Role of Indoleacetic Acid and Abscisic Acid in the Correlative Control by Fruits of Axiliary Bud Development and Leaf Senescence' - Plant Physiology
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Plant Physiol. (1981) 68, 476-481
0032-0889/81/68/0476/06/$0O.50/O
Role of Indoleacetic Acid and Abscisic Acid in the Correlative
Control by Fruits of Axiliary Bud Development and Leaf
Senescence'
Received for publication June 27, 1980 and in revised form February 19, 1981
IMRE A. TAMAS AND CAROL J. ENGELS2
Biology Department, Ithaca College, Ithaca, New York 14850
STUART L. KAPLAN3, JIM L. OZBUN4, AND DONALD H. WALLACE
Department of Vegetable Crops, Cornell University, Ithaca, New York 14853
ABSTRACT bud growth by fruits may affect overall plant size and the harvest
index (29). Fruit-induced leaf and plant senescence controls the
When fully filled pods of bean plants were deseeded, the rate of axillary duration of leaf activity and of overall plant life in monocarpic
bud growth and the chlorophyll content of leaves were increased. Applica- plants (19). The effect of fruits on the development of other fruits
tion of 0.1% indoleacetic acid (IAA) in lanoUn on the deseeded pods caused seems to be a means of competition among fruits (30), and may
abscission of axillary buds, inhibited growth of the remaining buds, and serve to regulate the number of fruits per plant.
decreased leaf chlorophyll content. The response of bud develpment to The mechanism of correlative control by fruits is not known. A
fruit-applied IAA was concentration dependent between 0.001 and 0.1% role for AbA in the correlative control of axillary bud and fruit
IAA (representing from 2 to 200 micrograms IAA per fruit) resulting In development was indicated when fruit removal caused a decrease
greater growth inhibition at higher IAA concentrations. of the AbA concentration in axillary buds (29) and also in other
When plants were defruited so that the number of fruits per plant was fruits remaining on the plant (30) along with an increase in
adjusted to 0, 6, 12, or 18, a dosage effect of fruits on photosynthesis was rate of development of these structures. The suggestion that AbA
the
observed. Removal of all fruits caused a rise in the C02-exchange rate may serve as the
(CER). With increasing fruit dosage, plants showed leaf senescence of applied AbA to promote leaf
correlative signal (19) was based on the ability of
senescence and on the increase in
increasing intensity and a corresponding decline in CER. In contrast to the endogenous AbA level in senescing leaves (16). The presence
the effect of fruit-applied IAA on leaves and buds, it delayed the senescence of AbA in phloem tissue (11) indicates the occurrence of long
of treated fruits. When axillary buds were treated directly with aqueous distance transport of AbA. On the other hand, there was no
solutions of IAA, no growth inhibition occurred. correlation between the AbA content of fruits and their ability to
Abscisic acid (AbA) applied on deseeded pods, up to a concentration of suppress the growth of axillary buds (29) suggesting that AbA was
0.1% AbA in lanolin, failed to inhibit axillary bud development or to cause not the correlative signal released by fruits. Similarly, AbA was
leaf senescence. unable to replace the controlling effect of the apex. When the
The results support the hypothesis that the correlative control of axillary apical meristem of tomato was treated with AbA, lateral bud
bud development and leaf senescence by fruits involves the participation of growth was stimulated, rather than inhibited (34).
both IAA and AbA. IAA, released by the seeds, may play the role of the Wareing and Seth (37) showed that the senescence of bean
correlative signal that moves from the fruit to the target organ, where it leaves was decreased upon the excision of seeds, but was restored
stimulates the synthesis or accumulation of AbA. AbA, in turn, may be by the application of IAA to the deseeded pods. Assuming that
responsible for the inhibition of axiliary bud development and the enhance- seed tissue is typically rich in IAA (2, 9, 23), this finding suggests
ment of leaf senescence. the possibility that fruits control the development of other organs
through the agency of IAA as the correlative signal. The present
work explores the role of IAA and AbA in the correlative control
of axillary bud growth and leaf senescence by fruits.
