title: Isolation and characterization of HvNRT2.3 and HvNRT2.4, cDNAs encoding high-affinity nitrate transporters from roots of barley.
abstract: Two full-length cDNAs, HvNRT2.3 and HvNRT2.4, were isolated from roots of barley (Hordeum vulgare), using reverse transcriptase-PCR and RACE-PCR. The corresponding polypeptides, consisting of 507 amino acids (molecular masses of 54.6 kD), belong to the major facilitator superfamily (MFS), and are closely related (>87% identity) to those encoded by HvNRT2.1 and HvNRT2.2 (formerly BCH1 and BCH2, respectively) from roots of barley. The latter are considered to encode inducible high-affinity NO(3)(-) transporters (Trueman et al., 1996). HvNRT2 transcripts were undetectable in NO(3)(-)-deprived plants. Following exposure to either NO(3)(-) or NO(2)(-), transcript abundance and (13)NO(3)(-) influx increased to a maximum by 6 to 12 h, then declined in HvNRT2.1, HvNRT2.2, and HvNRT2.3. The pattern of HvNRT2.4 transcript abundance was different, remaining high after achieving peak abundance. When external NO(3)(-) concentrations were varied from 0 to 500 microM under steady-state conditions of NO(3)(-) supply, HvNRT2 transcript accumulation and (13)NO(3)(-) influx were highest in 50 microM NO(3)(-) -grown plants. When NH(4)(+) was provided together with NO(3)(-), transcript accumulation during the first 2 h was similar to that due to NO(3)(-) alone, but by 4 h the transcript level was significantly reduced. HvNRT2 transcript was undetectable in leaf tissues.
authors.affiliation: Department of Botany, University of British Columbia, 6270 University Boulevard, Vancouver, British Columbia, Canada.
authors.forename: J J
authors.initials: JJ
authors.lastname: Vidmar
authors.forename: D
authors.initials: D
authors.lastname: Zhuo
authors.forename: M Y
authors.initials: MY
authors.lastname: Siddiqi
authors.forename: A D
authors.initials: AD
authors.lastname: Glass
mesh_terms: D000595:Amino Acid Sequence; D027321:Anion Transport Proteins; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics* / Q000302:isolation & purification*; D018744:DNA, Plant / Q000235:genetics* / Q000302:isolation & purification*; D017343:Genes, Plant; D001467:Hordeum / Q000235:genetics* / Q000378:metabolism*; D008969:Molecular Sequence Data; D005810:Multigene Family; D000091285:Nitrate Transporters; D018517:Plant Roots / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D027321:Anion Transport Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D017931:DNA Primers; D018076:DNA, Complementary; D018744:DNA, Plant; D000091285:Nitrate Transporters; D012333:RNA, Messenger; D018749:RNA, Plant