Degradation and de novo synthesis of D1 protein and psbA transcript levelsin Chlamydomonas reinhardtii during UV-B inactivation of photosynthesis and its reactivation

UV-B induces intensity and time dependent inhibition of photosynthetic O-2 evolution and PS II electron transport activity in Chlamydomonas reinhardti i. The D1 and D2 proteins of chloroplast membranes are rapidly and specific ally degraded in the course of irradiation of cells to UV-B. Continuous syn thesis of the two proteins was essential for the repair of damaged PS II as chloramphenicol accelerated UV-B inactivation of photosynthesis and preven ted photoreactivation. Northern analysis revealed that W-B also affected th e expression of psbA gene coding for the D1 protein. Cells showing 72% inhi bition of PS II activity, revealed a modest net loss of 25% in the level of D1 protein. This shows that synthesis of D1 protein is not the only compon ent involved in the recovery process. Our results indicate that besides aff ecting the synthesis of the D1 protein UV-B may impair certain post-transla tional events, which in turn may limit the repair of damaged PS II.