Changes in amino acid composition and nitrogen metabolizing enzymes in ripening fruits of Lycopersicon esculentum Mill.

The free amino acid content of tomato (Lycopersicon esculentum Mill.) fruits from cultivars Platense, Vollendung and Cherry were determined during ripening. It was found that glutamate markedly increased in red fruits of the three cultivars under study. At this stage, the cv Cherry had the highest relative glutamate molar content (52%) of all the analyzed tomato fruit cultivars. Measurements of nitrogen-assimilating enzyme activities of these fruits showed a decrease in glutamine synthetase (GS, EC 6.3.1.2) during fruit ripening and a concomitant increase in NADH-glutamate dehydrogenase (GDH, EC 1.4.1.3) and aspartate aminotransferase (EC 2.6.1.1) activities. Western blot analysis of protein extracts revealed that while GS was principally present in green fruit extracts, GDH was almost exclusively observed in the extracts of red fruits. These results suggest a reciprocal pattern of induction between GS and GDH during tomato fruit ripening.