title: Root growth inhibition by NH(4)(+) in Arabidopsis is mediated by the root tip and is linked to NH(4)(+) efflux and GMPase activity.
abstract: Root growth in higher plants is sensitive to excess ammonium (NH(4)(+)). Our study shows that contact of NH(4)(+) with the primary root tip is both necessary and sufficient to the development of arrested root growth under NH(4)(+) nutrition in Arabidopsis. We show that cell elongation and not cell division is the principal target in the NH(4)(+) inhibition of primary root growth. Mutant and expression analyses using DR5:GUS revealed that the growth inhibition is furthermore independent of auxin and ethylene signalling. NH(4)(+) fluxes along the primary root, measured using the Scanning Ion-selective Electrode Technique, revealed a significant stimulation of NH(4)(+) efflux at the elongation zone following treatment with elevated NH(4)(+), coincident with the inhibition of root elongation. Stimulation of NH(4)(+) efflux and inhibition of cell expansion were significantly more pronounced in the NH(4)(+)-hypersensitive mutant vtc1-1, deficient in the enzyme GDP-mannose pyrophosphorylase (GMPase). We conclude that both restricted transmembrane NH(4)(+) fluxes and proper functioning of GMPase in roots are critical to minimizing the severity of the NH(4)(+) toxicity response in Arabidopsis.
authors.affiliation: Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China.
authors.forename: Qing
authors.initials: Q
authors.lastname: Li
authors.forename: Bao-Hai
authors.initials: BH
authors.lastname: Li
authors.forename: Herbert J
authors.initials: HJ
authors.lastname: Kronzucker
authors.forename: Wei-Ming
authors.initials: WM
authors.lastname: Shi
mesh_terms: D017360:Arabidopsis / Q000254:growth & development / Q000378:metabolism*; D002455:Cell Division; D049108:Cell Enlargement; D005030:Ethylenes / Q000378:metabolism; D007210:Indoleacetic Acids / Q000378:metabolism; D018519:Meristem / Q000254:growth & development / Q000378:metabolism; D009713:Nucleotidyltransferases / Q000378:metabolism*; D018517:Plant Roots / Q000254:growth & development* / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*
chemical_list: D005030:Ethylenes; D007210:Indoleacetic Acids; D000644:Quaternary Ammonium Compounds; C036216:ethylene; D009713:Nucleotidyltransferases; C026917:mannose 1-phosphate guanylyltransferase