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 nm). The specific growth rate immediately after the lag phase was 0.36±0.06 and 0.26±0.03 day−1 for unirradiated cultures and cultures irradiated with UV-B, respectively. UV-B irradiation significantly decreased ascorbate content by 54.5%, and increased the ascorbyl radical content/ascorbate content ratio by 2.25-fold in algae cultures in log phase. UV-B exposure significantly decreased by 95, 62 and 71% the content of α-tocopherol, β-carotene and total thiols, respectively, in cells in log phase of development. The cellular content of α-tocopherol, β-carotene and total thiols was reduced by 78, 43 and 44%, respectively in stationary phase, as compared to the antioxidant content in the cells during log phase of development. UV-B exposure reduced the content of α-tocopherol and total thiols in stationary phase of development by 64 and 91%, respectively, as compared to unirradiated cells. The content of β-carotene in stationary phase was not affected by UV-B exposure. The results presented here suggest that increased UV-B radiation was responsible for the development of oxidative stress conditions, assessed as the ascorbyl radical content/ascorbate content ratio, in Antarctic Chlorella sp cells. Moreover, a significant decrease in the content of both lipid and water soluble antioxidants might contribute to establish oxidative stress in the cells.