title: Complexation of Hg with phytochelatins is important for plant Hg tolerance.
abstract: Three-week-old alfalfa (Medicago sativa), barley (Hordeum vulgare) and maize (Zea mays) were exposed for 7 d to 30 µm of mercury (HgCl(2) ) to characterize the Hg speciation in root, with no symptoms of being poisoned. The largest pool (99%) was associated with the particulate fraction, whereas the soluble fraction (SF) accounted for a minor proportion (<1%). Liquid chromatography coupled with electro-spray/time of flight mass spectrometry showed that Hg was bound to an array of phytochelatins (PCs) in root SF, which was particularly varied in alfalfa (eight ligands and five stoichiometries), a species that also accumulated homophytochelatins. Spatial localization of Hg in alfalfa roots by microprobe synchrotron X-ray fluorescence spectroscopy showed that most of the Hg co-localized with sulphur in the vascular cylinder. Extended X-ray Absorption Fine Structure (EXAFS) fingerprint fitting revealed that Hg was bound in vivo to organic-S compounds, i.e. biomolecules containing cysteine. Albeit a minor proportion of total Hg, Hg-PCs complexes in the SF might be important for tolerance to Hg, as was found with Arabidopsis thaliana mutants cad2-1 (with low glutathione content) and cad1-3 (unable to synthesize PCs) in comparison with wild type plants. Interestingly, high-performance liquid chromatography-electrospray ionization-time of flight analysis showed that none of these mutants accumulated Hg-biothiol complexes.
authors.affiliation: Laboratory of Plant Physiology, Department of Biology, Universidad Autónoma de Madrid, 28049 Madrid.
authors.forename: Sandra
authors.initials: S
authors.lastname: Carrasco-Gil
authors.forename: Ana
authors.initials: A
authors.lastname: Alvarez-Fernández
authors.forename: Juan
authors.initials: J
authors.lastname: Sobrino-Plata
authors.forename: Rocío
authors.initials: R
authors.lastname: Millán
authors.forename: Ramón O
authors.initials: RO
authors.lastname: Carpena-Ruiz
authors.forename: Danika L
authors.initials: DL
authors.lastname: Leduc
authors.forename: Joy C
authors.initials: JC
authors.lastname: Andrews
authors.forename: Javier
authors.initials: J
authors.lastname: Abadía
authors.forename: Luís E
authors.initials: LE
authors.lastname: Hernández
mesh_terms: D017360:Arabidopsis / Q000737:chemistry / Q000235:genetics; D002853:Chromatography, Liquid; D001467:Hordeum / Q000737:chemistry*; D013058:Mass Spectrometry; D000455:Medicago sativa / Q000737:chemistry*; D008628:Mercury / Q000737:chemistry*; D054811:Phytochelatins / Q000737:chemistry*; D018517:Plant Roots / Q000737:chemistry* / Q000254:growth & development; D013052:Spectrometry, X-Ray Emission; D003313:Zea mays / Q000737:chemistry*
chemical_list: D054811:Phytochelatins; D008628:Mercury