Glutamate Dehydrogenase Play Major Role In The Nitrogen Metabolism Under Cadmium Stress In Solanum Lycopersicon

Glutamate (Glu) metabolism and amino acid translocation were investigated in the control and cadmium stressed leaves of tomato (Solanum lycopersicon) using 15N-ammonium and 15N-Glu tracers. Regardless of organ type, 15N-ammonium assimilation occurred via glutamine synthetase (GS; EC 6.1.1.3), both in the control and stressed plants, and it did not depend on Glu dehydrogenase (GDH; EC 1.4.1.2). The 15N-ammonium and ammonium accumulation patterns support the role of GDH in the deamination of 15N-Glu to provide 2-oxoglutarate and 15N-ammonium. In presence of cadmium, excess 15N-ammonium was incorporated into asparagines that served as an additional detoxification molecule. In the presence of MSO, glutamate, alanine and -amino butyrate of roots tissue continue to become labelled with 15N under Cd treatment. Free ammonia accumulates rapidly in both leaves and roots in response to MSO. The labelling kinetics of amino acids in roots of tomato plants in the presence of cadmium show that continued assimilation of 15N-ammonium can occur when the GS/GOGAT cycle is inhibited. GDH protein is more abundantly in the mitochondria of cadmium stress plants than control. These findings open, therefore, new perspectives toward a better understanding of the function of GDH, particularly in relation to cadmium stress.