Physiological responses of Lemna trisulca L. (duckweed) to cadmium and copper bioaccumulation

Aquatic plants are known to accumulate and bioconcentrate heavy metals. In this study, several physiological responses of aquatic vascular plant Lemna trisulca L. to elevated concentrations of cadmium (up to 10 mM) and copper (up to 50 muM) were investigated. It was found that Lemna fronds were able to accumulate both cadmium and copper, but Cu-treated material showed pron ounced toxic symptoms at concentrations 1000-fold lower in comparison to Cd . Lemna trisulca could tolerate elevated levels of Cd, i.e. up to 10 mM, wi thout significant changes in photosynthetic pigments concentration. On the contrary, Cu in concentrations 25 and 50 muM promoted significant pigment d egradation. The main processes affected by Cd in Lemna fronds were total ga s exchange and net photosynthesis. On the contrary, the inhibition of total gas exchange and net photosynthesis caused by Cu (2-50 muM) correlated wit h Chl a and carotenoid concentrations decrease as well as with the decay of fluorescence from PS II. Also, an increasing impact of respiration in tota l oxygen exchange was observed after treatment of Lemna with increasing Cd concentrations (up to 5 mM) and with Cu in concentration range between 2 an d 50 muM. In Cd-treated fronds, a dose-dependent accumulation of two polype ptides with apparent molecular weights IS and 10 kDa, respectively as well as the appearance of two smaller polypeptides (apparent molecular weights 8 and 7 kDa) was observed in SDS-PAGE. The nature of these polypeptides rema ins to be determined. On the contrary, in Cu-treated fronds neither accumul ation of existing proteins nor appearance of any extra protein was observed . (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.