Influence of NaCl on photosynthesis and nitrogen metabolism of cyanobacterium Nostoc calcicola

Nostoc calcicola, a halotolerant alkaliphilic, nitrogen-fixing cyanobacterium, was grown under various NaCl concentrations (from 500 to 2000 mM) at alkaline pH. In cyanobacteria, physiological and biochemical responses were correlated with the external salt stress. The optimal condition for cell growth of N. calcicola isolated from alkaline ‘Usar’ soils of northern India was 500 mM NaCl at pH 10.5, accompanied with an increase in photosynthetic O2 evolution, carbohydrate content and activities of nitrate reductase, glutamine synthetase, photosystem I and photosystem II. Under salt stress conditions above 500 mM NaCl, cell growth and carbohydrate contents reduced. The results indicate that production of carbohydrates under salinity stress at alkaline pH acts as major mechanism of salt tolerance in cyanobacteria.