Na+ regulation by combined nitrogen in Azolla pinnata–Anabaena azollae symbiotic association during salt toxicity

To study the regulation of Na+ ion by combined-N sources in Azolla pinnata–Anabaena azollae, Na+ influx, intracellular Na+ and Na+ efflux were investigated in the presence of different N-sources (N2, NH4+, NO3− and urea) and various NaCl concentrations. Sodium influx by Azolla pinnata fronds was minimum in the presence of NO3−. Almost identical levels of intracellular sodium, although less than N2 and NH4+ incubated fronds were observed in the presence of NO3− and urea. Efflux of sodium was minimum in urea and NO3− grown fronds. A low residual sodium was observed in the fronds incubated in NO3− and urea supplemented media. Results suggest that nitrate and urea curtailed the entry of sodium, reduced salt toxicity maximally by maintaining the minimum level of sodium and also conserved energy due to slow influx and efflux of Na+ within the fronds during salt shock and the process of adaptation.