Osmoregulatory role of alanine during salt stress in the nitrogen fixing cyanobacterium Anabaena sp. 287.

The freshwater cyanobacterium, Anabaena sp. 287 exhibited enhanced tolerance to NaCl in the presence of ammonium, nitrate, and the amino acids, alanine, valine, proline, lysine, histidine, methionine and aspartic acid. Apart from providing permanent protection to the growth during stress, like NO3- and NH4+, alanine also relieved the initial salt mediated inhibition on enzymes involved in nitrogen fixation, photosynthesis and respiration. The accumulation of sugars was observed only during molecular nitrogen growth in the presence of salt. The cellular total nitrogen content was inversely proportional to the total sugar concentration. All nitrogenous substances which supported growth in the presence of salt curtailed the Na+ influx. Sodium chloride concentration-dependent 3H]D-alanine uptake in this cyanobacterium favours the conclusion that alanine acts as an osmoregulator along with sugars.