MATERIALS AND METHODS
Fruits appear to play a major role in the correlative control of Plant Material. Bean seeds (Phaseolus vulgaris L. cv. Redkloud)
growth and development of other organs. The presence of fruits were sown in pots containing a mixture of equal amounts of top
has been shown to inhibit axillary bud growth (29), enhance soil, peat moss and vermiculite, and fertilized weekly with a 0.24%
senescence in leaves (14, 19, 20, 37) and apical meristems (17), (w/v) solution of a commercial fertilizer containing 20%Yo each of
and inhibit development of other fruits (30). Control of axillary total nitrogen, phosphoric acid and soluble potash. The plants
were grown in a controlled environment growth chamber at 28 C
'This work was supported in part by a grant from the Rockefeller day and 22 C night temperature, and 60 to 70%/o RH. Sixteen hours
Foundation. of daily illumination by fluorescent tubes (equal number of Cool
' Present address: Department of Pediatrics, Albert Einstein College of White and Gro-Lux tubes [Sylvania, Danvers, MA]) was supple-
Medicine, Bronx, New York 1046 1. mented by a small amount of incandescent light (eight 100-w
3 Present address: Department of Agronomy, University of Wisconsin, bulbs over a 1.4 -m2 area), providing a total energy of about 5 x
Madison, Wisconsin 53706. 104 ergs cm-2 s-'.
4 Present address: Department of Horticultural Science and Landscape Effect of Fruit-Applied IAA or AbA on Axillary Bud Develop-
Architecture, University of Minnesota, Saint Paul, Minnesota 55108. ment, Leaf Chi Content and Fruit Senescence. Plants were selected
476
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Copyright (c) 2020 American Society of Plant Biologists. All rights reserved.Plant Physiol. Vol. 68, 1981 IAA-AbA-CORRELATIVE EFFECTS OF FRUITS 477
at the stage of fully filled pods. All plants in a given experiment
were trimmed to six fruits per plant unless otherwise noted and
the seeds were removed. Inside each deseeded pod a measured 0~
0
amount of anhydrous lanolin paste containing IAA or AbA was - 2.0
spread evenly over the entire pod cavity. Pods of control plants
were also deseeded and treated with lanolin without hormone. oh.. -1
0
1.
There were three plants per treatment. To reduce viscosity, the 0' 1.0
lanolin paste was warmed to between 25 and 30 C and applied
with a glass syringe without a needle. At the time of treatment ,. 0.5
(day 0) and at intervals thereafter, the number and length of all CPx
axillary buds on a plant were determined. Total bud length per 0 2 4 6 8 10
plant represented the combined length of all buds present on a
given day. Mean bud length was obtained by dividing the total Leaf color score
bud length with the number of buds present. The data were FIG. 1. Relationship between Chl content of leaves and the visual color
expressed as the percentage of the value on day 0. score. Chl concentration was determined according to Arnon (I) on 4
To monitor leaf Chl content, all leaves on a plant were color- separate days and plotted against the subjective color score of individual
scored visually at intervals on a scale of 0-10 (0-yellow; 10-dark leaves on a scale from 0 (yellow) to 10 (dark green). X, Trial 1; 0, trial 2;
green) and the mean color score per plant was calculated. For El, trial 3; A, trial 4. The combined mean was derived from the data of all
each scoring, four leaf samples of varied color were also harvested, four trials and was plotted using regression analysis.
weighed, and extracted with 80%o (v/v) acetone, and their Chl
content was determined according to Arnon (1). Fruit senescence fresh leaf weight. These results show that visual color scoring can
was determined by visual scoring (0-dry; 5-yellow; 10-green) of give relative estimates of the Chl content of leaves. The method is
each fruit on a plant followed by calculation of the mean fruit semi-quantitative if the Chl content of representative samples is
score per plant. determined.
