Auxin Transport as Related to Leaf Abscission during Water Stress in Cotton

Abstract

Plant water deficits reduced the basipetni transport of auxin in cotyledonary petiole sections taken from cotton (Gossypium hirsutum L.) seedlings. A pulse-labeling technique was employed to eliminate complications of uptake or exit of "4C-indoleacetic acid from the tissue. The transport capacity or the relative amount of radioactivity in a 30-minute pulse which was basipetaUly translocated was approximately 30% per hour in petioles excised from well watered seedlings (plant water potentials of approximately -4 to -8 bars). No cotyledonary leaf abscission took place in weUl watered seedlings. Plant water potentials from -8 to -12 bars reduced the transport capacity from 30 to 15% per hour, and although the leaves were wilted, cotyledonary abscission did not increase appreciably at these levels of stress. The threshold water potential suffcient to induce leaf abscission was approximately -13 bars and abscission increased with increasing stress while the auxin transport capacity of the petioles remained relatively constant (15% per hour). The basipetal transport capacity of weU watered petioles tested under anaerobic conditions and acropetal transport tested under aUl conditions were typically less than basipetal transport under the most severe stress conditions. Cotyledonary abscission took place during and 24 hours after relief of stress with little or no abscission taking place 48 hours after relief of stress. Although the water potential returned to -4 bars within hours after rewatering the stressed plants, partial recovery of the basipetal transport capacity of the petioles was not apparent until 48 hours after rewatering, and at least 72 hours was required to return the transport capacity to near normal values. These data support the view that decreased levels of auxin reaching the abscission zone from the leaf blade influence the abscission process and further suggest that the length of time that the auxin supply is maxmally reduced is more critical than the degree of reduction.Various lines of indirect evidence suggest that foliar abscission resulting from water deficits may be at least partly mediated by a decrease in the availability of auxin reaching the abscission zone from the leaf blade. Since the work of Laibach (14) [PAR, nm] with a 15-hr photoperiod). Following emergence, the plants were watered with modified Hoagland solution (12). After 12 days from planting, those trays of seedlings destined for stress studies were transferred to a similar growth chamber programed for identical conditions but which supplied only 30% constant relative humidity. Four days in this low relative humidity chamber (without additional water) was sufficient to impose severe water stress (c -20 bars) on the seedlings. However, by removing trays for the transport experiments at the appropriate time, a range of 4, was obtained. Those plants destined to be controls remained in the high humidity growth chamber a total of 14 days from planting and were watered daily. Thus, all transport experiments were conducted on...

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

“…The application of 100 gM NPA to cotton seedlings results in the near total inhibition of basipetal auxin transport without any measurable effect on leaf abscission (JC Suttle, unpublished data). This observation is consistent with the reports of others (5,11,12) and indicates that, while a decline in polar auxin transport is a prerequisite for accelerated leaf abscission, it alone cannot induce the response. Presumably this inhibition must be accompanied by an increase in the level or activity of abscission promoters (ethylene/ABA) in order for leaf fall to occur.…”

“…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). The effects of chemical defoliants such as TDZ on polar auxin transport have not been reported.…”

Effect of Glyphosate on Auxin Transport in Corn and Cotton Tissues

“…The general procedure of Goldsmith (13) as modified by Davenport (12) was followed in all transport experiments. In each experiment, 10 corn coleoptile or 10 cotton hypocotyl sections were used for each treatment.…”

Movement of Kinetin and Gibberellic Acid in Leaf Petioles during Water Stress-induced Abscission in Cotton

“…Foliar abscission resulting from water deficits has recently been shown to be correlated with a decrease in the auxin transport capacity of subtending petioles (3). A clear understanding of the complex interactions of other hormones within the plant during the abscission process is imperative if we are to elucidate mechanisms of abscission induction.…”

“…This report relates results of experiments examining the capacity of cotton cotyledonary petioles to transport kinetin and GA3 prior to, during, and after exposure to such conditions. MATERIALS AND METHODS Plant culture and procedures for determination of transport capacity have been previously described in detail (2,3 [1,7,12,18-14C] GA3 (1.7 mCi/mmol, Amersham/Searle Corp., Amersham, England) were placed atop each section for 0.5 hr after which they were replaced with agar "chase" blocks containing nonlabeled 10 ,lM kinetin or 10 ,UM GA3, respectively. The relatively high concentration oflabeled GA3 was necessary to obtain sufficient radioactivity in the tissue sections.…”