Controls the flux of glucose into the hexosamine biosynthetic pathway (HBP) leading to glucosamine (GlcN) content homeostasis (PubMed:30775776). Involved in regulating the availability of precursors for N- and O-linked glycosylation of proteins (PubMed:30775776). Required during pollen maturation and pollen tube formation by triggering polar deposition of pectin and callose in the pollen cell wall (PubMed:30775776). Promotes tolerance to tunicamycin (Tm), an inhibitor of proteins N-glycosylation in endoplasmic reticulum (ER) (PubMed:30775776). D-fructose 6-phosphate + L-glutamine = D-glucosamine 6-phosphate + L-glutamate Nucleotide-sugar biosynthesis; UDP-N-acetyl-alpha-D-glucosamine biosynthesis; alpha-D-glucosamine 6-phosphate from D-fructose 6-phosphate: step 1/1. Homotetramer, may also exist as homodimers. Highly expressed in flowers specifically in mature anthers, mature pollen grains and pollen tubes (PubMed:30775776). Barely observed in roots, leaves and stems (PubMed:30775776). During flower development, first observed in the late tricellular pollen grains. Accumulates in response to tunicamycin (Tm, inhibitor of proteins N-glycosylation in endoplasmic reticulum) and dithiothreitol (DTT, reducing agent that blocks disulfide-bond formation of cytosolic and ER proteins). Male gametophytic sterility (PubMed:30775776). Impaired growth and pollen germination associated with reduced glucosamine (GlcN) content, and lower tolerance to tunicamycin (Tm) (PubMed:30775776). Mutant plants exhibit also reactive oxygen species (ROS) production, cell death and a decrease in protein N-glycosylation (PubMed:30775776). Abnormal pollen grains due to defects in a polar deposition of pectin and callose in the pollen cell wall (PubMed:30775776). These phenotypes are suppressed by GlcN supplementation (PubMed:30775776).