Accumulation of copper in the cell compartments of charophyte Nitellopsis obtusa after its exposure to copper oxide nanoparticle suspension.

Cu accumulation in the internodal cell of charophyte Nitellopsis obtusa or its compartments was investigated after 3-h-exposure to lethal effective concentrations (8-day LC50) of CuO nanoparticle (nCuO) suspension or CuSO4 solution, i.e. 100 mg/L nCuO or 3.18 mg Cu/L as CuSO4. In both cases, the major part of Cu accumulated in the cell walls. The presence of CuO NPs in the cell wall and within the cell was visualized by scanning electron microscope images as well as confirmed by energy dispersive X-ray spectrum data. Although a threefold higher intracellular concentration of Cu was found after treatment with nCuO suspension, 3.18 mg Cu/L as CuSO4 induced fast and substantial depolarization of cell membrane potential contrary to that of 100 mg/L nCuO. A delayed effect of nCuO on the survival of the cells was also observed. This suggests that internally accumulated Cu was far less active and further supports the hypothesis of delayed toxicity of internalized nCuO NPs to charophyte cells.