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

[14C4]GA53, [14C4]GA44, and [2H2/14C4]GA19 were injected separately into seedlings of rice (Oryza sativa) using a dwarf mutant (d35) 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, GA53-->GA44-->GA19-->GA20 and the presence of endogenous GA53, GA44, GA19, GA20 and GA1. Previous metabolic studies have shown the presence of the step, GA20-->GA1 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 GA12 and leads to bioactive GA1.