Gibberellin A(1) Biosynthesis in Pisum sativum L. : II. Biological and Biochemical Consequences of the le Mutation.
A comparative study of the metabolism of radiolabeled gibberellin (GA) 1, 19, and 20 in isolated vegetative tissues of isogenic Le and le pea (Pisum sativum) plants incubated in vitro with the appropriate GA substrate is described. The results of this study provide evidence that the enzymes involved in the latter stages of GA biosynthesis are spatially separated within the growing pea plant. Apical buds were not apparently involved in the production of bioactive GA(1) or its immediate precursors. The primary site of synthesis of GA(20) from GA(19) was immature leaflets and tendrils, and the synthesis of bioactive GA(1) and its inactive catabolite GA(8) occurred predominantly in stem tissue. GA(29), the inactive catabolite of GA(20), was produced to varying extents in all the tissues examined. Little or no difference was observed in the ability of corresponding Le and le tissues to metabolize radiolabeled GA(1), GA(19), or even GA(20). During a fixed period of 24 hours, stems of plants carrying the le mutation produced slightly more [(3)H]GA(1) (and [(3)H]GA(29)) than those of Le plants. It has been concluded that the le mutation does not lie within the gene encoding the GA(20) 3beta-hydroxylase protein.
Smith
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Department of Chemistry, University of Bristol, Bristol BS8 1TS, United Kingdom.