Effects of a Plant-Growth Regulator, Prohexadione, on the Biosynthesis of Gibberellins in Cell-Free Systems Derived from Immature Seeds

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Inhibition of the biosynthesis of gibberellins by prohexadione, 3,5-dioxo-4-propionylcyclo-hexanecarboxylic acid, was studied with cell-free systems derived from immature seeds of Cucurbita maxima, Phaseolus vulgaris and Pisum sativum. Prohexadione, at a concentration of 10^<-4> M, inhibited C-7 oxidation of GA_<12>-aldehyde, C-20 oxidation of GA_<15>, conversion of C_<20>-gibberellins to C_<19>-gibberellins, 3β-hydroxylation, 2,3-dehydrogenation of GA_<20>, 2,3-epoxidation of GA_5 and 2β-hydroxylation of GA_9 and GA_<20>. The 3β-hydroxylase activity appeared to be more sensitive to prohexadione than were the C-20 oxygenase and the 2β-hydroxylase activities. The conversion of mevalonic acid to GA_<12>-aldehyde and the 13-hydroxylation of GA_<12> were not affected by prohexadione at a concentration of 3 × 10^<-4> M. All of the steps inhibited by prohexadione are oxidation steps catalyzed by soluble enzymes that require 2-oxoglutarate, Fe^<2+> and oxygen, and all of them occur distal to the synthesis of GA_<12>-aldehyde in the biosynthesis of gibberellins.
日本植物生理学会の論文