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This is to certify that the

thesis entitled

PHYSIOLOGY 0F CUT 'FOREVER YDURS' ROSES
GIVEN SUPPLEMENTAL LIGHTING DURING
AND AFTER GREENHOUSE PRODUCTION

presented by

Wayne S. Johnson

has been accepted towards fulfillment
of the requirements for

 

Ph.D. degree in Horticulture

 

 

Major pr essor

Date 9/114/79

0-7639

PHYSIOLOGY OF CUT 'FOREVER YOURS' ROSES
GIVEN SUPPLEMENTAL LIGHTING DURING
AND AFTER GREENHOUSE PRODUCTION

By

Wayne 5. Johnson

A DISSERTATION

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Horticulture

1979

ABSTRACT

PHYSIOLOGY OF CUT 'FOREVER YOURS' ROSES
GIVEN SUPPLEMENTAL LIGHTING DURING
AND AFTER GREENHOUSE PRODUCTION
BY

Wayne S. Johnson

Short days and low light intensities during winter reduce the
quality and production of greenhouse roses in northern climates. Con-
sequently, high intensity discharge (HID) lamps are used to supplement
natural light to improve rose quality and production.

Na(HID) supplemental lighting had no effect on stomatal density or
average leaf size of 'Forever Yours' roses although the terminal leaflet
was larger. The terminal leaflet represented 35% of the total leaf area
and had the lowest diffusive resistance of the leaflets. Therefore, the
terminal leaflet was responsible for much of the difference in diffusive
resistance between greenhouse lighting regimes. Diffusive resistance
of leaves throughout the plant canopy was similar except the leaf near-
est the flower tended to have a higher diffusive resistance.

Diffusive resistance of benched Na(HID) grown roses was lower than
that of roses grown in natural light. Natural light grown roses had
higher diffusive resistance during 12 hours of dry storage in the light
and dark when compared to Na(HID) light grown roses which were high only

during dark storage. Following lighted storage both natural and Na(HID)

Wayne S. Johnson

light grown roses had increased diffusive resistance for several days.
Stomatal conductance was high in both greenhouse treatments after dark
storage. Light stored roses had significantly greater diffusive resist
tance during the remainder of vase life compared to dark stored roses.

The most bent neck roses occurred in dry, light stored and Na(HID)
grown roses. Increased temperature during lighted storage increased the
incidence of bent neck. The opposite occurred in dark, dry storage. Poor
keeping quality in Na(HID) light grown roses may have been the result of
high water deficits produced during dark storage by stomatal opening.
After storage, roses with closed stomates had reduced water uptake and
therefore decreased fresh weight and shorter vase life.

Roses stored in water at 0°C for l2 hours had high diffusive resis-
tance and low water uptake. Water uptake was higher and diffusive
resistance lower in Na(HID) grown roses than those produced under natural
light. No significant difference in keeping quality occurred between
Na(HID) and natural grown roses when stored in water.

There were no differences in net photosynthesis and respiration
during vase life between Na(HID) and natural light grown roses except
Na(HID) grown roses given dark first to begin l2 hour light-dark cycles
had higher rates of respiration. Water uptake and loss was low in cut
roses begun in the dark in water and then given l2 hour light-dark
periods. Na(HID) light grown roses in water had greater water uptake
for the first two days of vase life compared to natural light grown
roses. Cut roses placed in the light first had the best vase life com-
pared to those begun in the dark first which went bent neck during the
first three days.

Early water uptake in roses following any storage conditions was

Wayne S. Johnson

critical for cut flower longevity. Light induced stomatal opening after
storage or harvest favored gains in fresh weight and increased vase life.
Na(HID) light grown roses should be stored dry in the dark for best cut
flower longevity. Little difference existed in cut flower longevity
between Na(HID) and natural light grown roses when kept in water during

storage and vase life.

ACKNOWLEDGEMENTS

I express appreciation to those who have contributed to my
graduate education and assisted during this research. Special thanks
to Dr. H. P. Rasmussen for serving as major professor and providing
timely advice throughout these studies. To the guidance committee,
Drs. W. J. Carpenter, G. R. Hooper, A. A. DeHertogh, and J. W. Hanover,
I express gratitude for their direction, advice and willingness to make
their laboratories and equipment available to me. I am grateful to Dr.
J. A. Flore and Dr. R. Heines for their willingness to replace Dr.
Carpenter and Dr. DeHertogh on the committee. I appreciate the
scholarly example and the consideration extended by each in providing
most welcome suggestions and encouragement.

I am grateful to the departments of Horticulture and Entomology
for providing financial support during these graduate studies.

To my parents, Mark William (deceased) and Lucile Johnson, and
to my wife, Diane, I extend a special note of appreciation for their

patience, encouragement and support.

TABLE OF CONTENTS

List of Tables
List of Figures
Introduction
Literature Review
Origin and Economic Importance
Effect of preharvest light on Cut Rose Longevity
Color Changes in Senescing Rose Flowers
Sugar Metabolism
Respiration in Roses
Hormonal Effects on Senescence
Cytokinin
Abscisic Acid
Ethylene
Water Balance and Weight Changes in Roses
Nature of Vascular Blocking
Water Quality and Floral Preservatives
Cut Flower Handling
Materials and Methods
Greenhouse lighting
Leaf area and stomatal density.

Diffusive resistance

vii

l3
15
15
l6
l7
19
22
23
26
29
29
29
30

Storage

Water uptake and transpiration by cut flowers

Net photosynthesis and respiration by cut flowers

Leaf shading of cut flowers

Results

Discussion
Appendix A
Appendix B
Appendix C
Appendix D
Appendix E

Bibliography

31
31
32
33
3h
60
67
7o
75
77
79
93

LIST OF TABLES

Table l. Diffusive resistance (sec/cm) of greenhouse
rose leaves under natural and supplemental lighting
regimes.

Table 2. Leaflet area and stomatal density of 'Forever
Yours' roses as influenced by supplemental light.

Table 3. Leaf area (dmz) of the first five leaflet leaf
of roses grown under three lighting regimes.

Table A. Diffusive resistance (sec/cm) of the five-leaflets
of the first five-leaflet leaf of cut roses grown
under three lighting regimes.

Table 5. The effect of supplemental lighting during pro-
duction and light and dark, dry storage at three tem-

peratures on the keeping quality (2 bent neck) of roses.

Table 6. Diffusive resistance (rs) and water uptake (WU)
rates of natural and supplemental Na(HID) light grown
cut roses.

Table 7. Diffusive resistance (rs) and water uptake (WU)
rates of natural and supplemental Na(HlD) light grown
cut roses after dark storage for l2 hours at 0°C.

Table 8. Effects of storage (l2 hours, 0°C) on the dif-
fusive resistance (rs) and water uptake (WU) of cut
roses grown under natural light conditions.

Table 9. Effects of storage (l2 hours, 0°C) on diffusive
resistance (rs) and water uptake (WU) of cut roses
grown under supplemental Na(HID) light.

Table ID. The influence of shading on C02 exchange in
cut roses grown under natural or supplemental Na(HID)
light.

Table ll. The effect of shading on water uptake and loss in
cut roses grown under supplemental Na(HID) light.

34

35

37

38

46

47

48

50

El

57

59

Table Al. Histological and cytohistochemical techniques
and observations.

Table A2. The rate of C02 exchange and water loss from
potted roses at three relative humidities in light,
l3,000 lux, Na(HID), and dark.

Table A3. The effect of platn density per potometer on
water loss, water uptake and C02 exchange by natural
light grown roses.

Table AA. The effect of platn density per potometer on
water loss, water uptake and C02 exchange by supple-
mental light grown roses.

Table A5. Diffusive resistance (sec/cm) of cut roses grown

under natural daylight or con tinuous Na(HID) light
with and without 12 hours of dark prior to harvest.

vi

77

80

8h

8h

87

LIST OF FIGURES

 

Figure l. Diffusive resistance of greenhouse roses grown
under natural and supplemental, l8 hour, HID lighting;
light levels per data collection period included.

Figure 2. The effect of dark storage on the diffusive re-
sistance of cut roses grown under natural and supple-
mental Na(HID) light.

Figure 3. The effect of light storage on the diffusive re-
sistance of cut roses grown under natural and supple-
mental Na(HID) light.

Figure A. The effect of light and dark storage on the dif-
fusive resistance of cut roses.

Figure 5. Diffusive resistance of cut roses grown under
natural (-—-9 and supplemental Na(HID) (---) lighting
and stored at three temperatures with and without
light. LSD(0.05); dark trts. - 1.96 and light trts.
= 5.7.

Figure 6. The effect of l2 hour alternating light-dark
periods, A0,000 lux, at 35 i 5% relative humidity on
net photosynthesis and dark respiration in cut roses
grown under natural light.

Figure 7. The effect of l2 hour alternating light-dark
periods, 40,000 lux, at 35 f 5% relative humidity on
water uptake and loss in cut roses grown under
natural light.

Figure 8. The effect of l2 hour alternating light-dark
periods, l3,500 lux. at 35 f 5% relative humidity on
net photosynthesis and dark respiration in cut roses
grown under Na(HID) light.

Figure 9. The effect of l2 hour+alternating light-dark
periods, I3,500 lux, at 35 - 5% relative humidity on
water uptake and loss in cut roses grown under Na(HID)
light.

vii

36

40

Al

42

“3

52

53

55

56

Figure Al. The environmentally controlled measurement system
for simultaneous measurement of plant C02 exchange, trans-
piration and water utpake. Relative humidity-temperature
sensor (RHTS), Proportional electronic temperature con-
troller (PETC), Relative humidity controller-indicator
(RHCI), Infrared gas analyzer (IRGA), Potometer (P), Water
supply (WS), Potometer guage (PG), Input (I) and Exit (E)
port, Valves (V) l to A.

Figure A2. Water uptake and loss in cut roses grown under
natural light and held in continuous light, l3,000 lux.
at 35 T 5% relative humidity.

Figure A3. Net photosynthesis and dark respiration in cut
roses grown under natural light and held in continuous
light, l3,000 lux, and 35 f 5% relative humidity.

Figure Ah. Stomatal activity of cut roses grown under contin-
uous supplemental Na(HID) lighting and subjected to one
12 hour dark period immediately prior to harvest.

Figure A5. Overall diffusive resistance and water uptake
rates of cut roses treated with varying lengths of dark
4 consecutive nights prior to harvest.

Figure A6. The effect of preharvest, continuous Na(HID) lighting

of Na(HID) lighting plus 6 hours of dark, A consecutive
nights prior to harvest on the water uptake of cut roses.

Figure A7. Water uptake rates of cut roses that received

Na(HID) lighting plus 3 or 9 hours of dark, A nights
prior to harvest.

viii

7i

82

83

86

89

90

9|

INTRODUCTION

Roses, a major component of a multimillion dollar industry, have
an effective consumer vase life of two to ten days. To obtain a
quality product, growers, wholesalers, shippers, retailers and the
consumer must know how to properly handle the rose. The flower, when
removed from the plant, still carries on important physiological and
metabolic functions, the alteration of which may shorten or enhance the
useful vase life. Rose postharvest physiology and metaboTism has been
studied to minimize harmful practices and maximuze beneficial handling
procedures.

Recently, supplementary high intensity discharge (HID) mercury and
sodium lighting has been used in the northern temperate zones to
improve winter production and rose quality; both have historically been
poor in the winter due to low light intensities and short days.
Carpenter and Anderson (35) demonstrated increased yields and improved
quality of greenhouse roses with supplemental light. In 'Baccara'
roses, high temperatures, low light intensities and low CO2 concentra-
tion occurring during the latter stage of flower development caused
blueing (22). The effect of supplemental HID lighting on the vase life
of cut roses is not known. However, by optimizing those factors which
contribute to growth and sugar accumulation, cut flower longevity is
expected to be maximum (l8).

Cut flowers harvested following periods of low light did not keep

l

2

well (66, 93). Dry matter increased in roses produced in April, but
during December and poor light conditions, food reserves were barely
maintained (66). Winter and spring roses cut late in the afternoon kept
longer than those cut in the early morning. This was attributed to

the higher carbohydrate level of the afternoon cut flowers (66). There
were more bent neck roses in flowers harvested from the sides and
interior of the plant compared to roses cut from the top where light
intensities were higher (l37). Roses grown at low light levels, forced
at high temperatures, or cut at an immature stage produced bent neck
roses. Lack of lignified cells in the pedicel contributed to bent neck
(76).

Mayak g£_§l: (105) demonstrated the difference in vase life between
short- and long-lived cultivars was large under conditions promoting
high transpiration and was narrowed under mild conditions. During vase
life the stomates of the short-lived cultivar were more widely open and
consequently transpiration rates were higher and wilting occurred
earlier. They concluded that the earlier wilting of cut flowers of the
short-lived cultivar was mainly due to the lower ability to close
stomates in response to water stress conditions.

Mastalerz (9h) recommended that highest quality roses be held in
low temperature dry storage. Low carbohydrate levels within the rose
reduced its life expectancy and quality. The highest greenhouse light
intensities possible consistent with optimum production temperatures
were recommended to avoid the loss of quality and life in stored roses.

