Green gram is the richest protein source of human diet and livestock in poor areas. Apart from that, they are used as green manures and green fodder to animals. Mainly they are used for fixing atmospheric nitrogen to improve the physical and chemical properties of soil. Among the legumes, Green gram was considered as the most important traditional crops of India. Salinity-an abiotic stress is an ever increasing problem that seriously affects crop production in various parts of the world, especially in areas where are irrigated with water containing salts. Salt stress is one of major factors in constraining crop adjustment substances, soluble sugar content, proline production.

About 23% of the world’s cultivated lands are saline and 37% is sodic (Khan and Duke, 2001). Salinity affects 7% of the world’s land area of about 930 million hectares. Salinity reduces the yield of pulses by more than 50% (Bray, 2000). Soils can be saline due to geo-historical processes or they can be man-made. The water and salt balance, just like in oceans and seas determine the formation of salty soils, where more salt comes in than goes out. Here, the incoming water from the land brings salts that remain because there is no outlet and the evaporation water does not contain salts. Soil salinity in agriculture soils refers to the presence of high concentration of soluble salts in the soil moisture of the root zone. Salt stress induces the synthesis of abscisic acid which closes stomata when transported to guard cells. As a result of stomatal closure, photosynthesis declines and photo inhibition and oxidative stress occur. Chlorophyll is the principal agent responsible for photosynthesis and, under adverse conditions, chlorophyll level is a good indicator of photosynthetic activity (XinWen et al., 2008). The deleterious effect of salinity is increased osmotic pressure which restricts the absorption of water into the seeds (Tester and Davenport, 2003). It is also toxic to the embryo and seedlings. Enzyme called α – amylase which is essential for seed germination is inhibited due to salt stress. Starch to sugar conversion occurs during germination is also affected by salinity. It also delays the synthesis of nucleic acids and RNAase. As regard to the chlorophyll content of the salinized plant, it is apparent that the chlorophyll content was reduced with increasing salinity. When salinity has affected the warning signs were sick or dying trees and declining vegetation. As salinity impacts on any remaining native vegetation and the wildlife that depends on it for survival, the loss of biodiversity escalates. Salinity also reduces the productivity of crops and the sustainability of agriculture. Based on the above constraints, we are taken the objective of Screening of Green gram varieties for NaCl stress tolerance through physiological analysis.

The experiment was carried out at Vanavarayar Institute of Agriculture (TNAU affiliated), Pollachi, Tamil Nadu, India during 2013-2014. The experiment consists of ten treatments with three replications were laid out in completely randomized block design with two cultivars of CO5 and CO6. Seeds of green gram varieties obtained from Department of Pulses, Tamil Nadu Agricultural University, Coimbatore, were used for the study and the details of the varietal characters were listed in Table 1. Green gram varieties (Table1) were screened for tolerance to various levels of sodicity stress, based on germination per cent, seedling growth and vigour index, seeds were allowed to germinate in Petri dishes. The germination medium was prepared following the procedure mentioned below. Petri dishes were sterilized using 0.01% HgCl₂ and 70% ethanol and finally washed with distilled water. Before placing the germination sheet, Petri dishes were cleaned thoroughly with a cotton swab. The surface sterilized (70% ethanol) 15 seeds from each variety were placed in each Petri dish. For imposing sodicity (11 levels as considered as Treatments) stresses, sodium chloride (NaCl) solution at the concentration of T₁: control (without NaCl), T₂:10, T₃:20, T₄:30, T₅:40, T₆:50, T₇:60, T₈:70, T₉:80, T₁₀:90 and T₁₁:100 ppm were prepared. The seeds were allowed to germinate, by sprinkling the salt solution of 10 mL each in alternate days. Distilled water was used for maintaining the control. The pH and EC details of the salt solution used for experiment were given in Table 2.

Soluble protein content: Soluble protein content of leaf was estimated as per the method of Lowry et al. (1951) and expressed as mg/g fresh weight.

Proline content of the leaf sample was estimated by the method of Nicholas et al. (1976) and expressed as µg of NO₂ g^-1·hr^-1 of fresh weight.

Proline content of the leaf sample was estimated by the method of Bates et al. (1973) and expressed as µg/g of fresh weight.

Catalase activity of the leaf sample was assayed as per the procedure adopted by Gopalachari (1963) and expressed as µg H₂O₂ g^-1·min^-1.

The soluble protein content of the leaf, being a measure of RuBP carboxylase activity was considered as an index for photosynthetic efficiency. There were reports that RuBP-case enzyme forms nearly 80 per cent of the soluble proteins in leaves of many plants (Joseph et al., 1981). The result on soluble protein content was significantly differed in all the treatments. Among the treatments, T1 showed highest Soluble protein content in green gram both CO6 and CO8 (4.19 and 9.16), which was followed by T₃, T₄ and T₅. The lowest soluble protein content was recorded in T₇, T₈ and T₁₁ treatments (Table 3). Martignone et al. (1987) observed that in soybean soluble protein content was the first nitrogenous compound affected under stress conditions, which at severity got denatured and lost the activity. It was further explained that soluble protein, world’s most abundant protein containing the enzyme RUBISCO, is involved in CO₂ assimilation; therefore, the reduction in soluble protein might have a direct adverse effect on photosynthesis.

The result on nitrate reductase activity was significantly differed in all the treatments. Among the treatments, T₂ showed highest nitrate reductase activity in green gram both CO6 and CO8 (83.60 and 85.15), which was followed by T₃, and T₄. The lowest nitrate reductase activity was recorded in T₁₀ and T₁₁ treatments (Table 3).

 3.3 Proline (mg/g)

The result on catalase activity was significantly differed in all the treatments. Among the treatments, T₂ showed highest catalase activity in green gram both CO6 and CO8 (77.10 and 72.02), which was followed by T₃, T₄ and T₅. The lowest catalase activity was recorded in T₈, T₉, T₁₀ and T₁₁ treatments (Table 4). In this present study, we noticed that, the increase in enzyme activity with external salinity may be due to increased synthesis of enzyme. Transgenic plants over expressing ROS scavenging enzymes, such as super oxide dismutase (Alscher et al., 2002), ascorbate peroxidase (Wang et al., 1999) and glutathione S-transferase / glutathione peroxidase (Roxas et al., 1997 and 2000) showed increased tolerance to osmotic and oxidative stresses.