Growth and cellular ion content of a salt-sensitive symbiotic system Azolla pinnata-Anabaena azollae under NaCl stress

摘要

Salinity, at a concentration of 10mM NaCl affected the growth of Azolla pinnata-Anabaena azollae association and became lethal at 40mM. Plants exposed up to 30mM NaCl exhibited longer roots than the control, especially during the beginning of incubation. Average root number in plants exposed to 10 and 20mM NaCl remained almost the same as in control. A further rise in NaCl concentration to 30mM reduced the root number, and roots shed off at 40mM NaCl. Presence of NaCl in the nutrient solution increased the cellular Na(+) of the intact association exhibiting differential accumulation by individual partners, while it reduced the cellular Ca(2+)level. However, cellular K(+) content did not show significant change. Cellular Na(+) based on fresh weight of respective individual partners (host tissues and cyanobiont) remained higher in the host tissues than the cyanobiont, while reverse was true for K(+) and Ca(2+) contents. The contribution of A. azollae in the total cellular ion content of the association was a little because of meagre contribution of the cyanobiont mass (19-21%). High salt sensitivity of Azolla-Anabaena complex is due to an inability of the association to maintain low Na(+) and high Ca(2+) cellular level.