Metabolism of Tritiated Gibberellins in d-5 Dwarf Maize

Abstract

Metabolism of [(3)H]gibberellin A(1) ([(3)H]GA(1)) was followed in intact seedlings and excised apices and leaf tissue of both dwarf and normal (tall) plants of d-5 maize (Zea mays L.). The three metabolites produced were tentatively identified as [(3)H]GA(s), [(3)H]GA(s)-glucoside ([(3)H]GA(s)-glu), and [(3)H]GA(1)-X, an unknown.In 3-hour, pulse-labeling experiments with tissues of incubated, expanding leaves, more than 70% of the [(3)H]GA(1) taken up was metabolized to the three products within 12 to 15 hours. [(3)H]GA(1) fed to the roots of 7-day-old seedlings was readily translocated to the leaves, and all three metabolites were found in both roots and leaves. [(3)H]GA(1)-X was the major metabolite in roots, whereas in leaves the major metabolite was [(3)H]GA(s)-glu. There were no consistent differences in [(3)H]GA(1) metabolism between dwarf and normal plants, indicating that dwarfism in d-5 maize is not associated with modified GA(1) metabolism.In excised, mature leaf tissue, [(3)H]GA(1) metabolism was slower than in excised, young leaf tissue. Mature leaf tissues produced [(3)H]GA(s)-glu as by far the major metabolite, with [(3)H]GA(s) and [(3)H]GA(1)-X as minor metabolites. In contrast, in young leaves the three metabolites appeared sequentially in significant proportions: [(3)H]GA(8) first, followed by [(3)H]GA(s)-glu and, finally, [(3)H]GA(1)-X.