Low-affinity proton-dependent bidirectional nitrate transporter. Involved in nitrate loading into xylem and not in nitrate uptake. Not involved in histidine or dipeptides transport. High expression in roots. Barely detected in shoots. Expressed in root pericycle cells close to the xylem. Up-regulated slowly by nitrate. Down-regulated by cadmium and high pH. Circadian-regulation. Expression increase during the dark phase and decrease during the light phase. No visible phenotype when grown under normal conditions. Lower nitrate concentration in xylem sap. Decreased long-distance root-to-shoot transport of nitrate but not of sulfate or phosphate. Belongs to the major facilitator superfamily. Proton-dependent oligopeptide transporter (POT/PTR) (TC 2.A.17) family.