title: In situ distribution and speciation of toxic copper, nickel, and zinc in hydrated roots of cowpea.
abstract: The phytotoxicity of trace metals is of global concern due to contamination of the landscape by human activities. Using synchrotron-based x-ray fluorescence microscopy and x-ray absorption spectroscopy, the distribution and speciation of copper (Cu), nickel (Ni), and zinc (Zn) was examined in situ using hydrated roots of cowpea (Vigna unguiculata) exposed to 1.5 μm Cu, 5 μm Ni, or 40 μm Zn for 1 to 24 h. After 24 h of exposure, most Cu was bound to polygalacturonic acid of the rhizodermis and outer cortex, suggesting that binding of Cu to walls of cells in the rhizodermis possibly contributes to the toxic effects of Cu. When exposed to Zn, cortical concentrations remained comparatively low with much of the Zn accumulating in the meristematic region and moving into the stele; approximately 60% to 85% of the total Zn stored as Zn phytate within 3 h of exposure. While Ni concentrations were high in both the cortex and meristem, concentrations in the stele were comparatively low. To our knowledge, this is the first report of the in situ distribution and speciation of Cu, Ni, and Zn in hydrated (and fresh) plant tissues, providing valuable information on the potential mechanisms by which they are toxic.
authors.affiliation: School of Agriculture and Food Sciences, The University of Queensland, St Lucia, Queensland 4072, Australia. p.kopittke@uq.edu.au
authors.forename: Peter M
authors.initials: PM
authors.lastname: Kopittke
authors.forename: Neal W
authors.initials: NW
authors.lastname: Menzies
authors.forename: Martin D
authors.initials: MD
authors.lastname: de Jonge
authors.forename: Brigid A
authors.initials: BA
authors.lastname: McKenna
authors.forename: Erica
authors.initials: E
authors.lastname: Donner
authors.forename: Richard I
authors.initials: RI
authors.lastname: Webb
authors.forename: David J
authors.initials: DJ
authors.lastname: Paterson
authors.forename: Daryl L
authors.initials: DL
authors.lastname: Howard
authors.forename: Chris G
authors.initials: CG
authors.lastname: Ryan
authors.forename: Chris J
authors.initials: CJ
authors.lastname: Glover
authors.forename: Kirk G
authors.initials: KG
authors.lastname: Scheckel
authors.forename: Enzo
authors.initials: E
authors.lastname: Lombi
mesh_terms: D003300:Copper / Q000378:metabolism / Q000633:toxicity*; D007887:Fabaceae / Q000187:drug effects* / Q000254:growth & development; D008856:Microscopy, Fluorescence; D009532:Nickel / Q000378:metabolism / Q000633:toxicity*; D018517:Plant Roots / Q000187:drug effects* / Q000254:growth & development; D014867:Water / Q000494:pharmacology*; D056928:X-Ray Absorption Spectroscopy; D015032:Zinc / Q000378:metabolism / Q000633:toxicity*
chemical_list: D014867:Water; D003300:Copper; D009532:Nickel; D015032:Zinc