AbstractChanges in expression of glutamine synthetase (GS) have effect on plant nitrogen metabolism. In order to improve nitrogen use efficiency, several attempts at over-expressing GS II genes in plants have been previously undertaken, however few GSI and III genes are found such application. In this study, two GS I genes were cloned from bacterial strains and were transformed into Arabidopsis thaliana. Expression of the genes was confirmed under both mRNA and protein levels. Phenotypic studies revealed that all transgenic Arabidopsis lines showed enhanced fresh weight (12%) and dry weight (13%) compared with the wild-type plants at two concentrations of nitrate supplies. Further biochemical characterization confirmed that the transgenic lines had higher total nitrogen content (increased by 5-8%), soluble protein concentration (increased by 7-11%), total amino acid content (increased by 4-8%), leaf GS activity (enhanced by 8-14%) and free NO
