Adaptation of the common ice plant to high copper and zinc concentrations and their potential using for phytoremediation

A facultative halophite Mesembryanthemum crystallinum L. (the common ice plant) was shown to grow successively at the high concentrations of Cu and Zn. Although 25 mu M CuSO4 or 800 mu M ZnSO4 retarded markedly plant growth, they did not interfere with the completion of plant development and the formation of viable seeds. In such plants, leaves accumulated more than 200 mu g of Cu and 1700 mu g of Zn per 1 g of dry weight. A damaging effect of heavy metals (HMs) was manifested in a reduced content of water in leaves and proline accumulation in them. As copper is a metal with transient valence, copper salts are more toxic than zinc salts, which was manifested in a stronger inhibition of the chlorophyll synthesis. Both HMs induced oxidative stress, as evident from increased activities of guaiacol peroxidase and lipoxygenase. Moderate Cu and Zn concentrations did not damage cell membranes in leaves, as evident from the absence of their action on electrolyte leakage either under optimum conditions or after heat treatment. A capability of a substantial HM accumulation by the common ice plant and their considerable transport to shoots (up to 50 mu g of Cu and 560 mu g of Zn per plant) make it possible to consider the common ice plant as a promising phytoremediator.