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This is to certify that the
thesis entitled
A STUDY OF SIMULATED ENVIRONMENTAL SHIPPING CONDITIONS
ON SENESCENCE AND TRANSPLANT RECOVERY OF SEEDLING GERANIUM
(PELARGONIUM X HORTORUM BAILEY)

 

presented by

Marjorie Susan Dean

has been accepted towards fulfillment
of the requirements for

MASTER OF SCIENCE degreein HORTICULTURE

 

 

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Major professor

Date 5713/ 73

0-7639

 

 

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PER ITEM

Return to book drop to remove
this checkout from your record.

 

 

 

 

A STUDY OF SIMULATED ENVIRONMENTAL
SHIPPING CONDITIONS ON SENESCENCE
AND TRANSPLANT RECOVERY OF
SEEDLING GERANIUM

(PELARGONIUM X

 

HORTORUM

BAILEY)

BY

Marjorie Susan Dean

A THESIS

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

MASTER OF SCIENCE

Department of Horticulture

1979

ABSTRACT

A STUDY OF SIMULATED ENVIRONMENTAL
SHIPPING CONDITIONS OF SENESCENCE
AND TRANSPLANT RECOVERY OF
SEEDLING GERANIUM
(PELARGONIUM x
HORTORUM
BAILEY)

 

BY

Marjorie Susan Dean

The effect of ethylene, benzyladenine, and
environmental factors were investigated in simulated
shipping conditions for up to 96 hours for seedlings of

Pelargonium x hortorum Bailey (cv. Sprinter Scarlet).

 

Leaf yellowing decreased when plants wereshipped at
cool temperatures (e.g. 2 to 10°C) except for plants at
10°C in waxed cardboard boxes. Increase in duration of
darkness caused an increase in leaf mortality and the
number of days to flower after potting, while decreasing
the ability of plants to recover after planting. A dose
of ethylene 0.1 ul/liter for 48 hours increased leaf
yellowing, while higher concentrations (1-10 ul/liter)
caused leaf yellowing when applied for 12 to 48 hours.
Delay in flowering was caused by as little as 0.1 ul/

liter of ethylene and 1 and 10 ul/liter produced the

Marjorie Susan Dean

same results. Leaf abscission increased after 96 hours
of treatment with l or 10 ul/liter. CO2 at 5 percent v/v
in air did not inhibit the ethylene effects noted.
Ethylene synthesis decreased after 24 hours of darkness
to a steady state in drought stressed plants, while
normally watered or heavily watered plants decreased to
a low steady state of ethylene production at 24 hours.
Leaf yellowing was not affected by watering regimes.
Drought stressed plants showed greater leaf mortality and
resulted in shorter plants.

BA (10 -4M) applied as a foliar spray when
applied to geraniums decreased yellowing of plants held
in the dark and reduced plant height, but 48 percent of

the leaves on these plants were damaged by BA.

DEDICATION

To my parents and grandparents

who gave me my agricultural heritage and appreciation.

ii

ACKNOWLEDGMENTS

Appreciation is expressed to Dr. W. H. Carlson
and Dr. Hans Kende for guidance and laboratory facilities.
Sincere gratitude and appreciation are offered to
Dr. D. R. Dilley for guidance, assistance, and laboratory
facilities throughout the preparation of this thesis.
Appreciation is expressed to Dr. E. C. Cress and
Mr. M. Leon for their guidance in statistical analysis,
and to A. Armitage for assistance in preparation of the
manuscript. Also, thanks are directed to C. Turner,
A. Eurich, C. Tegler, and N. Hildebrandt for technical
assistance.
Special thanks are extended to Speedling Inc.
of Sun City, Florida, for their financial and material

support.

iii

TABLE OF CONTENTS

Page
LIST OF TABLES O I O O 0 O O O O O O 0 Vi

LIST OF FIGURES O O O O C O C O O O O O Viii

INTRODUCTION . . . . . . . . . . . . . 1
LITERATURE REVIEW . . . . . . . . . . . 3
Physiology of Senescence . . . . . . . 3
Classification . . . . . . . . . 3
Physiological Changes . . . . . . . . 3
Metabolic Changes . . . . . . . . . 4
Environmental Regulation . . . . . . . 7
Temperature . . . . . . . . . . . 7
Nutrients . . . . . . . . . . . . 7
Darkness . . . . . . . . . . . . 8
Water Stress . . . . . . . . . . . 10
Hormonal Regulation . . . . . . . . . ll
Cytokinins . . . . . . . . . . ll
Gibberellic Acid, Auxin and Abscisic Acid . 18
Ethylene . . . . . . . . . . . . 19
Literature Cited . . . . . . . . . . 27

SECTION ONE: THE EFFECT OF ETHYLENE AND ENVIRON-

 

MENTAL FACTORS ON PELARGONIUM X HORTORUM BAILEY . 36
Abstract . . . . . . . . . . . . . 37
Introduction . . . . . . . . . . 38
Materials and Methods . . . . . . . . 40

Experiment 1 . . . . . . . . . . . 4O
Experiment 2 . . . . . . . . . . . 4l
Experiment 3 . . . . . . . . . . . 43
Experiment 4 . . . . . . . . . . . 43
Experiment 5 . . . . . . . . . . . 44
Results . . . . . . . . . . . . . 45
Experiment 1 . . . . . . . . . . . 45
Experiment 2 . . . . . . . . . . . 50
Experiment 3 . . . . . . . . . . . 52
Experiment 4 . . . . . . . . . . . 59
Experiment 5 . . . . . . . . . . . 59

iv

Page

Discussion . . . . . . . . . . . . 66
Literature Cited . . . . . . . . . . 72

SECTION TWO: THE EFFECT OF BENZYLADENINE ON

 

SEEDLINGS OF PELARGONIUM X HORTORUM BAILEY . . . 75
Abstract I O O O O O 0 O O O O O O 76
Introduction . . . .- . . . . . . . 76
Materials and Methods . . . . . . . . 77
Experiment 1 . . . . . . . . . . . 77
Experiment 2 . . . . . . . . . . . 78
Results and Discussion . . . . . . . . 79
Literature Cited . . . . . . . . . . 82

SUMMARY AND CONCLUSIONS . . . . . . . . . 83

LIST OF TABLES

Section One
Table Page

1. Effect of temperature and container type
on ethylene concentrations in shipping
containers upon arrival . . . . . . . 51

2. Effect of ethylene concentration, duration
of treatment, and handling of plants on the
percent of dead or abscised leaves . . . 52

3. The effect of duration of treatment on
recovery of seedling geraniums . . . . 53

4. The effect of duration of ethylene
treatment in the dark on yellowing of
leaves . . . . . . . . . . . . 54

5. The effect of ethylene concentration and
duration of exposure while in the dark on
the percent of leaves which turn yellow . 55

6. The effect of duration of treatment on the
percent of dead leaves and days to flower . 56

7. The effect of ethylene concentration on
the number of days to flower a seedling
geranium . . . . . . . . . . . . 57

8. The effect of duration of treatment on the
recovery rating of seedling geraniums . . 58

9. The effect of ethylene concentration on
percent leaf yellowing during darkness,
of seedling geraniums . . . . . . . 60

10. The effect of duration of dark on the
percent Of yellow leaves on seedling
geraniums . . . . . . . . . . . 61

11. The effect of ethylene concentrations and
duration of treatments on percent of leaf
abscission . . . . . . . . . . . 62

vi

Table

12.

13.

14.

Effect of air and C02, ethylene concen-
trations and duration of treatment on
percent yellow and abscised leaves . .

Effect of various water regimes and
duration of ethylene production . . .

Effect of various water regimes on leaf
yellowing, mortality, and plant height

Section Two

 

Effect of BA on chlorophyll degradation
of geranium leaf discs exposed to 6
days of dark . . . . . . . . .

Effect of BA on leaf yellowing, death
and damage, and plant height . . .

vii

Page

63

64

65

79

81

LIST OF FIGURES

Figure Page

1. Effect of temperature and duration of
treatment, in regular containers on
leaf yellowing of seedling geraniums
two weeks after transplanting . . . . . 46

2. Effect of temperature and duration of
treatment, in EPS containers on leaf
yellowing of seedling geraniums two
weeks after transplanting . . . . . . 47

3. Effect of temperature and duration of
treatment, in regular containers on
leaf death of seedling geraniums two
weeks after transplanting . . . . . . 48

4. Effect of temperature and duration of
treatment, in EPS containers on leaf
death of seedling geraniums two weeks
after transplanting . . . . . . . . 49

viii

INTRODUCTION

Pelargonium x hortorum Bailey, Geranium, is one

 

of the largest growing floricultural crops in the 0.8.
(Voigt, 1971). The introduction of cv. Nittany Lion Red
(a seedling geranium) started a breeding selection pro-
gram for earliness of flowering and reduced plant height.
This improved the cultural practices and production
efficiency for this crOp which was traditionally
propagated by cuttings (Craig, 1971).

As seed lines were introduced and seed production
increased, a market developed for seedlings to be
"finished off" by growers as a potted crOp. Along with
this came problems in shipping the seedlings to the
growers. Plants (80 days old) shipped to producers have
shown severe leaf yellowing and stunting (Carlson, 1977).
The present study investigates the effects of environ-
mental factors such as duration of darkness, temperature
as a pretreatment and in simulated transit, and handling
of plants on leaf yellowing, leaf death, replant sur-
vival, and days to flower. Ethylene was studied as a
deteriorative factor in the environment during shipping

contributing to problems after potting. Benzladenine (BA)

was investigated as a supplement to endogenous cytokinins

to attenuate development of senescence.

