How do roots of the metal-resistant perennial bush Zygophyllum fabago cope with cadmium and zinc toxicities?

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. Methods: 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 CdCl or 50 μM ZnSO, and compounds involved in osmotic adjustment, protection of cellular structures and management of oxidative status were determined. Results: 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. Conclusions: 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. [ABSTRACT FROM AUTHOR]