title: Characterization of nitrite uptake in Arabidopsis thaliana: evidence for a nitrite-specific transporter.
abstract: Nitrite-specific plasma membrane transporters have been described in bacteria, algae and fungi, but there is no evidence of a nitrite-specific plasma membrane transporter in higher plants. We have used 13NO2(-) to characterize nitrite influx into roots of Arabidopsis thaliana. Hydroponically grown Arabidopsis mutants, defective in high-affinity nitrate transport, were used to distinguish between nitrate and nitrite uptake by means of the short-lived tracers 13NO2(-) and 13NO3(-). This approach allowed us to characterize a nitrite-specific transporter. The Atnar2.1-2 mutant, lacking a functional high-affinity nitrate transport system, is capable of nitrite influx that is constitutive and thermodynamically active. The corresponding fluxes conform to a rectangular hyperbola, exhibiting saturation at concentrations above 200 μM (Km = 185 μM and Vmax = 1.89 μmol g(-1) FW h(-1)). Nitrite influx via the putative nitrite transporter is not subject to competitive inhibition by nitrate but is downregulated after 6 h exposure to ammonium. These results signify the existence of a nitrite-specific transporter in Arabidopsis. This transporter enables Atnar2.1-2 mutants, which are incapable of sustained growth on low nitrate, to maintain significant growth on low nitrite. In wild-type plants, this nitrite flux may increase nitrogen acquisition and also participate in the induction of genes specifically induced by nitrite.
authors.affiliation: Department of Botany, University of British Columbia, 6270 University Boulevard, Vancouver, British Columbia, V6T1Z4, Canada.
authors.forename: Zorica
authors.initials: Z
authors.lastname: Kotur
authors.affiliation: Department of Botany, University of British Columbia, 6270 University Boulevard, Vancouver, British Columbia, V6T1Z4, Canada.
authors.forename: Yaeesh M
authors.initials: YM
authors.lastname: Siddiqi
authors.affiliation: Department of Botany, University of British Columbia, 6270 University Boulevard, Vancouver, British Columbia, V6T1Z4, Canada.
authors.forename: Anthony D M
authors.initials: ADM
authors.lastname: Glass
mesh_terms: D064751:Ammonium Compounds / Q000494:pharmacology; D027321:Anion Transport Proteins / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D017136:Ion Transport; D009154:Mutation; D009566:Nitrates / Q000378:metabolism; D009573:Nitrites / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism*
chemical_list: D064751:Ammonium Compounds; D027321:Anion Transport Proteins; D029681:Arabidopsis Proteins; D009566:Nitrates; D009573:Nitrites; D009584:Nitrogen
keywords: Arabidopsis; Atnar2.1 mutant; nitrate; nitrite; transporter