Abstract:
Effect of high light exposure (500 mmol m-2S-1 of photosynthetic active radiation: PAR) on Nostoc spongiaeforme Agardh, a fresh water cyanobacterium and Phormidium corium Agardh (Gomont), a marine cyanobacterium was studied with respect to photosynthesis, lipid peroxidation, antioxidant activity, membrane lipids and its fatty acid composition. The Fv/Fm ratio, which is indicative of photosynthetic efficiency, decreased due to the treatment. The damage to photosynthetic efficiency occurred at the level of antenna system, as Fo was affected and at the PS II level, as Fm was also affected. Peroxidation of membrane lipids was observed, indicating oxidative damage to lipids. Activity of superoxide dismutase (SOD) increased as a result of the treatments to mitigate oxidative stress. FTIR profile of the membrane lipids showed presence of both saturated as well as unsaturated fatty acids in both species in the ratio of 13:9. NMR profile of the membrane lipids showed peaks, representing major lipids. Quantitative changes in phospho- and glycolipids were also observed. Unsaturation level of fatty acids of total lipids remains unchanged while salutation level decreased, suggesting changes in the membrane fluidity. The changes in membrane lipids and fatty acids under our experimental conditions may primarily suggest an adaptation strategy by the organism against the high light conditions, then the oxidative damage, as unsaturated fatty acids remained unaffected by the treatment.
