The fate of endogenous gibberellins and applied radioactive gibberellin A₃ during natural and ethylene-induced senescence in citrus peel

The fate of gibberllins (GAs) was studied in the flavedo (the external colored peel layer) of green-harvested orange fruits, during natural and ethylene-induced senescence.GA-like substances were determined by the sugar-release barley endosperm bioassay. Careful solvent partition and TLC separation were undertaken to avoid interference of abscisic acid (ABA) and other growth inhibitors with the bioassay. Three zones of GA-like activity were detected in chromatograms of the acid fraction, all of which decreased sharply after 72 hr in 35 μl/liter ethylene.Tritium-labeled gibberellin A₃ (³H-GA₃) was applied to fruits at 5.6 mg/liter. After 5 days storage in air or ethylene, 28.5 and 20.2 percent, respectively, of extractable radioactivity were recovered as ³H-GA₃, whereas 37.0 and 59.7 percent, respectively, had been converted into water-soluble compounds.The significance of GA metabolism in senescent plant organs is discussed.