Post-transcriptional regulation of ascorbate peroxidase during light adaptation of Euglena gracilis

Abstract

When Euglena cells are grown heterotrophically in the dark, the chloroplast development stops at the proplastid stage. Upon exposure to light, the cells rapidly develop chloroplasts and the photosynthesis resumes. Here, we have investigated the regulation of cytosolic ascorbate peroxidase (APX) in Euglena gracilis during light adaptation of dark-grown cells. Both the activity and protein levels of APX increased by nearly fourfold in about 24 h of illumination. Northern hybridization with a partial cDNA of Euglena APX as the probe revealed a constant level of APX transcripts during the light adaptation. Similarly, cycloheximide almost completely inhibited APX induction whereas transcription inhibitors did not have a significant effect, suggesting that the light induction of APX is post-transcriptionally regulated. APX induction was abolished when the development of chloroplast was suppressed by norflurazon, which inhibits the carotenoid synthesis. However, treatment of the dark-grown cells with H 2O 2 or methyl viologen did not induce APX.