LI TE RATURE REVI EW

Physiology of Senescence

 

Classification

 

Senescence is the natural deterioration of a
partial or whole unit of life which leads to death
(Leopold, 1975). The external expressions of physio-
logical signals of senescence can be classified into
four basic categories. First is the "overall" death of
annual plants, bienneal and other monocarpic. Second,
"top senescence" is the death of the above ground parts
of biennial plant. Third, is "deciduous senescence" in
which leaves of trees and shrubs abscise annually but the
main stems and roots remain viable. Finally, there is
"progressive senescence" which is the gradual progres-
sion of leaf death from the base to the top of the plant

and is the topic of main consideration in this thesis.

Physiological Changes

 

The process of leaf senescence appears to be the
initiation of the collapse of individual cells which
develop into a large regionmofleaf yellowing. Examina-
tion of the ultrastructure reveals that various organ-
elles break down at different rates (Woolhouse, 1967).
Membrane degradation, causing an increase in cell

3

permeability has been shown in senescing tissue (Sacher,
1957; Eilam, 1965). Shaw and Manocha (1965) examined
senescing wheat leaves by electron microscopy and
observed that after two days of detachment from the
plant, the endOplasmic reticulum of the mesophyll cell
began to change and disappeared after four to five days
along with the cytOplasmic ribosomes. Chloroplast grana
disappeared, mitochondria became swollen with loss of
fine structure and nuclear damage was evident after
three days. By the eighth day the plasma membrane
showed damage and the mitochondria had disappeared along
with most of the nuclei and chloroplasts, resulting in

yellowing (Shaw and Manocha, 1965).

Metabolic Changes

 

Coinciding with these structural changes are
changes in metabolic activities. Lewington, et a1.
(1967) illustrated a decrease in protein as well as
chlorophyll as attached cucumber cotyledons senesced.
The reduction of protein is considered a part of senes-
cence as is reduction of chlorophyll (Leopold, 1975).

Two processes may explain the decline in protein
content: an interruption of protein synthesis or an
increase in the degradation of protein (Wareing and
Phillips, 1973). Parups (1971) has shown from electro—

phoresis of proteins that with aging there is a decrease

in proteins of leaves of Rosa hybrida L. cv. Forever

 

Yours, x Anthirrhinum majus L. cv. Thite Leton, Dianthus

 

caryophyllus L. cv. Sim, and Chrysanthemum morifolium

 

Ram cv. Fred Shoesmith. Also, with aging, proteins
seemed to become more heterogeneous.

The reduction of chlorophyll and protein may be
structurally associated. Woolhouse (1967) found chloro-
plast fraction I declined most rapidly and this protein
makes up almost 50 percent of the leaf protein. Chloro-

plasts rather than the cytoplasma of Oenothera (evening

 

primrose) were found to be a major source of proteins
(Zucker and Stenson, 1962).

Leaf senescence is also characterized by the
decline in levels of RNA. Osborne (1962) found this

decrease in Xanthium pennsylvanicum Wall. She concluded

 

that materials which retard senescence maintain synthesis
of RNA. These materials caused an increase in incorpora-
tion of l4C--Gorotic acid to RNA in intact leaves. Similar
results were found by Fletcher (1969) in attached leaves

of Phaseolus vulgaris L. (red kidney bean). However,

 

the senescence retarding materials plus actinomycin-D, a
potent inhibitor of RNA synthesis on excised broccoli

(Brassica oleracea L. cv. italica, cv. Coastal) leaves,

 

stabilized the chlorophyll and protein content while RNA
level was reduced. Therefore, continued RNA synthesis

does not seem to be obligatory in regard to maintaining

protein and chlorophyll in this role of reduction of
senescence (Von Abrams and Pratt, 1968).

In peas (Pisum sativum L., cv. Alaska), a

 

decrease in tRNA Leu was found (Wright, et a1.,
1,2,5&6 __ __

1972) with yellowing of leaves after flowering. Chloro-

Plast preparations contained a smaller ratio of tRNA ii;
to tRNA gen than an intact leaf indicating general tRNA

in the leaf may be due to loss in the chloroplast.
Photosynthesis and respiration decline as part
of the general degradation process. Photosynthesis has
been shown to reach a maximum in pea leaves (Biggg
sativum L. cv. Laxton's Progress) before the leaf
reaches full size and then a slow fall was detected
(Smillie, 1962). In Nicotiana, the decline in photo-
synthesis was more pronounced in the younger leaves
than in the older basal leaves (Sestak and Catsky,
1962). Smillie (1962) found respiration of pea leaves
declined continuously as the leaf matured. However, in
other Species such as strawberries £1 temporary rise in
respiration was found which is similar to the climatric

found in fruits (Arney, 1947; Yemm, 1956).

Environmental Regulation

 

Environmental factors such as temperature, nut-
rients, darkness, water stress, and heat stress have

been shown to effect the rate of leaf senescence.

Temperature

 

Mothes and Engelbrecht (1963) found detached
tobacco leaves senesced faster when exposed to a high
temperature stress of 49°C for two minutes. Areas which
were exposed to high temperatures yellowed while green
areas acted as sinks for metabolites from the yellowed
regions. A general deterioration of proteins in associa-
tion with yellowing has also been demonstrated (Mothes
and Baudisch, 1958). Kaltaler (1962) found with

Pelargonuim x hortorum Bailey grown from cuttings,

 

plants maintained at low temperatures (40-420F) in
darkness yellowed or senesced slower. This may be due to
a general lowering of metabolism at the low temperature.
Chilling may also hasten senescence as evidence by the

acceleration of geranium leaf senescence (Yarwood, 1977).

Nutrients

 

In Algerian oats (Avena sativa, Linn.) plants

 

receiving low phosphorus (P) senesced more slowly
than plants with adequate P. Supplemental nitrogen

delayed senescence. High phosphorus levels were later

found to prevent senescence by delaying the net export

of nitrogen from the foliage (Williams, 1955).

Darkness

Vickery, 33 a1. (1937) exposed excised tobacco
leaves to continuous dark or light and found that dark—
ness speeds senescence. Organic solids were decomposed
into volatile products. For 72 hours, protein was broken
down at the same rate in light as in the dark. Subse-
quently, the dark cultured leaves decreased in proteins
at a faster rate than those in the light with an increase
of water soluble nitrogen including an increase in
ammonia.

Excised Bryophyllum calycinum leaves exposed to

 

prolonged periods of light increased in starch while
malic and citric acid decreased (Vickery, 1956). The
reverse was observed in the dark. When transferred
from dark to light the starch content increased and the
organic acids decreased. However, leaves exposed to
light for long periods and returned to the dark could no
longer convert acids to starch efficiently. This was
observed by comparing the carbon ratio of starch to
organic acids after each transfer.

Frank and Kenny (1955), using one-week old corn
(ESE.EEX§ L.) seedlings, followed the destruction of

chlorOphyll and carotenoids. After 120 hours at 27°C in

the dark all chlorOphyll disappeared while only 40% of
the carotenoids were destroyed (72% and 30%). The
destruction of chlorophyll and carotenoids was decreased
respectively, by adding sucrose during 48 hours of dark
treatment following 12 hours of light.

Phaseolus vulgaris, cv. Red Kidney, leaf discs

 

lose protein and chlorophyll in the dark faster than
discs remaining in light at 12, 16, and 36 days old.
Rate of loss of both constituents increased as the
plants grew older (Goldthwaite and Leatch, 1967).

In an effort to determine if chloroplast forma-
tion, degradation, or a combination of both occur in

Triticum vulgare, cv. Lemhi leaf tips in darkness; sec-

 

tions were treated with aminotriazole, an inhibitor of
chlorOplast formation. Light retarded the loss of
chlorophyll, maintained photosynthesis, and slowed the
breakdown of the chloroplast ultrastructure. When a
photosynthetic inhibitor, 3-(3, 4-dichlorophenyl)-l,
1-dimethylurea was added, it did not affect the above
measures. Also, when sugar was added to nonphotosynthe-
sizing tissues, chloroplast destruction was not slowed.
From this, it was concluded that chloroplast destruction

must be delayed by light (Haber, et 31., 1969).

10

Water Stress

 

Morton and Watson (1948) found in sugar beets
(HilleshOg) that leaf senescence was not significantly
affected by continuous water regimes except when high and
low regimes were alternated. Senescence was hastened
when high water regime plants were subjected to a dry
regime. Plants under a low water situation when trans-
ferred to high water conditions had less leaf death than
any other treatment.

A decrease in protein was reported by Petrie and

Arthur (1943) when tobacco (Nicotiana tobacum L. Hickory

 

Prior) plants were subjected to drought. If plants were
watered, the protein assimilation rate returned to a
rate similar to plants maintained continuously on a high
water regime. (In plants under dry a condition, the
maximum protein content of the leaves was reached later
than for leaves from fully watered leaves. This resulted
in a slower growth rate and a delay in whole plant
senescence.

Gates (1955) found a similar delay of whole plant

senescence in tomatoes (Lycopersicon esculentum, Mill.).

 

Dry weight of lamina decreased when plants wilted from
exposure to drought and returned to normal growth
rate when watered. The conclusion was drawn that

the plants stressed were physiologically younger upon

11

recovery, but no data were presented to support this
statement.

Shah and Loomis (1965) reported an increase in
soluble RNA and a decrease in other RNA fractions in

detached sugar beet leaves (Beta vulgaris L., cv. MS

 

NBIXNB4 hybrid). Protein decreased under dry conditions.

Hormonal Regulation

 

The internal regulation of senescence has been
investigated by applying natural and synthetic plant
hormones: cytokinins, auxins, gibberellic acids, and
ethylene. Senescence has been delayed or influenced by

the various regulators.

Cytokinins

 

Richmond and Lang (1957) were first to report a
delay in chlorophyll and protein loss in detached

Xanthium pennsylvanicum (cocklebur) leaves treated with

 

cytokinins. Primary leaves were removed and the petioles
were placedin solutions of water containing 1 or 5 mg of
kinetin per liter at 220 to 25°C. After 12 days, the
explants in water had lost 60% of the initial protein.
While those in 1 mg/l kinetin solution lost 50% and
only 15% of treated with 5 mg/l.

