Abscission Responses to Moisture Stress, Auxin Transport Inhibitors, and Ethephon

The effect of the defoliant thidiazuron (TDZ) on basipetal auxin transport in petiole segments isolated from cotton (Gossypium hirsutum L. cv LG102) seedlings was examined using the donor/receiver agar block technique. Treatment of intact seedlings with TDZ at concentrations of 1 micromolar or greater resulted in a dose-dependent inhibition of 14C-IAA transport in petiole segments isolated 1 or 2 days after treatment. Using 100 micromolar TDZ, the inhibition was detectable 19 hours after treatment and was complete by 27 hours. Both leaves and petiole segments exhibited a marked increase in ethylene production following treatment with TDZ at concentrations of 0.1 micromolar or greater. The involvement of ethylene in this TDZ response was evaluated by examining the effects of two inhibitors of ethylene action: silver thiosulfate, 2,5-norbornadiene. One day after treatment, both inhibitors effectively antagonized the TDZ-induced inhibition of auxin transport. Two days after TDZ treatment both inhibitors were ineffective. The decrease in IAA transport in TDZ treated tissues was associated with increased metabolism of IAA. The transport of '4C-2,4-dichlorophenoxyacetic acid was also inhibited by TDZ treatment. This inhibition was not accompanied by increased metabolism. Incorporation of TDZ into the receiver blocks had no effect on auxin transport. The ability of the phytotropin N-1-naphthylphthalamic acid to stimulate IAA uptake from a bathing medium was reduced in TDZ-treated tissues. This reduction is thought to reflect a decline in the auxin efflux system following TDZ treatment.The timing and extent of leaf abscission is largely determined by the physiological interplay between the leafand the subtending abscission zone. To a large extent, this interplay involves alterations in the levels and activities of endogenous growth substances (1, 6, 9).The manipulation of leaf and other organ abscission continues to be an important aspect of modern agricultural and horticultural practice. Although many chemical treatments have been devised to alter abscission to suit individual needs, all suffer from inherent problems, chief of which is inconsistent performance. It can reasonably be expected that future improvements in the deliberate manipulation of abscission will depend on increased fundamental knowledge of the physiology of the abscission process itself.To this end, a series of investigations has been initiated in this laboratory with the goal of developing a more thorough understanding of the physiology of leaf abscission through the systematic study of the action of a registered defoliant. TDZ' 2 is a recently introduced cotton defoliant. It is unique among defoliants in that it stimulates the premature shedding of seemingly healthy, turgid leaves (so-called 'green-drop'). It has been shown that TDZ treatment of cotton results in a massive and sustained increase in ethylene production and that ethylene is, at least partially, responsible for the subsequent leaf fall (16, 17).It is generally thought (1, 9) t...

Section: Resultssupporting

confidence: 82%

“…Compounds known to disrupt polar auxin transport have been shown to potentiate ethylene action in stimulating leaf abscission (11,12). A decline in polar auxin transport has been found to occur in petiole segments isolated from senescing or water-stressed leaves (5).…”

Section: Introductionmentioning

confidence: 99%

Disruption of the Polar Auxin Transport System in Cotton Seedlings following Treatment with the Defoliant Thidiazuron

Suttle¹

1988

“…Water deficit stress reduces auxin transport capacity (10). When plants subjected to water deficit stress were treated with auxin transport inhibitors and the ethylene releasing compound ethephon, ethephon had the greatest ability to promote abscission (27). This suggests that the effect that low i6w had on auxin transport was near maximal but that ethylene was limiting for induction of abscission.…”

Section: Discussionmentioning

confidence: 94%

Does Water Deficit Stress Promote Ethylene Synthesis by Intact Plants?

