Effect of UV-B radiation on growth, photosynthetic activity and metabolic activities ofChlorococcum sp

The impact of two intensities (2.5 W m −2 and 5 W m −2 ) of ultraviolet-B (UV-B) radiation on growth, photosynthetic pigments, photosynthetic activity and membrane leakage has been studied in Chlorococcum sp. isolated from El-Kased fresh water canal, Tanta, Egypt. Exposure of Chlorococcum sp. for 60 and 35 min of 2.5 and 5 W m −2 , respectively, inhibited growth by 50%. Chlorophyll a and chlorophyll b were decreased in Chlorococcum sp. by exposure to UV-B, but the effect was more pronounced on chlorophyll b . On the other hand, carotenoids were stimulated at small doses (time of exposure and intensity) of UV-B whether at 2.5 or 5 W m −2 . However, oxygen amount, total soluble carbohydrates, and total soluble proteins were inhibited by UV-B treatment at all exposure times but the effect of 5 W m −2 was more than that of 2.5 W m −2 and O 2 was completely abolished after 90 and 120 min at 2.5 and 5 W m −2 , respectively. With regard to extracellular polysaccharides, there was a significant increase at small doses of UV-B but reduction observed at high doses. Exposing cells to 2.5 and 5 W m −2 UV-B caused 22.7 and 39.6% increase, respectively, in electrolyte leakage than in control.