Macrophytes bioaccumulate metals, the suggestion being made that they be considered for phytoremediation. However, a thorough understanding of the mechanisms of metal tolerance in these plants is necessary to allow full optimization of this approach. The present study was undertaken to gain insight into Hg and Cd accumulation and their effects in a representative macrophyte, Elodea nuttallii. Exposure to methyl-Hg (23 ng dm(-3)) had no significant effect while inorganic Hg (70 ng dm(-3)) and Cd (281 mu g dm(-3)) affected root growth but did not affect shoots growth, photosynthesis, or antioxidant enzymes. Phytochelatins were confirmed as having a role in Cd tolerance in this plant while Hg tolerance seems to rely on different mechanisms. Histology and subcellular distribution revealed a localized increase in lignification, and an increased proportion of metal accumulation in cell wall over time. Proteomics further suggested that E. nuttallii was able to efficiently adapt its energy sources and the structure of its cells during Hg and Cd exposure. Storage in cell walls to protect cellular machinery is certainly predominant at environmental concentrations of metals in this plant resulting in a high tolerance highlighted by the absence of toxicity symptoms in shoots despite the significant accumulation of metals. (C) 2013 Elsevier B.V. All rights reserved.