Similar results have been found in several

species. In two species of tobacco plants (Nicotiana

 

tabacum var. Bright Yellow and N; rustica), detached leaf

12

5M of kinetin in

discs were floated in a solution of 10-
dark or light for two or three days at 30°C. In N;
tabacum the decrease in protein was suppressed fully in
nuclear, mitochondrial, microsomal, and final superna-
tant fractions. Kinetin caused nucleic acid accumula-
tion in the microsomal and supernatant fractions. N;
rustica showed no response to kinetin unless light or
sugar were present when protein and nucleic acid rose
compared to discs not treated (Suguira, et al., 1962).

In Red Kidney beans, leaf discs from plants 12
to 15 days old were floated on solutions or water
in the dark for eight days at 30°C. Kinetin and
6-benzylaminopurin (BAP) reduced protein and chlorOphyll
loss. Aging of leaf discs did not increase this effect
(Leopold and Kawase, 1964).

Three cytokinins have been shown to reduce

chlorophyll loss in Maianthemum canadence leaf discs at

 

25°C for three days of darkness. Kinetin and zeatin
were used at 2.5 mg/l and benzyladenine (BA) was used at
5 mg/l. When using BA the loss of chlorophyll was
greater in leaves sampled in September versus July
samples (Horton, 1977).

Similar effects have been shown in intact seven-

day old wheat seedlings (Triticum aiestivum L.) exposed

 

to darkness by Wittinbach (1977). BA at l u/l to

100 ul/l delayed chlorophyll degradation progressively

13

as a function of BA concentration. Zeatin (0.1 mM)
stimulated partial recovery of protein and chlorophyll
content during 12 days in the dark. Recovery of photo-
synthesis capacity was shown to follow a similar pattern.
Wright, gt gt. (1973) has shown t-RNA is higher

in intact young peas (Pisum sativum L. cv. Alaska) and

 

soybeans (Glycine max L., cv. Wayne) than at later

 

stages of natural senescence when sprayed with 10—4

zeatin. Also, peas sprayed with zeatin remained green
longer than controls.

The role of cytokinins in reducing the loss of
RNA and protein is uncertain as to whether it works via
promoting synthesis or decreasing degradation. The
investigation of incorporation of radioactive percursors
of protein and RNA during senescence has been investi-
gated in several plants to determine if stimulation of
snythesis is the mechanism. Osborne (1962) floated
Xanthium pennsylvanicum leaf discs on solutions of

l4C-l-leucine (t x 10-4M, 106

C-orotic acid (2.5 x 10-4M, 106 counts/

 

kinetin (40 mg/l) with
counts/m1) or 14
ml) at 24°C in darkness. Also, whole leaves were treated
one-half with kinetin and the other with water. Leaf

discs were then cut from the two halves and incubated for

1, 2, or 4 hours in either labeled leucine or orotic

acid. In both cases, protein and RNA content was greater

14

in kinetin treated leaves. Also, incorporation of radio-
active material was higher in the kinetin disc.

Maas and Klambt (1977) have shown cytokinin to
have a direct effect on protein synthesis independent of
an increase in RNA. 14C-amino acids were applied to

tobacco (Nicotiana tabacum L. cv. Wisconsin 38) pith

 

tissue in the presence of actinomycin D (100 ug/ml) to
block RNA synthesis. Kinetin (0.4 mg/l) in four hours
of darkness at 27°C caused an average increase of 35
percent in protein content over the controls.

In intact bean plants, Pozsar, gt gt. (1967) have
shown an increase in incorporation of labeled glycine into
protein by painting kinetin (50 ppm) and BA flfllppm) onto
half of leaves. BA was more effective. Leaf discs from
treated leaves were incubated in l4C—glycine for four hours.

Similar results were reported by Fletcher (1969)

with RNA and protein on intact red kidney bean (Phaseolus

 

vulgaris L.) plants. Higher levels of RNA, protein and
chlorOphyll were found in BA (30 mg/l) painted leaves.
Primary leaves were painted weekly with kinetin, water or
urea until plants had set fruit. BA treatments not only
caused higher RNA content but also showed a high level

of RNAase activity. The effect of kinetin was observed
at two weeks with its Optimum effect at six weeks. Urea
served as a nitrogen source and was used to show BA was

not just supplying N to the senescing plant. No

15

difference was found between the urea and control.
Throughout the life of the plant a higher rate of incor-
poration of radioactive leucine and arotic acid into
protein and RNA was observed in BA treated leaves. How-

l4C-leucine

ever, when plants flowered incorporation of
was found in protein.

Martin and Thimann (1971) theorized that protein
degradation is the active role of cytokinins in delaying
senescence. Detached oat leaves were placed in darkness
and treated with l-serine, kinetin, and cycloheximide
(CYC) alone and in combinations to test the theory that
proteases were functional in senescence. If this theory
were true, then kinetin should prevent protease increase
because it delays senescence. Also, serine which was
shown to enhance senescence with or without kinetin
should increase protease activity. Finally, CYC, a
protein inhibitor which was shown to delay senescence and
prevent serine enhancemenn should prevent protease
increases. Two proteolytic enzymes which were isolated
did react to the various treatments as expected. Activ-
ity of the proteases were decreased by kinetin and CYC and
increased by serine.

Further support for the theory of protein degrada-
tion was shown by Kuraisbi (1968). Leaf disc of Brassica
tgpg L. were floated on a solution of l4C-leucine at 25°C

in the dark to label existing proteins. After 24 hours,

16

the discs were transferred to solutions of kinetin

(5 x lO-SM) or water. Kinetin treated tissue retained
more radioactivity in the protein fraction than the
control tissue after 24 and 48 hours.

The above experiment does not rule out the pos-
sibility of cytokinins stimulating bulk protein synthesis
(Travares and Kende, 1970). To investigate this pos-
sibility, Travares and Kende prelabeled corn leaf disc
protein and measured the rate of degradation and the
specific activity of the protein. After incubation four

6

to five hours in 14C-leucine (1.5 x 10- M), discs were

12C-leucine (lo-4M) with or

placed in solutions of
without BA for 48 hours. Protein breakdown, both
labeled and bulk, was decreased by BA. If protein was
actively being synthesized during this 48 hours, it would
be unlabeled and the specific activity of the total
protein would have been lower. However, this was not the
case and the authors concluded that the primary action of
cytokinin in retarding senescence is mainly through the
inhibition of protein degradation.

The mobilization of metabolites to areas treated
with kinetin was reported by Mothes, gt gt. (1959).
Gunning and Barkley (1963) reported similar
results with detached oat leaves. Labeled carbon and

phosphorus (P32) accumulated where kinetin was applied.

A polarity was established as acropital. Mfiller and

17

Leopold (1966) found similar results in detached
corn leaves. Transport of P32 was axial and blockage
was caused by metabolic inhibitors and steam-killed

zones. Kinetin attracted P32 and Na22 and not Rb86,

C136 or I131. P32 was the only material which accumu-
lated. This transport was found to take place in the

phloem. BA (4.4 x I0M)3 was shown to attract 14C fol-

lowing assimilation of 14

CO2 by leaves of intact ytttg
vinifera L. Older leaves reSponded very little to BA
treatment unless they were placed in darkness (Quinlan
and Weaver, 1969). However, Seth and Wareing (1967)
found when kinetin was placed on defruited peduncles
there was no accumulation of P32. Also, Osborne (1962)
has shown in Zanthium leaves with discs treated with
kinetin and connected by a strip to another disc treated
with water or kinetin there was no difference in senes-
cence when compared to isolated discs treated the same.
The delay in senescence was due to the kinetin and not
metabolite movement. Therefore it can be concluded that
mobilization of metabolites by kinetin cannot explain
its retardation of senescence.

Protein decline as a result of water stress as
discussed earlier may also be kinetin related. Root
factors involved in growth and metabolic activity of
shoots have been postulated for years (Chibnall, 1939,

and Kulaeva, 1962). Later, kinetin-like factors were

18

isolated from root exudates of sunflowers (Kende, 1965)
and was linked to the reduction of leaf senescence
(Sitton, gt g_1., 1967). Itai, gt g_1. (1968) reported in sun—
flowers, bean, and tobacco when roots were water stressed
that cytokinin translocation decreased from their roots.
The decrease was found to be reversible.

Cytokinins present in the shoot may also be
affected by water stress. Itai and Vaadia (1971) have
shown in excised tobacco shoots a reduction of cytokinin
activity similar to activity caused by water stress
applied to roots. A chemical transformation was shown by

use of l4C-kinetin in wilting plants.

Gibberellic Acid, Auxin
and Abscisic Acid

 

 

Brian, gt gt. (1959) reported that fall color of
several tree species are affected by gibberellin (GA).
The delay of senescence has been shown in leaf discs of
several species (Beevers, 1966; Fletcher and Osborne,
1965; Whyte and Luckwill, 1966; Horton, 1977). However,
cytokinins have been shown to be more effective (Parups,
1970).

Auximsreportedly reduce protein and chlorophyll
loss (Parups, 1970; Richmond and Lang, 1957). However,
in Xanthium or broccoli leaves o-naphthaleneacetic acid
(NAA) did not influence senescence except by depressing

the effects of kinetin applications. However, MaaB and

19

Klambot (1977) found in tobacco that auxin has no effect
on protein synthesis.

Abscisic acid has also been reported to affect
the degradation of chlorophyll very slightly (Wittenbach,
1977). Horton (1977) reported enhanced senescence by
retarding the effects of cytokinins and GA.

