title: Root-to-shoot long-distance circulation of nicotianamine and nicotianamine-nickel chelates in the metal hyperaccumulator Thlaspi caerulescens.
abstract: Plant metal hyperaccumulator species are widely used as models to unravel the heavy metal tolerance and hyperaccumulation mechanisms. Thlaspi caerulescens is capable of tolerating and hyperaccumulating Zn, Cd, and Ni. A search for factors involved in the cellular tolerance to Ni, based on yeast screens, led to isolation of a cDNA encoding a functional nicotianamine (NA) synthase (NAS). The T. caerulescens genome appears to contain a single copy of the NAS gene named TcNAS whose expression is restricted to the leaves. The analysis of dose-response and time-course Ni treatments have revealed that the exposure to Ni triggers the accumulation of NA in the roots. Because neither TcNAS expression nor NAS activity were detected in the roots, the NA accumulation in roots is most probably the result of its translocation from the leaves. Once in the roots, NA, together with Ni, is subsequently found in the xylem, for redirection to the aerial parts. Using liquid chromatography coupled to inductively coupled plasma or electrospray ionization mass spectrometry, it has been shown that part of the Ni is translocated as a stable Ni-NA complex in the xylem sap. This circulation of NA, Ni, and NA-Ni chelates is absent in the non-tolerant non-hyperaccumulator related species T. arvense. Taken together, the results provide direct physiological and chemical evidence for NA and NA-heavy metal complex translocation in a hyperaccumulator species.
authors.affiliation: Biochimie et Physiologie Moléculaire des Plantes, CNRS (UMR 5004), Institut National de la Recherche Agronomique, Université Montpellier 2, Ecole Nationale Supérieure d'Agronomie, 2 Place Viala, F-34060 Montpellier cedex 2, France.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Mari
authors.forename: Delphine
authors.initials: D
authors.lastname: Gendre
authors.forename: Katia
authors.initials: K
authors.lastname: Pianelli
authors.forename: Laurent
authors.initials: L
authors.lastname: Ouerdane
authors.forename: Ryszard
authors.initials: R
authors.lastname: Lobinski
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Briat
authors.forename: Michel
authors.initials: M
authors.lastname: Lebrun
authors.forename: Pierre
authors.initials: P
authors.lastname: Czernic
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D001383:Azetidinecarboxylic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D001692:Biological Transport; D002614:Chelating Agents / Q000378:metabolism*; D002853:Chromatography, Liquid; D018745:Genome, Plant; D008969:Molecular Sequence Data; D009532:Nickel / Q000378:metabolism*; D010802:Phylogeny; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D018520:Plant Shoots / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D016415:Sequence Alignment; D021241:Spectrometry, Mass, Electrospray Ionization; D031227:Thlaspi / Q000378:metabolism*; D052584:Xylem / Q000378:metabolism
chemical_list: D002614:Chelating Agents; D010940:Plant Proteins; D012333:RNA, Messenger; C082893:nicotianamine; D001383:Azetidinecarboxylic Acid; D009532:Nickel; D019883:Alkyl and Aryl Transferases; C118230:nicotianamine synthase