EFFECTS OF LIGHT, DEVELOPMENTAL AGE AND PHYTOHORMONES ON THE EXPRESSION OF THE GENE ENCODING NADPH-PROTOCHLOROPHYLLIDE OXIDOREDUCTASE IN CUCUMIS-SATIVUS

NADPH-protochlorophyllide oxidoreductase (NPR, EC 1.3.1.33) catalyzes the light-dependent reduction of protochlorophyllide to chlorophyllide a in the chlorophyll biosynthetic pathway in angiosperms. We examined the effects of light, developmental age and phytohormones on the expr ession of the NPR gene in cucumber (Cucumis sativus L.). The levels of NPR mRNA in light-grown seedlings were 2 to 3 times higher than those in dark-grown seedlings. When light-grown seedlings were transferred to the dark, the levels of the NPR mRNA decreased. Re-illumination of the dark-adapted seedlings resulted in an increase in transcript level s. Thus, the positive light-regulation of expression of the NPR gene w as reversible. In dark-grown seedlings, the levels of the NPR mRNA inc reased during the 3 days after germination and then decreased. This pa ttern was same in light-grown seedlings, indicating that the expressio n of the NPR gene was regulated not only by light but also development al age. The phytohormones controlled the expression of the NPR gene. T he levels of the NPR mRNA in dark grown seedlings were increased by tr eatment with 6-benzyladenine (BA) and gibberelline A(3) (GA(3)) but we re decreased by abscisic acid (ABA) treatment. The effects of phytohor mones were consistent with their respective effects on the synthesis o f chlorophyll. The present results suggest that this positively light- regulated NPR gene mainly contributes to chlorophyll synthesis in gree ning leaves of cucumber, instead of the light-sensitive or light-insen sitive NPR gene which are dominant types in other angiosperms.