Gibberellin biosynthesis: metabolic evidence for three steps in the early 13-hydroxylation pathway of rice

x[C-14(4)]GA(53), [C-14(4)]GA(44), and [H-2(2)/C-14(4)]GA(19) were injected separately into seedlings of rice (Oryza sativa) using a dwarf mutant (d(35)) that has low levels of endogenous gibberellins (GAs). After 8 h incubation, the shoots were extracted and the labeled metabolites were identified by full-scan gas chromatography-mass spectrometry (GC-MS) and Kovats retention indices (KRIs). Our results document the metabolic sequence, GA(53)-->GA(44)-->GA(19)-->GA(20) and the presence of endogenous GA(53), GA(44), GA(19), GA(20) and GA(1). Previous metabolic studies have shown the presence of the step, GA(20)-->GA(1) in rice. Taken together, the data establish in vegetative shoots of rice the presence of the early 13-hydroxylation pathway, a pathway that originates from GA(12) and leads to bioactive GA(1). (C) 2000 Published by Elsevier Science Ltd.