Effect of Bud-Applied IAA on Bud Growth. A series of IAA Effect of the Removal of Seeds or Fruits on Axillary Bud
solutions, including 0, 1, 10, 100 and 1000 ,pm IAA, were prepared Development, CER, and Leaf Senescence. Deseeding the fruits
in 0.01% (v/v) Tween 80. All plants were completely defruited, caused a slight but satistically insignificant increase in both num-
and 5 jd of one of the IAA solutions containing 0, 0.88, 8.8, 88 or ber and mean length of axillary buds (Fig. 2, A and C). The total
880 ng IAA was applied to each axillary bud. The droplet of IAA bud length on deseeded plants (Fig. 2B) was increased significantly
solution was placed on the tip of the bud without contacting the over that of the intact controls (as judged by the size of the critical
base. Two plants were treated with each IAA concentration. Bud value) thereby reflecting the combined effects of increased bud
length was monitored as described above. number plus greater average bud length. Leaves of plants with
Effect of Fruit Removal on CER.' Four plants at the age of 36 deseeded fruits doubled their Chl content within 2 weeks after
days were selectively defruited (day 0), leaving either 0, 6, 12 or seed removal (Fig. 2E), whereas the leaves of control plants
18 fruits on each plant. CER of the center leaflet of each of the maintained a steady Chl concentration. The effect appeared to be
same four leaves per plant was measured (as mg CO2 dm-2 h-1) highly significant (see critical values) and uniform throughout the
every 2 or 3 days using an IR gas analyzer as described previously plant.
(8, 22). The measurements were made at a CO2 concentration of There was a dosage effect of fruit load on CER (F = 3.5, P =
355 ± 10uI CO2 1-1 air, 8.5 x 104 ergs cm-2 s-' light intensity, 0.000). Removal of all fruits caused a more than two-fold increase
50% RH and 27 C air temperature. Results were converted to the in CER in about 13 days, and a rate substantially above the
percentage of the value on day 0. original level was maintained for over 3 weeks (Fig. 3A). With 12
Statistical Analysis. The effects of fruit removal and hormonal or 18 fruits per plant, CER started to decline after about 2 weeks,
treatment were evaluated by analysis of variance using the com- and dropped to zero during the subsequent 2-week period (Fig.
puter program BMDP2V (developed at the Health Sciences Com- 3B). CER in both of these groups differed significantly from that
puting Facility, University of California, Los Angeles, revised in the defruited group throughout the 3rd and 4th week of the
April 1977) (5). F-values, with their associated probabilities, are experiment. Decreases in CER resulted from leaf senescence as
shown for treatment-time interactions. Critical values (mean), evidenced by a gradual loss of green color which was slower at a
denoting the minimum significant difference between means at lighter fruit load. For plants with only 6 fruits, CER was still
the 0.05 level of confidence, were calculated according to Cicchetti above 50% of the original value 4 weeks after the removal of the
(4). Regression analysis was done with the help of the computing other fruits (Fig. 3A).
program MINITAB II (24). Effects of Fruit-Applied IAA on Bud Development and Leaf
Senescence. Treating deseeded fruits with 0.1% IAA in lanolin
RESULTS caused almost complete inhibition of axillary bud growth (Fig.
2C). Senescence of bud tissue also occurred, resulting in extensive
Visual Scoring of Leaf Senescence. Scores between zero (yel- bud abscission (Fig. 2A). The combined total bud length per plant
low) and ten (dark green) for leaf color were plotted against dropped 80%1o within 2 weeks (Fig. 2B). In contrast, total bud
measured Chl contents of the leaves (Fig. 1). For each of the four length increased by about 170%o for deseeded fruits not treated
trials and for the combined data, R-values of 0.96 to 0.99 indicated with IAA. IAA also caused a 60%1o loss of leaves, and over 70% loss
high linearity between color score and the Chl content (R-values of Chl from the remaining leaves, indicating accelerated leaf
at to.om are significant above 0.95 for individual trials, and above senescence (Fig. 2, D and E). All the effects of IAA were highly
0.50 for the combined slope). The 95% confidence limit of the significant, as shown by the F-values and associated probabilities
regression slopes (0.19 to 0.28) of three of the four trials (Nos. 1, (for all effects, F _ 8, P _ 0.007 [time-IAA interaction]), and by
2, and 4) included the combined slope of 0.222. Similarly, the 95% the critical values shown on Figure 2. About 2 weeks after IAA
confidence limits of the mean Chl values of two trials (Nos. I and treatment of deseeded fruits, the difference between IAA-treated
