Abstract
A plant hormone abscisic acid (ABA) protects plants from water stress, so suppression of its metabolic inactivation could increase resistance of plants against water stress. ABA is metabolized to 8'-hydroxy-ABA by ABA 8'-hydroxylase, which spontaneously isomerizes to phaseic acid (PA). PA is converted to dihydrophaseic acid (DPA) and epi-DPA by PA 4'-reductase. 8'-Hydroxy-ABA and PA still have biological activity although it is low, but DPAs are almost inactive. The gene of ABA 8'-hydroxylase was identified in Arabidopsis, and its inhibitors have been developed. However, research on PA 4'-reductase has not progressed. The objective of this research is identification of PA 4'-reductase gene, and development of its inhibitor. We have already found that the extract of immature garden pea (Pisum sativum) showed the PA 4'-reductase activity. After centrifugation of the extract, the supernatant was purified with an anion exchange resin. The activity was eluted with a buffer of pH 8.0 containing 50mM NaCl. The active fraction was purified on a 2'5'ADP-Sepharose 4B. The activity was eluted by a buffer of pH 8.0 containing 1mM NADP^+. The specific activity was increased to 137-fold. The fraction was purified on Sephadex G-75. The SDS-PAGE analysis of the active fraction showed several bands after silver staining. Further purification of PA 4'-reductase is under progress.