Commercially, roses are harvested and stored at low temperatures
over night or until freight is available. It is critical that cut

flowers be rapidly cooled (l8). Dark refrigeration (0-l°C) was

3
recommended for flowers stored dry or in deionized or distilled water
containing a floral preservative (ll6). Light or dark storage and
variations in temperature during storage affect cut flower physiology
and may ultimately determine the vase life of the rose.
This research was initiated to determine if supplemental light
during production and short term storage under selected conditions

produces physiological differences in cut roses.

LITERATURE REVIEW

 

Origin and Economic Importance

 

The genus Rosa is distributed throughout the northern hemisphere
and includes 120 (ll8) to 200 (I32) species. Modern cultivated roses
are derived from descendants of the western summer-flowering shrub

species 5. gallica, R. damascena and R. moschata crossbred with lines

 

from oriental everblooming species R. gigantes and R. chinensis. The

 

 

most horticulturally desirable progeny are tetraploid roses grouped as
floribunda, hybrid tea and grandiflora types. Of these, the floribunda
and hybrid tea roses are most important in commercial greenhouse rose
bulture (I32).

Based on the I977 and l978 gross wholesale value for thirteen
selected cut and potted flowers marketed in the United States, roses
were second only to chrysanthemums. Among the five leading cut flowers
sold in 1977 and 1978, carnations, chrysanthemums, gladioli, roses and
snapdragons, roses were first in total sales. In I978 total sales of
these five cut flowers increased 7.5% from I977. Hybrid tea rose sales
were up 112 to $69.l million. The number of blooms sold increased by
2% to 307 million blooms even though the total number of plants in I978
decreased by 102 to l6.2 million plants. Sales of sweetheart roses fell
52 in numbers sold to ll2 million blooms and were up 82 in dollar
value to $l8 million. All roses accounted for 38.5% of the wholesale

value of cut flowers in I978 and hybrid tea roses represented 30.l% of

z,

this total (8, 9).

The wholesale value of roses has increased over the years; however,
due to competitive relationships in the market, the numbers of roses
sold per capita has declined and then leveled off. In l9h9 the total
number of blooms sold was 390 million compared to the l967 estimate of
386 million (190). Concurrently, the population increased and per
capita consumption declined by 25% from 2.6 roses in I999 to l.93 roses
in l967. With hl9.3 million total rose blooms sold in I978 (9) and a
population of 2I5 million (7), the per capita consumption was l.95 or a
l.0% increase over I967. The change in consumption was due to increased
sales of sweetheart roses through cash and carry marketing and wider
use of impulse purchasing programs at the retail level (lhO).

Staby §£_§l,(129) estimated that product shrinkage from harvest to
consumption for the floral industry is 20%. Shrinkage can be reduced
in the marketing chain with proper methods of handling and storage.
Each handling step for cut roses must include considerations for the
physiological, physical and metabolic requirements of the flower. To
optimize cut flower vase life, control of environmental conditions and
handling techniques is critical.

Effect of Preharvest Light on Cut Rose Longevity

Supplementary lighting of greenhouse roses grown in the northern
latitudes during the winter had increased yields and improved quality
compared to controls (35). The effect of supplementary HID lighting
on the vase life of cut roses is not known. Boodley (l8), in review,
concluded light has a profound affect on the production of sugars In
the plant which directly affects cut flower longevity. Vase life was

reduced in roses harvested following low light growing periods

(66, 93). Winter and spring roses cut during the morning did not keep
well compared to roses cut in the evening after a day of photosynthate
accumulation (66) nor did roses taken from within the shaded plant
canopy as opposed to those grown at the perimeter (l37). Supplemental
lighting with Na and Hg(HID) lamps increased the light Intensity and
the number of hours per day rose plants received light (35).

Color Changes in Senescing Rose Flowers

 

Senescing rose flowers may fade and change color or ”blue”, thus
shortening their effective vase life. Supplementary greenhouse
lighting with mercury and sodium high intensity discharge (HID) lamps
resulted in fading of flowers and leaves nearest the lamps. The
solarization response may have been due to heat stress compounded by an
induced plant water deficit (3h, l29). Temperatures in excess of 75°F
reduced flower pigmentation and increased blueing (l29).

Brian g£_§l, (22, 23, 2h, 25, 26, 27) elucidated many factors
determining changes in petal color of 'Baccara,‘ a red rose. High
temperatures, low light intensities and low C02 concentrations incident
to the latter stages of flower development caused blueing. These
conditions reduced sugar levels during maximum pigment production thus
lowering the pigment concentration which resulted in blueing (23.)
Exposure to short term heat and shade treatments during stem elongation
and early bud development had no effect on flower color (22). Ninety
percent of flower pigments were synthesized from the time the bud was
seventy-five percent to the time it was one hundred percent of its
diameter at opening. Subsequent to the period of synthesis petals
grew and ”diluted” the pigments present at opening (23). Heat stress

accelerated petal development (22) and thus the period of pigment

synthesis was shortened possibly affecting the final quality of the
rose (23). The treatment of individual organs (buds or leaves) or the
whole plant with cool temperatures or darkness during flower develop-
ment led to the conclusion that light intensity and temperature affected
flower growth and pigmentation by determining the availability of sugars
to the flower bud (2h).

Brian g£_§l, (25) found that partitioning of reflected and absorbed
light by the petal was influenced by both the colored epidermis and
the colorless mesophyll. Vigorous growth of the petal caused a color
shift from red to purple. When young and senescing petals were
compared (26), senescing flowers exhibited a bathochromic shift in
their light reflectance curve, a rise in pH of their cell sap and a
decrease in maleic acid concentration as the petal blued. Young petal
blueing increased with a decrease in fresh or dry weight and had a
lower concentration of pigment per unit area or per unit fresh weight
(26). In vitro, the petal extracted, crystalline pigment cyanin turned
from red to blue with dilution in acidic methanol. The dilution of
pigment caused a rise in reflectance particularly in the blue range.
Pelargonin, a red-orange pigment did not exhibit color shifts with
dilution. With a high total pigment concentration, a sharp increase in
the cyanin/pelargonin ration produced blueing. The concentration of
maleic acid and the pH were the same in both red and blue petals of
young flowers. It was concluded that the blueing of 'Baccara' petals
were caused by l) a reduced pigment concentration and/or 2) a sharp
increase in the ratio of cyanin to pelargonin (27).. Asen gt_gl, (l2)
have shown the stabilization of a co-pigmentation complex contributes

to blueing.

Curry (#8) reported a lack of tannins in the cell sap of 'George
Dickson,‘ a red rose, but Twigg (l38) found no change in tannins
throughout the aging of 'Better Times' petals. He proposed that color
changes were due to an increased ratio of anthoxanthin to anthocyanin
and an increased concentration of potassium. Weinstein (l42) however,
only found cyanidin 3, 5-diglucoside (anthocyanin) in 'Better Times'
rose petals. After harvest an initial increase in anthocyanin occurred
from 0 to AA hours, then decreased gradually with aging. He suggested
that the decrease during senescense was due to an increased activity of
an anthocyanase or that pigment synthesis was inhibited.

Chelation may be responsible for the reduction of color changes in
petals when selected compounds are added to the preservation solution
(ll, th). Weinstein and Laurencot (lh3) suggested the addition of
aluminum sulfate to the holding solution reduced blueing of red roses
due to the formation of an anthocyanin-aluminum complex. The formation
of pigment complexes is not unique to chelating agents. Asen gt_§1,
(I2) isolated an anthocyanin-flavonol co-pigment complex of cyanidin 3,
S-diglucosides and kaempferol or quercetin from 'Better Times' petals.
As the co-pigment complex is highly pH-color change responsive, they
hypothesized that the co-pigmentation complex and the high pigment
concentration of the petal are responsible for the color of the flower
in a pH range where anthocyanins are colorless (68). Asen gt_gl, (l3)
further suggested that changes in the molar ratio of anthocyanin to
co-pigments in the petal tissue could be responsible for blueing.

The cell sap of an intact or freshly cut flower has a pH of h-S.
An increase in the pH of the cut rose petal or the flowers' holding

solution is highly correlated with blueing (l2, I9, 20, 25, A7, 53, 69,

78, 79, 91, Ill, llS, 136, 138, th). Enhanced blue color followed
increased pH which was attributed to stimulating catabolism and
proteolysis with the subsequent release of amino-acids and ammonia at
toxic concentrations (19, 91, 9h, III, 192). Weinstein suggested that
free ammonia contributes to the blueing of roses (1&2). Mastalerz (9h)
indicated that dry, low-temperature storage inhibits such metabolism.
Others (19, 91, 9h, lll, 1&2) found that addition of sugar to the
holding solution reduces blueing and maintains a lower pH in the cell
sap by supplying the substrate for cellular metabolism thus reducing
cellular proteolysis.

Sugar Metabolism

Floral preservatives contain sugar, usually sucrose (Ill). The
uptake, distribution and metabolism of the preservative or its consti-
tuents may determine its effectiveness and provide information about
the physiology of senescence in cut flowers.

The major endogenous sugar constituent of 'Better Times' rose
petals was glucose. Ribose, xylose and mannose were in petal tissue,
but not sucrose (142). Fructose and glucose were predominant and
minute levels of sucrose were present in 'Red American Beauty' petals
(70), but 'Forever Yours' flower petals contained slightly more sucrose
than fructose and glucose (Al).

During the first #4 hours of vase life in distilled water glucose
levels remained proportionally high in 'Better Times' rose petals but
declined in stem and receptacle tissue, possibly due to translocation
into the petals (lh2). Even with high glucose levels in the petals,
proteolysis continued at a constant rate. Petals lost 402 of their

original protein nitrogen over 96 hours compared to receptacle tissue

IO

31%, leaf tissue 25%, and stem tissue 6%. Proteolysis was independent
of glucose availability, a respiratory substrate, and occurred early
during cut rose senescence. Consequently free amino acids accumulated
during early stages of aging. In petals, glutamic acid initially
increased through 44 hours and then declined. The level of malic acid
in petal tissue increased during the later stage of senescence and on a
whole flower basis free glucose was rapidly depleted. These data led
Weinstein (142) to postulate that with the complete utilization of a
preferential substrate such as glucose, petal tissues may utilize the
products of proteolysis, amino acids, as substrates for metabolic and
physiological processes. A decline in respiratory activity has been
associated with substrate limitations and preservatives were thought
to maintain substrate levels thus increasing cut flower longevity (46,
92). The limitation of substrate is thought to be the principle cause
of premature cut flower senescence (19, 46, 71, 122).

Changes in carbohydrate levels in petals of cut roses is variety
dependent 'Red American Beauty' petals held in distilled water lost
glucose rapidly one day after harvest (70), while 'Forever Yours'
maintained a near harvest level for 9 days and then declined gradually
(71). In the first, glucose decline preceded senescence, while in the
second, senescence preceded the decline in sugar levels. When both
received preservatives containing sugar, sugar levels in the petals
were increasing at the end of vase life. Therefore, the end of vase
life was not due to limited substrate (19, 71).

Cut roses held in distilled water and maintained in light exhibi-
ted maximum water uptake 24 and 48 hours after harvest with a gradual

decline thereafter while roses held in the dark absorbed water at

ll

uniformly low rates until discarded (37). With the decline of water
uptake rates, the accumulation within the rose of sugar and other
preservative components was restricted (28, 53, 79, 85, 111). Both
physical and physiological blocking has been described in rose stems
(2, 15, 28, 91, 137) and will be discussed later.

Vascular conductivity of stems subjected to mild pressure (0.097
Atm) was dependent upon the composition of the test fluid (56).
Distilled water movement declined rapidly within 12-18 hours, but with
sucrose the conductivity declined gradually over 60 hours and then
continued at a low rate. Sucrose + 8-hydroxyquinoline citrate (8-HQC)
or 8-HQC alone increased stem conductivity to levels 25% greater than
' stems held in distilled water' such treatments maintained high levels
of stem conductivity for 120 hours. These results confirmed work by
Kuc (79) with regard to glucose conductivity in stems subjected to
slight vacuum pressures. In other experiments, Sacalis and Durkin
(125) concluded that initially uptake of sugars is via the xylem.
Regardless of conductivity rate through the xylem, accumulation of
sugar in the petals occurred at the same rate and thus reduction or
changes in xylem conductivity may not be correlated with sugar accumu-
lation in flower petals (70).

In cut flowers with leaves, ll'C--sucrose moved into leaves and
stems first and then was redistributed to the flower petals via the
phloem (125). Kaltaler and Steponkus (70) found little phloem-mediated
transport of exogenously supplied sucrose below the first 5-1eaf1et
leaf of cut roses. This suggests that xylem to phloem transfer occurs
within the leaf (60). Chin and Steponkus (41) later demonstrated that

14 14

C from C-sucrose moved uniformly from xylem to phloem along the

l2

entire length of the rose stem irrespective of the concentration within
the xylem. Hydrolysis of llIC-sucrose occurred rapidly as the reducing
sugars constituted between 20 and 40% of the total sugar in the vascular
bundles of the stem, petals and leaves. Less sucrose was isolated from
the petals than the receptacle, leaves or stem. It was suggested that
invertase in the xylem controlled the hydrolysis of sucrose and may
regulate the movement of sugars into the petals. A second paper (42)
demonstrated, however, that sucrose was absorbed undegraded into petal
tissue and that inversion was not necessary. .

Buxton and Stoltz (32) found that the pentose phosphate shunt (PPS)
is active in the sugar metabolism of roses. As much as 50% of the glu-
cose oxidized in the petals was through the PPS throughout the vase
life of the flower. The relative activity between the PPS pathway, the
Embden-Meyerhof-Parnas and tricarboxylic acid cycle did not change over
time.

