Effect of Salt Stress on Growth, Antioxidant Enzymes, Lipid Peroxidation and Some Metabolic Activities in Some Fresh Water and Marine Algae

THE OBJECTIVE of this research was to compare physiological response of fresh water algae (Chlorella vulgaris) and marine algae (Chlorella salina) to different salinity levels. These algae were isolated and cultivated in appropriate media for a period of 8 days. C. vulgaris could survive till 0.8 molar NaCl, while the marine strain (C. salina) survived up to 2 molar NaCl. Thus, the marine alga showed a wide range of salinity tolerance, whereas the fresh water alga showed a narrows range of salinity tolerance. The dry weight of C. salina was 2-folds at 1M NaCl and slightly changed at 2 M NaCl as compared to the control value. In C. vulgaris dry weight was progressively decreased with increase of salinity. Hypo and hyper saline media induced significant stimulation in photosynthesis pigments, carbohydrate, protein, Na+ and K+ contents in C. salina. On the other hand, free amino acids, proline, MDA contents and antioxidant enzyme activities (SOD, CAT, POD and APX) were generally decreased. In contrary, salt stress exerted inhibitory effects on photosynthetic pigments, carbohydrate, protein and K+ contents of the fresh water alga. Free amino acids, proline, Na+ , MDA contents and antioxidant enzyme activities were markedly increased in C. vulgaris with increase of salinity stress. The great salinity tolerance of C. salina, compared to C. vulgaris may be due to the effect of habitat on the behavior of the algae as being controlled with specific habitat gene (s).