UV-B RADIATION INDUCED DIFFERENTIAL PHYSIOLOGICAL AND BIOCHEMICAL RESPONSES IN NOSTOC COMMUNE AND ANABAENA VARIABILIS

Batch cultures of two cyanobacterial species i.e., Nostoc commune and Anabaena variabilis were used to evaluate the impact of UV-B radiation on growth, photosynthetic pigments, lipid peroxidation, proline content, protein content as well as on the enzymes nitrate reductase and glutamine synthetase. The essential targets of UV-B radiation are the photosynthetic apparatus, photosynthetic pigments, and the excitation energy transfer. The UV-B radiation adversely inhibited the growth and photosynthetic pigments in both cyanobacterial strains. The content of Malondialdehyde increased by two-fold in both cyanobacterial species upon prolonged UV-B exposure. Protein content showed varied responses in both cyanobacterial species on UV-B exposure. Anabaena variabilis showed a decrease in protein content, whereas in Nostoc commune protein content elevates with an increase in UV-B exposure duration. With the increase in the duration of UV-B exposure up to 72 hrs the proline content in both species of cyanobacteria increased. Following the different duration of UV-B exposure in the following species, the in-vivo Nitrate reductase activity increased while in-vivo Glutamine synthetase activity decreased, although the complete decline in glutamine synthetase activity was not observed even after 72 hrs of exposure. The results showed that damages at different levels are caused due to UV-B exposure in both Anabaena variabilis and Nostoc commune.