Cellular response of Chlorella zofingiensis to exogenous selenium

An investigation of the cellular response of the freshwater microalga Chlorella zofingiensis to exogenous selenium showed that Chlorella cells can tolerate sodium selenite up to a concentration of 100 mg l(-1). Cells grown in such a selenium-supplemented medium accumulated boiling-stable proteins in a concentration-dependant manner. Western blot analysis revealed that three of these boiling-stable proteins cross-reacted with anti-dehydrin antibody. Selenium was also found to exert an effect on antioxidative enzymes: superoxide dismutase (Fe-SOD and Mn-SOD isoforms) accumulated in response to selenium stress of 100 mg l(-1) sodium selenite, as did a new form of selenium-dependent glutathione peroxidase. Upon transfer of the cells to a selenium-free medium, the boiling-stable proteins, the superoxide dismutase isoforms and the selenium-dependent glutathione peroxidase were all down regulated. The accumulation of boiling-stable proteins and the increased activities of the antioxidant enzymes in selenium-treated Chlorella cells suggest that these compounds are probably involved in the mechanism(s) of selenium tolerance of this alga.