High-affinity glutamine synthetase involved in ammonium assimilation (PubMed:15918879, PubMed:21255162). Seems to be a major component of the cytosolic glutamine synthetic pathway in leaf blades (PubMed:15918879, PubMed:21255162). Plays an important role in maintaining carbon and nitrogen metabolic balance during ammonium assimilation in shoots and roots, thus controlling plant growth and development (PubMed:21255162, PubMed:24743556). Plays an important role in maintaining broad range of metabolites and transcripts involved in the maintenance of plant metabolic homeostasis and development of plastid in roots (PubMed:32024696). ATP + L-glutamate + NH4(+) = ADP + H(+) + L-glutamine + phosphate Measured at pH 7.8 and 30 degrees Celsius for all experiments. Homooctamer. Highly expressed in leaf blades, at intermediate levels in spikelets (rice flower) and at lower levels in roots. Expressed in metaxylem and phloem of parenchyma cells and in sclerenchyma cells of developing leaf blades. Induced in roots under nitrogen-limited condition (PubMed:15574840, PubMed:23509111). Down-regulated in roots under ammonium supply (PubMed:17350935). Down-regulated by treatment with cadmium (PubMed:23743654). Plants show marked reduction in leaf blades elongation, plant height, panicle size and grain filling. Plants overexpressing GLN1-1 exhibit a poor plant growth phenotype and yield, and decreased carbon/nitrogen ratio in the stem caused by the accumulation of nitrogen in the stem. Belongs to the glutamine synthetase family.