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[17- 13 C, 3 H 2 ]GA 9 was administered to 4-week-old seedlings of normal, dwarf 1 and dwarf 5 seedlings at the 3–4 leaf-stage. After 12 or 24 hr incubation, shoots were harvested, extracted with methanol and the extracts purified by solvent partitioning and HPLC. The resulting radiolabelled fractions were analysed by full-scan GC mass spectrometry with Kovats Retention Indices (R l ). The major metabolite was [ 13 C]GA 20 , with [ 13 C]GA 51 , [ 13 C]GA 69 , [ 13 C]GA 70 , [ 13 C]3-epi- GA 4 and [ 13 C]3-epi- GA 1 being identified as minor metabolites. The metabolism of GA 9 to GA 20 demonstrates the possibility of late convergence of the two biosynthetic branch pathways, the presumptive non-early 3,13-hydroxylation pathway and the early 13-hydroxylation pathway, both of which originate from GA 12 . There was no evidence for the metabolism of GA 9 to GA 1 , GA 4 , GA 5 , GA 3 , GA 7 , or 2,3-dehydro-GA 9 . |
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