UV-B effects on Antarctic Chlorella sp cells

Growth of Antarctic Chlorella sp cells was measured in cultures irradiated with 30 kJ m(-2) UV-B (280-320 mn). The specific growth rate immediately af ter the lag phase was 0.36 +/-0.06 and 0.26 +/-0.03 day(-1) for unirradiate d cultures and cultures irradiated with UV-B, respectively. UV-B irradiatio n significantly decreased ascorbate content by 54.5%, and increased the asc orbyl radical content/ascorbate content ratio by 2.25-fold in algae culture s in log phase. UV-B exposure significantly decreased by 95, 62 and 71% the content of alpha -tocopherol, beta -carotene and total thiols, respectivel y, in cells in log phase of development. The cellular content of alpha -toc opherol, beta -carotene and total thiols was reduced by 78, 43 and 44%, res pectively in stationary phase, as compared to the antioxidant content in th e cells during log phase of development. UV-B exposure reduced the content of alpha -tocopherol and total thiols in stationary phase of development by 64 and 91%, respectively, as compared to unirradiated cells. The content o f beta -carotene in stationary phase was not affected by UV-B exposure. The results presented here suggest that increased UV-B radiation was responsib le for the development of oxidative stress conditions, assessed as the asco rbyl radical content/ascorbate content ratio, in Antarctic Chlorella sp cel ls. Moreover, a significant decrease in the content of both lipid and water soluble antioxidants might contribute to establish oxidative stress in the cells. (C) 2001 Elsevier Science B.V. All rights reserved.