Implication of glutamate, isocitrate and malate deshydrogenases in nitrogen assimilation in the cadmium-stressed tomato.

Implication of glutamate, isocitrate and malate deshydrogenases in nitrogen assimilation in the cadmium-stressed tomato. Tomato seedlings grown on nitric medium and treated with various cadmium concentrations (0 to 50 PM) were used. Results obtained show that cadmium remains predominantly located in the roots, which then seem to play the role of trap-organs. Increasing cadmium concentration in the medium leads particularly to a decrease in NO3- accumulation, together with a decrease in the activity of glutamine synthetase and in the quantity of plastidic isoform ARNm (GS2), and, on the contrary, to an increase of the cytosolic isoform ARNm (GS1). On the other hand, stimulations were observed for NADH-dependent glutamate synthase, NADH-dependent glutamate dehydrogenase, ARNm quantity of this enzyme, ammonium accumulation, and protease activity. In parallel, stimulations were observed for NAD(+) and NADP(+)-dependent malate dehydrogenase and NADP(+)-dependent isocitrate dehydrogenase. These results were discussed in relation to the hypothesis attributing to the dehydrogenase enzymes (GDH, MDH, ICDH) an important role in the plant defence processes against cadmium-induced stresses.