Transport and metabolism of exogenously applied gibberellins to Malus domestica Borkh. cv. Jonagold

The radio-labeled gibberellins GA(1), GA(3), GA(4), and GA(7) were applied to intact developing apple fruits (Malus domestica Borkh. cv. Jonagold) dur ing the period when GAs are suggested to inhibit flower bud induction for t he following year. Radioactivity from these compounds was found to be trans ported into adjacent tissues as there are pedicels and bourses (4%). Applic ation to pedicels, after removal of the fruits, enhanced the transport into adjacent bourses up to 11%. The bud-carrying lateral bourse shoots contain ed only minor amounts of radioactivity on average 0.4% in both cases. These export rates were identical, 1 or 5 days after application. After applicat ion of the corresponding deuterium-labeled GAs and analyses by mass spectro metry the specific metabolization of GA(1) to GA(1) 13-O-glucoside and of G A(3) to GA(3) 13-O-glucoside was demonstrated. Additional metabolites of GA (1) and GA(3) were not detected. After fruit application of GA(3) the ratio of GA(3) to GA(3) 13-O-glucoside was found to be 1:2 in the fruit. Pedicel application led to ratios of 1:4 and 1:5, respectively, in the pedicel and in the adjacent bourse. After the application of GA(4) and GA(7), neither glucosylation products nor other GA-like metabolites could be identified. T his is the first report of the metabolism of GAs to GA 13-O-glucosides in d eveloping apple fruits. The possible function of the GAs as a signal in flo wer bud formation for the following year is discussed.