A Plant Growth Retardant, Uniconazole, Is a Potent Inhibitor of ABA Catabolism in Arabidopsis
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.
- Bioscience, biotechnology, and biochemistry
Bioscience, biotechnology, and biochemistry 70(7), 1731-1739, 2006-07-23
Japan Society for Bioscience, Biotechnology, and Agrochemistry