Cadmium is one of the most toxic heavy metals that can be taken up by plants. Although cadmium toxicity in plants is well established, the mechanism of Cd actions at the cell level is not entirely known. The aim of this work was the investigation of Cd effects on cation contents (K, Ca, Mn, Fe, Cu, Zn) and cytological changes in sycamore cells (Acer pseudoplatanus L.). Sycamore cells were treated with 20 µM CdSO4, a sub-lethal concentration, for 7 days. Energy-dispersive x-ray fluorescence (EDXRF) spectrometry was applied to quantify cation concentrations in cells. Cd concentration was measured by total reflection x-ray fluorescence (TXRF) spectrometry. The quantification was performed with cells taken directly from the culture and also after being washed in an acidified medium. Light and scanning microscope observations showed several modifications of cadmium-treated cells, namely increased cell volume and vacuolation. Cells exposed to cadmium also showed variations in cation concentrations. An increase in Mn, Fe, Cu and Zn contents and a decrease in K content were observed in Cd-stressed cells. Fe was the most increased element, followed by Mn and Cu and a similar behaviour was observed for Ca and Zn. K was the only cation showing a decreased concentration under Cd stress. The high levels of Cd in cells exposed to Cd are in agreement with the amount of Cd accumulated within the cells. The results obtained allowed differentiation between adsorption of ions on the cell wall and uptake of ions into the intracellular compartments. Copyright © 2005 John Wiley & Sons, Ltd.