Gibberellin Biosynthesis in Maize. Metabolic Studies with GA15, GA24, GA25, GA7, and 2,3-Dehydro-GA9

[17-14C]-Labeled GA15, GA24, GA25, GA7, and 2,3-dehydro-GA9 were separately injected into normal,dwarf-1 (d1), and dwarf-5 (d5) seedlings of maize (Zea mays L.). Purified radioactive metabolites from the plant tissues were identified by full-scan gas chromatography-mass spectrometry and Kovats retention index data. The metabolites from GA15 were GA44, GA19, GA20, GA113, and GA15-15,16-ene (artifact?). GA24 was metabolized to GA19, GA20, and GA17. The metabolites from GA25 were GA17, GA25 16α,17-H2-17-OH, and HO-GA25 (hydroxyl position not determined). GA7was metabolized to GA30, GA3, isoGA3 (artifact?), and trace amounts of GA7-diene-diacid (artifact?). 2,3-Dehydro-GA9was metabolized to GA5, GA7 (trace amounts), 2,3-dehydro-GA10 (artifact?), GA31, and GA62. Our results provide additional in vivo evidence of a metabolic grid in maize (i.e. pathway convergence). The grid connects members of a putative, non-early 3,13-hydroxylation branch pathway to the corresponding members of the previously documented early 13-hydroxylation branch pathway. The inability to detect the sequence GA12 → GA15 → GA24 → GA9 indicates that the non-early 3,13-hydroxylation pathway probably plays a minor role in the origin of bioactive gibberellins in maize.