title: AtAMT1 gene expression and NH4+ uptake in roots of Arabidopsis thaliana: evidence for regulation by root glutamine levels.
abstract: The mechanisms involved in regulating high-affinity ammonium (NH4+) uptake and the expression of the AtAMT1 gene encoding a putative high-affinity NH4+ transporter were investigated in the roots of Arabidopsis thaliana. Under conditions of steady-state nitrogen (N) supply, transcript levels of the AtAMT1 gene and Vmax values for high-affinity 13NH4+ influx were inversely correlated with levels of N provision. Following re-supply of NH4NO3 to N-starved plants, AtAMT1 mRNA levels and 13NH4+ influx declined rapidly but remained high when the conversion of NH4+ to glutamine (Gln) was blocked with methionine sulfoximine (MSX). This result demonstrates that end products of NH4+ assimilation, rather than NH4+ itself, are responsible for regulating AtAMT1 gene expression. Consistent with this hypothesis, AtAMT1 gene expression and NH4+ influx were suppressed by provision of Gln alone, or together with NH4NO3 plus MSX. Furthermore, AtAMT1 transcript levels and 13NH4+ influx were negatively correlated with root Gln concentrations, following re-supply of N to N-starved plants. In addition to this level of control, the data suggest that high cytoplasmic [NH4+] may inhibit NH4+ influx.
authors.affiliation: Department of Botany, University of British Columbia, Vancouver, Canada.
authors.forename: S R
authors.initials: SR
authors.lastname: Rawat
authors.forename: S N
authors.initials: SN
authors.lastname: Silim
authors.forename: H J
authors.initials: HJ
authors.lastname: Kronzucker
authors.forename: M Y
authors.initials: MY
authors.lastname: Siddiqi
authors.forename: A D
authors.initials: AD
authors.lastname: Glass
mesh_terms: D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000235:genetics*; D027682:Cation Transport Proteins; D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D005973:Glutamine / Q000378:metabolism; D009566:Nitrates / Q000494:pharmacology; D010940:Plant Proteins; D018517:Plant Roots / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism / Q000493:pharmacokinetics*; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D013997:Time Factors; D014158:Transcription, Genetic
chemical_list: D002352:Carrier Proteins; D027682:Cation Transport Proteins; D009566:Nitrates; D010940:Plant Proteins; D000644:Quaternary Ammonium Compounds; D012333:RNA, Messenger; C088952:ammonium transporters, plant; D005973:Glutamine; C006568:ammonium nitrate