Journal
PLANT CELL AND ENVIRONMENT
Volume 34, Issue 5, Pages 778-791Publisher
WILEY
DOI: 10.1111/j.1365-3040.2011.02281.x
Keywords
biothiols; EXAFS; mass spectrometry; mercury; phytochelatins; soluble fraction; X-ray absorption spectroscopy
Categories
Funding
- Fundacion Ramon Areces
- Spanish Ministry of Science and Innovation [AGL2010-15151-PROBIOMET, AGL2007-61948]
- Comunidad de Madrid [EIADES S2009/AMB-1478]
- Junta Comunidades Castilla-La Mancha [PBI07-0091-3644]
- Aragon Government [A03]
- EU
- Department of Energy
- Office of Biological and Environmental Research
- National Institute of Health, National Centre for Research Resources
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Three-week-old alfalfa (Medicago sativa), barley (Hordeum vulgare) and maize (Zea mays) were exposed for 7 d to 30 mu m of mercury (HgCl2) 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.
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