High-affinity glutamine synthetase (PubMed:14757761, PubMed:16338958). May contribute to the homeostatic control of glutamine synthesis in roots (PubMed:14757761). ATP + L-glutamate + NH4(+) = ADP + H(+) + L-glutamine + phosphate Measured at pH 7.8 and 30 degrees Celsius for all experiments (PubMed:14757761). kcat is 2.96 sec(-1) with ammonium as substrate (PubMed:16338958). kcat is 4.18 sec(-1) with glutamate as substrate (PubMed:16338958). Homooctamer (By similarity). Interacts with GRF3. Expressed in the pericycle in the region of lateral root emergence. Down-regulated by ammonium supply. Belongs to the glutamine synthetase family.