Mobilization of assimilates has also been shown
to be affected by GA and auxins. 3-Indolyl acetic acid
(IAA) when applied to defruited peduncles of French beans
enhanced the movement of 32F. GA and kinetin when
applied alone had no significant effect. However, the
greatest accumulation of 32P occurred when the three
hormones were used together (Seth and Wareing, 1966).
Gunning and Barkley (1963) found conflicting results in
detached oat leaves where no movement of radioactive sub-

strates was observed when GA and IAA were applied. In

geraniums (Pelargonium zonale L.) Auxin, 2,4-D, NAA, BA,

 

and GA3 was reported to attract movement through the

phloem of 32F, 358, 86Rb(K), but had no effect on 45Ca

or 36C1 (Penot and Beraud, 1977). GA3 was found to be

the most effective hormone (Penot and Beraud, 1977).

Ethylene

The economic importance of ethylene as air
pollutant affecting greenhouse crop production is a well

recognized fact. Carroll and Jansma (1972) surveyed five

20

counties in southeastern Pennsylvania and found ethylene
was responsible for 48.1 percent of a total crop loss of
$17,564. Abeles (1971) reported ethylene levels as high
as 0.387 ul/liter in atmosphere around Washington, D.C.,
and most plants are sensitive to ethylene at a level of
0.1 ul/liter.

Krone (1937) reported damage from natural gas
(6.1 percent ethylene) on several species of plants. The
symptoms of injury were yellowing, premature abscission,
epinasty, increased growth of weakened side shoots.
Similar results were found (Heck and Pires, 1962) when
89 species from 39 different families were fumigated with
ethylene (2,5 and 100 ul/liter) for ten days. Symptoms
were death, stunting, inhibition of leaf expansion,
injury or death of floral parts, increased abscission,
epinasty, chlorosis, and necrosis. Stunting may be the
effect of ethylene inhibiting cell elongation. Ethylene
inhibited shoot elongation of pea seedlings (Harvey,
1915) and wheat seedlings (Roberts, 1951). Flower inhibi-

tion has been shown in Xanthium pennsylvanicum Walln.

 

(Abeles, 1967) when exposed to 10 and 100 ppm of ethylene.
Lower concentrations of 1-4 ul/liter of ethylene caused

failure of flowering in Chrysanthemum morifolium Ramat

 

under short day conditions. Exposure to alternating
concentration showed similar results (Tjia, gt gt.,

1969).

21

Geraniums have been reported (Reed, 1975) to
respond to Florel, an ethylene releasing plant growth
regulator, by increased number of branches and flower
bud abortion. Krone (1937) reported yellowing and
slight leaf abscission when several species of plants
were exposed to "Michigan gas" at 2 percent in air for
60 hours.

Chlorophyll degradation by ethylene in celery
was reported a practical way for blanching celery
(Harvey, 1925). Also, curing tobacco was hastened by
ethylene (Pratt and Goeschl, 1969). However, Wittenbach
(1977) has shown on intact wheat seedlings ethephon, an
ethylene producing compound, has no effect on chloro-
phyll.

Conflicting reports on other parameters used to
measure senescence, RNA and protein, are known. Abeles
and Holm (1966) reported an increase in RNA and protein
in bean explants in response to ethylene. In wheat
seedlings ethylene stimulated protein synthesis in the
embryo (Roberts, 1951). However, in pea seedlings ethy-
lene was shown to reduce protein content (Harvey, 1915).
Whittenbach (1977) reported not effect on protein content
when wheat seedlings were exposed to ethylene. In Rgggg
discolor leaf sections, auxin stimulated protein and RNA
synthesis, but ethylene inhibited this stimulation

(Sacher and Salminen, 1969).

22

Ethylene has been shown to influence leaf yellow-
ing by inducing leaf abscission (Abeles, 1971). In this
case, leaves would senesce as in detached tissue.
Ethylene has been shown to cause abscission of the fruit
(McAfee and Morgan, 1972), and this action is widely
used in commerCial horticulture.

Most of the work in leaf abscission has been on
explants since the work of Kendell (1918). Ethylene,
auxin, and ABA have all been shown to play an important
role in leaf abscission of explants. Auxin has been
shown to inhibit abscission (LaRue, 1936). Naturally,
the leaf blade has been shown to be inhibitory in
petiole abscission, and this was explained as the effect
of the auxin content of the blade (Myers, 1940).

Rubinstein and Leopold (1963) reported auxin
to have two effects on bean explant abscission called
stage I, auxin prevented abscission, and stage II,
auxin promoted abscission. This is reflected by the
aging of the leaf where younger leaves have a longer
inhibition stage (1) than older leaves (Chaterjee and
Leopold, 1964).

Ethylene has also been shown to be involved with
auxin in this two-stage process. During stage I
explants when exposed to ethylene have been shown to

be relatively insensitive to the promotive effect of

23

ethylene on abscission (Abeles, gt gt., 1967; Jackson
and Osborne, 1970). In stage II, ethylene accelerated
abscission (Abeles and Rubinstein, 1964).

Jackson and Osborne (1970) found that bean
explants produce a surge of ethylene as a response to
wounding and then the rate subsides until just before
abscission occurred. Also, ethylene applied within 24
hours of leaf blade removal had no effect on abscission,
supporting the two-stage theory.

For ethylene to be a factor in seedling damage
in transport, a source of ethylene production would have
to be available for concentration to reach toxic levels
in the shipping containers. Healthy plants produce
ethylene at low rates and diseased or injured plants
produce much more. The seedlings can also be "gassed"
with ethylene as an air pollutant. The internal combus-
tion engine produces large amounts of ethylene as well
as carbon monoxide which mimics ethylene action (Abeles,
1971). Gasoline engines (1957 to 1966) produced an
average of 211.3 ul/liter. A idling diesel-driven truck
produced 64 ul/liter. This could be an important dele-
terious factor in loading areas if trucks are left running
or fork lifts are in active use (Hasek, gt gt., 1969).

Plants in stress have been shown to produce
ethylene. Virus infection in several species of plants

caused an increase in ethylene production (Williamson,

24

1949; Ross and Williamson, 1951). Jackson and Osborne
(1970) reported an increase in ethylene production from
the cutting of leaf tissue of peas.

Water stressed cotton plants have also been
shown to produce ethylene around the petiole. McMichael,
gt gt. (1972) reported that excised or intact cotton
petioles, when water deficient, produced more ethylene.
Also 12th node petioles (excised) produced almost twice
as much ethylene as those from the 5th node. Similar
results were found byIWfliee and Morgan (1971). The pos-
sible difference could be due to leaf age. Intact
plants did not show this node difference. After the
stressed plants were watered, ethylene production
dropped to normal (McMichael, gt gt., 1972).

Lime plants enclosed in containers for four days
of darkness in various ethylene concentrations (0.1 to
10 ul/liter) responded with increased abscission as
ethylene increased (Cunningham and Staby, 1975). In
every case, the ethylene concentration decreased
slightly with time. Samples of air from unOpened ship-
ping cartons from Florida were lower than 0.01 ul/liter
ethylene. However, leaves still abscised. Kays, gt gt.

(1976) has shown pepper transplants (Capsicium annuum L.)

 

produced more ethylene in darkness. Plants exposed to
ethylene at levels greater than 0.1 ul/liter were slower

to recover when planted in the field than plants receiving

25

less ethylene. Leaf abscission was greater as the
ethylene concentration increased. Carbon dioxide showed
a general trend of inhibiting abscission but was not
significantly different from ambient ethylene maintained
at low levels.

Atmospheric conditions also influence ethylene
production. Oxygen is required for ethylene production
(Burg, 1962; Burg and Burg, 1967). In cut flowers CO2
(carbon dioxide) reversed all known effects of ethylene
(Parsons,gt gt.,l967;Smith and Parker, 1966; Uota, 1969).

Low pressure storage (hypobaric, LPS) has been
shown to reduce the effects of ethylene. A low 02 level
is automatically obtained as the total air pressure is
reduced and gases produced by the crop are flushed away
by a flow of water saturated air in LPS (Burg, 1973),
preventing desication.

LPS has been shown to extend the storage time of
ornamental cuttings and plants with no effect on shelf
life. Burg (1973) found potted Chrysanthemums could be
stored two to three weeks longer in LPS than cold storage
with no damage. Easter lilies stored for six weeks with
color showing responded as normal plants when removed.

Chrysanthemum cuttings have also been shown to
have extended storage life in LPS (Burg, 1973; Eisenberg,
gt gt., 1977). Rooted cuttings from conventional cold

storage rooted readily on out planting but developed

26

slowly while cuttings from LPS storage rooted and
developed normally when placed in prOpagation beds
(Burg, 1973). Eisenberg, gt gt. (1977) reported cold
storage of 15 genera declined more rapidly than LPS
over time. A reduction of pathological invasion,
defoliation, and yellowing was observed.

LPS of geranium cuttings was shown to be suc-
cessful (Eisenberg, gt gt., 1977). Experiments were
conducted on unrooted and rooted cuttings of geraniums,
LPS storage in chambers maintained at 1/30 atm with 1
air exchange per hour at 95—98 percent relative
humidity (2.20C), and cold storage in chambers at 2.2°C
and 95-98 percent relative humidity. LPS storage
produced acceptable quality plants after 4 to 6 weeks
while plants in cold storage developed damage after 2
weeks. Rooting response was maintained longer in LPS.
Rooted cuttings were stored 2, 4 and 6 weeks in LPS.
Those at four weeks showed yellowing when transplanted,
and after six weeks developed chloroticanuinecrotic areas
when transplanted. Cold storage, however, showed com-
plete yellowing at 4 to 6 weeks of storage. Therefore,
the removal of ethylene during LPS and the reduced 02
(necessary for ethylene synthesis) may be responsible

for extending the storage life of geranium cuttings.

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In G. E. W. WOlstemholme (ed.), CIBA Colloq.
Aging 2:207-214.

Zucker, M., and H. T. Stenson. 1962. ChlorOplasts as the
major protein-bearing structures in Oenothera
leaves. Arch. Biochem. Biophys. 96:637-647.

