Salinity tolerance mechanism in the aquatic nitrogen fixing pteridophyte Azolla : a review

Salinity is one of the major constraints for agricultural productivity and the problem of salinity is likely to increase further. The aquatic fern Azolla is employed as an important bio-inoculant for the cultivation of rice paddy. In addition to this it is also used as feed supplement for cattle and poultry. However, increasing soil salinity is a serious threat for its wider exploitation. Stressors such as salinity leads to drastic changes in the metabolic activities especially the photosynthesis and nitrogen fixation. The potential of plants to tolerate salinity is determined by efficient mechanisms operating at cellular and sub-cellular levels. Several adaptation strategies are required to cope with salinity stress. Complicated interactions between the host plant Azolla and its symbiont should be considered if this organism is employed as bio-inoculant. Therefore, in the present review we discuss on the effect of salinity on Azolla and its cyanobiont with an emphasis on the physiological, biochemical and molecular mechanisms of salinity tolerance.