4) included the combined mean value of 1.13 mg Chl per gram
and untreated plants in bud number, total bud length, leaf number
and Chl content was at least three times greater than the critical
5 Abbreviation: CER: C02-exchange rate. value (Fig. 2).
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Copyright (c) 2020 American Society of Plant Biologists. All rights reserved.478 TAMAS ET. AL. Plant Physiol. Vol. 68, 1981
I I I
250
150 O-
0) 200
a 9 E0
p100 lSO
10
0
CP
c
m 50 100
0
x
0 N
50
0
0
s 250 0
i i i i i
c'
_ _ 200 250 -
150
200
0
30 0
c 150
_a 100
o 50 4-
0) 100
_ 50 &
C 50
0
0
0
C 200
0 5 10 15 20 25 30
R
I 50
Time from fruit removal
100
(days)
o
0 50
FIG. 3. Photosynthesis in bean leaves as influenced by fruit removal.
0 5 10 15 I 0 5 10 15 Four 36-day-old plants were defruited leaving either 0, 6, 12 or 18 fruits
on each plant. CER of the center leaflet of the same four leaves on each
Ti me from treatment (days) plant was measured at 2 or 3 day intervals, and the mean CER value for
FIG. 2. Axillary bud development and leaf senescence as influenced by each plant was calculated for each date. Measurements were at a CO2
fruit-applied IAA. The number of fruits was adjusted to eight fruits each concentration of 355 ± 10 Pl CO2 1' air, 8.5 x 104 ergs cm-2 s-' light
on 47-day-old plants (day 0). On one group of plants, all fruits were split intensity, 50%o RH and 27 C leaf temperature. The number of fruits per
lengthwise, deseeded, and treated with 0.1 ml of 0.1% (w/w) IAA (con- plant was: x, 0; 0, 6; E, 12; A, 18. Results are expressed as the percentage
taining 100 ,ug IAA per fruit) in lanolin (0) or with 0.1 ml lanolin without of the CER value on day 0 (about 22 mg CO2 dm-2 h-'). Vertical bars
IAA (A). Fruits of a third group of plants (controls) were split lengthwise represent critical values (means), shown where significant difference exists
without injuring the seeds and treated with 0.1 ml lanolin (x). Results are among treatments.
the mean from three plants, expressed as the percentage of the value on at any IAA concentration (F = 0.93, P = 0.56; see also critical
day 0 (about seven buds per plant with a mean length of about 12 mm). value in Fig. 6B). IAA treatment did not affect the number of
Each vertical bar represents the critical value (means), equal to the axillary buds.
minimum significant difference between means. These are shown where
treatments differ significantly at the 0.05 level of confidence.
DISCUSSION
As the IAA concentration increased from 0.001% to 0.1% (rep- When bean fruits were deseeded, the growth rate of axillary
resenting from 2 to 200 jig IAA per fruit) there was a gradual buds and also the Chl content of leaves were all increased.
decrease in bud number (Fig. 4, A and B), and in the mean and Application of IAA to these deseeded pods not only prevented
combined bud lengths (Fig. 4, C, D, E, and F). The differences these responses, it greatly inhibited bud growth and accelerated
due to IAA treatment became significant after about 2 weeks. bud and leaf senescence. The IAA effect on bud development
In contrast to the increased senescence of leaves and buds, there increased with dosage per bud, and leaf senescence was accelerated
was delayed senescence of IAA-treated pods. Deseeded pods with increasing fruit load per plant. These data suggest that IAA
treated with 0 or 0.001% IAA started to senesce after 1 week and is a correlative signal that originates from the seeds and controls
were completely dry after 2.5 weeks but 0.1% IAA delayed the development in buds and leaves.
onset of senescence significantly by several days and kept the pods Seed tissue has been shown to be rich in IAA in many plants,
partially green until the end of the experiment at 16 days (Fig. 4, including corn (2, 9), peaches (23), soybeans, oats, and beans (2).
