High-affinity glutamine synthetase involved in ammonium assimilation (Probable). Plays an important role in the primary assimilation of ammonium taken up by roots (PubMed:23509111). Plays a role in maintaining nitrogen metabolic balance during ammonium assimilation, thus controlling plant growth and development (PubMed:24743556). Reassimilates ammonium generated during lignification within developing tillers, which is probably required for the outgrowth of axillary buds (PubMed:25429996). Required for nitrogen-dependent biosynthesis of cytokinin (PubMed:28186255). Active cytokinin in axillary bud meristem is required for axillary bud outgrowth and necessary for tillering (PubMed:28186255). ATP + L-glutamate + NH4(+) = ADP + H(+) + L-glutamine + phosphate Measured at pH 7.8 and 30 degrees Celsius for all experiments. Homooctamer. Expressed in roots and at lower levels in leaf blades and spikelets (rice flower). Induced in roots by ammonium supply. Reduced number of tillers and panicles. Plants overexpressing GLN1-2 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.