THE DWARF-1 (D1) MUTANT OF ZEA-MAYS BLOCKS 3 STEPS IN THE GIBBERELLIN-BIOSYNTHETIC PATHWAY

In plants, gibberellin (GA)-responding mutants have been used as tools to identify the genes that control specific steps in the GA biosynthe tic pathway, They have also been used to determine which native GAs ar e active per se, i.e., further metabolism is not necessary for bioacti vity. We present metabolic evidence that the D1 gene of maize (Zea may s L.) controls the three biosynthetic steps: GA(20) to GA(1), GA(20) t o GA(5), and GA(5) to GA(3). We also present evidence that three gibbe rellins, GA(1), GA(5), and GA(3), have per se activity in stimulating shoot elongation in maize, The metabolic evidence comes from the injec tion of [17-C-13,H-3]GA(20) and [17-C-13,H-3]GA(5) into seedlings of d 1 and controls (normal and d5), followed by isolation and identificati on of the C-13-labeled metabolites by full-scan GC-MS and Kovats reten tion index, For the controls, GA(20) was metabolized to GA(1), GA(3), and GA(5); GA(5) was metabolized to GA(3), For the d1 mutant, GA(20) w as not metabolized to GA(1), GA(3), or to GA(5), and GA(5) was not met abolized to GA(3). The bioassay evidence is based on dosage response c urves using d1 seedlings for assay. GA(1), GA(3), and GA(5) had simila r bioactivities, and they were 10-times more active than GA(20).