Expression of the bacterial gdhA gene encoding a NADPH glutamate dehydrogenase in tobacco affects plant growth and development

We investigated the effects of genetic modification of nitrogen metabolism via the bacterial glutamate dehydrogenase (GDH) on plant growth and metabol ism. The gdhA gene from Escherichia coli encoding a NADPH-GDH was expressed in tobacco plants under the control of the 35 S promoter. The specific act ivity of GDH in gdhA plants was 8-fold of that in E. coli. Damage caused by spray application of 1.35 mM of phosphinothricin (PPT) herbicide, a glutam ine synthetase (GS) inhibitor, was less pronounced in gdhA plants as compar ed with the control plants which suggests that the introduced GDH can assim ilate some of the excess ammonium, at least during GS inhibition. However, gdhA plants were susceptible to 2.7 mM PPT. Biomass production was consiste ntly increased in gdhA transgenic plants grown under controlled conditions and in the field. Total free amino acids and total carbohydrates were incre ased in gdhA plants grown in the greenhouse suggesting that both nitrogen a nd carbon metabolism were altered. We conclude that the modifications in tr ansgenic plants may result from both increased nitrogen efficiency and alte red gene expression and metabolism.