14.
We have observed the effect of copper and zinc on the biology of
Euglena gracilis. The cells displayed different sensitivities to these metals, as the apparent LC
50 for Cu
2+ was 0.22 mM, and for Zn
2+ it was 0.88 mM. While Zn
2+ was able to increase cell proliferation even at 0.1 mM, the minimal CuCl
2 concentration tested (0.02 mM) was sufficient to impair cell division. Higher concentrations of these metals not only inhibited cell division in a concentration-dependent manner, but also interfered with the metabolism of
E. gracilis. A higher accumulation of proteins and lipids per cell was observed at the DI
50 concentration for metal-treated cells. These results suggest that the test concentration of both metals leads to a failure in completing cell division. Ultrastructural analysis indicated a chloroplast disorganization in copper-treated cells, as well as the presence of electron dense granules with different shapes and sizes inside vacuoles. Microanalysis of these granules indicated an accumulation of copper, thus suggesting a detoxification role played by the vacuoles. These results indicate that
E. gracilis is an efficient biological model for the study of metal poisoning in eukaryotic cells. They also indicate that copper and zinc (copper being more poisonous) had an overall toxic effect on
E. gracilis and that part of the effect can be ascribed to defects in the structure of chloroplast membranes.
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