Effect of salinity (0, 50, 100, 250, 500 and 750 mM NaCI) was observed on some important physiological parameters of nitrogen metabolism such as nitrate uptake, intracellular and extracellular ammonium status and activities of nitrogenase, nitrate reductase, nitrite reductase and glutamine synthetase among Frankia strains differing in their salt tolerance capacity. Nitrogenase activity closely followed the growth pattern with regular decline on NaCI supplementation. All the other enzymes showed optimum activity at 100 mM and declined further. Co-regulation of the nitrate uptake system and sequential enzyme activities plays a crucial role in governing the nitrogen status of strains during salt stress. HsIil0 experiencing minimum decline in enzyme activities and best possible nitrogen regulation under NaC1 replete condition showed adequate nutritional management. Among all the strains, HsIil0 proved to be salt tolerant on account of above features while the salt sensitive strain HsIi8 lacked the ability to regulate various steps of nitrogen metabolism during salinity, and thus Frankia strain HsIil0 can potentially serve as a potential biofertilizer in the saline soil.