The respiratory rate of cut flowers declines from the beginning to
the end of vase life (69, 122). By monitoring the respiratory control
(RC) of mitochondria isolated from roses held in preservative or dis-
tilled water, Kaltaler and Steponkus (71) found that the decline in the
rates of respiration was not due to substrate limitations. They con-
cluded exogenous application of sugar maintained the structure and
function of the mitochondria. They proposed three modes of action.
First, the structure and semi-permeability of the plasma membrane, as
suggested by Aarts (2), would be maintained, preventing the leakage of
phenolic compounds detrimental to mitochondria. Second, exogenous
sugar maintains a low pH (69) and thus the integrity of the mitochondria.

And third, it would reduce protein catabolism which includes the

'3

degradation enzymes necessary for metabolism of respiratory substrates
and carbohydrate distribution and absorption.
Respiration in Roses

Kaltaler (69) reviewed the literature on respiration in cut roses
and Coorts (44) broadened the topic to include internal metabolic
changes in various cut flowers.

The respiratory activity of intact and cut flowers is distinctly
different. Coorts g£_§l, (46) demonstrated that 'Velvet Times' roses
had a greater preharvest than postharvest rate of respiration. The
maximum rate of respiration occurred coincidently with sepal unfolding
prior to harvest and the minimum respiration rate and maximum fresh
weight occurred three days after harvest. They found that the whole
flower exhibited respiratory time drifts similar to those observed in
leaves (15); but they did not compare the rise in respiration of
senescing flowers to the climacteric of fruits. Siegelman (128)
demonstrated a downward trend in respiration rates of 'Better Times'
cut roses regardless of storage temperature and concluded that commer-
cially harvested roses are either in a post-climacteric stage or are
non-climacteric.

The respiratory rate of petals from 'Forever Yours' flowers
declines throughout their vase life. Regardless of treatment with
distilled water or preservative, the inner petals exhibit higher rates
of respiration than the outer petals (32). Similar data led Siegelman
(128) to conclude that the whole flower is not at a uniform stage of
development therefore respiration studies of the whole flower lead to
an average of many different tissue stages on the overall pattern of

postharvest activity. '

l4

Investigators have shown that lowering the temperature of cut
flowers increases rose longevity (65, 82, 94, 128, 135). Laurie (82)
concluded that increased cut flower longevity was due to reduced
respiration at low temperatures. Flowers with the highest respiratory
rates had the poorest keeping quality and shortest longevity (14, 128).
This led to the recommendation of low temperature storage to reduce
respiration and conserve respirable substrates with a slowing of
metabolic processes (44, 69, 94, 122, 128).

Roses can be successfully stored dry at 31°F for 15 days and have
equal quality and longevity after storage compared to freshly cut roses.
Low temperature and dry conditions reduce respiration (94). However,
dry, low-temperature storage for more than 15 days reduces vase life
and the roses open poorly (21).

A rapid decline in respiration after harvest has been reported,
but with the addition of floral preservatives the rate of decline can
be slowed (32, 46, 69, 90, 134). Sucrose, a component of floral
preservatives, increased respiration as much as 40% over controls (46,
90). The respiratory rates after harvest were not affected by 8-HQC
nor silver nitrate until the end of vase life when a slight rise
occurred (90, 126).

Sucrose increased cut flower vase life, quality and rate of
respiration as compared to both contols, distilled water and preserva-
tive solutions without sucrose (2, 46, 71, 126, 134). Therefore,
contrary to the popular hypothesis that sucrose acts as a respiratory
substrate to retard senescence, cut flower longevity may be dependent
upon mitochondrial structure and function and sucrose may influence

either or both to increase vase life (71). Borochev et al. (19) also

15

concluded that carbohydrate limitations were not necessarily coupled
to senescence.
Hormonal Effects on Senescence

The role of plant hormones in the senescence of cut roses has not
been fully elucidated. Harvest and postharvest handling procedures
interfere with normal rose water status, metabolism and physiology.
Livine and Vaadia (88) have discussed the role of several hormones and
deficit water relations found in plants. The effects of absissic acid
and cytokinin in rose senescence as affected by water deficits has
been investigated and are discussed in subsequent sections (20, 62, 63,
78, 102, 104).

Cytokinin

Cytokinins are involved in regulation of senescence, induction of
stomatal opening and enhancement of wilting (88). Harvesting the rose
eliminates the source of cytokinin. The amount of cytokinin in the rose
petal declined with the onset of senescence, with the greatest activity
in physiologically younger flowers (101, 104). The cytokinin level
peaked as flowers opened on the plant suggesting that endogenous levels
of cytokinin are important to flower opening and maturation. Cytokinin
content in roses was variety dependent. The long-lived variety 'Lovita'
had higher endogenous cytokinin levels than the short-lived variety
'Golden Wave' (101).

Dipping the buds of 'Lovita' in N6-Benzyladenine (BA) produced
little response, while BA treatment of 'Golden Wave', delayed senescence
in both young and old flowers, especially at high temperatures and low
relative humidities (101). Cut roses exhibited extended longevity in

kinetin solutions even though stomatal opening increased, increasing

l6

transpiration rates. Fresh weight was initially higher and then declined
slower than controls. Water uptake exceeded water loss thus improving
water balance. Petal fresh weight of leafless cut flowers declined upon
harvest, but at a lesser rate when treated with kinetin. When the rose
was stressed kinetin initially increased water absorption, petal growth,
fresh and dry weights, and delayed petal fading. During the latter days
of vase life, the process of senescence was retarded, RNase activity and
dry weight loss was reduced while petal turgidity was maintained (103).
These date support the theory that cytokinins are involved in endogenous
regulation of senescense and improving water balance in cut roses (61).
Gilbart and Dedolph (55) reported BA treatment of cut roses pro-
duced no visual differences in vase life quality or longevity.
Blueing and abscission of petals were not influenced. Respiration
rates of petal tissue increased with BA treatments but decreased in
leaf tissue. Both were accentuated over time. Leaf tissue exhibited
a transitory decrease in photosynthetic rates with BA treatment;
however, with a continuing decrease in respiration net photosynthesis
occurred in BA treated roses. With intact plants, net carbohydrate
accumulation was higher in BA treated plants but many flowers abscissed.
The remaining flowers had greater longevity.

Abscisic Acid

 

When flowers developed normally on the plant ABA concentrations
increased with aging. ABA levels were higher in the short-lived
cultivar 'Golden Wave' than the long-lived Cultival 'Lovita' (104).

Livine and Vaadia (88) reported that abscisic acid (ABA) closed
stomates thus reducing transpiration and increasing cellular tugor.

Increased water stress increased ABA activity and stomatal closure

17

occurred. This could likely occur in cut roses moving through the
marketing channels. Concentrations of ABA as low as 1 ppm reduced water
loss in cut roses by closing stomates and reducing wilt, thereby
extending cut flower longevity (62, 63, 78).

Opposite effects of ABA have been demonstrated on roses with leaves
removed (19, 20, 62, 63). Removal of the leaves does not compound the
effect ABA has on water balance through stomatal closure (19, 88). The
ABA treated leafless system had increased petal fading, protein decline
and RNase activity (63). Leafless roses placed in a 1% sucrose solu-
tion had higher ABA levels and greater water deficits in the petals
compared to controls until late senescence when the reverse occurred
(20).

Opposing effects of sucrose and ABA were shown to include several
processes and phenomena related to senescence (19). ABA applied to the
bud of cut flowers promoted petal growth, respiration and sugar conver-
sion, from sucrose to reducing sugars. Brochov ££_§l, (19) concluded
that ABA triggers the metabolic processes leading to aging.

Ethylene

Ethylene, a gas present in the atmosphere as a contaminant and
also produced by plants as a growth regulator, accelerated senescence
in plants, particularly in detached organs (4, 29, 30, 122). Ethylene
activity was involved in the aging of intact (104) and cut roses (36,
62). Roses produced low levels of ethylene for several days and then
rates increased sharply in the flower petals until loss of tugor
occurred (36, 62, 102). Intact roses reacted similarly (104). However,
leaves produced higher levels of ethylene when young with declining

levels during maturity and senescence (102). The onset of increased

18

ethylene activity was variety dependent (62, 104) as it occurred earlier
in the short-lived variety 'Golden Wave' as compared to 'Lovita' a long-
lived variety. This early rise in ethylene production was postulated

to be the stimulus activating the ABA-synthesizing process which

hastens rose petal senescence. As ABA-treated flowers exhibited
decreased rates of ethylene production, ABA may control ethylene
production, via a feed-back mechanism (62, 102, 104).

Exogenous applications of ethylene increased endogenous ethylene
production thus reducing longevity (36, 62, 102). Zimmerman g£;al.
(150) found that ethylene caused rapid bud Opening and petal abscission
in cut rose flowers of several varieties. Development of petal color
was also inhibited upon opening.

Ethylene oxide inhibited the production of ethylene and delayed
senescence in 'Better Times' roses (97). Ethylene oxide delayed
opening of some varieties and in all cases longevity and flower size
were reduced. However, two yellow varieties opened more rapidly in
the presences of ethylene oxide (15). Sodium phytate and p-chloro-
phenoxyisobutyric acid (ethylene inhibitors) were marginally effective
in extending rose vase life, particularly in combination with
8-hydroxyquinoline sulfate (36).

Parups and Peterson (112) found that 8-hydroxyquinoline compounds
(8-HQ) suppressed ethylene production in apple slices and rose stamens
in both sterile and non-sterile systems. The effect was derived from
an independent action of 8-HQ ethylene production, and may explain
its beneficial senescence-reducing effect on cut flowers. Also 8-HQ

would affect any ethylene production by microorganism in non-sterile

19

holding solutions thus influencing cut flower longevity indirectly.
Low temperature and controlled atmosphere (CA) holding reduces
ethylene production in plants (36, 150). Techniques of maintaining
high CO2 concentrations, low 02 levels or increasing ventilation
around cut flowers are only partially effective in controlling endoge-
nous ethylene levels. Therefore, it was proposed that CA storage at
reduced atmospheric (hypobaric) pressure, would be more effective in
controlling ethylene damage. Many flowers were effectively stored in
hypobaric conditions, but roses were not successfully stored as they
turned blue or became diseased after a short time (36). Elimination of
these problems may make hypobaric storage useful to the rose industry.

Water Balance and Weight Changes in Roses

 

Mayak and Halevy (103) found that petals of intact roses increased
with time in size and fresh and dry weight. No weight reduction was
found in old petals with fading. Protein content declined and RNase
activity increased slightly with aging of intact roses.

Changes in cut roses have been associated with water status,
respiratory substrates, flower longevity (45, 53, 61, 90, 91, 92, 111)
and the hormonal status of the flower (103). Roses with the greatest
increase in fresh weight exhibited the best keeping quality and
longevity (46, 91). Brantly (21) found blossom fresh weight and
aesthetic beauty correlated for at least 5 days during rose vase life.
The best rose quality occurred 2 days prior to the beginning of weight
loss. weinstein (142) showed that fresh weight of 'Better Times'
petals increased until the bloom was fully open and then gradually
decreased through senescence.

Coorts, et al. (46) reported that the fresh weight of cut ’Velvet

20

Times' roses increased to a maximum three days after harvest, when
placed in water or a preservative solution, and then steadily declined.
The end of vase life coincided with a 10% reduction from the original
fresh weight of the flowers. Water uptake began to decline the second
or third day after harvest. Likewise Carpenter and Rasmussen (37, 38)
indicated that l to 3 days after harvest, water uptake in roses held
continuously in light exceeded loss and cut flower weight increased
after which water uptake gradually declined.

In 'Forever Yours' roses, the stem accounted for 20.4% of the total
water uptake, while leaves were responsible for 78.5%. When both
flowers and leaves were removed from the stem water uptake was reduced
95.2%. Stomate action of the leaves contributed to both water uptake
and loss, thus helping to regulate cut rose fresh weight and water
status (38).

Mayak gt_gl, (105) reported cut flower transpiration rate declined
the first 3 days then became steady. Water uptake declined and the
water potential was steady for 6 days then declined rapidly to wilting.
They concluded that this drop in water potential was not associated
with senescence because intact flowers exhibited a steady water poten-
tial during their opening and senescence.

Rate of transpiration, as measured by the difference between water
uptake and the daily weight increment of the flower, was nearly steady
for the long-lived cultivar, 'Super-Star' over nine days. Transpira-
tion gradually declined in the short-lived cultivar 'Golden Wave'.
Water uptake followed a similar pattern except that in the long-lived
cultivar rates fell sharply after seven days while in 'Golden Wave' it

declined rapidly after 5 days (105).

21

Under severe environmental conditions, 30°C and 40% relative
humidity, transpiration increased 2-fold resulting in wilted flowers
and reduced vase life. The differences in longevity between short and
long-lived cultivars were evident in that the short-lived 'Golden Wave'
transpired more, developed lower tissue water potentials and thus
wilted earlier (105).

