Abscission: Role of Abscisic Acid

Abstract

Th2 effect of abscisic acid on cotton (Gossypium hirsutuin L. cv. Acala 4-42) and bean (Phaseolus vulgaris L. cv. Red Kidney) explants was 2-fold. It increased ethylene producticn from the explants, which was found to account for some of its ability to accelerate abscission. Absci ic acd also increased the activity of cellulase. Increased synthesis of cellulaso was not du to an increase in aging of the explants but rather was an effect of abscisic acid on the processes that lead to cellulase synthesis or activity. The ability of a diffusible substance from cotton fruit to accelerate the abscission of cotton exlplants ultimately led to the discovery of what is now known as abscisic acid, a plant hormone capable of regut-lating a number of plant processes (9, 16). The role of abscilc acid in abscission however, remains uncer.ain. The substance promotes the abscission of explants, but then so do a large numnber of other compounds, manv of which are not normal constitu-ents of leaves (1). Evidence bo.h for (9) and against (15) a role for thiis hornmone in abscission has been pre ented. However the work of Dale and Milford (15) has been criticizcd becau-e chromo-tographic behavior of tlheir compound differed from the 8-inhibitor and did not pronlote abscission of young cotton fruit. This paper presents a series of experinments