Toxicological effects of nanometer titanium dioxide (nano-TiO2) on Chlamydomonas reinhardtii
2012
The toxicological effects of nanometer titanium dioxide (nano-TiO₂) on a unicellular green alga Chlamydomonas reinhardtii were assessed by investigating the changes of the physiology and cyto-ultrastructure of this species under treatment. We found that nano-TiO₂ inhibited photosynthetic efficiency and cell growth, but the content of chlorophyll a content in algae did not change, while carotenoid and chlorophyll b contents increased. Malondialdehyde (MDA) content reached maximum values after 8h exposure and then decreased to a moderately low level at 72h. Electron microscopy images indicated that as concentrations of nano-TiO₂ increased, a large number of C. reinhardtii cells were noted to be damaged: the number of chloroplasts declined, various other organelles were degraded, plasmolysis occurred, and TiO₂ nanoparticles were found to be located inside cell wall and membrane. It was also noted that cell surface was surrounded by TiO₂ particles, which could present an obstacle to the exchange of substances between the cell and its surrounding environment. To sum up, the effect of nano-TiO₂ on C. reinhardtii included cell surface aggregation, photosynthesis inhibition, lipid peroxidation and new protein synthesis, while the response of C. reinhardtii to nano-TiO₂ was a rapid process which occurs during 24h after exposing and may relate to physiological stress system to mitigate damage.
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