Involved in nitrate transport, but does not seem to be able to mediate transport by its own. Acts as a dual component transporter with NAR2.1. Imports nitrate with high affinity when expressed with NAR2.1 in a heterologous system (Xenopus oocytes). Plays a key role in long-distance nitrate transport from root to shoot particularly at low external nitrate supply. Heterotetramer composed of two NRT2.3 and two NAR2.1 (By similarity). Isoform 1 interacts with NAR2.1, but not isoform 2. Expressed in the stelar cells of both primary and lateral roots, particularly at the site of lateral root emergence, root-shoot junction zone, vascular tissues of adventitious root primordia, leaves, germ tips and seed scutellum. Circadian-regulation with a peak in the middle of the morning and at the end of the light period. Isoforms 1 and 2 are induced by sucrose in roots. Isoform 1 is induced by nitrate in roots, but not isoform 2. Isoform 1 is down-regulated by ammonium, glutatmate and aspartate in roots, but not isoform 2. Plants silencing isoform 1 of NTR2.3 have impaired xylem loading of nitrate and decreased plant growth at low nitrate supply (0.5 mM). Belongs to the major facilitator superfamily. Nitrate/nitrite porter (TC 2.A.1.8) family.