Cut flowers deteriorate rapidly under water stress and as few as
4 hours of water stress will enhance senescence (3, 20, 51, 57, 62, 92,
113, 122). An improved water balance decreased senescence in cut
flowers. Ion exchange columns attached to the end of cut rose stems
enhanced water uptake, fresh weight gain, cut flower longevity and
eliminated bent neck roses (124) It was postulated the ion exchange
column may remove charged particles, act as a simple filter or modulate
water flow into the cut rose. Commercial preservatives increased
fresh and dry weights, reduced declines in fresh weight and prolonged
vase life of cut roses when compared to tap, distilled and deionized
water alone (21, 45, 46, 53, 77, 90, 91, 92, 111, 122). Holding solu-
tions may contain bactericides, sugar and growth regulators which affect
cut rose water status and fresh and dry weights. Marousky (90, 91)
indicated bactericides lower the holding solution's pH reducing micro-
bial growth and thus stem blocking which interferes with water
absorption. Stomatal closure was confirmed and correlated with changes
in fresh weight (38); sucrose closes stomates, improves water retention
(90) and flower opening and extended longevity of cut roses with
foliage (62, 63, 78). Dry weight rapidly declined when flowers were
held in distilled water (142), but kinetin greatly reduced the decline

over three’days (101). Correlating physiological responses with

22

components of preservatives contributes to a better understanding of
water relations and senescence phenomena in the cut rose and allows
engineering of solutions to control causal factors (91), particularly
for transport and conditioning of cut flowers (61).

Nature of Vascular Blocking

Increases in flower water deficit due to restricted water flow
through the stem results in the loss of turgor, which contributes to
”bent neck” (28) and the rapid senescence of cut flowers (2, 3, 28, 75,
78, 91). Both physical blocking substances and physiological phenomena
contribute to the reduction of water movement through rose stems (l, 3,
28. 37. 53. 56, 85, 90, 101, 122).

The main prerequisite for a long life of cut flowers is unimpeded
water uptake (3). The plugging of xylem tissue of cut rose stems has
been attributed to microbial activity, stem produced blocking substances,
and physiological changes with senescence (2, 3, 35, 53, 85, 89, 90,
108, 109). Aarts (3) and others (28) have demonstrated that in addition
to the physical presence of microorganisms, exudates from bacteria are
toxic and reduce water conductivity through cut stems. The toxic
constituents of the exudates have not been isolated to date. Under
sterile conditions Durkin and Kuc (53) and Marousky (89) found that
vascular blockage continued. Kuc, however, indicated that tissue
breakdown occurs before microorganisms can affect longevity thus
supporting the hypothesis that a physiological mechanism is responsible
for vascular occlusion.

Investigators localized sites of stem blocking substances at the

cut end of the rose stem, bacterial occlusions, and above the level of

23

the holding solution (3, 86). Scanning electron microscopy studies
indicated little difference in concentration of blocking materials
throughout the stem's length and it was suggested that breakdown
products of secondary cell walls were responsible for occluding vascu-
lar tissue (117).

Plugging of vascular bundles has been shown to increase with time
and the number of occluded vessels has ranged from less than 2% to
approximately 22% (28, 86, 117, 124). Appendix 0 summarizes the
histological and histochemical nature of rose stems and their blocking
substances. Tyloses were not present in occluded tissues and plugs
were not composed of callose, tannins, lignins, nor microorganisms,
except at the base of the stem. Physiological blocking substances are
best characterized as plant gums containing pectin, lipid, and protein-
like compounds, carbohydrates, secondary wall constituents and possible
enzymes which precipitate vascular blockage. Such occlusions occur
above holding solution levels (2, 3, 28, 86, 110), are present under
sterile conditions (53, 91), and may be influenced in their formation
by toxins or enzymes from microorganisms (3). The occurance of stem
occlusion by microorganisms has been shown to increase in the presence
of sucrose, and was localized at the cut end of the rose stem (2, 28,
86, 90). However, some investigators have concluded that physical
plugging by microorganisms is secondary to physiological blocking (10,
53. in).

Water Quality and Floral Preservatives

Cut flowers are adversely affected when placed in water of poor

quality (61, 84, 141). High levels of salts and minute levels of

flourides reduce flower vase life (84, 141). The effectiveness of

24

floral preservatives may decrease when added to poor quality water
(61, all).

Coorts and Gartner (45) demonstrated that hooks on the stem had no
significant effect on keeping quality, stem weight or water absorption
with either tap or deionized water. Without hooks all three parameters
were significantly improved by tap water as compared to deionized water.
Commercial floral preservatives were superior to either tap or deionized
water and resulted in continued growth until flower maturity with the
inner petals expanded and vase life extended for several days (45). On
the other hand, Halevy and Mayak (61) reported that tap water plus the
commercial floral preservative 'Floran' was less effective than
deionized water or deionized water plus 'Floran'.

Effective floral preservatives reduce the rate of normal flower
opening and petal expansion, supply substrates for respiration, avert
the deveIOpment of undesirable color shifts in the petals and maintain
or restore high levels of flower turgidity after harvest. Preservative
components are sugar, usually sucrose, a bactericide, a heavy metal,
and an acidifying agent (21, 95, 109, 111, 121). I

Sucrose or glucose should not act as a growth medium for micro-
organisms, but should be absorbed, translocated, and metabolized in
sufficient quantities to provide energy for respiration and to.
regulate the plant water balance by closing stomates (2, 44, 46, 90,
91, 92, 95, 121, 122). Sucrose used alone was ineffective or detri-
mental to flower longevity (l9).

Mastalerz (95) reported that Aarts (2), Weinstein and Laurencot
(143) and Scholes (126) screened 50, 120 and 112 chemicals respectively

for their effect upon extending cut flower longevity. Most were

25

ineffective or phytotoxic (95); however, from these reports and
other investigations several chemicals have been found to be effective
in floral preservatives.

Silver acetate and silver nitrate, two bactericides extend vase
life of cut flowers (95). Mayak §£_§l, (100) found that carnation stems
pretreated in 1000 ppm silver nitrate had increased longevity and
reduced microbial populations in the holding solution. Microorganisms
in the stem were reduced only slightly. Filtrates from microbial
suspensions of untreated holding solution reduced flower life and
increased petal water deficit; whereas silver nitrate in solution
reduced the damaging effects.

Treatment of roses with maleic hydrazide compounds, followed by
aluminum sulfate, citric acid, glucose and hydrazine sulfate was an
effective preservative (143). Maleic hydrazide alone reduced rapid bud
opening, but increased discoloration of red roses unless metal salts
were added. Citric acid was added as a chelate to protect the maleic
hydrazide from precipitation. Mayak g£_gl. (103) found that hydrated
aluminum sulfate restricts growth of microorganisms. However effective,
the Weinstein formulation has not found wide use in the floriculture
industry.

The quinoline compounds, 8-hydroxyquinoline sulfate and citrate,
have been effective in extending vase life, Increasing fresh weight and
maintaining the quality of cut flowers (46, 52, 56, 81, 90, 91. 92, 95,
111, 112). The quinoline compounds increased cut flower fresh weight
by increasing water absorption and conductivity through the stem and
closing stomates (46, 80, 9D, 91, 133, 148). Larson and Cromarty (81)

found a reduction in microbial activity with 8-HQC which decreased stem

26

blockage and increased cut flower longevity. The growth of bacteria,
yeasts and fungi was inhibited at 10 ppm 8-HQC and completely suppressed
at 300 ppm. Odom (108) described 8-HQC as a fungicide and metal-
chelating compound which reduced flower wilting. After experiments
involving aseptic techniques, Marousky (90, 91, 92) concluded 8-HQC

does not act primarily as a bactericide or by lowering the pH of the
solution. Alternatively he proposed the quinoline esters chelate metal
ions which inactivate enzymes thus enhancing senescence. In support of
such a hypothesis Parups and Peterson (112)reported 8-HQC suppressed
ethylene synthesis and secondarily functioned as an antimicrobial agent.

Brantley (21) found that ammonium ethyl carbamoylphosphate (AECP),
alone or in conjection with commercial floral preservatives, used in
l'hardening", storage and consumer solutions, improved cut rose longevity,
quality and size in several cultivars. Incidence of "bent neck",
”frozen buds“ and ”flat face" were reduced, but not eliminated and there
were no detrimental effects demonstrated with its use.

Sodium dichloro-S-triazinetrione (SDT) (74, 75) extended cut flower
longevity in carnations by 8-12 days. 'Forever Yours' and 'Golden Wave'
rose cultivars in SDT lasted four days longer than those held in
deionized water, but SDT was less effective than silver nitrate.

In 1973 Parups and Chan (Ill) developed the 'Ottawa' preservative
solution. The new preservative contained 100 ppm Na-isoascorbate, 4%
sucrose and 50 ppm 8-HQC. Results indicated the 'Ottawa' solution
increased vase life, maintained respiration and amino acid incorpora-
tion, and 02 uptake while reducing blueing of petals.

Cut Flower Handling_

 

Market shrinkage of cut flowers has been estimated to be 20% (129).

27

Recommendations to reduce product 1055 from harvest to consumption and
to improve cut flower quality and longevity have been made by several
investigators (58, 59, 61, 129).

Rapidly cooling cut roses is critical (18). Mastalerz (94)
recommended low temperature, dry storage. He suggested low temperature
(31°F) reduces metabolic activity, particularly respiration and
proteolysis. Dark refrigeration (0-1°C) with flowers dry or in
deionized or distilled water containing a floral preservative was
recommended in handling roses throughout the marketing chain (116).

Refrigerated transport is not always available and container pre-
cooling may be ineffective. After removal from a cold room, flower
temperature within cardboard shipping containers rose 10°C in 30
minutes and within 3-9°C of ambient temperatures in 4-8 hours. The
cardboard containers were unsatisfactory for air transport (61).

Parups (109) reported that Flower Care (trade name of the 'Ottawa'
preservative) was most effective when used by the consumer. In this
analysis flowers were carried throughout the marketing chain in solu-
tion. Concerned with dry transport by air, Halevy and Mayak (60, 61)
recommended pre-shipment treatments of 3-6 hours in solutions containing
high concentrations of sucrose and a bactericide, 8-HQC or AgN03, with
a 15 minute dip in BA. They pointed out that many cut flowers are
harvested before their complete development and during postharvest
handling they require moisture, a proper balance of hormones, and
energy to complete their development and open properly. After harvest
rates of photosynthesis and water uptake drop markedly and an imbalance
in hormones may occur; therefore, pre-treatments prior to shipment

”load” the cut flower with respiratory substrate, reduce vascular

28

blockage, control Stomate Opening and regulate metabolic activity.
Pre-shipment treatments decreased senescence and enhanced bud opening
thus improving longevity and quality even when flowers were exposed to
water stress developed by high temperatures and low pH during transport.
Burg (30) reported that roses in the bud stage can be held for
very long periods in low pressure storage (40 mm Hg) without affecting
flower opening or shelf life. However, 'Forever Yours' roses were
susceptable to decay and blueing when stored in low pressure storage
and pre-treatment with a preservative solution did not eliminate the

blueing of the petals (36).

MATERIALS AND METHODS

Greenhouse lighting. 'Forever Yours' roses were grown according to

 

standard greenhouse culture (96). Sodium Lucalox and mercury Multivapor
400-W, high intensity discharge lamps were used for supplemental
lighting. From September 1 to October 31 and March 16 to April 30 lights
were on from 6 P.M. to 6 A.M. Roses were lighted continuously from
November 1 to March 15. Controls were subject to natural light inten-
sity and daylengths (9 hours to 12.5 hours).

Leaf area and stomatal densi_y, Leaf area was determined by the

 

photocopy method. Photocopies of the leaves were cut out, dried (22°C
for 12 hours), weighed and the total area calculated. A sample from
each lot of paper was weighed as the standard for calculating the area
per gram of paper.

To determine stomatal density, leaves were washed in chloroform to
remove the epicuticular waxes, stained with crystal violet, rinsed with
water and viewed through a light microscope. Ten areas, 0.2 mmz, were
randomly selected for counting stomata. The counting areas were
centrally located on the lower surface of the leaf and excluded veins.

The terminal leaflet from the first five-leaflet leaf was used to
determine the effect of the light treatments on leaf area and stomatal
density. Ten stems per treatment were analyzed.

Roses from each light treatment were harvested at commercial

maturity (firm bud, calyx reflexed and outer whorl of petals opening),

29

30

placed immediately in water and transported to the laboratory within
1/2 hour. Flowers were 40-45 cm long and had one three-leaflet leaf
and two or three five-leaflet leaves. In the laboratory, stems were
recut under distilled water to avoid air blockage of the vascular
system.

In'a second experiment, differences in individual leaflet area and
diffusive resistance were determined for the first five-leaflet leaf on
five stems from each lighting regime. Leaflets were numbered right to
left beginning with the right proximal leaflet in adexial view.

Diffusive resistance. A portable Lambda Diffusive Resistance

 

meter was used to measure stomatal resistance in the greenhouse and
laboratory. During vase life, roses were held at 25: 1.5°C, 17,000 lux
under 40-W cool white fluorescent lamps, and 40 to 70 percent relative
humidity, unless specified differently. Three leaves were left on each
flower during vase life. Diffusive resistance was measured at the
terminal leaflet of each leaf.