G and H). Treatment with 0.0 1% IAA appeared to have an The observation that seed removal eliminates the controlling effect
intermediate, but statistically insignificant, effect (Fig. 4H). of fruits over buds and leaves agrees with the proposed role of
Effect of Fruit-Applid AbA on Bud Development. Fruit-applied IAA as a correlative signal. There is ample evidence indicating
AbA did not cause inhibition of bud development in contrast with that IAA serves as a correlative signal in apical dominance (31-
the effect of IAA. There was slight reduction in bud number, bud 33, 35, 36, 38). Furthermore, Sorrells et al. (28) found that injection
length and pod color at certain AbA concentrations (Fig. 5), but of the IAA-transport inhibitor N- I naphthylphthalamic acid into
none of these changes were statistically significant since they were corn stem between two ears stimulated lower ear development
smaller than the critical values. suggesting that IAA is involved in upper ear dominance over the
Effect of Bud-Applied IAA on Bud Growth. Whereas fruit- lower ear.
applied IAA strongly inhibited axillary bud growth, placing IAA Efficient movement within the plant is a necessary attribute of
solution directly on the tip of the bud had the opposite effect (Fig. the correlative signal when distance of the target organs (buds and
6, A and B). All concentrations tested, between 1 and 1000 Mm leaves) from the dominant organs (fruits) and their wide distri-
IAA (representing from 0.88 to 880 ng IAA per bud), appeared to bution on the plant are considered. Rapid, long-distance transport
stimulate bud growth. However, due to the variability of the data, of IAA occurs in phloem tissue (3, 7), satisfying this requirement.
statistically significant stimulation of bud growth was not observed Hein et al. (10) demonstrated a large amount of IAA transport
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Copyright (c) 2020 American Society of Plant Biologists. All rights reserved.Plant PhYSiOl. VOl. 68,1981 IAA-AbA-CORRELATIVE EFFECTS OF FRUITS 479
. . . . .. . w w
-0- 140
*0
120 %4 +fI
100 A.
1700 .
.0--900
500
o 100
I I
1300
, 900 A
_0
500-
. .
0 0
I0 .
0 G 'l H I
0
0
1-
5
in
U._ 0,
0 5 10 151 0
:
5 10
. _
15
. .
0 5 10 1510 5 10 IS
Time from first treatment (days) Time from first treatment (doys)
FIG. 4. Bud development and fruit senescence as influenced by the FIG. 5. Bud development and fruit senescence as influenced by the
concentration of fruit-applied IAA. Fruit number was adjusted to six fruits concentration of fruit-applied AbA. The experimental methods and num-
each on 49-day-old plants (day 0). All fruits were deseeded and treated ber of plants were the same as in Figure 4, except AbA replaced IAA. A
with 0.2 ml of lanolin paste containing IAA at one of four concentrations. to H, see Figure 4. AbA concentrations in lanolin (%): x, 0; 0, 0.001; 0,
Three plants were used with each IAA concentration. The number and 0.01; A, 0.1. These represent, respectively, 0, 2, 20 and 200 Mg AbA applied
length of axillary buds were determined at intervals and reported as the per fruit. Vertical bars are critical values (means) included to show the
percentage of the value on day 0. Fruit senescence was monitored by absence of significant difference among treatments.
visual scoring (0, dry; 5, yellow; 10, green). A and B, number of buds per
plant; C and D, combined total bud length per plant; E and F, the mean
length of existing buds on a plant; G and H, visual score of fruit senescence. Soo 5
IAA concentrations in lanolin (%): x, 0; 0, 0.001; 0.01; A, 0.1. These
El,
~Too0 A B
represent, respectively, 0, 2, 20, and 200 ,ug IAA applied per fruit. Vertical
600
bars are critical values (means), shown where significant difference exists C
among treatments. *500
.~400-
through debladed petioles of soybeans into EDTA-containing .o300
solutions. The transport rate was three times greater in plants with C200
pods attached than in depodded plants, indicating that fruits
supply IAA to leaves and possibly also to other organs. The 100
behavior of the hypothetical "senescence signal" from soybean 0 5 10 20 0 5 10 20
fruits (19) shows certain characteristics expected of IAA. The Time from treatment (days)
signal seems to be released from seeds and it initiates leaf senes-
cence during the period of most rapid seed growth. Leaves senesce FIG. 6. Bud growth as influenced by the concentration of bud-applied
below but not above the fruits of partially defruited plants sug- IAA. Plants were defruited at 43 days of age (day 0), and each axillary
gesting that the senescence signal is transported basipetally (20). bud was treated with 5 ,ul of one of five IAA concentrations in 0.01% (v/
Labeled IAA, injected into young fruits of broad-bean plants, has v) Tween 80 (day 0). The number and length of buds were determined at
been shown to move in the stem mainly in a basipetal direction intervals. A and B, mean length of axillary buds. IAA concentrations
(3). (uM): X, 0; 0, 1; 10; A, 100; *, 1000. These represent, respectively, 0,
El,
The mechanism through which IAA from fruits controls the 0.88, 8.8, 88 and 880 ng IAA applied per bud. Results are expressed as the
development of other organs is not known. In previous work, it percentage of the bud length on day 0, and represent the mean obtained
was observed that fruits suppressed the development of axillary from two plants. Vertical bars are critical values (means), included to show
buds (29) and of other fruits (30). Removal of the dominant fruits the absence of significant difference among treatments.
