Spatial distribution of cadmium in leaves of metal hyperaccumulating Thlaspi praecox using micro-PIXE

Localization of cadmium (Cd) and other elements was studied in the leaves of the field-collected cadmium/zinc (Cd/Zn) hyperaccumulator Thlaspi praecox from an area polluted with heavy metals near a lead mine and smelter in Slovenia, using micro-PIXE (proton-induced X-ray emission). The samples were prepared using cryofixation. Quantitative elemental maps and average concentrations in whole-leaf cross-sections and selected tissues were obtained. Cd was preferentially localized in the lower epidermis (820 mu g g(-1) DW), vascular bundles and upper epidermis, whereas about twice the lower concentrations were found in the mesophyll. Taking into account the large volume of the mesophyll compared with the epidermis, the mesophyll is indicated as a relatively large pool of Cd, possibly involved in Cd detoxification/dilution at the tissue and cellular level.