Nitrate assimilation and biomass production in Sesamum indicuml. Seedlings in a lead enriched environment

Seed germination was delayed and seedling growth inhibited by 0.04 to 1.9 mM Pb⁺² in Sesamum indicum L. var HT-I. In root, shoot and leaf Pb⁺² accumulation increased with increasing Pb⁺² concentration in the nutrient solution. In root and leaf tissues in vivo and in vitro nitrate reductase activity was inhibited significantly which was well correlated with the concentration of Pb⁺² supplied and its accumulation in the plant parts. The inhibition of the NR enzyme activity could be, however, reversed by simultaneous treatment of Sesamum seedlings with K₂HPO₄, CaCl₂ and KNO₃ dissolved in nutrient solution. Total organic N and soluble protein of roots and shoots/leaves, on the other hand, increased with increasing concentration of Pb⁺² while the same treatment caused a decrease in the N content of cotyledons. It appears therefore, that the increase in N and protein in the roots, shoots/leaves may be a result of increased translocation of N from the cotyledons to the roots and shoots/leaves during early seedling growth in a Pb⁺² enriched environment.