An experiment was conducted to determine the effect of supplemental
light on stomatal activity prior to harvest. Leaf position down the
stem was used to evaluate the effect of shading on diffusive resistance
within each treatment. Three uniform roses mature enough for harvest
within 24 hours were selected per treatment. Leaves were numbered 1
through 6 beginning with the first three-leaflet leaf nearest the flower.
Diffusive resistance of the terminal leaflet of each leaf was measured.
Supplemental lights were turned on at 6 A.M. and off at 12 A.M. Control
plots were separated from HID lighted plots with black plastic after
sunset and prior to sunrise. This eliminated stray light in the control

plots. Diffusive resistance and light intensity readings were taken

31

at 11 A.M. - 1 P.M., 3 - 5 P.M., 9 - 12 P.M., 7 - 9 A.M. and 11 A.M. -

12 P.M. Cut roses were held in the laboratory at 21 :-1°C and 930 lux

(cool white fluorescent lamps) for the postharvest diffusive resistance
measurements.

Storage. Thirty flowers per greenhouse treatment (control and two
separate Na(HID) lighted plots) were divided into 6 sets of 5 flowers
and stored dry for 12 hours in black or clear plastic bags at 0, 9 or
22 i-2°C. During storage roses were lighted at 7,000 - 9,000 lux
(cool white fluorescent lamps). Diffusive resistance was recorded
prior to harvest, 1 - 2 hours after beginning and before ending storage,
and during vase life. This experiment was repeated twice.

An experiment was conducted to determine the interaction effect of
supplemental light during production and short term storage on diffusive
resistance, water uptake, and cut flower longevity. Ten roses were
selected from the control and Na(HID) lighted plots. Five were put in
potometers immediately and five were stored in distilled water in the
dark at 0 i-2°C for twelve hours. After storage the roses were put in
potometers and treated the same as the roses without storage. The
relative humidity during vase life ranged between 27 and 49 percent.
The number of bent neck roses per treatment was analyzed.

Water gptake and transpiration by cut flowers. Potometers were
used to measure the water uptake of single flowers (38). Transpiration
was determined by measuring the change in relative humidity over time
within a closed assimilation chamber. The water lost per dm2 of leaf
area was calculated (Appendix C). Potometers within the assimilation
chamber held 1 to 3 flowers and were used to measure water uptake and

loss at the same time. Septum stoppers, punched to accomodate varying

32

sized stems in the potometers, were sealed water tight with nonphyto-
toxic RTV 11 Liquid Silicone Rubber (General Electric Co.).
Net_photo§ynthesis and respiration by cut flowers. Net photo-
synthesis and respiration were measured under controlled conditions in
an assimilation chamber (33, 119, 123). Temperature and relative
lumfidity were controlled at 24.5 i-2°C and 30-i-lO% respectively.
Adjustable, overhead, Hg(HID) or Na(HID) lamps (400-W) illuminated the
flowers from O to 53,000 lux. A water jacket absorbed the heat of the
lamps. Respiration measurements were made by covering the chamber with
black cloth. A Beckman infrared gas analyzer was incorporated into the

system to measure CO exchange. See Appendix B. Plants outside the

2
assimilation chamber were maintained under the experimental environment
in growth chambers.

Experiments were designed to evaluate the effect of alternating

dark-light periods on C0 exchange and water activity in cut roses.

2
Control grown roses produced in the fall (natural daylength ranged
from 10.5 to 12 hours) were put 3 to a potometer and given 12 hours
alternating dark-light periods during vase life. Two potometers were
alternated in and out of the assimilation chamber during the experiment.
One potometer was begun in the dark and the other in the light. A
Hg(HID) lamp illuminated the roses at 40,000 lux. Data were recorded
at the end of each light or dark period, except during the first light
period in which data were also recorded 1 hour after the roses were
placed in the chamber. Supplemental light grown roses were treated
similarly. Whereas these were fall grown roses and daylength were

becoming shorter, they were continuously lighted only 25 days prior to

harvest. They received 12 hours of supplemental light per day prior

33

to the continuous lighting. After harvest, the roses were illuminated
during the light periods with a Na(HID) lamp at 13,500 lux. These
experiments were run twice.

Leaf shading of cut flowers. Experiments were carried out to

 

test the effect of varying postharvest light intensity on supplemental
and natural light grown roses. Water uptake and loss and net photo-
synthesis were measured. Winter grown roses were held in a dark
assimilation chamber for 6 to 8 hours prior to illumination at 5,400,
13,000 and 53,000 lux with a Na(HID) lamp. Data were collected at
the same light intensities a second day after 12 - 16 hours of dark.
Data collection was begun at each light intensity after a fifteen
minute conditioning period. In similar experiments, leaves were
removed from the three roses in the potometers to eliminate leaf
shading. Each set of experiments was run three times. A comparison of
shaded and non-shaded treatments was made.

Experimental design, data analysis and mean separation were
according to established procedures (6, 87, 131). The Michigan State
University State System 3 for the CDC 6500 computer was used to process

raw data.

RESULTS

Stomatal opening of fall grown roses was affected by light (Table
l). Roses grown under Na(HID) lamps exhibited significantly lower
diffusive resistance than roses grown under natural light. Sodium and
Hg(HID) lighted roses did not differ significantly in stomatal resis-

tance. Neither did Hg(HID) lighted and control grown roses. Diffusive

Table l. Diffusive resistance (sec/cm) of greenhouse rose leaves under
natural and supplemental lighting regimes.

 

 

 

Lightx Leaf's Posi ion Treatmenty
Treatment Distal on Stem Proximal Mean
1 2 3 4 5
Natural 9.8a 8.6ab 8.6ab 8.0b 8.5ab 8.69a
Hg(HID) 6.8a 5.7a 5.9a 5.7a 5.6a 5.9ab
Na(HID) 3.7a 3.23 2.8a 3.6a ZLBa 3.22b
Mean 6.763 5.85ab 5.73b 5.75b 5.66b

 

zMean separation in rows by Tukey's multiple comparison test, 5% level.

yMean separation in this column by Tukey's multiple comparison test,
5% level.

xNatural daylength, 10.5 - 12.0 hr/day; supplemental lighting 18 hr/day.

resistance was not affected by leaf position on the stem. However, the
most distal leaf tended to exhibit the greatest diffusive resistance in
each light regime.

Diffusive resistance was proportional to the radiation striking

34

35

the leaf up to 28,700 lux when diffusive resistance was similar for the
two supplemental light treatments (Figure I). At high light intensities
and optimum growing conditions stomata were wide open as demonstrated by
low diffusive resistance, but roses held at the same light intensity
exhibited equal diffusive resistance. Hg(HID) grown roses had the
highest diffusive resistance after harvest.

Plants grown continuously under HID lamps during the winter had
larger terminal leaflets than roses grown under natural light (Table 2).
There was no difference in leaflet area between Hg and Na(HID) grown
roses. Stomatal density between leaflets grown in the three light

regimes was not different even though leaf primordia and buds had

Table 2. Leaflet area and stomatal density of 'Forever Yours' roses as
. . z
lnfluenced by supplemental llght.

 

 

 

Lighting Terminal Le flet Stomatal Degsity Stomate/Leaflet
Area (cm ) (no./mm ) (X 1000)
l 2 3
Na(HID) 37.2a 94.1a 350.1a
Hg(HID) 38.0a 101.2a 384.6a
Natural 31.3b 94.3a 295.2b

 

zMean separation in columns by Tukey's multiple comparison test, 1%
level.

developed under the light conditions. Thus stomatal density was not
influenced by differences in light source, intensity nor duration.
Roses grown under HID lighting had the greatest total number of stomata
per leaflet (Table 2). Therefore, they had a greater potential for gas

and water vapor exchange per stem.

36

 

 

 

LSD(0.05)
25" L14
r—l 20-
'a
3’: [NATURAL LIGHT
L” 15-1
E H L
2 G IGHT
u; / /
a / \
E 5 / \ /
Q ..
/ ........ \ /
)7 ooooo r °....\ ...... N0°
NA LIGHT
10AM 4PM 101m 41m 102m
TIME I
CUT
NAT. 58.0 83.3 0.04 0.12 0.93
HG 48.5 59.7 3.7 28.7 0.93
NA 48.7 48.0 10.1 34 0 0.93
Lux X 1000

Figure l. Diffusive resistance of greenhouse roses grown under natural
and supplemental, 18 hour, HID lighting; light levels per data
collection period included.

37

Table 3. Leaf area (dmz) of the first five leaflet leaf of roses

grown under three lighting regimes.

 

 

 

Lighting Leaflet Positionx Treatmenty
(% of total leaf area) mean
1 2 3 4 5
Na(HID) .098 .210 .342 .210 .100 .I92a
(10.2) (21.9) (35.6) (21.9) (10.4)
Hg(HID) .085 .193 .303 .186 .076 .169a
(10.1) (22.9) (35.9) (22.1) (9.0)
Natural .109 .196 .312 .213 .108 .188a
(11.6) (20.9) (33.3) (22.7) (11.5)
Leaflet .O97c .200b .319a .203b .095:
Mean2 (10.6) (21.9) (34.9) (22.2) (10.4)

 

zMean separation in row by Tukey's multiple comparison test, 1% level.

yMean separation in this column by Tukey's multiple comparison test,

5% level.

xLeaflets were numbered from right to left in adaxial view beginning
with the right proximal leaflet.

38

Total leaf area of the first five-leaflet leaf was not significantly

different among light treatments (Table 3). The Na(HID) leaf had the
largest terminal leaflet, leaflet 3, and the Hg(HID) grown leaf the
smallest first and fifth leaflets. Rose leaves characteristically have
2 or 3 leaflet pairs and a terminal leaflet. Area differences within
the first leaf's five leaflets were different between pairs of leaflets
and between the terminal and either leaflet pair. The distal leaflet
accounted for thirty-five percent of the total leaf area while the
middle pair and the proximal pair of leaflets contributed forty-four
and twenty-one percent respectively. Seventy-nine percent of the total
leaf area was accounted for by the three distal leaflets.

Diffusive resistance of cut roses was greatest in leaves grown
under natural light (Table 4). The HID lighted roses exhibited reduced
resistance. The distal leaflet and the middle pair of leaflets had the

lowest diffusive resistance in all three treatments.

Table 4. Diffusive resistance (sec/cm) of the five-leaflets of the
first five-leaflet leaf of cut roses grown under three lighting

 

 

 

regimes.
Lighting Leaflet Positionx TreatmentY
Mean
1 2 3 4 5
Na(HID) 6.2 5.2 4.8 5.5 8.3 6.00ab
Hg(HID) 6.8 5.6 5.1 5.7 6.2 5.89b
Natural 8.4 6.6 5.5 6.4 8.2 7.04a
Leaflet 7.14b 5.83a 5.12a 5.88a 7.58b
Mean

 

yMean separation in this column by Tukey's multiple comparison test,5%
level.

xLeaflets were numbered from right to left in adaxial view beginning
with the right proximal leaflet.

39

The pattern of stomatal activity per leaflet within the leaf was similar
in all three light regimes i.e., the proximal pair of leaflets had the
highest diffusive resistance, the middle leaflets intermediate and the
distal leaflet the lowest.

The stomatal activity of cut roses during and after storage was
significantly affected by supplemental, Na(HID) lighting of winter grown
roses (Figure 2). Naturally lighted roses had higher diffusive resis-
tance during dark storage than roses grown under Na(HID) light. Three
hours after dark storage natural light grown roses had a minor increase
in diffusive resistance for 4-5 hours. Afterward diffusive resistance
was the same for both treatments.

Diffusive resistance of natural and Na(HID) lighted roses was the
same during lighted storage (Figure 3). However, stomata of Na(HID)
lighted roses were more open after lighted storage than were those of
the naturally lighted roses.

Light stored roses exhibited the highest diffusive resistance after
storage (Figure 4). Little or no differences in diffusive resistance
existed during storage. The differences in stomatal activity between
light and dark stored roses were greatest immediately following the
twelve hours of storage. Dark stored roses exhibited the largest
change in diffusive resistance after storage with little fluctuation in
stomatal activity during the remainder of vase life.

During storage, diffusive resistance of roses grown under Na(HID)
light was greatest at 22°C, least at 9°C and intermediate at 0°C
(Figure 5). Roses from the natural light treatment had higher diffusive
resistance than Na(HID) grown roses when stored in the dark at 9°C and

0°C. After storage in the dark, diffusive resistance decreased

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Figure 5. Diffusive resistance of cut roses grown under natural ( )
and supplemental Na(HID) (- - -) lighting and stored at three
temperatures with and without light. LSD(0.05); dark trts. . 1.96
and light trts. = 5.7.

44

DARK STORED LIGHT STORED

22°
zol

 

 

 

 

DIFFUSIVE RESISTANCE sec oCM—l

00

N
E ‘?

 

   

 

 

 

c F
6AM 6AM 6AM 6AM 6AM 6AM
I-—-——I . I-——-—I
TIME TIME

Figure 5.

45

immediately to near or below preharvest levels for all treatments. Only
the natural light grown roses stored at 0°C exhibited a short-term
increase in diffusive resistance after dark storage.

Diffusive resistance during lighted storage at 22°C was the same
for both greenhouse light treatments (Figure 5d). Roses grown under
natural light had the greatest diffusive resistance during lighted
storage at 9°C and 0°C (Figures 5e and 5f). Natural light grown roses
had the greatest diffusive resistance after lighted storage at the three
temperature treatments. Roses stored in the light at 9°C and 22°C
returned gradually to a low diffusive resistance, while dark stored
roses had lower rates immediately after removal from storage and place-
ment in water. At 0°C, the pattern of stomatal opening and closing
(Figure 5c and 5f) was affected very little by light during storage.

