A Plant Growth Retardant, Uniconazole, Is a Potent Inhibitor of ABA Catabolism in Arabidopsis
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Plant growth retardants (PGRs) reduce the shoot growth of plants by inhibiting gibberellin biosynthesis. In this study, we performed detailed analyses of the inhibitory effects of PGRs on <I>Arabidopsis</I> abscisic acid (ABA) 8′-hydroxylase, a major ABA catabolic enzyme, recently identified as CYP707As. In an <I>in vitro</I> assay with CYP707A3 microsomes expressed in insect cells, uniconazole-P inhibited CYP707A3 activity more effectively than paclobutrazol or tetcyclacis, whereas the other PGRs tested did not inhibit it significantly. Uniconazole-P was found to be a strong competitive inhibitor (<I>K</I><SUB>i</SUB>=8.0 n<small>M</small>) of ABA 8′-hydroxylase. Uniconazole-P-treated <I>Arabidopsis</I> plants showed enhanced drought tolerance. In uniconazole-P-treated plants, endogenous ABA levels increased 2-fold as compared with the control, and co-application of GA<SUB>4</SUB> did not suppress the effects, indicating that the effects were not due to gibberellin deficiency. Thus uniconazole-P effectively inhibits ABA catabolism in <I>Arabidopsis</I> plants. We also discuss the structure-activity relationship of the azole-type compounds on ABA 8′-hydroxylase inhibitory activity.
- Agricultural and Biological Chemistry
Agricultural and Biological Chemistry 70(7), 1731-1739, 2006-07-23
Japan Society for Bioscience, Biotechnology, and Agrochemistry