Involved in nitrate transport, but does not seem to be able to mediate transport by its own (PubMed:8180624). Acts as a dual component transporter with NAR2 (system 1) (PubMed:8180624, PubMed:10682832). Imports nitrate with high affinity when expressed with NAR2 in a heterologous system (Xenopus oocytes) (PubMed:10682832). Involved in a high affinity and a high capacity transport specific for both nitrate and nitrite (PubMed:8567664). Nitrite transport mediated by system 1 is very sensitive to inhibition by nitrate. Up-regulated by nitrate (PubMed:8111016, PubMed:9648741). Up-regulated by nitrite (PubMed:9648741). Belongs to the major facilitator superfamily. Nitrate/nitrite porter (TC 2.A.1.8) family.