Localization of Zinc and Cadmium in Thlaspi caerulescens (Brassicaceae), a Metallophyte that can Hyperaccumulate both Metals

The compartmentation of Zn and Cd in roots of Thlaspi caerulescens J. & C. Presl, a metallophyte that hyperaccumulates both metals, was investigated by means of EDAX. Two methods for sample preparation, Na2S-fixation and freeze-substitution, were compared. Na2S-fixation was not suitable for preventing the loss of metal ions from the samples. According to our results from freeze-substituted samples, Cd accumulated mainly in the apoplast and, to a lesser extent, in vacuoles, whereas Zn was principally found in vacuoles and, to a lesser extent, in cell walls.