EVIDENCE FOR THE ULTRAVIOLET-B (280-320 NM) RADIATION-INDUCED STRUCTURAL REORGANIZATION AND DAMAGE OF PHOTOSYSTEM-II POLYPEPTIDES IN ISOLATED-CHLOROPLASTS

Direct evidence for the possible loss of photosystem II (PS II) activity in chloroplasts of Vigna sinensis L. cv. Walp after ultraviolet-B (UV-B, 280-320 nm) radiation treatment was provided by polyacrylamide gel electrophoretic analysis of PS II polypeptides. A 30 min UV-B treatment of chloroplasts caused a 50% loss of PS II activity. The artificial electron donor, Mn2+ failed to restore UV-B radiation induced loss of PS II activity, while diphenyl carbazide (DPC) and NH2OH only partially restored activity. Such a loss in PS II activity was found to be primarily due to a loss of 23 and 33 kDa extrinsic polypeptides. UV-B treatment induced the synthesis of a few polypeptides and a 29 kDa light-harvesting chlorophyll protein.