Increase in Free and Bound Abscisic Acid during Natural and Ethylene-induced Senescence of Citrus Fruit Peel

Abstract

Free and bound abscisic acid and neutral growth inhibitors were detected in citrus fruit peel using two bioassays and gasliquid chromatography. None of the inhibitor components seems to be directly associated with chloroplasts or chromoplasts in citrus fruit peel.Green, nonsenescent fruits contain mostly neutral inhibitors and relatively low amounts of free and bound abscisic acid. Upon harvest and storage in ethylene, 50 microliters per liter, both free and bound abscisic acid accumulate rapidly, attaining within 24 hours a level of 1 microgram per gram. After 48 hours bound abscisic acid reaches a much higher level than free abscisic acid. Fruits allowed to senesce on the tree follow a similar course of abscisic acid accumulation, attaining finally a 10: 1 ratio of bound to free abscisic acid.