How do roots of the metal-resistant perennial bush Zygophyllum fabago cope with cadmium and zinc toxicities?
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Background and aims
Zygophyllum fabago is a perennial species tolerating high concentrations of Cd and Zn through protection of photosynthetically active leaves and regulation of Cd and Zn translocation from the roots to the shoots. This study aimed to assess metabolites involved in detoxification of those heavy metals in roots in relation to their coordination.
Zn and Cd K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy measurements were performed on root samples from plants exposed for 2 and 4 weeks to 10 μM CdCl2 or 50 μM ZnSO4, and compounds involved in osmotic adjustment, protection of cellular structures and management of oxidative status were determined.
Cd was mainly coordinated with thiol groups (77 %) while a minor part was ascribed to complexation with carboxyl and hydroxyl groups. In Zn-treated plants, Zn–O/N–C coordination was predominant (86 %) and only 14 % was coordinated to thiol groups. Phytochelatins increased in response to Cd but remained unaffected in Zn-treated roots. Conversely, polyamines accumulate in Zn-treated plants only. Heavy metals did not compromise root water or oxidative status.
Roots of Z. fabago are able to cope with Cd and Zn accumulation through efficient complexation processes which differ between Cd and Zn but are, for each element, similar to those previously recorded for photosynthetically active tissues.
KeywordsHeavy metal Phytoremediation Speciation X-ray spectroscopy
Extended X-ray absorption fine structure
Total non-protein thiols
X-ray absorption near edge structure
This work was supported by the Slovenian Research Agency research programme (P1-0112 and P1-0212), by Elettra for provision of synchrotron radiation facilities at beamline XAFS (project 20115112) and by the European Synchrotron Radiation Facility (ESRF), Grenoble, France, for provision of synchrotron radiation facilities at beamline BM23 (project LS-2209) and three members of the experimental team acknowledge the financial support of ESRF for travel, accommodation and subsistence expenses related to the experiment LS-2209. The authors are grateful to Gleb Parakhonskiy and Olivier Mathon for assistance in using beamline BM23 and Giuliana Aquilanti and Luca Olivi for expert advice on beamline XAFS.
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