The dwarf-1 (d1) mutant of Zea mays blocks three 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 biosynthetic pathway, They have also been used to determine which native GAs are active per se, i.e., further metabolism is not necessary for bioactivity. We present metabolic evidence that the D1 gene of maize (Zea mays L.) controls the three biosynthetic steps: GA(20) to GA(1), GA(20) to GA(5), and GA(5) to GA(3). We also present evidence that three gibberellins, GA(1), GA(5), and GA(3), have per se activity in stimulating shoot elongation in maize, The metabolic evidence comes from the injection of [17-C-13,H-3]GA(20) and [17-C-13,H-3]GA(5) into seedlings of d1 and controls (normal and d5), followed by isolation and identification of the C-13-labeled metabolites by full-scan GC-MS and Kovats retention 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) was not metabolized to GA(1), GA(3), or to GA(5), and GA(5) was not metabolized to GA(3). The bioassay evidence is based on dosage response curves using d1 seedlings for assay. GA(1), GA(3), and GA(5) had similar bioactivities, and they were 10-times more active than GA(20).