Effects of Calcium Chloride on Metabolism of Salt-stressed Dioscorea Rotundata Cheruth Abdul Jaleel*, Ragupathi Gopi, Muthiah Gomathinayagam

Soil salinity affects plant growth in a variety of ways, reducing water uptake, causing toxic accumulation of sodium and chloride, and reducing nutrient availability. Salinity also induces water deficit even in well-watered soils by decreasing the osmotic potential of soil solutes, thus making it difficult for roots to extract water from their surrounding media (Jaleel et al., 2007a). Excessive sodium inhibits the growth of many salt-sensitive plants, which includes most crop plants. The typical first response of all plants to salt stress is osmotic adjustment. Compatible solute accumulation in the cytoplasm is considered a mechanism to impart salt tolerance (Hare et al., 1998; Jaleel et al., 2007b). Chemical treatment and crop management practices have been tried to alleviate salinity effects without much success. A widespread practice to reduce salt content in soils is leaching. With the rising cost of water, this method may not be feasible in the future. In addition, economic pressures on water supplies may force agriculture to use greater amounts of lower-quality water with higher salinity. One possible approach to reducing the effect of salinity on plant productivity is through the addition of calcium supplements to irrigation water (Sohan et al., 1999; Jaleel et al., 2007c). Under saline conditions, root growth has been found to be regulated by calcium, and to mitigate the adverse effects in barley (Cramer et al., 1990; Jaleel et al., 2007d). Several scales of physiology have been applied to study responses to salt stress tolerance mechanisms and methods to overcome salt stress in field crops over recent years (Panneerselvam et al., 1998; Sankar et al., 2006). However, little information has been gained about the physiological basis of salt stress in medicinal plants (Jaleel et al., 2007e). Therefore it seems useful to test important medicinal plants for their halotolerance, and methods to overcome salt stress. Roots and tubers are the most important food crops in the tropics and subtropics; they are of very ancient origin and are intimately associated with human survival and socio-economic history. White yam (Dioscorea rotundata Poir.) is one of the important edible tuber crops cultivated in India and many other tropical countries including those of Africa (Jaleel et al., 2007f). Yams are a valuable source of carbohydrates and fiber, and are low in fats, which makes them a good dietary source (Jaleel et al., 2007g,h). In Dioscorea rotundata plants the ameliorative effect of CaCl2 during growth under NaCl stress has not been subjected to detailed physiological study. This study aims to understand the effect of salinity on the physiological parameters of Dioscorea rotundata