Metabolism of [3H]gibberellin A5 by immature seeds of apricot (Prunus armeniaca L.)

Immature seeds of apricot (Prunus armeniaca L.) were fed the native gibberellin A5 (GA5) as 1- and 1,2-[3H]GA5 at doses 2 to 530 times the expected endogenous level. After 4 days of incubation, seeds were extracted and free [3H]GA-like metabolites were separated from the highly H2O-soluble [3H]metabolites. For high specific activity feeds the retention times (Rts) of radioactive peaks were compared with Rts of authentic GAs on sequential gradient-eluted → isocratic eluted reversed-phase C18 high performance liquid chromatography (HPLC)-radiocounting (RC). From high substrate feeds (530 and 230 x expected endogenous levels) HPLC-RC peak groupings were subjected to capillary gas chromatography-selected ion monitoring (GC-SIM), usually six characteristic ions. The major free GA metabolites of [3H] GA5 were identified as GA1, GA3, and GA6 by GC-SIM. The major highly water soluble metabolite of [3H]GA5 at all levels of substrate GA5 had chromatographic characteristics similar to authentic GA1-glucosyl ester. Expressed as a percentage of recovered radioactivity, low substrate [3H]GA5 feeds (2 x expected endogenous level) yielded a broad spectrum of metabolites eluting at the Rts where GA1, GA3, GA5 methyl ester, GA6, GA22, GA29 (17, 14, 1.6, 7, 1.1, 0.5%, respectively) and GA glucosyl conjugates of GA1, GA3, GA5, and GA8 (33, 11, 1, 0.1%, respectively) elute