Glutamate Dehydrogenase Of Tomato Induced In The Cytosol Of Phloem When Ammonia Is Provided Under Cadmium Stress Conditions

Glutamate (Glu) dehydrogenase (GDH), enzyme preferentially occurs in the mitochondria of companion cells of a number of plant species grown on nitrate as the sole nitrogen source. For a better understanding of the controversial role of GDH either in ammonium assimilation or in the supply of cadmium, we studied the localization of GDH in tomato (Solanum Lycopersicon 63/5F1) plants grown either on absence of cadmium (AC) or on presence of cadmium (PC). Production of GDH and its activity were strongly induced when plants were grown on presence of cadmium. The induction mainly occurred in highly vascularized organs such as stems and midribs and was likely to be due to accumulation of phloem-translocated ammonium in the sap. GDH was increased in the mitochondria and appeared in the cytosol of companion cells. Taken together, our results suggest that the enzyme plays a dual role in companion cells, either in the mitochondria when mineral nitrogen availability is low or in the cytosol when ammonium concentration increases under cadmium stress conditions.