Catalyzes the hydrolysis of glutamine to glutamate and ammonia as part of the biosynthesis of pyridoxal 5'-phosphate. The resulting ammonia molecule is channeled to the active site of PDX1. Involved in the indirect resistance to singlet oxygen-generating photosensitizers. aldehydo-D-ribose 5-phosphate + D-glyceraldehyde 3-phosphate + L-glutamine = H(+) + 3 H2O + L-glutamate + phosphate + pyridoxal 5'-phosphate H2O + L-glutamine = L-glutamate + NH4(+) kcat is 0.023 min(-1) for L-glutamine. Cofactor biosynthesis; pyridoxal 5'-phosphate biosynthesis. Interacts with PDX1.1 or PDX1.3, but not with PDX1.2. Binds to RPA2A. Strongly expressed in roots, stems, leaves and flowers. Embryonic lethality when homozygous. In plants, synthesis of vitamin B6 does not involve deoxyxylulose 5-phosphate but utilizes intermediates from the pentose phosphate pathway and from glycolysis. Vitamin B6 is an essential quencher of singlet oxygen in plants, that can protect cellular membranes from lipid peroxidation. Belongs to the glutaminase PdxT/SNO family. Truncated N-terminus.