated to the shoot following gibberellin treatment was increased to a greater extent under short than long days. As the plants matured, the uptake of phosphorus by the roots of plants treated with gibberellin was inhibited to a greater extent under long than short days. This relationship would indicate a similarity between the metabolic i\ 155. and the vegetative aspects of growth as modified by gibberellin. It is of interest that the prOposed schemes (I and II) might partially explain the differences observed. In young seedlings, the balance between en- dogenous inhibitors and gibberellin under short days is represented in Scheme I, while those under long days is represented by Scheme 11. Con- sequently, the addition of an exogenous supply of gibberellin to plants under short days results in an increased growth response which is moderated by the inhibitor present. After 6 weeks of preconditioning the inhibitor content is so intense under short days that the exogenous source of gibberellin is masked. In contrast, the inhibition of uptake under long days by roots of Catalpa plants preconditioned for six weeks, as compared to those preconditioned for 3 weeks, would indicate that the balance between the endogenous inhibitor and gibberellin was sufficient to moderate the effects of an exogenous source of gibberellin after 3 weeks, but not so after 6 weeks of preconditioning. An increase in the gibberellin-inhibitor ratio could result in an increased rate of respiration in the shoots and therefore a reduced rate of uptake, because of an insufficient supply of photosynthate moving to the roots. In contrast to findings reported herein, Linck and Sudia (1960) reported an increase in the quantity of phosphorus absorbed by roots of bean plants treated with 1 ppm of gibberellin. The rate and method of application mdght account for the discrepancy in results. 156. SMY Certain woody plants (Catalpa speciosa. Lirigendrg Tulipifera, Viburnum Carlesii, Acer saccharum, Pinus sylvestris, Pgacantha coccinea Lalandii, Sgigga vulgaris and 3mm Fortunei vegetus) exhibiting a known photoperiodic response and a broad range of temperature adaptation were selected for this investigation. Two aspects of plant behavior were followed. The plants were subjected to photoperiods of 9 (short) and lb (long) hours, thermOperiods of ao°r (low) and 7o°r (high) night tequeratures and to sprays of gibberellin at 0 and 50 ppm for the evaluation of the various vegetative growth responses. Alterations in metabolism were determined by using a radio-labeled source of phosphorus applied to the foliage or roots of Catalpa specios . These plants were subjected to various photoperiods, gibberellin concentrations and root teqeratures prior to or during the 1’32 treatment. Gibberellin simulated a shoot extension response which is typical of long days or cool night temperatures. In addition, gibberellin re- placed the affect of high night tameratures on shoot elongation in plants which grew more favorably under this regime. The photoperiodic response of vegetative shoot elongation was replaced to a greater extent by gibberellin than the thermOperiodic response. Although gibberellin could replace the shoot elongation which was stimulated by the various environ- mental regimes iqosed, replacement was not evident in leaf, root and old shoot wood dry weights. Differential responses to gibberellin under the various photOperiods and thermOperiods isposed indicated an interaction between endogenous 157. growth regulators and an exogenous source of gibberellin. A.mechanism for the hormonal control of growth and development in the woody plants investigated is prOposed. Alterations in the metabolism of Catalpa speciosa by gibberellin suggest that the reserves in the old wood are the primary source of carbohydrate in the shoot which is induced to elongate rapidly. These reserves may be partially spared by an increase in the leaf area per plant. Phosphorus uptake and distribution by the roots of Catalpa speciosa seedlings was altered by gibberellin at the high but not at the low root temperatures. The phosphorus distribution in the young short day gibberellin treated Catalpa plants was similar to those not treated under long days. In contrast, as the plants matured, gibberellin was effective in inhibiting the uptake and distribution of phosphorus only under the long day regime. Both induced vegetative growth responses and alterations in the metabolism suggest that endogenous growth regulators modify the effects of an exogenous source of gibberellin. 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