ANTAGONISTIC EFFECT OF SODIUM-CHLORIDE TO DIFFERENTIAL HEAVY-METAL TOXICITY REGARDING BIOMASS ACCUMULATION AND NITRATE ASSIMILATION IN SESAMUM-INDICUM SEEDLINGS

Combinations of 1.0 mM Pb2+, Cu2+ and Cd2+ (1:1) differentially inhibited growth, biomass accumulation and in vivo nitrate reductase activity (NRA, EC 1.6.6.1) in root and leaves of five-day-old Sesamum indicum L cv PB-1 seedlings. Addition of 2 EC and 10 EC NaCl to the nutrient media slightly inhibited root fresh weight of the seedlings (statistically not significant), whereas it increased the leaf fresh weight and dry weight of the plant parts with a variable magnitude. The presence of NaCl could abolish the negative effect of the metal combinations on the root fresh weight to a good extent, and it caused an increase in the tissue dry mass in the presence of the metals in most of the cases. However, recovery in the leaf fresh weight was observed only if NaCl was added with Cu2+ + Cd2+ in, the nutrient media. In vivo NRA of root and leaf in this cultivar was increased two-three-fold with the supply of NaCl and this increase was maintained even in the presence of the metal combinations by counteracting the toxic effect of the metals on the enzyme activity. A corresponding increase in total organic nitrogen content of the roots was also recorded. In vitro NRA, in either of the tissues, on the other hand, was drastically inhibited by the addition of 10 EC NaCl to the nutrient media. Our results show that toxic effect of Cd2+, Cu2+ and Pb2+ combinations on the seedling growth and nitrate assimilation especially in the roots of sesame PB-1 was not persistent in the NaCl affected growth environment. However, in vitro NRA was drastically inhibited by some modulating effect of the salt on the enzyme.