Effects of selenite, CO 2 and illumination on the induction of selenium-dependent glutathione peroxidase in Chlamydomonas reinhardtii

Abstract

When sodium selenite was added to Chlamydomonas reinhardtii cells grown in the absence of sodium selenite under illumination (10 000 lux) and ordinary air (0.03% CO 2 concentration), glutathione peroxidase activity increased to a peak after 24 h, and ascorbate peroxidase activity concomitantly disappeared after 6 h. The effect of cycloheximide and the immunochemical titration with antibody directed against bovine erythrocyte glutathione peroxidase showed that the increase in glutathione peroxidase activity was due to protein synthesis. Transfer of Chlamydomonas cells either from low CO 2 concentration (ordinary air: 0.03% CO 2) to high CO 2 concentration (5% CO 2) or from light to dark together with the addition of sodium selenite stopped the increase in the glutathione peroxidase activity. The effect of illumination was saturated at a light intensity of about 6000 lux. The results reported here indicate that low CO 2 concentration in the atmosphere and illumination are required for the induction of glutathione peroxidase, and suggest that selenium-induced glutathione peroxidase as well as catalase can play an important role in the scavenging of H 2O 2 generated in pseudocyclic electron transport of Chlamydomonas chloroplasts.