SECTION ONE

THE EFFECT OF ETHYLENE AND ENVIRONMENTAL

FACTORS ON PELARGONIUM X

 

HORTORUM BAILEY

36

THE EFFECT OF ETHYLENE AND ENVIRONMENTAL

FACTORS ON PELARGONIUM X

 

HORTORUM BAILEY.

Abstract. The effect of ethylene, benzyladenine,
and environmental factors were investigated in simulated
shipping conditions for up to 96 hours for seedlings of

Pelargonium x hortorum Bailey (cv. Sprinter Scarlet).

 

Leaf yellowing decreased when plants were shipped at
cool temperatures (e.g. 2 to 10°C) except for plants at
10°C in waxed cardboard boxes. Increase in duration of
darkness caused an increase in leaf mortality and the
number of days to flower after potting, while decreasing
the ability of plants to recover after planting. A dose
of ethylene 0.1 ul/liter for 48 hours increased leaf
yellowing, while higher concentrations (l-lO ul/liter)
caused leaf yellowing when applied for 12 to 48 hours.
Delay in flowering was caused by as little as 0.1 ul/
liter of ethylene and 1 and 10 ul/liter produced the same
results. Leaf abscission increased after 96 hours of
treatment with 1 or 10 ul/liter. CO2 at 5 percent v/v
in air did not inhibit the ethylene effects noted.
Ethylene synthesis decreased after 24 hours of darkness

to a steady state in drought stressed plants, while

37

38

normally watered or heavily watered plants decreased to
a low steady state of ethylene production at 24 hours.
Leaf yellowing was not affected by watering regimes.
Drought stressed plants showed greater leaf mortality

and resulted in shorter plants.

 

Transit of commercial floricultural seedlings

is a relatively unexplored area. Marketing of seedling
geraniums to commercial growers has raised some problems
in leaf yellowing, plant mortality, leaf abscission and
stunting of plants in transit or soon after transplant-
ing.

High temperature induction of senescence
is well known (Mothes, gt gt., 1961). Storage of rooted
and unrooted cuttings of nursery stock and floricultural
crops is improved with low temperature with little or no
adverse effects on quality (Snyder and Hess, 1955; Pryor
and Stewart, 1962; Flint and McGuire, 1962; Schneider,
1964). Kaltaler (1962) found less damage to geranium
cuttings during simulated transit at low temperature than
at high temperatures.

Continuous darkness speeds senescence in excised
tobacco leaves (Vickery, gt gt., 1937). Seedlings

exposed to darkness lose chlorophyll, protein, and RNA

39

more rapidly than lighted plants (Frank and Kenny, 1955;
Goldthwaite and Leatch, 1961).

Drought stress hastens senescence. This also
happens when plants are watered excessively and then
allowed to dry out. Plants under low water situations
when transferred to high water conditions showed less
leaf death (Morton and Watson, 1948). Whole plant
senescence is sometimes delayed rather than hastened
by drought (Petri, gt gt., 1943; Gates, 1955).

Ethylene is another factor that may contribute
to plant senescence during transit. Ethylene was
related to leaf yellowing (Krone, 1937; Heck and Pires,
1962). The yellowing effect caused by ethylene could
be related to its role in leaf abscission. Flowers
have been shown to be delayed in opening (Abeles, 1967;
Tjia, gt_gt., 1969) or damaged by ethylene (Heck and
Pires, 1962).

Ethylene concentration in transit could be
affected by poor ventilation of containers and trucks,
air pollution (Halevy and Kofranek, 1967), mechanical
damage to plants (Jackson and Osborne, 1970), and
natural plant production.

The natural production rate of ethylene has not
been established for seed geraniums. Also, the sen-
sitivity of the plants to various ethylene concentra-

tions and durations is now known. Symptoms of ethylene

40

damage to the plant are unknown other than the obvious
parameters of leaf yellowing and abscission.

This study was conducted to further define the
effect of temperature, removal of plants from their
flats for shipment, type of shipping container, dark-
ness, and ethylene on geranium plants in simulated
shipping. The synthesis of ethylene was investigated
with respect to various water regimes and high tempera-
ture treatments. From this information it may be
possible to set guidelines for manipulating the
environment of the shipment to reduce plant senescence

in transit.

Materials and Methods

 

Experiment 1 - Eighty day old seedling geraniums

 

(cv. Sprinter Scarlet) were grown in Sun City, Florida.
Expanded polystyrene trays consisting of seventy-two
cubes per tray were used as a growing container. Each
cube was 5 cm. deep, 3.7 cm. square at the top tapper-
ing to 0.94 cm. at the base, and 1.5 cm. apart. Plants
were removed from the trays and placed in a waxed card-
board shipping container with four side vents (regular)
or an expanded polystyrene (EPS) container with no
ventilation. All yellow leaves were removed from the
plants before the following treatments were applied:

1. Stored at 25°C - 35°C (no cooling).

41
2. Precooled to 10°C beforg the containers were
closed and stored at 10 C.
3. Stored at 10°C.

4. Precooled to 2°C before the containers were
closed and stored at 2°C.

5. Stored at 2°C.
Four containers of 72 plants of each container type
were used for each treatment. At 0, 24, 36 and 72
hours after treatment one container from each treatment
combination was flown to Lansing, Michigan. Ethylene
samples (1 ml) were taken by syringe as the containers
were Opened. Thirty plants were removed randomly
from each container and assigned to three blocks with
ten observations per treatment combination. Plants
were potted in 10 cm. pots containing equal parts of
soil, peat, and perlite by volume. The number of
yellow leaves per plant was recorded, but the leaves
were not removed from the plants. Plants were grown
in March at 21°C days and 17°C nights on a constant
liquid feed rotation of 200 ul/liter of 20-20-20 and
25-0-25. After two weeks the number of dead leaves was

recorded.

Experiment 2 - The effects of ethylene and

 

handling procedures on leaf yellowing, leaf death, leaf
abscission, and ability of seedling geraniums (cv.

Sprinter Scarlet) to recover were investigated. Plants’

42

received from Sun City, Florida, were grown for two
weeks in East Lansing, Michigan, in polystyrene trays
with seventy-two plants per tray as described in
experiment 1. Twenty-four, ninety day old plants were
selected and placed in four blocks with one observation
for each treatment combination. Half of the plants were
randomly left in their containers and half were removed
to expose the root mass. This treatment was to observe
what effect the damage from pulling the plants from
the tray would have on the yellowing of plants in dark-
ness. Four pulled and four non-pulled plants were
placed in ten liter buckets with lids fitted with two
ports. The inlet port was connected to an air stream
containing 10 ul/liter of ethylene as described by
Saltveit (1978), or to a stream of ethylene-free air
from a Purafil scrubber. The air flow was held constant
at 110 ml/min with a capillary flow meter. The outlet
port was used for gas sampling to ascertain the ethylene
level.

The experiment was performed in growth chamber
at a temperature of 20°C. At 0, 24, 48, 72, and 96
hours, plants were removed from each treatment combina-
tion and transplanted into 10 cm. pots in an equal mix
by volume of soil, peat, and perlite by volume. The
number of yellow leaves was recorded. Plants were grown

at 21°C days and 17°C nights on a constant liquid feed

 

43

of 200 ul/liter alternated between 20-20-20 and 25-0—25.
The number of dead or abscissed leaves was recorded after

one week.

Experiment 3 - To further define the effect of

 

ethylene, ninety-nine day plants were exposed to four
concentrations of ethylene (0, 0.1, 1.0 and 10 ul/liter)
for 12, 24, 48 and 96 hours in a 20°C growth chamber.
Concentrations were established as in the previous
experiment. All plants were removed from their trays and
placed in 10 m1. buckets for treatment application. Four
replications and three observations per treatment com-
bination was used. Upon removal from the buckets, plants
were treated as in experiment 1. After six weeks of
growth, plants were visually rated on a scale of l to 5

from poor to high quality, respectively.

Experiment 4 - To determine if ethylene action is

 

promoting senescence of leaves, and if so could it be

inhibited by CO An experiment like experiment 2 was

2.
conducted except 5 percent CO2 was used or was not used
with ethylene at 0, 0.1, l and 10 ul/liter in air.

Plants were 105 days old when treated. Four replications
and three observations per treatment combination were
used. Number of yellow leaves was recorded after treat-

ment and number of dead leaves was recorded one week

after treatment. Ethylene analysis was by gas

44

chromatography employing a flame ionization detector and

a column of activated alumina using N2 as the carrierwgas.

Experiment 5 - Seventy day old plants received

 

from Sun City, Florida, were grown in Lansing, Michigan,
for eleven days before treatments were applied. Trays
described in experiment 1 were cut into sections contain—
ing nine plants. Plants in twelve sections were exposed
to 200 or 35°C for twelve hours. At each temperature,
plants were watered: (l) on a normal watering schedule,
(2) one in which the soil mass was saturated for 48 hours
before data measurement, or (3) watered 48 hours before
data measurement and not watered until transplanting 96
hours later, after the data were taken.

After the 12 hours at various temperatures, the
trays were placed in 10 liter desiccators which were con-
nected to continuous flow system as described in experi-
ment 2 at a rate of 100 nu/min. The air was scrubbed free
of ethylene with a Purafil filter before entering the
containers. The experiment was replicated four times.
One ml. samples were taken by syringe at 0, 24, 48, and
96 hours of darkness and analyzed for ethylene as in
experiment 5. At 96 hours plants were transplanted into
10 cm. pots containing equal parts of soil, peat, and
perlite by volume. The number of yellow leaves and

plant height was recorded. Plants were grown at the

45

same temperature and on the same fertilization program
as in experiment 1. After two weeks the number of dead

leaves was recorded.

