Cysteine- and glutathione-mediated uptake of lead and cadmium into Zea mays and Brassica napus roots.

This study examines a new mechanism for the uptake of Pb and Cd into Brassica napus and Zea mays roots. During hydroponic experiments, the uptake of Pb and Cd was enhanced in the presence of cysteine and glutathione, whereas no or very low uptake was observed in EDTA and penicillamine controls. Uptake rates were also enhanced after pre-exposure to cysteine or glutathione and inhibited in the presence of vanadate, suggesting a biological mechanism of uptake. Increasing concentrations of glutathione in solution resulted in decreasing Pb uptake rates, indicating competition for transport between free-glutathione and Pb-glutathione species. Pb uptake in the presence of increasing cysteine concentrations resulted in decreased uptake initially but linearly increasing uptake at higher concentrations. Experimentation showed concentration dependent Pb uptake rates. We speculate that there are specific transporters for these thiol ligands and describe what barriers remain for application of this novel transport mechanism in chelator-assisted phytoremediation.