Abstract
Compounds with an N-containing heterocycle, such as triazoles and imidazoles, are known to act as inhibitors for cytochrome P450 monoxygenase (P450). We have recently identified the CYP707A family as a major ABA catabolic enzyme, ABA 8'-hydroxylase. Among several P450 inhibitors tested so far with the CYP707A3 microsomes expressed in insect cells, uniconazole-P strongly inhibited the activity of ABA 8'-hydoxylase (Ki = 8.0 nM). This indicates that uniconazole-P is a potent inhibitor for ABA 8'-hydoxylase. Next, we have examined the effect of uniconazole-P upon ABA catabolism in planta. When uniconazole-P was fed to Arabidopsis plants, increase in ABA content was observed. Upon drought stress, uniconazole-P treated plants showed remarkable drought tolerance. The endogenous ABA level in the treated plants was increased, and the level of phaseic acid, a major ABA catabolite, was decreased. These results indicate that uniconazole-P effectively inhibit ABA catabolism in addition to gibberellin and brassinolide biosynthesis.
