Differential response of growth, photosynthesis, antioxidant enzymes and lipid peroxidation to UV-B radiation in three cyanobacteria

AbstractOur studies indicate differential response of growth, photosynthesis, antioxidant enzymes and lipid peroxidation of three cyanobacteria: Nostoc muscorum, Plectonema boryanum and Aphanothece sp. to UV-B stress and the sensitivity to UV-B was maximum in N. muscorum and minimum in Aphanothece sp. Cyanobacteria exhibited varied sensitivity to UV-B radiation (280–315 nm: 0.4 W m−2) as 30 min of UV-B exposure caused 32, 88 and 95% growth yield after 10th day of treatment in N. muscorum, P. boryanum and Aphanothece sp., respectively. Photosynthetic pigment contents, whole cell oxygen yield, 14C-fixation and PS II activity decreased with increasing doses of UV-B exposure (15 and 60 min), however, the inhibitory effect in N. muscorum was more pronounced than in P. boryanum and a least effect was noticed in Aphanothece sp. Among the photosynthetic pigments, phycocyanin was severely affected by UV-B in N. muscorum followed by P. boryanum and Aphanothece sp. 14C-fixation was found to be more sensitive parameter to UV-B than whole cell photosynthetic oxygen evolution. UV-B exposed spheroplasts exhibited severe damage on PS II activity and little effect on the activity of PS I. Partial restoration of PS II activity by electron donors (NH2OH, MnCl2 and DPC) suggested that UV-B interrupted the electron flow by affecting the component of water oxidation site as well as reaction center of PS II and the extent of damage on PS II was dependent on UV-B exposure time as well as the cyanobacterial strains. Suppression in emission peak (λmax 651 nm) of phycocyanin revealed that UV-B altered the energy transfer efficiency of phycocyanin to PS II reaction center. Furthermore, UV-B with increasing doses enhanced lipid peroxidation and the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD). However, the enhancement in SOD activity in N. muscorum (13–25%), P. boryanum (18–34%) and Aphanothece sp. (24–53%) was high as compared with CAT and POD activity