Salinity Induced Alterations in the Growth and Cellular Ion Content of Azolla caroliniana and Azolla microphylla

The nitrogen fxing aquatic pteridophyte Azolla is often found in the rice felds and is responsible for maintaining the soil fertility and productivity. Salinity is known to severely afect approximately half of the irrigated lands worldwide. Therefore, in the present study, the salinity stress response in the whole plants, freshly isolated cyanobionts and the roots of A. caroliniana and A. microphylla exposed to 90 mM NaCl for 9 days was evaluated in terms of growth and ion content. Growth of the whole plant was estimated as increment in the dry weight. NaCl (90 mM) inhibited the growth of A. caroliniana and A. microphylla. The root length and the number of roots of A. caroliniana and A. microphylla were estimated and A. microphylla showed signifcant increase in the length and number of roots. Accumulation of Na+, K+ and Ca2+ ions was also estimated in the whole plant, freshly isolated cyanobionts and the roots. The whole plant of A. microphylla accumulated less Na+ and more K+ whereas A. caroliniana accumulated more Na+ and less K+. Roots of A. microphylla accumulated less Na+ as compared to A. caroliniana and the cellular K+ and Ca2+ content was high in the roots of A. microphylla. Differential levels of Na+, K+ and Ca2+ ion accumulation were observed in the freshly isolated cyanobionts. The results showed signifcant genotypic diferences in growth and ion content of the whole Azolla plants and its cyanobionts. These results possibly suggest that A. microphylla and its cyanobionts exhibit better growth potential in response to salinity through efcient maintenance of ion content