Results

Experiment 1 - The temperature, container type,

 

and duration of treatment all affected the number of
yellow and dead leaves per plant (Figures 1, 2, 3, and
4). At 0 and 24 hours there was very little difference
in the number of yellow leaves between any of the treat-
ments while at 48 hours the plants with no cooling showed
more damage (Figures 1 and 2). Plants at the 72 hour
period showed less damage when precooled or shipped at
2°C and precooled to 10°C.

The number of dead leaves in all treatments
increased slightly over time. Apparently, some leaves
which were yellow at planting time recovered since in
some cases there were fewer dead leaves after 2 weeks
than there were yellow leaves. The greatest damage was
seen with plants precooled to 10°C at 72 hours of treat-
ment (Figures 3 and 4). An increase in temperature did
not result in an increase in leaf mortality.

Ethylene accumulation in EPS containers was
greater when plants were not cooled or precooled to 10°C
and stored for 10°C. In general, EPS containers accumu-

lated more ethylene at warmer temperatures (Table 1).

46

 

 

 

{3
7 a .
F
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Figure l.--Effect of temperature and duration of treatment,
in regular containers on leaf yellowing of
seedling geraniums two weeks after transplanting.

47

 

 

 

 

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Figure 2.--Effect of temperature and duration of treatment,
in EPS containers on leaf yellowing of seedling
geraniums two weeks after transplanting.

 

48

 

 

 

 

 

 

 

 

 

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Figure 3.~-Effect of temperature and duration of treatment,
in regular containers on leaf death of seedling
geraniums two weeks after transplanting.

49

 

 

 

 

 

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Figure 4.--Effect of temperature and duration of treatment,
in EPS containers on leaf death in seedling
geraniums two weeks after transplanting.

50

TABLE l.—-Effect of temperature and container type on
ethylene concentrations in shipping containers
upon arrival.

 

Ethylene (nl/liter)

 

 

Temperature
Regular container EPS container

No cooling 7 100
Precooled 10°C and

stored 10°C 10 142
Stored 10°C 6 68
Precooled 2°C and

stored 2°C 7 40
Stored 2°C 39 83

hsd for two container means at the same level of
.05 . .
cooling is 65.76.
hsd 05 for two cooling means at the same or different
' levels of containers is 105.4.

 

Experiment 2 - The manner in which a plant was

 

handled was not significant for any parameter except
percent of abscised leaves where a two-way interaction
involving duration of treatment and ethylene concentra-
tion was noted (Table 2). However, abscission occurred
only with 10 ul/liter of ethylene when exposed for more
than 48 hours. There was not significance found with
respect to percent of yellow leaves which died (Table
2). It appears that pulling the plants may make

them more sensitive to ethylene, but this must be exam-

ined further before a conclusion can be drawn.

51

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52

Rate of recovery on planting was significantly
reduced by extending darkness. The longer the plant
was exposed to darkness at 20°C the lower the quality
of the plants when grown to salable product (Table 3).

The effect of ethylene on the percent of yellow
leaves varied with time (Table 4). The data indicate
that the longer the plants are in the dark beyond 72
hours the more leaf yellowing occurs and the presence

of 10 ul/liter ethylene enhances this effect.

Experiment 3 - As the ethylene concentration

 

increased, the percent of yellow leaves increased and
generally more so the longer the duration of treatment
(Table 5). As the treatment duration increased, only
48 and 96 hour treatments showed a significant increase
in yellow leaves. However, at every level of duration,
as ethylene increased percent yellow leaves increased
significantly. As the duration of ethylene treatment
increased the days to flower increased. This was also
true for the percent of dead leaves (Table 6). When
the effect of ethylene treatment is compared over all
durations it is clear that flowering is delayed by 7 to
10 days at concentrations from 0.1 to 10 ul/liter
(Table 7).

Recovery on planting was influenced by duration

of treatment (Table 8). Plants exposed 96 hours showed

53

TABLE 3.-—The effect of duration of treatment on recovery
of seedling geraniums.

 

 

Duration of treatments Recovery rating2
24 hours 4.5y

48 hours 4.0

72 hours 3.8

96 hours 3.2

hsd .05 0.97

 

2Six weeks after treatment, plants growing in the
greenhouse were rated from 1 to 5, lowest to highest
quality, respectively.

yMeans over handling and ethylene treatments.

54

TABLE 4.--The effect of duration of ethylene treatment

in the dark on yellowing of leaves.

 

Duration in dark

Percent yellow leaves
Ethylene (pl/liter)

 

 

0 10

0 hours 11 10

24 hours 10 28
48 hours 20 54
72 hours 45 62
96 hours 60 97

hsd at 5% level for two
level of concentrations

hsd at 5% level for two concentrations means at the

same level of durations

duration means at the same

is 34.2.

is 15.83.

 

55

TABLE 5.--The effect of ethylene concentration and dura-
tion of exposure while in the dark on the
percent of leaves which turn yellow.

 

Ethylene concentration

 

 

Duration of treatment (pl/liter)

0 0.1 l 10
12 hours 3 19 41 72
24 hours 23 33 50 92
48 hours 18 27 54 94
96 hours 25 32 62 100

hsd .05 of two concentration means at the same or dif-
ferent levels of duration is 17.45.

hsd .05 of two duration means at the same or different
levels of concentration is 17.23.

 

56

TABLE 6.-—The effect of duration of treatment on the
percent of dead leaves and days to flower.

 

 

Duration of z 2
treatment Percent dead leaves Days to flower
12 hours 12 99

24 hours 18 101

48 hours 22 112

96 hours 42 127

hsd .05 19.93 10.48

 

z .
Means over ethylene concentrations.

57

TABLE 7.--The effect of ethylene concentration on the
number of days to flower a seedling geranium.

 

Concentration of ethylene Days to flowerz

 

(ul/liter)
0.0 103
0.1 110
1.0 114
10.0 113
hsd .05 5.79

 

z .
Means over duration of treatments.

58

TABLE 8.-—The effect of duration of treatment on the
recovery rating of seedling geraniums.

 

 

Duration of treatment Recovery rate2
12 hours 3.58
24 hours 3.67
48 hours 4.02
96 hours 3.23
hsd .05 0.34

 

2Six weeks after treatment, plants growing in
the greenhouses were rated from 1 to 5, lowest to
highest quality respectively. Ratings are means over
ethylene treatments.

59

poorest recovery while 48 hour exposure had little

effect.

Experiment 4 - As the ethylene dose increases,

 

the percent of yellow leaves increase. Significant
damage begins at 1.0 ul/liter or at 48 hours of treat-
ment (Tables 9 and 10) which increases significantly at
96 hours. Leaf abscission starts after 96 hours and
abscission increases as ethylene concentration increases.
However, there were not significant differences between
1.0 ul/liter and 10 ul/liter (Table 11).

Five percent V/V CO in air had no effect on any

2
ethylene treatments (Table 12). However, 1 ul/liter with
CO2 at 48 hours shows more yellowing, while yellowing is

more noticeable at 96 hours without C02. There is little

difference seen at 12 or 24 hours when exposed to the air

mixture.

Experiment 5 - Ethylene synthesis was signif-

 

icantly decreased and maintained between 3 and 7 nl/plant/
hr after 24 hours of darkness in drought stressed plants.
In normal or heavily watered plants, the decrease was
significant after 48 hours and was maintained at a rate

of 2 to 12 nl/plant/hr. When soil masses remained
saturated ethylene production rose at 24 hours (Table

13).

60

TABLE 9.--The effect of ethylene concentration on percent
leaf yellowing during darkness, of seedling

 

 

geraniums.
C?:ii§§:::;0n Percent yellow leaves2
0 41
0.1 43
1.0 55
10.0 56
hsd 7.78

 

z .
Means over durations of treatment.

61

TABLE lO.--The effect of duration of dark on the percent
of yellow leaves on seedling geraniums.

 

 

Time Percent of yellow leaves2
12 hours 29

24 hours 32

48 hours 54

96 hours 81

hsd .05 6.85

 

z .
Means over concentrations of ethylene.

62

TABLE ll.--The effect of ethylene concentrations and
duration of treatments on percent of leaf
abscission.

 

Concentration of ethylene Duration Of treatment

 

 

(pl/liter) 12 24 48 96

0 o o o 2

0.1 0 0 0 3

1.0 o o o 18

10 o o o 7
hsd 11.92

.05

 

63

TABLE 12.--Effect of air and C02, ethylene concentrations and
duration of treatment on percent yellow and abscised

 

 

 

 

leaves.
Ethylene Time Percent Yellow Percent abSCised
- . leaves - leaves
concentration in x
Ul/liter hours Air CO Air co
2 2
0 12 23 32 28 o 0
48 45 37 41 o o
96 68 64 66 7 o
24 26 34 30 o o
96 83 68 76 29 6
l 12 25 32 28 0 0
48 61 72 66 0 o
10 12 42 22 32 0 . O
24 37 31 34 0 O
48 61 77 69 o 0

96 100 80 90 3 o

 

64

TABLE l3.--Effect of various water regimes and duration
of darkness of ethylene production.

 

Ethylene (nl/plant/hr.)

 

Watering regimes

 

0 hr. 24 hrs. 48 hrs. 96 hrs.
Normal 22 16 12 5
Soil saturated 21 31 9 2
Drought stressed 23 8 3 7

hsd at the 5% level for the differences between two times
means at the same water regime is 8.3.

hsd at the 5% level for the difference between means of
two water regimes at the same or different levels of time
is 8.7.

 

65

Pretreating the plants for 12 hours at 20°C or
35°C did not alter ethylene production with plants from
both temperatures producing 13 nl/plant/hr. However,
due to the lack of replication of temperature this area
should be investigated further.

Drought stressed plants had slightly fewer yellow
leaves than the other two treatments (Table 14) but this
was not significant. It is possible that the loss of
leaves may have contributed to the lower rates of
ethylene production noted with these plants (Table 13).
Leaf mortality was greater in drought stressed plants as
may be expected. Plant height, a measure of etiolation,
was lower for drought stressed plants possibly because
growth was limited by the lack of water directly as

opposed to growth regulator effects (Table 14).