Morgan¹,

He²,

Greef³

et al. 1990

Self Cite

120

The effect of plant water deficit on ethylene production by intact plants was tested in three species, beans (Phaseolus vulgaris L.), cotton (Gossypium hirsutum L.) and miniature rose (Rosa hybrida L., cv Bluesette). Compressed air was passed through glass, plant-containing cuvettes, ethylene collected on chilled columns, and subsequently assayed by gas chromatography. The usual result was that low water potential did not promote ethylene production. When plants were subjected to cessation of irrigation, ethylene production decreased on a per plant or dry weight basis of calculation. No significant promotion of ethylene production above control levels was detected when water deficit-treated bean or cotton plants were rewatered. The one exception to this was for cotton subjected to a range of water deficits, plants subjected to deficits of -1.4 to -1.6 MPa exhibited a transient increase of ethylene production of 40 to 50% above control levels at 24 or 48 hours. Ethylene was collected from intact leaves while plants developed a water deficit stress of -2.9 megapascals after rewatering, and no significant promotion of ethylene production was detected. The shoots of fruited, flowering cotton plants produced less ethylene when subjected to cessation of irrigation. In contrast, the ability of bench drying of detached leaves to increase ethylene production several-fold was verified for both beans and cotton. The data indicate that detached leaves react differently to rapid drying than intact plants react to drying of the soil with regard to ethylene production. This result suggests the need for additional attention to ethylene as a complicating factor in experiments employing excised plant parts and the need to verify the relevance of shock stresses in model systems.interest because the ethylene could be responsible for senescence and abscission induced by water deficits (13,25,26).Although the promotion of ethylene synthesis by water deficits appears firmly established, there are a number of concerns. First, to have a convenient experimental system, water deficits have often been imposed rapidly by drying detached leaves or fruits (3-6, 16, 18, 24, 31). In contrast, under natural drought the soil water is depleted slowly and plants progress through a series of drying cycles during which #w3 falls during the day and rises at night as plants recover due to reduced evaporative demand (30). Second, the experimental measurement of ethylene has usually required that detached plant parts be concentrated in a sealed container from which air samples are withdrawn and analyzed for ethylene. The air supply in these containers has often been static which is of some concern because oxygen is needed for the conversion of ACC to ethylene (2) and CO2 can either promote or reduce the production of ethylene (33). Finally, there are a few reports in the literature where investigators failed to observe a promotion of ethylene release with water deficit treatment of intact plants (6,9,13,19).With the development of flowing air sys...

“…Furthermore, the inactive role of ethylene in the mechanism of sealing action in delaying deterioration of lemon and pepper fruits is likely the exception rather than the rule which is that ethylene is greatly involved both as a cause and effect in several water stress phenomena. There are many reports of the enhancement of ethylene production by water stress (1,9,10,22,26,28). Furthermore, ethylene-enhanced production was shown to be the cause of defoliation under water stress as an adaptation by the plant to resist water stress (9,28).…”

mentioning

confidence: 99%

“…There are many reports of the enhancement of ethylene production by water stress (1,9,10,22,26,28). Furthermore, ethylene-enhanced production was shown to be the cause of defoliation under water stress as an adaptation by the plant to resist water stress (9,28). Generally speaking the involvement of the various plant hormones both in water stress and in membrane properties may indicate a possible role for them in the sensing mechanism for water stress (2,10,20,22).…”

mentioning

confidence: 99%

Mode of Action of Plastic Film in Extending Life of Lemon and Bell Pepper Fruits by Alleviation of Water Stress

Ben-Yehoshua¹,

Shapiro²,

Chen³

et al. 1983

129

The mechanism by which seal-packaging individual fruit in high density polyethylene film delays deterioration was ration of other perishable, living fruit items.The control of deterioration of fruit by plastic film had been generally explained by the modification of the concentrations of C02, 02, and ethylene (21). However, this theory was not supported by our data (1O, 13). Endogenous levels ofthe above gases were similar in fruit sealed in HDPE or not sealed, but their rates of physiological deterioration were altogether different. The major effect of sealing appears to be the provision of a watersaturated microatmosphere (8). This may alleviate water stress, which is important in controlling life processes (15, 20). However, so far only the inhibition of transpiration, shrinkage, and shriveling has been ascribed to the high humidity that is found in the microatmosphere of the sealed fruit (21). Therefore, we set out to investigate the hypothesis that sealing delays deterioration of lemon and bell pepper fruits by alleviating water stress. The importance of transpiration as a major process leading to physiological deterioration of citrus fruit has been demonstrated (7). This paper reports our attempts to relate water stress to various physiological parameters in sealed and nonsealed fruit. Lemons and peppers were selected for these studies because they responded very favorably to the seal-packaging technique. These fruits do not have the marked ripening and climacteric processes that could disturb our objective by masking the effects of the sealing per se on fruit behavior. Among the various techniques developed to extend fruit postharvest life, the use of plastic film is growing in importance because it is convenient in the many different conditions throughout the chain of handling from producer to consumer (8, 21). Ben-Yehoshua (8) found that seal-packaging individual fruit with a thin film ofHDPE2, 5 to 15 ,m in thickness, doubled storage life of various fruits. The flavor of the fruit was not spoiled; on the contrary, the sealed fruit maintained its normal flavor, as well as its firmness and fresh appearance for at least twice as long as nonsealed fruit. Surprisingly, sealed citrus fruit kept at 20C lost less weight and was firmer than nonsealed fruit at optimal (lower) temperatures.Seal-packaging delayed several parameters of physiological deterioration of fruit better than cooling; which is usually considered the best means of delaying senescence of detached living organs (1 1, 21). Accordingly, it is hoped that the elucidation of the mode of this action of seal-packaging would also help better understand the mechanism of senescence of detached plant organs and their causes. Such information might also be useful 2Abbreviations: HDPE, high density polyethylene; WSA, water-saturated atmosphere; WSD, water saturation deficit; AIS, alcohol-insoluble solids. In one pepper experiment, two other treatments were performed: WSA and sealed atmosphere with around 85% RH. The WSA was obtained by placing no...