Metabolism of Tritiated Gibberellins in d-5 Dward Maize

After 30 minutes of incubation of young leaf sections of d-5 maize (Zea mays L.) in [(3)H]gibberellin A(1) ([(3)H]GA(1)), the metabolite [(3)H]GA(8) was present in significant amounts, with a second metabolite, [(3)H]GA(8)-glucose ([(3)H]GA(8)-glu), appearing soon after. A third [(3)H]GA(1) metabolite, the polar uncharacterized conjugate [(3)H]GA(1)-X, took more than 1 hour to appear. The protein synthesis inhibitor cycloheximide inhibited the production of all [(3)H]GA(1) metabolites, indicating a possible protein synthesis requirement for [(3)H]GA(1) metabolism.By preincubating leaf sections in unlabeled GA(1) before exposure to [(3)H]GA(1) or by reducing the specific radioactivity of the [(3)H]GA(1) supplied, it was possible to reduce greatly the conversion of radioactive GA(1) to [(3)H]GA(8)-glu, without affecting conversion to [(3)H]GA(1)-X. Increasing the molar concentration of the [(3)H]GA(1) fed greatly increased the molar yield of [(3)H]GA(1)-X, whereas the molar yields of [(3)H]GA(8) and [(3)H]GA(8)-glu were much less affected.The principal metabolite of [(3)H]GA(3) was a very polar compound having chromatographic properties similar to those of the conjugate [(3)H]GA(1)-X produced from [(3)H]GA(1). The naturally occurring GAs [(3)H]GA(1), [(3)H]GA(3), and [(3)H]tetrahydroGA(3) were metabolized to a much greater extent than were the artifical derivatives [(3)H]ketoGA(1), [(3)H]GA(1)-methyl ester, and [(3)H]pseudoGA(1). Only [(3)H]GA(1) and [(3)H]GA(3), with their identical D ring structures, were converted to [(3)H]GA(1)-X type compounds; [(3)H]-ketoGA(1) and [(3)H]tetrahydroGA(3), with modified D rings, were not converted to this type of conjugate.