Scanning Electron Microscopy


The intracellular localization of heavy metals in yeast cells was studied by means of energy-dispersive X-ray microanalysis. The yeast, Saccharomyces cerevisiae, was pretreated with phosphate and then loaded with different metal ions, by suspending the cells in salt solutions (Ni, Zn, Cd, Pb, Al and Cr). For the analysis, the cells were embedded in gelatin, rapidly frozen, and thin cryosections were cut on a dry knife.

A considerable uptake of divalent cations by the yeast cells was found to occur. The cations were bound to the polyphosphate granules localized in or close to the cell vacuoles. Immediately after phosphate loading, the polyphosphate granules were predominantly located in the cytoplasm, but as the incubation progressed, they migrated to the vacuole. As for trivalent cations, Cr was taken up and also stored in the polyphosphate granules, but Al could not be demonstrated with certainty in the cells, only in the cell walls. Incubation of the cells with zinc, cadmium or lead ions caused a significant decrease of the relative size of the vacuole.

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