reversed these effects and caused decline of the AbA concentration
in the target tissues. When AbA was applied to axillary buds, bud opment when applied to deseeded fruits. Treating axillary buds
growth was inhibited (29). These results suggested that AbA may directly with IAA did not inhibit bud growth. Therefore, the
play a role in correlative inhibition. In the present work, however, mechanism of control may involve synthesis and export of IAA
only IAA, but not AbA, was able to inhibit axillary bud devel- from the fruits, stimulation by IAA of AbA synthesis or accumu-
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Copyright (c) 2020 American Society of Plant Biologists. All rights reserved.480 TAMAS ET. AL. Plant Physiol. Vol. 68, 1981
lation in the target tissue, and evocation by AbA of developmental in the regulation of bud growth by fruits. This suggests that the
effects in the target tissue. correlative control of axillary bud growth by the apical meristem,
That leaf senescence involves auxin-stimulated synthesis of a and also by fruits, may be viewed as two essentially similar
senescence factor is supported by the finding of Osborne (21) that phenomena mainly differing in the source organ of.the correlative
treatment of a small area of the leaf blade with ester of 2, 4-D signal. In young plants the growing vegetative apex is the domi-
caused senescence in the surrounding tissue while the treated nant structure, whereas, in mature plants the fruits become the
portion remained green. Spreading of the senescing area led to source of correlative influence. Control is eventually extended
yellowing of the complete leaf blade except the treated area. From over the development of several organs including axillary buds,
these results Osborne concluded that some product of auxin- leaves, and other fruits. The extent to which these phenomena
stimulated metabolism moved outwards and induced the senes- share a common hormonal mechanism requires clarification.
cence of the surrounding tissues. Osborne proposed that the action In soybeans the removal of flowers and fruits starting at mid-
of this product must be antagonized by auxin since the tissue bloom inhibited leaf photosynthesis (18), apparently as a result of
directly treated with auxin did not senesce. Osborne's hypothesis AbA accumulation and consequent stomatal closure (26). At a
would explain why correlative effects of IAA, imposed from later stage of development starting about 45 days after midbloom,
distant organs, result in growth inhibition and senescence of the defruiting also delayed Chl loss and leaf senescence (18). Evi-
target organ, whereas, direct treatment with IAA or a rise in its dently, these two effects of defruiting on soybean leaves occurred
endogenous level gives the opposite effect. There are a number of independently of each other at different stages of development
reports describing this seemingly contradictory behavior of IAA. and may be expected to alter the rate of photosynthesis in opposite
The endogenous auxin level in the lateral buds of Viciafaba (32), directions. In soybeans (18) the effect of defruiting on stomatal
Pisum sativum (12) and Brassica oleracea var. gemmifera (33), was closure had the greater impact and caused a net reduction in
found to increase rather than decrease when the buds were re- photosynthesis throughout the duration of the experiment despite
leased from the growth-suppressing effect of the apex after decap- the delay in the loss of Chl that occurred later. In contrast,
itation. The lateral buds of these plants, however, remained in- defruiting at an advanced state of development (when fruits were
hibited if the cut stump was treated with IAA (31-33). When IAA fully grown) in this study caused not only a delay in Chl loss from
was applied directly to buds (young shoots) of pea plants, growth bean leaves but resulted also in increased photosynthetic activity.
stimulation rather than inhibition was observed (25). Similarly, The degree to which these multiple and conflicting effects of
direct application of IAA to axillary buds of bean plants in the defruiting on photosynthesis are influenced by the species and
present study failed to inhibit bud growth. Sachs and Thimann developmental state of the plant needs to be further explored.
