Effects of 3-Methylgibberellin Analogs on Gibberellin 3β-Hydroxylases and Plant Growth

Abstract

Six 3-methylgibberellin analogs were synthesized, and their effects on the GA 3β-hydroxylases from immature seeds of Phaseolus vulgaris and Cucurbita maxima, and /or on the growth of dwarf rice (Oryza sativa L.cv.Tan-ginbozu) and cucumber (Cucumis sativus L.cv.Spacemaster) were investigated. 3-Methyl-GA₅ and 2, 3-didehydro-3-methyl-GA₉ inhibited the conversion of [2, 3-³H₂]GA₉ to [2-³H]GA₄ by GA 3β-hydroxylases from both P.vulgaris and C.maxima at 3μM and higher. Their C/D-ring-rearranged isomers, 2, 3-didehydro-3-methyl-DGC and 16-deoxo-2, 3-didehydro-3-methyl-DGC, inhibited 3β-hydroxylation by the enzyme from P.vulgaris threefold more strongly than the non-C/D-ring-rearranged compounds, but exhibited no effect on 3β-hydroxylation by the enzyme from C.maxima. In a dwarf rice seedling assay, 3-methyl-GA₅ and 2, 3-didehydro-3-methyl-GA₉ promoted shoot elongation at doses of 300 ng/plant and higher, and 3α-methyl-GA₁ and 3α-methyl-GA₄ at doses of 30 ng/plant and higer. In contrast 2, 3-didehydro-3-methyl-DGC inhibited shoot growth to half that of the control at a dose of 300 ng/plant, and 16-deoxo-2, 3-didehydro-3-methyl-DGC showed no effect on growth. IN a cucumber seedling assay, 3α-methyl-GA₄ promoted hypocotyl elongation at doses of 300 ng/plant and higher. The other C-3 methyl compounds showed no effect on the hypocotyl elongation of cucumber seedlings.