Oxidative damage to chloroplasts from Chlorella vuigaris exposed to ultraviolet-B radiation

MALANGA G; CALMANOVICI G; PUN TARULO S

PHYSIOLOGIA PLANTARUM

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 1997 vol. 101 p. 455 - 462

0031-9317

Upon UV-B irradiation, Chlorella vuigaris cells and isolated chloroplasts increased in size and starch accumulation. Photosynthetic capacity and chlorophyll content of chloroplasts isolated from irradiated algae decreased by 72 and 66%, as compared to chloroplasts isolated from control cells. Dihydrorhodamine 123 conversion to rhodamine 123 was used as a sensitive method for detection of peroxide (presumably hydrogen peroxide) formation in isolated chloroplasts. The accumulation of rhodamine 123 is higher in irradiated than in nonirradiated chloroplasts and the increased accumulation of rhodamine 123 depended on the UV-B dose. Quantitation of alkyl radical-EPR signals in chloroplasts indicated that UV-B exposure significantly increased radical content in the membranes. The content of an oxidized DNA base (8- hydroxy-2'-deoxyguanosine) in chloroplasts was increased by 72 and 175% after irradiation of the algal culture with 17.3 and 42.6 kJ m~", respectively. The chioropiastic activity of superoxide dismutase decreased by 50% as compared with control values after irradiation with 42.6 kJ m"" and no changes in ascorbate peroxidase activity and ascorbic acid content were detected at the irradiation doses tested. The y5-carotene content in chloroplasts was not affected by the irradiation, but the a-tocopherol content increased approximately 4-fold after UV-B irradiation. The results suggest that oxidative damage related to UV-B exposure is responsible for alterations in chloroplasts function and integrity, and that an antioxidant response is triggered in chloroplasts through an increase in a-tocopherol content.