Ref ID : 6004
S. Dunlop and G. Chapman; Detoxication of Zinc and Cadmium by the Freshwater Protozoan Tetrahymena pyriformis. II. Growth experiments and Ultrastructural Studies on Sequestration of Heavy Metals. Environ.Res. 24:264-274, 1981
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Sublethal concentrations of zinc and cadmium limited the growth of batch cultures of the ciliate Tetrahymena pyriformis. Electron microscopy of cultured populations revealed many electron-dense cytoplasmic granules in cells exposed to zinc (60 ppm), but fewer in cells grown with less zinc (6 ppm) or cadmium (2 ppm). Ultrastructural abnormalities were observed only in cells grown with cadmium. These contained autophagic vacuoles and had damaged nuclei. Zinc was shown to exert a protective effect against cadmium toxicity both in terms of growth and ultrastructural appearance. Electron probe X-ray microanalysis revealed both zinc and cadmium within the cytoplasmic granules of cells exposed to these metals. Since the granules are normally composed predominantly of calcium and magnesium, these ions are implicated in the intracellular detoxication of zinc and cadmium. Zinc was detected only in the granules, while cadmium was also found in autophagic vacuoles and damaged nuclei.