The keeping quality of roses from each treatment was analyzed

post priori. General appearance, color, and flaccidness of the petals

 

and leaves was poorer in roses stored in light, especially at high
temperatures. Light stored roses had the highest percentage of bent
neck roses (Table 5). Likewise, the most bent neck roses were grown
under Na(HID) light. The higher the temperature during lighted storage,
the greater the number of bent neck roses. The reverse occurred in
dark storage. The interactions between greenhouse lighting, storage
lighting and storage temperature were not significantly different.
However, roses grown under naturallight tended to have fewer bent neck
flowers under both light and dark storage and at all three temperatures.
Diffusive resistance was lower in winter grown roses given supple-
mental light compared to those grown under naturallight from 12 through

36 hours of vase life (Table 6). A trend toward low diffusive

46

resistance continued until the last 12 to 18 hours of vase life when
diffusive resistance increased and exceeded that of the natural light
grown roses. Na(HID) grown roses had significantly higher water uptake
at 12 hours than the natural light grown roses. The trend continued

through vase life.

Table 5. The effect of supplemental fighting during production and light
and dark, dry storage at three temperatures on the keeping quality
(% bent neck) of roses.

 

 

 

 

Storage Storage Temperaturesz
Lighting

0°C 9°C 22°C Mean
Dark 503A lObA OcA 20A
Lighted (ch) 573A 73bB 77bB 693
Mean 533 423 383
Greenhouse Plot 1 Plot 2
Lighting Natural Na(HID) Na(HID)

233 57b 53b

 

zMean separation in rows (lower case letters) and columns (upper case
letters) by Tukey's multiple comparison test, 5% level.

As diffusive resistance decreased, water uptake increased for each
treatment (Table 6). During the first 24 to 36 hours, fluctuations in
the rate of water uptake and diffusive resistance were greatest; but
during the last two-thirds of vase life extreme fluctuations did not
occur. Gradually water uptake decreased and diffusive resistance in-
creased, particularly in the Na(HID) lighted roses.

Diffusive resistance was greater and water uptake was lower in the

control compared to Na(HID) grown roses stored in the dark at 0°C

47

Table 6. Diffusive resistance (rs) and water uptake (WU) rates of
natural and supplemental Na(HID) light grown cut roses.

 

 

Greenhouse Lighting

 

Na(HID) Naturalz
Hours after
harvest rs wu rs wu
(sec/cm) (ml/dmZ/hr) (sec/cm) (ml/dmZ/hr)

1 5.13 1.013 4.73 1.083
6 6.23 1.223 5.03 .973
12 6.53 .973 8.58 .62b
18 5.83 .893 8.6b .583
24 4.23 1.133 5.7b 1.023
36 4.83 1.063 6.7b .943
48 4.7a ° 1.123 5.23 .933
’ 60 5.3a 1.053 5.8a .69b
72 5.23 1.063 6.43 .67b
84 6.03 .843 6.53 .553
96 6.53 .753 6.03 .613
108 8.23 .533 6.5b .523

 

zMean separation for diffusive resistance or water uptake between
greenhouse lighting conditions per time period by Duncan's multiple
tange test, 5% level.

48

Table 7. Diffusive resistance (rs) and water uptake (WU) rates of
natural and supplemental ;[N3(HID)] light grown cut roses after
dark storage for 12 hours at 0°C.

 

 

Greenhouse Lighting

 

Na(HID) Naturalz
Hours after
harvest rS WU rS WU
(sec/cm) (ml/dmZ/hr) (sec/cm) (ml/dmzlhr)

1 4.53 1.553 4.33 .81b
6 4.93 1.173 5.03 .68b
12 6.63 .873 7.5b .35b
18 4.73 .943 8.9b .573
24 5.13 1.293 6.13 .69b
36 5.53 .963 5.83 .873
48 4.93 1.113 6.23 .953
60 5.13 .923 6.03 .673
72 4.83 .883 5.63 .543
84 6.23 .713 6.53 .553
96 8.33 .623 6.53 .523
108 9.93 .483 7.3b .423

 

zMean separation for diffusive resistance or water uptake between
greenhouse lighting conditions per time period by Duncan's multiple
range test, 5% level.

49

(Table 7). Water uptake and stomatal opening demonstrated corresponding
but opposite high and low activity similar to those treatments without
cold storage.

Stored roses tended to exhibit lower water uptake rates than those
not stored (Tables 8 and 5!). This was particularly true for roses from
the naturally lighted treatments (Tables 8 and El). Stored and unstored
Na(HID) roses had 3 lower diffusive resistance than the natural light
grown roses. Water uptake declined in stored and unstored roses after
50 hours and diffusive resistance gradually increased, especially in
roses from the Na(HID) treatments.

There was no difference in respiration for naturally grown roses
harvested and given either 12 hours of dark or light followed by 12
hour periods of alternating light-dark through vase life (Figure 61).
Net photosynthesis was similar for roses subjected to both treatments.

Water uptake and loss was initially higher for natural light grown
cut roses first lighted for 12 hours compared to those placed first in
the dark for twelve hours (Figure 17). Water 1055 was not different
between treatments during the lighted periods throughout vase life;
however, water uptake by roses given light first tended to be greater.
Water uptake and loss during the dark periods of vase life were low,
0.13 i 0.05 ml HZO/dmzlhr, except during the initial dark period for
roses held first in the light. In that case, uptake and loss were 0.73
and 0.33 ml H20/dm2/hr, respectively.

Natural light grown roses held first in the dark and then given
alternating light-dark periods in the dark exhibited poorer quality
vase life after 48 hours compared to those begun in the light. After

72 hours they exhibited bent neck, whereas roses placed first in the

50

Table 8. Effects of storage (12 hours, 0°C) on the diffusive
resistance (rs) and water uptake (WU) of cut roses grown under
natural light conditions.

 

 

Hours after Unstored Storedz
harvest rs WU rS WU
(sec/cm) (ml/dmZ/hr) (sec/cm) (ml/dmzlhr)

l 4.73 1.083 4.33 .81b
6 5.03 .973 5.03 .68b
12 8.53 .623 9.33 .35b
18 8.63 .583 8.93 .573
24 5.73 1.023 6.13 .69b
36 6.73 .943 5.83 .873
48 5.23 .933 6.23 .953
60 5.83 .693 6.23 .953
72 6.43 .673 5.63 .54b
84 6.53 .553 6.53 .553
96 6.03 .613 6.53 .523
108 6.53 .523 7.33 .423

 

zMean separation for diffusive resistance or water uptake between
storage treatment and control per time period by Duncan's multiple
range test, 5% level.

51

Table 9. Effects of storage (12 hours, 0°C) on diffusive resistance
and water uptake (WU) of cut roses grown under supplemental

r
NaIHlD) light.

 

 

 

Unstored Storedz
Hours after
harvest rS WU rS WU
(sec/cm) (ml/dmz/hr) (sec/cm) (ml/dmzhr)

1 5.13 1.013 4.53 1.55b
6 6.23 1.223 4.93 1.173
12 6.53 .973 6.63 .873
18 5.83 .893 4.73 .943
24 4.13 1.133 5.13 1.293
36 4.83 1.063 5.53 .963
48 4.73 1.123 ' 4.93 1.113
60 5.33 1.053 5.13 .923
72 5.23 1.063 4.83 .883
84 6.03 .843 6.23 .713
96 6.53 .753 8.33 .623
108 8.23 .533 9.93 .483

 

zMean separation for diffusive resistance or water uptake between
storage treatment and control per time period by Duncan's multiple
range test, 5% level.

52

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54

light had no bent neck and displayed adequate turgor color and quality
through four and one-half days.

Net photosynthesis was the same through 84 hours for Na(HID) light
grown roses held first in the light compared to those held first in the
dark (Figure 8). After 96 hours net photosynthesis nearly ceased in
roses given dark immediately following harvest. Net photosynthesis
continued at approximately 1.0 mg C02/dm2/hr in the roses held first in
the light. Respiration was highest for 72 hours in roses first held in
the dark compared to those held first in the light (Figure 8). Roses
first given 12 hours of light respired at 1.5 mg COZ/dmzlhr for 72 hours
after which the rate declined to 1.0 mg C02/dm2/hr. Respiration of dark
held rose also declined after 72 hours. Respiration rates approximately
doubled for roses held first in the dark when compared to those held
first in the light until the last two days of the experiment when they
were similar.

Water uptake and loss during the light periods of Na(HID) light
grown roses was significant during the first two days of vase life
(Figure 9). Water activity during the dark treatment is not represented
but was 0.1 :_.06 m1 HZO/dmZ/hr except for an initial rate of 1.40 ml
HZO/dmZ/hr for water uptake and 0.93 ml HZO/dmzlhr for water loss.

Na(HID) light grown roses exposed to 12 hours of light first during
vase life exhibited the best keeping quality with 3 gradual decline with
time. Roses begun in the dark exhibited bent neck conditions 48 hours
after harvest.

Respiration and net photosynthesis of cut roses grown in natural

or under supplemental Na(HID) light were light dependent (Table 10).

55

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57

Table 10. The influence of shading on C0 exchange in cut roses grown
under natural or supplemental Na(HID) Iight.

 

 

C02 Exchangez

 

 

 

(mg/dmzlhr)
Lighting Supplemental Natural
Assimilation chamber (lux) Shaded Leaves
Day 1 Dark 2.13 2.21
5400 0.39 0.19 Pn
13000 0.69 Pn 0.15 Pn
53000 4.67 Pn 5.37 Pn
Day 2 Dark 1.97 0.95
5400 0.68 0.31
13000 0.68 Pn 1.10 Pn
53000 4.82 Pn 3.85 Pn
Unshaded Leaves
Day 1 Dark 4.55 4.92
5400 2.54 1.03
13000 0.55 Pn 0.70 Pn
53000 9.17 Pn 8.18 Pn
Day 2 Dark 4.16 4.43
5400 0.95 1.60
13000 0.55 Pn 0.80 Pn
53000 7.60 Pn 8.82 Pn

 

zTreatment means for respiration and net photosynthesis (Pn).

58

Photosynthesis increased with increasing illumination. Respiration was
highest in plants without leaf shading. Respiration decreased in both
treatments on the second day. Likewise, net photosynthesis was higher
in roses with no leaf shading. Differences in C02 exchange between
supplemental and natural light grown roses at the various light inten-
sities were inconsistent.

Water uptake and loss increased with increasing light intensities
and were influenced by leaf shading (Table 11). Leaf shading signifi-
cantly reduced water uptake, with only minor differences in water loss.

Naturally grown roses with leaf shading had more water uptake and loss

the second day of treatment than roses without shading.

Table 11.

59

The effect of shading on water uptake and loss in cut roses
grown under supplemental Na(HID) light.

 

 

Water Uptake

Water Loss

 

 

 

(ml/dmZ/hr) (ml/dmZ/hr)
Lighting Supplemental Natural Supplemental Natural
Assimilation Chamber
Treatments (Lux) Shaded Leaves
Day 1 Dark .25 .17 .16 .07
5400 .44 .31 .23 .13
13000 .65 .43 .30 .16
53000 1.08 .57 .58 .45
Day 2 Dark .24 .42 .12 .23
5400 .31 .45 .18 .25
13000 .57 .91 .28 .46
53000 .83 1.01 .47 .52
Unshaded Leaves
Day 1 Dark .45 .31 .12 .12
5400 .73 .60 .26 .29
13000 .93 .73 .32 .34
53000 1.39 1.33 .56 .57
Day 2 Dark .50 .35 .21 .18
5400 .72 .70 .41 .41
13000 1.03 .83 .66 .35
53000 1.47 1.30 .74 .65

 

DISCUSSION

 

Stomatal conductance in roses in the greenhouse increased with
supplemental light. The leaf nearest the flower had higher diffusive
resistance than leaves throughout the canopy which had equal diffusive
resistance. Continuous supplemental lighting had no effect on stomatal
density. Since leaf primordia, buds, shoots and leaves developed
entirely either under supplemental or natural light conditions stomate
density was not under photoperiodic control. However, terminal leaf—
lets grown under supplemental light had the most stomata per leaflet.
This was due to the fact that larger terminal leaflets developed
under supplemental light, although total leaf area was independant of
greenhouse light regimes. These morphological and physiological dif-
ferences between leaves grown with and without supplemental light con-
tributed to the differences in water uptake found between treatments.
Leaf area was the morphological character of cut roses most closely
associated with water uptake in both light and dark (37). Leaves of
roses grown under supplemental light had larger terminal leaflets and
greater stomatal conductance which contributed to the physiological
differences between roses grown with and without supplemental light.

Studies of stomatal opening and closing typically include stomatal
response to temperature, plant hormones, relative humidity, wind
speed, illuminance and water status. The effect of supplemental

lighting on stomatal activity of cut roses has not been reported.

60

61
Stomatal opening prior to and after harvest was affected by supple-
mental lighting during production. Diffusive resistance was higher
after harvest in natural light grown roses throughout vase life.
After dry, lighted storage, supplemental light grown roses exhibited
lower diffusive resistance than natural light grown roses. These
results imply that the preharvest lighting conditions affected the
opening and closing of rose stomates after harvest. Rose stomates
on leaves grown under continuous HID supplemental lighting opened the
widest due to high light intensities and may have never closed during
growth in the greenhouse without diurnal light and dark periods during
production. The rates and degree of opening and closing under environ-
mental conditions conducive to closing may have been altered in stomates
developed under continuous supplemental light.

