Differential Counteraction of Ethylene Effects by Gibberellin A3 and N6-Benzyladenine in Senescing Citrus Peel

Abstract

Treatment of mature citrus fruit (Citrus sinensis) with ethylene induced rapid chlorophyll destruction, a rise in respiration, a release of free amino acids, an accumulation of reducing sugars and an appearance of phenylalanine ammonia lyase activity. Gibberellin A3 (GA3) and N6-benzyladenine (BA) opposed the effects of ethylene on chlorophyll, amino acids and to a lesser extent, reducing sugar levels. The ethylene-induced respiratory rise was only slightly modified by GA3 and BA. Phenylalanine ammonia lyase activity was not affected by GA3. The antagonism between ethylene and the senescence delaying regulators GA3 and BA seems to operate mainly within the chloroplast, but might not be confined to this compartment. The accumulation of reducing sugars exhibits the antagonism, although it is not apparently related to the chloroplast.