INHIBITION OF CHLOROPHYLL SYNTHESIS BY SELENIUM - INVOLVEMENT OF LIPOXYGENASE MEDIATED LIPID-PEROXIDATION AND ANTIOXIDANT ENZYMES

Chlorophyll (Chi) biosynthesis intermediate compounds (like protoporphyrin-IX, Mg-protoporphyrin methyl ester and protochlorophyllide), Chl (a + 6), heme, cytochrome P-450 (cyt P-450) and lipid peroxide levels as well as the activities of superoxide dismutase, catalase and lipoxygenase were studied in selenium treated mung bean seedlings. Chi (a + 6) content and heme levels were decreased with a concomitant accumulation of all the three porphyrins studied. Se treatment enhanced the lipoxygenase activity and correspondingly increased lipid peroxide levels. Se inhibited both the antioxidant enzymes catalase and superoxide dismutase in a dose-dependent manner. However, cyt P-450 levels were enhanced under Se exposure. Hence the inhibitory effect of Se on Chl synthesis is not only by acting on constituent biosynthetic enzymes but also through lipoxygenase-mediated lipid peroxide levels and inhibition of antioxidant defence component system.