Transpiration and water uptake in cut roses increased with increased
stomatal conductance. Diffusive resistance decreased and water uptake
increased in cut roses grown under supplemental light. This suggests
that the pattern of diffusive resistance and water uptake in cut roses
was dependent upon pre- as well as postharvest environments. Discre-
pancies among investigators exist in the pattern of transpiration and
water uptake in cut flowers through vase life.

Mayak g£_§l, (103) studied roses from a commercial greenhouse
grown under normal daylengths and operating conditions. He found that
water absorption and loss in cut roses under constant conditions fol-
lowed distinct patterns. The rate of water uptake declined steadily
after harvest in a rhythmic pattern of daily high and low rates. Trans-
piration declined rapidly the first three days and then at 3 slower,
steady rate throughout vase life. Carpenter and Rasmussen (37) found

a different water uptake pattern in cut roses held at constant conditions.

62

Roses in their experiments were grown under continuous supplemental
lighting to improve quality and production. Water uptake did not
decline initially but increased to a maximum between 24 and 48 hours
after which uptake declined gradually. A fluctuating or rhythmic
pattern in water uptake was evident only when the roses were given a
12 hour light-dark treatment immediately upon harvest. The con-
trasting water uptake patterns may be attributed to the different
greenhouse growing conditions prior to their experiments. Cut roses
used by Mayak §£_§l, may have been predisposed by diurnal patterns in
natural light during production to continue diurnal patterns of sto-
matal opening and water uptake after harvest. Roses used by Carpenter
and Rasmussen were grown under continuous light and no diurnal patterns
in water uptake were observed after harvest.

Supplemental lighting of roses and lighting during dry storage
significantly increased the number of bent neck roses (Table 5). How-
ever, Mastalerz (92) in 1953 recommended that greenhouse light intensi-
ties be as high as possible consistent with optimum temperature control
for improved dry storage of roses and that reduced light intensities
during production shortened storage time and vase life. He concluded
that optimum growing conditions at the highest light intensity would
produce a high quality rose with increased carbohydrate reserve for
longer storage capacity and improved vase life. The effect of continuous
supplemental lighting on the dry storage of roses was not discussed by
Mastalerz. The opposite results of these experiments (Table 5) may have
been due to excessive water loss and/or reduced water uptake rather than

the carbohydrates status of the roses.

63

The stomates of supplemental light grown roses consistently
opened as wide or wider, during and after storage, as stomates of
natural light grown roses (Figure 9). Open stomates during dry,
lighted storage tend to dehydrate the flower and increase the tendency
for bent neck. Excessive water loss during dry storage and an inability
to restore turgor after storage accounted for the high number of bent
neck roses following 0°C and 9°C storage in light.

During high temperature storage (22°C), the high vapor pressure
deficit between the leaf and the atmOSphere may have caused the stomates
to close (Figure 9) and the total water loss from the leaves during
storage was reduced. After storage at 22°C, the stomates of the roses
kept in the dark opened immediately and completely while the stomates
of the roses stored in the light opened slowly and only partially. An
optimum water balance is necessary for cut flower longevity and reduced
bent neck (1, 37). Rapid and complete opening of the stomates following
storage may have re-established the transpiration stream and quickly
resupplied the cells with water. Thus, the water balance of the rose
would be maintained or improved and bent neck reduced, provided water
loss did not exceed water uptake. Therefore, the rate and degree
of stomate opening during and after storage was a contributing factor
in the number of bent neck roses between light and dark storage treat-
ments.

Light and dark treatments of cut roses held in the assimilation
chamber affected the number of bent neck roses produced and gave con-
flicting results compared with the light-dark, dry storage treatments.
Supplemental and natural light grown roses produced numerous bent neck

flowers when the 12 hour, light-dark treatments were begun in the dark.

64

Bent neck occurred after 72 hours in supplemental light grown roses and
after 42 hours in the natural light grown roses. The bent neck con-
dition was not reversible under these environmental conditions. Roses
in the dry storage experiments were held in plastic bags and roses in
the assimilation chamber were not. High C02 concentrations within the
bags may have closed the stomates and influenced the final longevity
of the roses. Carpenter and Rasmussen (37) found that roses in the
light were flaccid and had bent necks, but when returned to the dark
they regained turgor and recovered from bent neck. They demonstrated
increased water uptake in the light with low rates in the dark and sug-
gested that light mediated stomate activity regulates the transpiration
rate which in turn is closely related to the rate of water uptake. When
water loss exceeds water uptake bent neck occurred.

Water uptake exceeded water loss in the Na(HID) and natural light
grown roses regardless of whether they were started in the light or
dark. This was true in the dark or at several light intensities during
the first two days of vase life (Table 11). Water uptake in roses held
continuously in light exceeded loss for 1 to 3 days after harvest during
which flower weight increased (37, 38). In the dark water uptake was
very low and there was little if any increase in fresh weight. Under an
alternating light-dark regime, water uptake during the first two days
of vase life equalled corresponding rates in continuous light or dark (37).
Increases in fresh weight would alternate accordingly. Therefore, roses
given 12 hours of light first may have had a sufficient increase in fresh
weight during the first two days of vase life to avoid bent neck. Roses
placed in the dark first may not have gained fresh weight and thus became

bent neck. Roses that exhibit the greatest increase in fresh weight have

65

the best keeping quality (46, 91).

Dark respiration in supplemental light grown roses was higher in
the roses first held in the dark. Respiration was also higher in roses
with leaves removed to prevent shading. High concentrations of CO2
within the microclimate of the roses may contribute to the regulation of
the stomates. Whereas in these experiments the roses were held in dis-
tilled water, no supplemental carbohydrate was available for respiration.
Thus vase life may also be reduced in one lighting treatment compared to
another due to carbohydrate depletion and subsequent proteolysis as
suggested by Weinstein (140).

Several authors have stated that cut flower longevity is directly
related to the maintenance of a proper water balance or fresh weight
(1, 4, 89, 119, 124). These studies demonstrate the control stomatal
opening and closing has on cut flower water balance and that lighting
during production and vase life may alter stomatal activity thus influ-
encing flower longevity. The water uptake of roses in these experiments
was greater than water loss and therefore other factors affected vase
life.

Mastalerz (94) has outlined the postharvest handling procedures
which maximizes vase life in roses given long-term dry storage. Recom-
mendations for the proper handling of cut roses by the grower, whole-
saler, retailer and consumer have been given by Rasmussen (116). These
recommendations are sound for both Na(HID) and natural light grown roses.
It should be emphasized that stomata of Na(HID) lighted roses tended
to be more open under similar conditions than those of natural grown
roses therefore care should be taken to eliminate environments that

would lead to water stress. Avoid light during dry storage and drafts

66

during vase life.

These studies were made in distilled water. Recommendation for
the use of floral preservatives are sound. Other factors undoubtedly
mediate deterioration of cut roses but have not been within the sc0pe
of this work. Floral preservatives affect respiration, microorganisms,
etc., and are known to increase longevity and therefore are highly

recommended.

APPENDICES

APPENDIX A

 

The transpiration rate E, in ug/cmz/sec, is expressed as the

3

difference in water vapor density dV in ug/cm , between the internal

leaf and the ambient air and the sum of the boundary layer diffusion
resistance Ra and the leaf diffusion resistance Rl’ both in sec/cm.

Therefore

AdV

R3R1

E3

and if cuticular water loss is minimal, RI is equivalent to the stomatal
diffusion resistance RS which may be measured directly with a stomatal
diffusion porometer (54, 72). Several investigators (67, 83 cited by
54) have determined that R5 is primarily due to the density of stomates
per leaf and width of stomatal opening. Stomatal length and depth are
lesser components determining Rs' Drake gt_§l, (50) determined boundary
layer resistance by exposing black, dry leaf models to known radiation
flux densitites and wind speeds, and recording the temperatures of the
models. Others (54, 139) determined the evaporation rate and tempera-
ture of wet blotter paper in a controlled environment to compute

boundary layer diffusion, where

gAdV
R a . E O

Kanemasu, et al. (72) have designed a diffusion porometer to measure
leaf resistance directly. Results indicate agreement with those

obtained by leaf energy balance determinations. Stomatal activity i.e.,

67

68

diurnal patterns of opeining and closing in response to water stress,
changing energy flux densities, varying C02 concentrations and changing
environment, may be measured reproducibly and accurately.

In this study a Lambda diffusive resistance meter (diffusion) was

used to measure stomatal activity of Rosa hybrida 'Forever Yours'

 

flowers subjected to various pre- and postharvest environments. This
instrument is portable and was used in the laboratory and the greenhouse
according to the manufacturer's instructions.

Raw data included sec/cm and leaf temperature in microamperes.
Microamperes were adjusted to compensate for temperature effect on the
diffusive resistance porometer. The manufacturer's conversion graph
gave the best fit conversion equation, Temperature Conversion Factor:

TCF = .00124471 (raw number)2 + .715907 (raw number) - 13.3804.
Valid comparisons between treatments at different temperatures were
made when all conversion factors were adjusted to 25°C by the following
ploynomial:

TCF c = (.00229604 (TCF)2 - .0478203 (TCF) + .742184.

25°
Therefore:

sec/cm 3t 25 C = (sec/cm) . TCF25°C

The Lambda diffusive resistance meter was calibrated by use of a
calibration plate, following manufacturer's instructions. A constant
temperature (27.3 137°C) and relative humidity (91%) was established
in a plastic chamber. Resistances were calculated according to the
following equation:

' Wd 2

R=L/a=4A (Lo+'8—) /0._r1’11d

where L is the effective diffusion path length, a is the diffusivity

of water vapor in air, L0 is the actual length of each hole in the

69

calibration plate, A is the insert aperture area, 2_is the number of
holes in the plate, and d is the diameter of each hole. ”End effects”
were corrected by adding gg-to the actual diffusion path of each tube.

A regression analysis and curve fitting program were used to
describe the relation between the time (At, seconds) required for
readings compared-to the sec/cm measured. The linear equation:

sec/cm adjusted = .7629989 + .15149274 (At)
was used to adjust the data for computer analysis. Early greenhouse
experiments required exceptionally long periods of time per data point
and were restricted to a 150 sec limit. Due to the nature of the
treatments, early mornings, late evenings or shaded conditions,
extended time periods were involved. In such treatments intermediate
measurements fell between 45 and 90 seconds and rapid periods of

measurements between 15 and 45 seconds.

APPENDIX B

 

Figure A1. illustrates the environmentally controlled measurement
system used to simultaneously measure C02 exchange, transpiration and
water uptake rates. The assimilation chamber accommodated both potted
plants and excised plant parts. Three walls and the ceiling were water
jacketed to maintain uniform internal temperatures while the fourth
wall contained a glove insert for mechanical manipulations within the
closed chamber and the parts through which the potometer was attached
to the plant materials. Air temperature was monitored by the relative
humidity-temperature sensor (RHTS) and adjustments made automatically
with the heating unit through the proportional electronic temperature
controller (PETC). Relative humidity was controlled by condensation
and evaporation onto or away from the cooling coils. Eight narrow
range relative humidity sensors (RTS) measured the relative humidity
within the system. They were electronically coupled to a relative
humidity controller (RHCI) which opened and closed a coolent control
valve to maintain the relative humidity within the chamber at the
selected relative humidity. The change in relative humidity within
the selected range was monitored by hygrometer and was reliably control-
led within :.5% of the desired relative humidity. A high volume gas
tight fan circulated the air. Wind speeds within the chamber were
measured with a thermo-anemometer and were 168 cm/sec at the walls and

25 cm/sec in the center of the chamber. Wind speeds of 25-100 cm/sec

7O

Figure Al. The environmentally controlled measurement system for
simultaneous measurement of plant CO exchange, transpiration and
water uptake. Relative humidity-temperature sensor(RHTS), Pro-
portional electronic temperature controller (PETC), Relative humidity
controller-indicator (RHCI), Infrared gas analyzer (IRGA), Potometer

(P), Water supply (W8), Potometer guage (PC), Input (I) and Exit
(E) ports, Valves (V) 1 to 4.

 

 

 

 

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73

were recorded through the plant material. Air circulation was regulated
with valves l through 4. A pressure relief port through vacuum oil
eliminated pressure instabilities and maintained the internal pressure
of the chamber equal to atmospheric pressure. A portion of the air was
drawn off by a Masterflex tubing pump at 900 ml/min, dried with CaSOh,
and the C02 concentration analyzed by a Beckman CO2 analyzer equipped
with a strip chart recorder and then returned to the main air stream.
An overhead hOO-watt high intensity discharge sodium vapor lamp
(Lucolux) suspended above the chamber was used to illuminate the plant
through 53,000 lux. For studies of dark respiration, black cloth
covered the assimilation chamber.