TABLE l4.--Effect of various water regimes on leaf yellowing,
mortality, and plant height.

 

 

. Percent yellow Percent dead . 2
Water regimes leavesz'Y leavesz Plant height
Normal 92 28 4.8
Soil saturated 92 31 4.6
Drought stressed 82 - 38 3.9
hsd -- 8.79 0.38

.05

 

z .
Means over duration of darkness.

YMeans were not found significantly different by the F
test at the 5 percent level.

66

Discussion

 

The results of this study indicate leaf yellow-
ing and leaf mortality of seedling geraniums shipped
at cool temperatures (2°C to 10°C) are influenced by
the duration of the shipment and the type of shipping
container (Figures 1, 2, 3 and 4). Snapdragons,
alyssum, petunia, salvia, and marigold have success—
fully been stored at 5°C for 4 to 6 weeks when supplied
with 18 hours of light per day (Kumpf, et 31., 1966).
Also, tomato transplants have been successfully stored
for 6 days at 5 to 15°C (Kretchman and Short, 1972).
Kaltaler (1962) noted a slight amount of leaf yellowing
occurred while storing geranium cuttings for 5 days at
5°C and for 1 to 3 days at 20-30°C. In this investiga-
tion, storage at 2°C or precooling at 10°C and storing
at 10°C appeared to cause no damage for 48 hours in
the dark (Figures 1 and 2). Some of the leaves that
were counted as yellow at the end of the thermal-
storage duration treatments regreened rather than died
or abscissed (Figures 3 and 4).

The reduced occurrence of yellowing at the
low temperatures in the dark may be caused by a general
lowering of metabolism at the low temperature. Darkness
normally is considered to speed senescence by decreasing

protein and chlorophyll syntheses (Frank and Kenny,

67

1955; Vickery, 3: 31., 1937, 1956; Goldthwaite and
Laetsch, 1967).

In experiment 3 increasing the duration of
darkness increased leaf mortality. However, this was
not observed in experiment 1 (Table 2). This can not
be explained directly, but the nine day age difference
may play a role. Younger leaves are less prone to
abscise than older leaves (Chaterjee and Leopold,
1964).

Darkness affected other parameters directly.
The ability of plants to overcome the stress imposed
by increasing darkness was impaired as the duration
of darkness increased from 24 to 96 hours (Table 3).

It appears to take 2 to 3 days of darkness to affect
a significant decrease in recoverability.

As the duration of darkness in simulated transit
increased the number of days required to flower
increased (Table 6). A delay in flowering was observed
after a 48 hour dark treatment.

Ethylene has been reported to cause leaf yellow-
ing (Krone, 1937; Heck and Pires, 1962). The present
work indicates leaf yellowing of seedling geraniums is
affected by ethylene concentration as well as the dura-
tion of exposure to ethylene while the plants are in

darkness (Tables 4 and 5). At 0.1 ul/liter ethylene,

68

yellowing was significantly enhanced in about 12 hours
and at 10 ul/liter 72 percent of the leaves were yellow
(Table 5). Increasing the duration of exposure to
ethylene significantly enhanced leaf yellowing at all
ethylene levels (Table 5). The longer plants were in the
dark the more leaf yellowing occurs even without supple-
mental ethylene.

Removing seedlings from their growing containers
could cause mechanical damage resulting in ethylene
production. Several forms of stress cause plants to pro-
duce ethylene (Williamson, 1950; Jackson and Osborne,1970).
The only parameter significant in this treatment was
abscission, but no trend was observed for pulled plants
vs. non-pulled plants. However, it appears that pulling
the plants free of their containers may make them more
sensitive to ethylene with regards to leaf mortality
(Table 2). Differences are not significant, and
further examination must be made before a conclusion
can be drawn.

Carbon dioxide (C02) treatment at alevel of 5% v/v
did not effectively negate ethylene action in reducing
ethylene enhanced leaf yellowing (Table 12). The reason
for this is not clear. Kays, 23 a1. (1976) found similar
results with pepper transplants and leaf abscission.

The action of endogenous ethylene as the factor respon-

sible for leaf yellowing during 96 hours in the dark was

69

also not affected by the presence of 5 percent C02.
There is no clear indication of CO2 inhibition of leaf
abscission although less leaf abscission was observed in

the presence of CO at 0 and 0.1 ul/liter of ethylene.

2
More experimentation is necessary to validate this point.

The injury or death to flower parts (Heck and
Pires, 1962) following ethylene treatment is well estab-
lished (Abeles, 1967; Tjia, 33 31., 1969). Flowering
date was particularly affected by treating plants with
exogenous ethylene (Table 7). Flowering date was inhib-
ited by seven days at 0.1 ul/liter and did not vary
significantly from this at l or 10 ul/liter ethylene.
This may indicate that the threshold for ethylene action
on this parameter is quite low and in keeping with other
actions of ethylene shows no further activity beyond the
saturating level. A possible action of ethylene would be
bud abortion, but the flowers once formed seemed normal
in outward appearance.

If ethylene is a contributing factor in leaf
senescence during transit, a source of ethylene produc-
tion needs to be present to produce concentrations high
enough to cause damage. Healthy plants produce ethylene
at low rates and diseased or injured plants produce much
more (Williamson, 1949; Jackson and Osborne, 1970). Kays,
33 31. (1976) found pepper transplants produced ethylene

in darkness while enclosed accelerating leaf abscission.

70

However, in lime plants whose leaves abscised in
enclosed containers shipped from Florida contained no
detectable ethylene. In the present work, ethylene
production in plants shipped from Florida (Table l)
depended on the type of container used and the tempera-
ture of the shipment. Reflecting a slower metabolism
rate, ethylene generally decreases as the temperature is
dropped. This is significant only in EPS containers
when precooled and stored at 10°C. EPS containers
accumulated more ethylene at the two highest tempera-
tures than regular containers. The EPS containers' lack
of ventilation could be the reason for the accumulation.

In experiment 5 ethylene production generally
decreased with exposure to darkness. The effect of dark-
ness was also influenced by the way the plants were
watered. Ethylene production by drought stressed plants
decreased the fastest (Table 13). Morton and Watson
(1948) found in sugar beets under a low water situation
when transferred to high water condition had less leaf
mortality than any other treatment. This supports the
present study and the ethylene data because the seedlings
were transferred to desiccators where humidity was high
which would represent watering. However, dead leaves are
shown to increase in dry regimes only (Table 14).

McAfee and Morgan (1971) found that the leaf

petiole of cotton produced more ethylene when drought

71

stressed. It could be possible that the area around the
abscission zone is producing more ethylene while the
remainder of the plant is decreasing in synthesis causing
a saturation.

Plant height is also the reverse of what might
be predicted (Table 14). Ethylene is known to inhibit
cell elongation (Harvey, 1915; Roberts, 1951). The fail-
ure of drought stressed plants to grow as high as plants
watered adequately may merely reflect a water requirement
as Opposed to any action of ethylene. Plants will

elongate in darkness if provided water.

Literature Cited

 

Abeles, F. B. 1967. Inhibition of flowering in
Xanthium pensylvanicum Walln. by ethylene.
Plant Physiol. 42:608—609.

 

 

Chaterjee, S. K., and A. C. Leopold. 1964. Kinetin and
gibberellin actions on abscission process.
Plant Physiol. 39:334-337.

Flint, H. L., and J. J. McGuire. 1962. Response of
rooted cuttings of several woody ornamental
species to overwinter storage. Proc. Amer. Soc.
Hort. Sci. 80:625-629.

Frank, S., and A. L. Kenney. 1955. Chlorophyll and
carotenoid destruction in the absence of light
in seedlings of Zea mays L. Plant Physiol. 30:
413-418. "‘

Gates, C. T. 1955. The response of the young tomato
plant to a brief period of water shortage.
II. The individual leaves. Australian J. Biol.
Sci. 8:215-230.

Goldthwaite, J. J., and W. M. Laetsch. 1967. Regulation
of senescence in bean leaf discs by light and
chemical growth regulators. Plant Physiol. 42:
1757-1762.

Halevy, A. H., and A. M. Kofranek. 1976. The prevention
of flower bud and leaf abscission in pot roses
during simulated transport. J. Amer. Soc. Hort.
Sci. 101(6):658-660.

Harvey, E. M. 1915. Some effects of ethylene on the
metabolism of plants. Bot. Gaz. (Chicago) 60:
193-214.

Heck, W. W., and E. Gerald Pires. 1962. Effect of

ethylene on horticultural and agronomic plants.
Texas Agr. Exp. Sta. MP613:l-12.

72

73

Jackson, M. B., and D. J. Osborne. 1970. Ethylene, the
natural regulator of leaf abscission. Nature 225:
1019-1022.

Kaltaler, R. E. L. 1962. Environmental factors and
chemical treatments affecting premature senes-
cence of Pelargonium X hortorum Bailey during
shipment. Thesis, Penn. State University.

 

Keys, S. J., C. A. Jaworski, and H. C. Price. 1976.
Defoliation of pepper transplants in transit by
endogenously-evolved ethylene. J. Amer. Soc.
Hort. Sci. 101 (4):449-451.

Kende. 1971. The cytokinins. Int. Rev. Cytol. 31:
301-338.

Kretchman, D. W., and T. H. Short. A preliminary study
on the storage of bare-root tomato transplants.
Ohio Agri. Res. and Dev. Cen. Res. Sum. 57:11-12.

Krone, P. R. 1937. The reaction of greenhouse plants to
gas in the atmosphere and soil. Mich. Exp. Sta.
Spec. Bul. 285:1-35.

Kumpf, J. F. Horton, and R. W. Langhams. 1966. Seedling
storage. N.Y. State Flower Growers' Bul. 244:
1-3.

