title: Contrasting effects of nicotianamine synthase knockdown on zinc and nickel tolerance and accumulation in the zinc/cadmium hyperaccumulator Arabidopsis halleri.
abstract: Elevated nicotianamine synthesis in roots of Arabidopsis halleri has been established as a zinc (Zn) hyperaccumulation factor. The main objective of this study was to elucidate the mechanism of nicotianamine-dependent root-to-shoot translocation of metals. Metal tolerance and accumulation in wild-type (WT) and AhNAS2-RNA interference (RNAi) plants were analysed. Xylem exudates were subjected to speciation analysis and metabolite profiling. Suppression of root nicotianamine synthesis had no effect on Zn and cadmium (Cd) tolerance but rendered plants nickel (Ni)-hypersensitive. It also led to a reduction of Zn root-to-shoot translocation, yet had the opposite effect on Ni mobility, even though both metals form coordination complexes of similar stability with nicotianamine. Xylem Zn concentrations were positively, yet nonstoichiometrically, correlated with nicotianamine concentrations. Two fractions containing Zn coordination complexes were detected in WT xylem. One of them was strongly reduced in AhNAS2-suppressed plants and coeluted with (67) Zn-labelled organic acid complexes. Organic acid concentrations were not responsive to nicotianamine concentrations and sufficiently high to account for complexing the coordinated Zn. We propose a key role for nicotianamine in controlling the efficiency of Zn xylem loading and thereby the formation of Zn coordination complexes with organic acids, which are the main Zn ligands in the xylem but are not rate-limiting for Zn translocation.
authors.affiliation: Department of Plant Physiology, University of Bayreuth, Bayreuth, Germany; INRA, UMR 1391 ISPA, F-33140, Villenave d'Ornon, France; Bordeaux Sciences Agro, UMR 1391 ISPA, F-33170, Gradignan, France.
authors.forename: Jean-Yves
authors.initials: JY
authors.lastname: Cornu
authors.forename: Ulrich
authors.initials: U
authors.lastname: Deinlein
authors.forename: Stephan
authors.initials: S
authors.lastname: Höreth
authors.forename: Manuel
authors.initials: M
authors.lastname: Braun
authors.forename: Holger
authors.initials: H
authors.lastname: Schmidt
authors.forename: Michael
authors.initials: M
authors.lastname: Weber
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Persson
authors.forename: Søren
authors.initials: S
authors.lastname: Husted
authors.forename: Jan K
authors.initials: JK
authors.lastname: Schjoerring
authors.forename: Stephan
authors.initials: S
authors.lastname: Clemens
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000235:genetics* / Q000378:metabolism; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D001383:Azetidinecarboxylic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D002104:Cadmium / Q000378:metabolism*; D002264:Carboxylic Acids / Q000378:metabolism; D004361:Drug Tolerance; D018506:Gene Expression Regulation, Plant; D055785:Gene Knockdown Techniques; D049810:Genetic Speciation; D009532:Nickel / Q000378:metabolism / Q000494:pharmacology*; D018517:Plant Roots / Q000201:enzymology / Q000235:genetics / Q000502:physiology; D052584:Xylem / Q000201:enzymology / Q000235:genetics / Q000502:physiology; D015032:Zinc / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D029681:Arabidopsis Proteins; D002264:Carboxylic Acids; D002104:Cadmium; C082893:nicotianamine; D001383:Azetidinecarboxylic Acid; D009532:Nickel; D019883:Alkyl and Aryl Transferases; C118230:nicotianamine synthase; D015032:Zinc
keywords: Arabidopsis halleri; metal hyperaccumulation; metal tolerance; nicotianamine (NA); organic acids; speciation analysis; xylem transport