title: Toward the mechanism of NH(4) (+) sensitivity mediated by Arabidopsis GDP-mannose pyrophosphorylase.
abstract: The ascorbic acid (AA)-deficient Arabidopsis thaliana mutant vtc1-1, which is defective in GDP-mannose pyrophosphorylase (GMPase), exhibits conditional hypersensitivity to ammonium (NH(4) (+) ), a phenomenon that is independent of AA deficiency. As GMPase is important for GDP-mannose biosynthesis, a nucleotide sugar necessary for protein N-glycosylation, it has been thought that GDP-mannose deficiency is responsible for the growth defect in vtc1-1 in the presence of NH(4) (+) . Therefore, the motivation for this work was to elucidate the growth and developmental processes that are affected in vtc1-1 in the presence of NH(4) (+) and to determine whether GDP-mannose deficiency generally causes NH(4) (+) sensitivity. Furthermore, as NH(4) (+) may alter cytosolic pH, we investigated the responses of vtc1-1 to pH changes in the presence and absence of NH(4) (+) . Using qRT-PCR and staining procedures, we demonstrate that defective N-glycosylation in vtc1-1 contributes to cell wall, membrane and cell cycle defects, resulting in root growth inhibition in the presence of NH(4) (+) . However, by using mutants acting upstream of vtc1-1 and contributing to GDP-mannose biosynthesis, we show that GDP-mannose deficiency does not generally lead to and is not the primary cause of NH(4) (+) sensitivity. Instead, our data suggest that GMPase responds to pH alterations in the presence of NH(4) (+) .
authors.affiliation: Department of Biology, West Virginia University, 5228 Life Sciences Building, 53 Campus Drive, Morgantown, West Virginia 26506-6057, USA.
authors.forename: Chase F
authors.initials: CF
authors.lastname: Kempinski
authors.forename: Rawaa
authors.initials: R
authors.lastname: Haffar
authors.forename: Carina
authors.initials: C
authors.lastname: Barth
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D029681:Arabidopsis Proteins / Q000378:metabolism*; D001205:Ascorbic Acid / Q000032:analysis; D002453:Cell Cycle; D002462:Cell Membrane / Q000378:metabolism; D002473:Cell Wall / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006031:Glycosylation; D006155:Guanosine Diphosphate Mannose / Q000096:biosynthesis; D006863:Hydrogen-Ion Concentration; D009154:Mutation; D009713:Nucleotidyltransferases / Q000378:metabolism*; D018517:Plant Roots / Q000254:growth & development; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D013312:Stress, Physiological
chemical_list: D029681:Arabidopsis Proteins; D000644:Quaternary Ammonium Compounds; D006155:Guanosine Diphosphate Mannose; D009713:Nucleotidyltransferases; C026917:mannose 1-phosphate guanylyltransferase; D001205:Ascorbic Acid