Abstract
Plant glutamate dehydrogenase is an enzyme interconverting L-glutamate and 2-oxoglutarate and providing a link between carbon and nitrogen metabolism. In Arabidopsis thaliana, this enzyme is encoded by three genes. Two of them, GDH1 and GDH2, provide most of the enzyme activity in plant leaves and roots. Expression of GDH1 and GDH2 genes is very low in the light and high in the dark. The molecular signals and mechanisms that provide the light-dependent GDH genes regulation remain unknown. Using photosynthetic electron transport inhibitors 3-(3.4-dichlorophenyl)-1.1-dimethylurea (DCMU) and 2.5-dibromo-3-methyl-6-isopropyl benzoquinone (DBMIB) we demonstrate that transcript levels of the GDH1 and GDH2 genes in Arabidopsis leaves change in accordance with a redox state of chloroplast electron transport chain: they are low when it is highly reduced and high when it is oxidized. Hydrogen peroxide or high light treatment did not result in decreasing of GDH1 or GDH2 expression, so reactive oxygen species cannot be the signals that reduce expression of these genes during dark-to-light shifts. There was no significant difference between the glucose content in the leaves of plants treated with DCMU and the plants treated with DBMIB, so glucose is not the only or the main factor that regulates expression of the studied genes. We presume that expression of Arabidopsis GDH1 and GDH2 genes depends on the chloroplast electron transport chain redox state. This regulatory mechanism could arise because of a need to avoid a competition for substrate between tetrapyrrole synthesis, glutathione synthesis and using of L-glutamate as an energy source during prolonged darkness.
Glutamate dehydrogenase isoenzyme 3 (GDH3) of Arabidopsis thaliana is regulated by a combined effect of nitrogen and cytokinin