(25) noted that auxin treatment caused elongation only when the Acknowledgments-The authors thank B. Gravatt and J. Koch for competent
buds (young shoots) of pea plants were at least 5 to 7 mm long, technical assistance, L. Jones of the Ithaca College Academic Computer Services for
and already had developed internodes. If the buds were small help with statistical analysis, and M. Brenner for reviewing the manuscript.
(31), or the plants were etiolated (15), auxin inhibited bud growth.
These results showed that the nature of growth response of pea LITERATURE CITED
buds was influenced by the developmental state of the buds. The
1. ARNON DI 1949 Copper enzymes in isolated chloroplasts. Polyphenoloxidase in
axillary buds of bean plants in the present study had well devel- Beta vulgaris. Plant Physiol 24: 1-15
oped basal internodes and were about 11 to 13 mm in length, 2. BANDURSKI RS, A SCHULZE 1977 Concentration of indole-3-acetic acid and its
comparable to the pea buds used by Sachs and Thimann (25). In derivatives in plants. Plant Physiol 60: 211-213
both cases, the buds responded to correlative inhibition involving 3. BOURBOULoux A, JL BONNEMAIN 1973 Transport of ["Clauxin from young pods
IAA but were not inhibited by direct IAA application. The way of Viciafaba L. Planta 115: 161-172
4. CICCHETTI DV 1972 Extension of multiple-range tests to interaction tables in the
auxin affects leaf senescence seems to depend also on the site of analysis of variance: A rapid approximate solution. Psychol Bull 77: 405-408
auxin application. Leaves of bean plants were found to show 5. DIXON WJ 1975 BMDP. Biomedical Computer Programs. University of Califor-
increased senescence when fruits were treated with IAA (37), nia Press, Berkeley, pp. 711-760
6. ELIASSON L 1975 Effect of indoleacetic acid on the abscisic acid level in stem
whereas, senescence of soybean leaves was retarded when the tissue. Physiol Plant 34: 117-120
leaves were sprayed with naphthaleneacetic acid (13). 7. GOLDSMITH MH, DA CATALDO, J KARN, T BRENNEMAN, P TRIP 1974 The rapid
The foregoing evidence suggests that IAA may help in mediat- non-polar transport of auxin in the phloem of intact Coleus plants. Planta 1 16:
ing correlative control by fruits over axillary buds and leaves, but 301-317
it does not directly cause bud growth inhibition or leaf senescence. 8. GRAVATT BA, JC O'TOOLE, PM LUDFORD, JL OZBUN 1976 System for measuring
photosynthetic and transpiration rates of intact leaves under controlled condi-
It may accomplish these tasks indirectly through the agency of tions. Lab Pract, May
another growth regulating substance. Osborne's hypothesis (21) 9. HAAGEN-SMIT AJ, WB DANDLIKER, SH WIrTWER, AE MURNEEK 1946 Isolation
suggests the existence of a mobile factor whose synthesis is stim- of 3-indole-acetic acid from immature corn kernels. Am J Bot 33: 118-120
10. HEIN MB, ML BRENNER, WA BRUN 1979 Source/sink interactions in soybeans.
ulated by auxin. Whether such a factor participates in the correl- II. A possible role of IAA. Plant Physiol 63: S43
ative effect of fruits remains to be demonstrated. 11. HOAD GV 1973 Effect of moisture stress on abscisic acid levels in Ricinus
Tucker and Mansfield (36) found a dramatic drop in the AbA communis L with particular reference to phloem exudate. Planta 113: 367-372
content of the axillary buds of Xanthium after decapitation re- 12. JABLANOVIC M, M NESKOVIC 1977 Changes in endogenous level of auxins and
leased the buds from the dominance of the apical meristem. When cytokinins in axillary buds of Pisum sativum L in relation to apical dominance.
Biol Plant 19: 34-39
apical dominance was enhanced by far-red illumination, the con- 13. KAHANAK GM, Y OKATAN, DC RuPP, LD NOODEN 1978 Hormonal and genetic
alteration of monocarpic senescence in soybeans. Plant Physiol 61: S26
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