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

摘要

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 (N_2, NH_4~+, NO_3~- and urea) and various NaCl concentrations. Sodium influx by Azolla pinnata fronds was minimum in the presence of NO_3~-. Almost identical levels of intracellular sodium, although less than N_2 and NH_4~+ incubated fronds were observed in the presence of NO_3~- and urea. Efflux of sodium was minimum in urea and NO_3~- grown fronds. A low residual sodium was observed in the fronds incubated in NO_+~- 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.