Ecophysiological tolerance of Elodea canadensis to nickel exposure.

Biological accumulation of nickel and concomitant ecophysiological responses were studied in the leaves of Elodea canadensis treated with different concentrations of Ni (1-50 microM) for 5d. In low concentrations nickel was accumulated mainly in the soluble protein fraction, which correlated with its highest observed accumulation coefficient. In higher concentrations, Ni binding in the non-protein soluble fraction was observed. The effects of increasing nickel concentrations on the accumulation of photosynthetic pigments, gas exchange rates, lipid peroxidation, biosynthesis of thiol-containing compounds and the activity of selected enzymes--markers of oxidative stress were investigated. The appearance of several new polypeptides with apparent molecular weights below 20 kDa, was found by SDS-PAGE in Ni-treated Elodea leaves. Our results indicate that Ni, in concentrations up to 10 microM could induce sub-lethal oxidative stress in Elodea leaves. In response, plants developed detoxification mechanisms including an enhanced biosynthesis of thiol-containing compounds which facilitated Ni accumulation and sequestration in plant tissues effectively. Hence, E. canadensis could be used in the biological removal of Ni from polluted water up to 10 microM concentration.