EFFECT OF CADMIUM ON ENZYMES OF NITROGEN-METABOLISM IN PEA-SEEDLINGS

One-month-old pea (Pisum sativum L. cv Bonneville) plants were supplied with 0-10 mM cadmium chloride and activities of a number of enzymes of nitrogen metabolism were determined 6 and 12 days after the treatment. Cadmium, in excess of 5 mM, significantly depressed biological nitrogen fixation per plant but acetylene reduction per g nodules decreased to a relatively smaller extent. Activity of glutamine synthetase (EC 6.3.1.2) in leaves was affected only slightly but declined markedly in the roots. Nitrate reductase (EC 1.6.6.1) and glutamate synthase (EC 1.4.7.1) activities in leaves decreased 6 days after treatment but after 12 days these were comparable to that of the control seedlings. The adverse effect on root nitrate reductase, however, became more pronounced with time. This metal enhanced the levels of glutamate dehydrogenase (EC 1.4.1.3), aspartate aminotransferase (EC 2.6.1.1) and alanine aminotransferase (EC 2.6.1.2) both in the levels and roots. After 12 days, though leaves tended to regain normal levels of these enzymes, roots continued to maintain higher activity of glutamate dehydrogenase but both the aminotransferases were affected adversely. The results are discussed in relation to impact of cadmium on nitrogen metabolism in leaves and roots of pea seedlings.