Nitrogen metabolism in tomato plants under cadmium stress

Young seedlings of tomato (Lycopersicon esculentum Mill.) grown on nitric medium and treated with different cadmium (Cd) concentrations (0-50 muM) were used. Results obtained show that Cd remains predominantly located in the roots, which then seem to play the role of trap-organs. Increasing Cd concentration in the medium leads particularly to a decrease in NO3- accumulation, together with decrease in the activities of nitrate reductase (NR), nitrite reductase (NiR), and glutamine synthetase (GS). On the other hand, stimulations were observed for ammonium accumulation, anabolitic activity of glutamate dehydrogenase (GDH) and protease activity. Contrarily, decreases were obtained for soluble protein contents and catabolitic activity of GDH. These results were discussed in relation to the hypothesis attributing to the mitochondrial enzyme NADH-dependent GDH, an important role in the plant defense processes, in maintaining the glutamate pool in conditions where the need for NH4+ detoxification is increased by heavy metals.