title: A plant growth retardant, uniconazole, is a potent inhibitor of ABA catabolism in Arabidopsis.
abstract: 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 Arabidopsis abscisic acid (ABA) 8'-hydroxylase, a major ABA catabolic enzyme, recently identified as CYP707As. In an in vitro 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 (K(i)=8.0 nM) of ABA 8'-hydroxylase. Uniconazole-P-treated Arabidopsis 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(4) did not suppress the effects, indicating that the effects were not due to gibberellin deficiency. Thus uniconazole-P effectively inhibits ABA catabolism in Arabidopsis plants. We also discuss the structure-activity relationship of the azole-type compounds on ABA 8'-hydroxylase inhibitory activity.
authors.affiliation: Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan.
authors.forename: Shigeki
authors.initials: S
authors.lastname: Saito
authors.forename: Masanori
authors.initials: M
authors.lastname: Okamoto
authors.forename: Shoko
authors.initials: S
authors.lastname: Shinoda
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Kushiro
authors.forename: Tomokazu
authors.initials: T
authors.lastname: Koshiba
authors.forename: Yuji
authors.initials: Y
authors.lastname: Kamiya
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Hirai
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Todoroki
authors.forename: Kanzo
authors.initials: K
authors.lastname: Sakata
authors.forename: Eiji
authors.initials: E
authors.lastname: Nambara
authors.forename: Masaharu
authors.initials: M
authors.lastname: Mizutani
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism*; D017360:Arabidopsis / Q000187:drug effects / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000037:antagonists & inhibitors*; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System; D008861:Microsomes / Q000187:drug effects / Q000378:metabolism; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors*; D010937:Plant Growth Regulators / Q000494:pharmacology*; D010940:Plant Proteins; D014230:Triazoles / Q000494:pharmacology*
chemical_list: D029681:Arabidopsis Proteins; D065607:Cytochrome P-450 Enzyme Inhibitors; D010937:Plant Growth Regulators; D010940:Plant Proteins; D014230:Triazoles; C511205:uniconazole-P; C053723:tetcyclacis; C053370:paclobutrazol; D000040:Abscisic Acid; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; C107203:abscisic acid 8'-hydroxylase