Involved in high-affinity nitrate transport. Might be involved in the transfer of nitrate from stored pools to cytoplasm. Expressed in roots and shoots. Low transient up-regulation by nitrate both in shoots and roots. Very low induction by growth on low nitrate concentration, but strong induction in mutant with disruption in both NRT21. and NRT2.2. However, this overexpression could not restore the nitrate influx. Belongs to the major facilitator superfamily. Nitrate/nitrite porter (TC 2.A.1.8) family.