EDDS-enhanced metal phytoextraction by Brassicaceae species. Uptake and translocation of CuEDDS complexes by Brassica carinata and responses at transcriptional and metabolic levels.

The present research deals with the phytoremediation of a metal-polluted, markedly degraded area located at Torviscosa (Udine, North-East Italy) and included within the perimeter identified as a site of national interest for restoration. The cleaning up of this disused dump for pyrite cinders derived from ore roasting for sulphur extraction requires effective approaches as the use of the EDTA structural isomer (S,S)-N,N’-ethylenediamine disuccinic acid (EDDS) in a chelant-enhanced phytoextraction programme. The easily biodegradable EDDS exerts its effects by solubilising target metals from soil and making them more available for plant uptake and translocation to shoots and by preventing movement of metal complexes into groundwater. The phytoextraction effectiveness was investigated using the two accumulator crops Raphanus sativus and Brassica carinata. These crops were grown in opaque PVC pots filled with the multiple polluted soil mixed with sand (1:1, w/w) and amended with single(2,5 or 5 mmol kg-1) or repeated doses (1 mmol kg-1) of EDDS distributed in different growth stages. The lower single application and B. carinata were more effective in phytoextraction compared to the other treatments and crop because no metal leaching and dry biomass reduction occurred together with a higher metal translocation (+31%). Among the metals present in the cinders, Cu – which exceeded 14-fold the national legal limits – showed the highest rate of complexation (log K 18.4). Therefore, to improve the knowledge of the main key mechanisms of chelant-stimulated metal acquisition, uptake and translocation of CuEDDS complexes by B. carinata were studied both in excised and intact roots. CuEDDS treatment determined a lower Cu uptake compared to the metal alone because the complex had to be split before Cu uptake. At the same time, the CuEDDS treatment resulted in a higher metal translocation. To gain a better understanding of Cu uptake, elemental maps of Cu were generated by micro-PIXE technique. In B. carinata roots Cu was found to be localized mainly in the xylem system and transported to specific tissues for subsequent use and sequestration. Finally, B. carinata reacted positively to CuEDDS exposure, developing adaptive mechanisms by adjusting gene expression and showing tolerance to oxidative stress induced by Cu.