Adjustments of nitrogen and carbon metabolisms were the mainly strategy followed in ammonium-fed tomato to alleviate cadmium toxicity

It was known that cadmium (Cd) toxicity evoked protective reactions that could induce cell death. But the question arises was the effect of nitrogen regime on Cd plant responses. To got more explications, we examined the effects of Cd in NH4+-fed tomato plants treated continuously or transitory by 25µM of CdSO4. Reduction of glutamine synthetase (GS) activity by Cd disappeared progressively after transfer of Cd-stressed tomato to control medium. It has been shown that Cd enhanced activity and protein accumulation of cytosolic isoenzyme (GS1) and reduced those of chloroplastid isoenzyme (GS2). When Cd-treated tomato plants were transferred on control medium, GS1 protein level diminished. Whereas, GS2 protein level remained unchanged. Our data showed that Cd stimulated the seven isoenzymes activities of glutamate deshydrogenase (NADH-GDH). Cadmium reduced too, phosphoenolpyruvate carboxylase (PEPC) and isocitrate dehydrogenase (ICDH) activities. Thus, we suggested that CO2 anaplerotic fixation into organic acids was secondary in leaves. Especially as photosynthetic rate (Amax) and photochemical quenching (qp) were stimulated and non-photochemical quenching was reduced (NPQ) by Cd in leaves of NH4+-fed tomato.