EDTA reduces the physiological damage of lead on cardoon plants grown hydroponically

Cardoon seedlings (Cynara cardunculus L.) were grown hydroponically in nutrient solution and exposed to lead (Pb 2+ : 1mM) in the presence of a range of different EDTA concentrations (EDTANa 2 : 0, 0.5, 1 or 2mM). Analyses were performed to establish whether the coordination of Pb 2+ transport by EDTA enhances the mobility of this metal within the plant and to determine the toxic effects of these treatments during a phytoextraction process. Net photosynthesis, transpiration rate and stomatal conductance decreased dramatically in plants treated with Pb 2+ or Pb-EDTA at doses below 1 mM. In these treatments, most of the Pb 2+ accumulated in the roots, and only a very low amount of it was translocated to the shoots. Increasing the EDTA doses up to Pb 2+ equimolarity, increased the Pb 2+ shoot content more than 10-fold without any physiological evidence of toxicity. The treatment with higher doses of EDTA (Pb 2+ 1 mM + EDTA 2 mM) did not show toxicity symptoms, but the Pb 2+ concentration in the aboveground tissues decreased when compared with the equimolar treatment. The interaction with the absorption of some essential cations such as Ca 2+ and phytotoxicity on chelated-assisted phytoextraction is discussed.