McAfee, J. A., and P. W. Morgan. 1971. Rates of produc-
tion and internal levels of ethylene in the
vegetative cotton plant. Plant Cell Physiol. 12:
839-847.

Morton, A. G., and D. J. Watson. 1948. A physiological
study of leaf growth. Ann. Botany 12 (47):281-
310.

Mothes, K., L. Engebrecht, and H. R. Schutte. 1961.
Uber die akkumulation von aaminoisobutterséure
im blattgewebe unter dem einfluss von kinetin.
Physiol. Plant 14:72-75. (Cited by Kende, 1970).

Petrie, A. H., J. I. Arthur, and J. G. Woods. 1943.
Physiological ontogeny in the tobacco plant.
Australian Jour. Expt. Biol. Med. Sci. 21:191-
200.

Pryor, R. L., and R. N. Stewart. 1962. Storage of
unrooted softwood azalea cuttings. Amer. Soc. of
Hort. Sci. 82:483-484.

74

Roberts, D. W. A. 1951. Some effects of ethylene on
germinating wheat. Can. J. of Bot. 29:10-25.

Saltveit, M. 1978. Personal communication. Michigan
State University.

Schneider, E. F. 1964. Survival of rooted cuttings of
three woody plant species after low temperature
storage. Amer. Soc. of Hort. Sci. 87:557-562.

Snyder, W. E., and C. E. Hess. 1955. Low temperature
storage of rooted cuttings of nursery crops.
Proc. Amer. Soc. Hort. Sci. 67:545-548.

Tjia, B. O. S., M. N. Rogers, and D. E. Hartley. 1969.
Effects of ethylene on morphology and flowering
of Chrysanthemum morifolium Ramat. J. Amer.
Soc. Hort. Sci. 94:35-39.

Vickery, H. G. 1956. The capacity of leaves of
Byrophyllune calycinum to recover from prolonged
exposure to darkness or to light. Plant Physiol.
31:455-464.

 

, G. W. Pucher, A. J. Wakeman, and C. S.
Leavenworth. 1937. Chemical investigations of
the tobacco plant. Vi. chemical changes in
light and darkness. Conn. Agr. Expt. Sta.

(New Haven) Bul. 399:757—828.

Williamson, C. E. 1950. Ethylene, a metabolic product
of diseased or injured plants. Phytopathology
40:205-208.

SECTION TWO

THE EFFECT OF BENZYLADENINE ON SEEDLINGS

OF PELARGONIUM X HORTORUM BAILEY.

 

75

THE EFFECT OF BENZYLADENINE ON SEEDLINGS

OF PELARGONIUM X EQRTORUM BAILEY.

 

Abstract. BA (10 -4M) applied as a foliar spray
when applied to geraniums decreased yellowing of plants
held in the dark and reduced plant height, but 48 percent

of the leaves on these plants were damaged by BA.

 

The market for seed geraniums to commercial
growers is relatively new. A problem of this new market
is transit induced senescence typified by leaf yellowing
and abscission in transit or after transplanting
(Carlson, 1977). This study was conducted to determine
if a foliar application of the cytokinin, benzyladenine,
would alternate senescence development of seed geraniums
during simulated transit conditions.

Kinetin markedly delays senescence of excised
leaves. This was first demonstrated by Richmond and
Lang (1957). Cytokinins, N6 benzylamino purine (BA) and
kinetin, also delay senescence in intact wheat seedlings
induced to senesce by darkness (Wittenbach, 1977), and
in bean plants induced to senesce by natural fruiting
(Fletcher, 1969).

76

77

Pre- or post-harvest applications of cytokinins
delay senescence of green vegetables such as broccoli
(Dedolph, 33 31., 1962). Also, leaf abscission and
senescence in pot roses has been delayed by cytokinins
(Halevy and Kofranek, 1976).

The present study investigated the effect of BA
applied to seedlings geraniums as a treatment prior to
simulated shipment in the dark for several days in an
attempt to prevent or attenuate leaf senescence. Treat-
ment of seed geraniums with BA could then serve as a
simple treatment, by growers and shippers to maintain

the quality of the plants during shipment.

Materials and Methods

 

Experiment 1 - Seventy day old seed geraniums

 

(cv. Sprinter Scarlet) from Sun City, Florida, were
grown in East Lansing, Michigan, for 14 days. Leaves
were removed from the second and third node and surface
sterilized with 10 percent ethanol. Leaf disc with a
1/2 cm. radius were cut from intervenial areas and
transferred to petri dishes containing a 5 ml aqueous

4 5 6

solution of BA at o, 1 x 10' , 1 x 10' , 1 x 10' ,

1 x 10'7

M and a filter paper. Leaves were placed on 4
blocks according to size with 5 leaves per block. One
disc per leaf was cut for each treatment. All procedures

were carried out in a sterile transfer hood using sterile

78

materials autoclaved for 20 minutes at 115°C, and
instruments were flamed between transfers. Petri dishes
were then wrapped in aluminum foil to exclude light and
placed in a 20°C chamber for six days. Chlorophyll was
extracted in 80% ethanol, 5 ml/S sections, using a 75-
80°C water bath until the leaf discs were bleached (30-
45 minutes). The optical density was determined at 665
nm using a spectorphotometer and the data are expressed

as percent of the control (0 [BA]).

Experiment 2 - Seventy day old plants from Sun

 

City, Florida were grown for 21 days in East Lansing,
Michigan. Expanded polystyrene trays consisting of
seventy two cubes per tray were used as a growing con-
tainer. Each cube was 5 cm. deep, 3.7 cm. square at the
top, tappering to 0.94 cm. at the base, and 1.5 cm.
apart. Trays were cut into sections containing nine
plants.

Plants were treated by spraying leaves and stems
in benzyladinene solutions at concentration of 0,

4 5 M, l x 10"6 M, containing 0.1

1 x 10’ M, 1 x 10'
percent tween 20. Twelve hours after treatment plants
were placed in 10 liter desicators in a growth chamber
at 20°C. Ethylene concentration in the treatment

chambers was monitored by gas chromatography employing a

79

flame ionization detector and a column of activated

alumina using N as the carrier gas.

2

Results and Discussion

 

There was no significant difference in chloro-
phyll degradation found between water and any BA concen-
tration. However, the control is less than any BA
treatments (Table 1). BA reduced chlorophyll degradation
slightly in leaf disc exposed to six days of darkness.
This has been well supported in several species (Richmond
and Lang, 1957; Suguira, 3E 31., 1962; Leopold and

Kawase, 1964).

TABLE 1.--Effect of BA on chlorophyll degradation of
geranium leaf discs exposed to 6 days of dark.

 

 

Benzyladenine Chlorophyll
[M] (% of control)

0 (control) 100

1 x 10"7 32.5

1 x 10"6 49.7

1 x 10'5 40.0

1 x 10"4 42.7

 

2No significant difference was found by the F-
test at the 5 percent level.

Intact bean plants have been shown to be higher

in RNA, protein and chlorophyll if BA (30 mg/l) was

80

painted on leaves before (Fletcher, 1969). In the case
of potted roses in transit, an application of BA was
found to reduce leaf senescence and abscission (Halevy
and Kofranek, 1976). In the present work, leaf yellow-

4 M BA (Table 2). The percentage

ing was reduced by 10-
of dead leaves was not affected by the treatment (Table
2). Plant height (Table 2) was also reduced which is
an advantage, because control of plant height is a prob-
lem in seedling geranium production. The one problem
encountered was a damage of 48 percent of the plants at
10.4 M. Other cytokinins (natural) may not have this
toxic effect. Therefore, further investigation into

. this area is necessary before any conclusions can be

made.

81

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Literature Cited

 

Carlson, W. H. 1977. Personal communication. Michigan
State University.

Dedolph, R. R., S. H. Wittger, V. Tuli and D. Gilbart.
1962. Effect of N -benzylamino purine on respira-
tion and storage behavior of broccoli. (Brassica
oleracea var. Italica). Plant Physiol. 37:509-

Fletcher, R. A. 1969. Retardation of leaf senescence by
benzyladenine in intact bean plants. Planta. 89:
1-8.

Halevy, A. H., and A. M. Kofranek. 1976. The prevention
of flower bud and leaf abscission in pot roses
during simulated transport. J. Amer. Soc. Hort.
Sci. 101(6):658-660.

Leopold, A. C., and M. Kawase. 1964. Benzyladenine effects
on bean leaf growth and senescence. Am. J. Bot.
51:294-298.

Richmond and A. Lang. 1957. Effect of kinetin on pro-
tein content and survival of detached Xanthium
leaves. Science 125:650-651.

Sugiura, M., K. Umemura, and K. Oota. 1962. The effect
of kinetin on protein level of tobacco leaf
disks. Physiol. Plant. 15:457-464.

Wittenbach, V. A. 1977. Induced senescence of intact

wheat seedlings and its revesibility. Plant.
Physiol. 59:1039-1042.

82

SUMMARY AND CONCLUSIONS

From the simulated shipping treatments, transit
at cooler (2° - 10°C) temperature slows senescence and
ethylene synthesis. Shipping containers with ventilation
reduce ethylene synthesis.

Transit should be as short as possible, because
darkness has been shown to enhance damage while delaying
flowering by as much as 1 week.

Ethylene at concentrations as low as 0.1 ul/liter
causes a later flowering date delaying the crop. Ethylene
also caused leaf yellowing at 0.1 ul/liter for 48 hours,
and at 1-10 ul/liter for 12 to 48 hours. Production of
ethylene is not shown in darkness. However, this may be
due to the drop in ratio ethylene products of the whole
plant versus ethylene production of the abscission zone.

BA (10 -4M) can delay senescence, while reducing
plant height. However, 48% of the leaves were damaged
by this high of a concentration. Investigations of
other cytokinins may not cause damage and should be

further investigated.

83