Sites of Inhibition by a Plant-Growth Regulator, 4'-Chloro-2'-(a-hydroxybenzyl)-isonicotinanilide (Inabenfide), and its Related Compounds in the Biosynthesis of Gibberellins

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Inhibition of the biosynthesis of gibberellins by 4'-chloro-2'-(α-hydroxybenzyl)-isonicotinanilide (inabenfide) was investigated with cell-free systems prepared from immature seeds of Cucurbita maxima. Phaseolus vulgaris and Pisum sativum. Inabenfide specifically inhibited the oxidation of kaurene, kaurenol and kaurenal but it did not inhibit the oxidation steps that lead to kaurenoic acid. The (S)- and (R)-forms of inabenfide and 2'-benzoyl-4'-chloro-isonicotinanilide (compound [1]) also inhibited the same oxidation steps. The (S)-form was the most active in inhibition of the oxidation of kaurene; the racemic form (inabenfide) was one half as effective; and the (R)-form and compound [1] had little effect on the biosynthesis of gibberellins. Growth-retardant activities of these compounds were also examined using seedlings of C. maxima. Since the growth-retardant activity of these compounds was correlated with their ability to inhibit the oxidation of kaurene in cell-free systems, we suggest that the growth-retardant activity of inabenfide is due to inhibition of the three oxidation steps from kaurene to kaurenoic acid in the biosynthesis of gibberellins.
日本植物生理学会の論文