Forms of zinc accumulated in the hyperaccumulator Arabidopsis halleri.
The chemical forms of zinc (Zn) in the Zn-tolerant and hyperaccumulator Arabidopsis halleri and in the non-tolerant and nonaccumulator Arabidopsis lyrata subsp. petraea were determined at the molecular level by combining chemical analyses, extended x-ray absorption spectroscopy (EXAFS), synchrotron-based x-ray microfluorescence, and muEXAFS. Plants were grown in hydroponics with various Zn concentrations, and A. halleri specimens growing naturally in a contaminated site were also collected. Zn speciation in A. halleri was independent of the origin of the plants (contaminated or non-contaminated) and Zn exposure. In aerial parts, Zn was predominantly octahedrally coordinated and complexed to malate. A secondary organic species was identified in the bases of the trichomes, which contained elevated Zn concentrations, and in which Zn was tetrahedrally coordinated and complexed to carboxyl and/or hydroxyl functional groups. This species was detected thanks to the good resolution and sensitivity of synchrotron-based x-ray microfluorescence and muEXAFS. In the roots of A. halleri grown in hydroponics, Zn phosphate was the only species detected, and is believed to result from chemical precipitation on the root surface. In the roots of A. halleri grown on the contaminated soil, Zn was distributed in Zn malate, Zn citrate, and Zn phosphate. Zn phosphate was present in both the roots and aerial part of A. lyrata subsp. petraea. This study illustrates the complementarity of bulk and spatially resolved techniques, allowing the identification of: (a) the predominant chemical forms of the metal, and (b) the minor forms present in particular cells, both types of information being essential for a better understanding of the bioaccumulation processes.
Sarret
Géraldine
G
Environmental Geochemistry Group, Laboratoire de Géophysique Interne et Toctnophysique, University of Genoble and Centre National de la Recherche Scientifique, Grenoble cedex, France. gsarret@ujf-grenoble.fr
Saumitou-Laprade
Pierre
P
Bert
Valérie
V
Proux
Olivier
O
Hazemann
Jean-Louis
JL
Traverse
Agnès
A
Marcus
Matthew A
MA
Manceau
Alain
A
D000222:Adaptation, Physiological / Q000187:drug effects / Q000502:physiology*; D017360:Arabidopsis / Q000378:metabolism*; D022081:Cell Surface Extensions / Q000378:metabolism; D019343:Citric Acid / Q000378:metabolism; D008293:Malates / Q000378:metabolism; D010070:Oxalates / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D018520:Plant Shoots / Q000378:metabolism; D012989:Soil Pollutants / Q000378:metabolism; D013052:Spectrometry, X-Ray Emission; D015032:Zinc / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D017967:Zinc Compounds / Q000378:metabolism
D008293:Malates; D010070:Oxalates; D010710:Phosphates; D012989:Soil Pollutants; D017967:Zinc Compounds; C043952:zinc phosphate; D019343:Citric Acid; C030298:malic acid; D015032:Zinc