Most investigators now utilize infrared gas analyzers to measure
photosynthesis and respiration and for several reasons; they are
accurate, rapid, may be portable and are nondestructive to plant tissue
(l6, l27). The assimilation chamber and associated CO2 analysis
apparatus was after Carpenter (33), Reicosky (ll9) and Rottink (123).
Measurements of C02 exchange were made within the closed system after
plant materials were allowed to acclimate for a minimum of 20 minutes.
The rate of C02 depletion or increase in the system between 200 and
450 ppm was used to measure net photosynthesis and dark respiration
respectively. The CO concentration was increased within the chamber

2
by opening it to the laboratory air. To reduce the CO2 concentration
within the system, laboratory air was bubbled through a potassium
hydroxide scrubber attached to the input port.
Transpiration rates may be determined by infrared gas analysis,

but generally are not, due to the cost of duplicating expensive equip-

ment and the ease and low cost of other techniques, i.e., weighting

74

whole plants or excised plant parts and psychrometric methods using
hygrometers (l6). Rates of water loss were determined in these studies
by calculating the grams of water lost into the internal atmosphere from
changes over time in the relative humidity within the system. Measure-
ment periods were short, less than l0 minutes and usually I to 5 minutes,
and initial and ending temperatures in the chamber were recorded for the
calculations. Experiments determining rates of transpiration were
conducted at low relative humidities, 30 to ho percent, and room
temperatures, 2% :_2°C. Simultaneous water uptake rates were recorded
with the use of a potometer as described by Carpenter and Rasmussen
(37). Rates of transpiration and water absorption were expressed as

mg H20/dm2/hr.

Simultaneous measurements were conducted after the desired
environmental conditions were established and flowers acclimated.

Valves l and h were closed and 2 and 3 were opened during data collec-
tion. Lighted plants transpired rapidly and after a 5 minute sampling
it was necessary to reopen valves 1 and h to lower the internal relative
humidity for replicate samplings. This altered the CO2 exchange rate
slightly and therefore such rates were determined immediately before
determinations for water loss and uptake.

The system was calibrated for both CD2 exchange and water loss by
adding measured amounts of carbon dioxide and water to the atmosphere
within the system and recording the measured response. The measurement
of the carbon dioxide concentration was 7h.09 percent efficient, s =
.78], while that for water loss was 76.9 percent, 5 - .055. Raw C02

exchange and water loss data were corrected accordingly.

APPENDIX C

 

The rate of transpiration was computed from the change in relative
humidity with time. The initial and ending relative humidities at
their respective temperatures were determined from the accompanying
manufactueres calibration charts for each narrow range sensor.

By Dalton's law the total number of moles of gas in a mixture is
equal to the sum of the number of moles of the individual gasses and
therefore with all else held constant a change in the partial pressure
of one gas may be evaluated independently. In order to find the partial
pressure of water at a given temperature, relative humidity and atmos-

pheric pressure, one may utilize a definition for relative humidity.

= xoc

R. H. V0

X lOO

 

C

where X is the partial pressure of water at the given temperature and
atmospheric pressure and V is the saturated vapor pressure for the same.
Thus,

x0 = R. Ho X VOC X 0.0]

C

and by the gas law one may determine the moles of water per liter,
n/V = P/RT
The moles of water per liter may then be converted to grams of water

per liter;

X l89/nH 0

g/l = n
H20/l 2

75

76

The rate of water loss from the plant was computed by subtracting the
initial from the final grams of water in the total volume of the system

and dividing by the part of the hour required for the measurement.

77

 

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APPENDIX E

The following ancillary experiments were not included in the body
of the thesis. They are placed in this appendix for reference and
general information.

Experiment Al. The objective of this experiment was to determine

 

the effect relative humidity has on the rate of photosynthesis,
respiration and transpiration in 'Forever Yours' roses prior to harvest.

Terminal cuttings from 'Forever Yours' roses were propagated and
grown during the winter and early spring in 6 inch clay pots according
to standard greenhouse culture without supplemental lighting. Potted
roses were selected at a uniform stage of flower development, watered
and their pots enclosed in two polyethylene bags. The bags were tied
at the base of the stem to prevent evaporation and respiration from the
soil. Plants were placed in the assimilation chamber and carbon
dioxide exchange and water loss were recorded in the light (13000 lux)
and dark. The relative humidity was regulated at three treatment levels
during the light and dark periods i.e., 35, 50, and 75 :_52. The plant
was allowed to acclimate for 2 hours prior to recording data. The dark
period was l2 hours long. This experiment was repeated twice.

Lighted roses exhibited higher photosynthesis at 75 1.5% relative
humidity than at 35 or 50 :_5% (Table A2). There was no difference in
dark respiration at the three relative humidities. The mean CO2

exchange was greater in the light than in the dark, 8.l2 and h.l2 mg

79

80

C02/dm2/hr, respectively. Water loss was negligible in the dark and in
the light when the relative humidity was 75 :_5%. Water loss from roses
in the light was greater with decreasing relative humidity and although
dark held roses followed a similar pattern, differences were not sig-

nificant.

Table A2. The rate of CO exchange and water loss from potted roses at
three relative humidities in light, i3000 lux, Na(HID), and dark.

 

 

 

602 Exchange Water Loss

Treatment (mg/dmzlhr) (ml/dmzlhr)
Light net photosynthesis

752 R. H. 13.25aY .ozocZ

502 " ” 5.85b .409b

35% " ” 5-25b .5798
Dark dark respiration

752 ” " 4.0b .00lc

50% " ” h.6b .066c

35% ” ” 3-75b -07SC

 

yTreatment means for net photosynthesis and dark respiration.

zMean separation, within columns, by Tukey's multiple comparison test,
5% level.

Experiment A2. This experiment was conducted to determine the rate

 

of photosynthesis, respiration, water uptake, and transpiration in roses
held continuously in the light or dark.

Roses grown under natural light conditions were placed three to a
potometer and held continuously in the light at h0,000 lux (Hg(HID)) or
in the dark. When not in the assimilation chamber, the roses were
held in growth chambers at the prescribed conditions.

Under continuous light, water uptake and loss declined after an

8]

initial 12 hour surge (Figure A2). In continuous dark water uptake and
loss were significantly reduced and except for the two initial water
uptake readings of .3] and .25 ml HZOIdmzlhr, both rates were
.l(:_.l)mi H20/dm2/hr. No diurnal patterns were observed after one day
of vase life.

CO exchange in the light and dark declined rapidly during the

2
first two days of the experiment and then gradually thereafter with
minor fluctuations (Figure A3). Roses in the light exhibited zero net
C02 exchange after four days, i.e., photosynthesis equalled respiration
or neither were active. Diurnal patterns of C02 exchange were not

evident.

Experiment A3. The purpose of this experiment was to determine if

 

the number of cut roses per potometer affected the rate of net photo-
synthesis, respiration, water uptake and transpiration and if supple-
mental lighting contributed to the results.

Roses were removed one at a time from a potometer containing three.
Rates of net photosynthesis, respiration, water uptake and transpiration
were recorded before removing each flower. Roses from the sodium
lighted and control plots were evaluated. in the assimilation chamber
roses were illuminated with a Na(HID) lamp at l3,000 lux. This experi-
ment was repeated three times.

Due to the small sample size and a large variation between data,
plant density was not shown to significantly affect water uptake, water
loss or C02 exchange. Light and dark treatments were significantly
different, but the interaction between light or dark and plant density
was not statistically significant (Tables A3 and Ah). However, several

trends were evident. Na(HID) grown roses exhibited lower rates of

82

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83

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84

water and £02 movement compared to natural light grown roses. They
had higher respiration with one or two roses in the potometer and were
less active photosynthetically at l3,000 lux than roses grown under

natural light conditions.

Table A3. The effect of plant density per potometer on water loss,
water uptake and C02 exchange by natural light grown roses.

 

 

 

Light Number Water ptake Water 055 C02 Exghangez
(Lux) of stems (ml/dm /hr) (ml/dm /hr) (mg/dm /hr)
l .267 .lhl l.23
0 2 .l85 .lOl l.63
3 .l73 .ll7 l.79
l l.867 .997 3.l0
13000 2 1.530 .979 l.lS
3 l.lh5 .696 0.98

 

zTreatment means for respiration and net photOSYnthBSls'

Table Ah. The effect of plant density per potometer on water loss,
water uptake and 002 exchange by supplemental light grown roses.

 

 

Light Number Water Bptake Water 055 £02 Exfihangez
(Lux) of stems (ml/dm /hr) (ml/dm /hr) (mg/dm /hr)
l .l76 .07] 2.35
0 2 .l70 .085 2.61
3 .l63 .089 l.86
l .938 .561 2.l0
13000 2 .654 .h37 1.02
3 2.2l3 l.l08 0.02

 

zTreatment means for respiration and net photosynthesis.

85

Experiment Ah. The purpose of this experiment was to test the

 

effect one dark period prior to harvest would have on diffusive resis-
tance in cut flowers.

Five roses from each of two, continuously, Na(HID) lighted plots
and one naturally lighted plot were selected. Opaque plastic bags were
place over the roses in one Na(HID) lighted plot and the naturally
lighted plot. To avoid overheating and allow for gas exchange, the
bags were left open at the base. Stray light under each bag was less
than 30 lux. Uncovered roses in the Na(HID) plot received approximately
l0,000 lux. In the greenhouse, diffusive resistance measurements were
made prior to covering the roses at 8 P.M. and before uncovering them
at 8 A.M. In the laboratory, determinations were made periodically
over the next four days. The experiment was repeated twice.

Twelve hours of dark prior to harvest did not significantly change
the postharvest diffusive resistance of roses grown continuously under
Na(HID) lighting (Figure Ah). Significant differences only occurred
prior to harvest between leaf positions (Table A5). The third leaf had
greater resistance than either the first or second leaf which exhibited
equal stomatal activity. Roses under natural light exhibited higher
diffusive resistance prior to harvest than Na(HID) grown roses. After
harvest (h8 - 72 hours), stomatal resistance of Na(HID) grown roses
exceed preharvest levels. Diffusive resistance of natural light grown
roses responded similarly, (Figure Ah). Bent neck, when present,

occurred about 72 hours after harvest in all treatments.

86

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Table A5. Diffusive resistance (sec/cm) of cut roses grown under
natural daylight or continuous Na(HID) light with and without l2
hours of dark prior to harvest.

 

 

 

Lightingy Leaf Position Treatmentz

Distal Proximal Mean

l 2 3

Na(HID) 6.0 6.8 7.7 6.8a
Continuous
Na(HID) 6.7 6.7 8.] 7.2a
Dark l2 hours
Natural 8.h 8.] 9.3 8.6a
Dark l2 hours
Leaf Mean 7.0a 7.2a 8.ha

 

zMean separation by Tukey's multiple comparison test, 5% level.
YNatural daylength 9.5 - 10.5 hr/day.

Experiment A5. The objective of this experiment was to determine

 

the effect of the length of the dark period prior to harvest on cut
rose water uptake and diffusive resistance.

Twelve 'Forever Yours' rose plants with buds near harvest stage
were selected from among many which had been grown as recommended (96)
without supplementary lighting. The plants were placed in a growth
room under Na(HID) lamp. Buds were illuminated at 9,000 to l8,000 lux,
dependent upon their position under the lamps. Four night-lighting
regimes with three plants per treatment were initiated four nights
befour harvest. Treatments included: I) continuous lighting, 2) 3
hours, 3) 6 hours and h) 9 hours of dark per 2h hours. Three roses
were cut per treatment for diffusive resistance and water uptake meas-

urements. Data were analyzed and comparisons made as the sequence of

88

processing occurred i.e., after 3, 6, and 9 hours of dark when plants
were harvested.

Overall water movement into the flower increased, with fluctuations,
through 36 to h8 hours and then declined in a decreasing harmonic
pattern until the fourth or fifth day when water uptake became negli-
gible (Figure A5). Diffusive resistance decreased sharply after harvest.
After 3 to h days, diffusive resistance began to increase. Diurnal
fluctuations in diffusive resistance were reflected in fluctuations in
water uptake. Fluctuation occurred with roses held under continuous
light and in a uniform environment. Fluctuations in water uptake and
diffusive resistance were minimal during the last days of vase life.

The effect of differing lengths of dark period prior to harvest on
stomatal activity was not significant and there was no significant
difference in diffusive resistance attributable to time of harvest.
However, roses from all treatments except the continuously lighted
treatment tended to exhibit diurnal fluctuations in diffusive resis-
tance, particularly after the first day of vase life. Diffusive
resistance was greatest during the pre-harvest dark treatment.

Water uptake in cut roses was significantly affected by dark
length treatments four consecutive nights prior to harvest (Figures
A6 and A7). Roses that received 9 hours of dark had identical post-
harvest water uptake compared to the continuously lighted control to
the end of vase life. Roses from the 6 hour dark treatment had reduced
water uptake after the second day of vase life while those of the 3
hour dark treatment exhibited intermediate water uptake after 3 days
compared to the 6 hour treatment and the control. Maximum water uptake

occurred 25 to ho hours after harvest in dark treated roses compared

89

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92

with peak rates 5 to ID hours after harvest in continuously lighted
roses. Maximum water uptake for the 3, 6, and 9 hour dark treatments
occurred hO, 35, and 27 hours after harvest respectively.

Each treatment exhibited a decreasing, cyclic pattern of water uptake
after the period of maximum uptake.

With zero as the time of the start of the dark treatments, the
fluctuating patterns of water uptake for the four treatments coincide
over time but not in magnitude. The highest rates occurred 37 hours
after the start of the dark period except for the control which had the
greatest water absorption rate l6 hours postharvest and then a second
but lower peak rate at 37 hours. The diurnal patterns of water uptake
continued until the end of vase life regardless of the length of the
night period or the time of harvest. Night length did influence the
rate of water uptake. For example, the 6 hour dark treatment had
lower water absorption than the continuous treatment, although cyclic

highs and lows were similar.

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IO.

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