Evaluation of the effect of UV-B radiation on growth, photosynthetic pigment, and antioxidant enzymes of some cyanobacteria

The current study is focused on the effects of artificial UV-B radiation on growth, proteins, and pigments, as well as the activities of several enzymatic and non-enzymatic antioxidant enzymes in some cyanobacterial strains. Cultures were maintained at 25 degrees C +/- 1 degrees C under a white fluorescent tube of intensity 30-40 mu E m-2s-1 with a 14:10 light and dark cycle in the laboratory and analyzed at an interval of 25, 32, 39, 46, and 53 days. The test cultures were exposed to UV-B stress for 24 h at the same intervals. We found that exposure to UV-B showed increased production of phycocyanin and carotenoids in four strains, namely, Scytonema javanicum, Nostoc muscorum, Aphanothece naegeli, and Synechococcus elongates. We also look into the effects of UV-B radiation on the proline content, non-protein thiols, radical scavenging activity, ascorbic acid, and tocopherol, total flavonoid content (TFC), total phenolic content (TPC) on these strains. Variation in the non-enzymatic antioxidants and expression levels of enzymatic enzymes and reducing power activity as compared to the non-irradiated control was found. Our study showed that cyanobacteria impart prominent antioxidant and radical scavenging prop-erties which facilitate the defence mechanism against UV-B induced cell damage.