Genotoxicity of titanium dioxide nanoparticles and triggering of defense mechanisms in Allium cepa

Titanium dioxide nanoparticles (TiO(2)NPs) are widely used and may impact the environment. Thus, this study used a high concentration of TiO(2)NP (1000 mg/L) to verify the defense mechanisms triggered by a plant system – an indicator of toxicity. Furthermore, this study aimed at completely characterizing TiO(2)NP suspensions to elucidate their toxic behavior. TiO(2)NPs were taken up by meristematic cells of Allium cepa, leading to slight inhibition of seed germination and root growth. However, severe cellular and DNA damages were observed in a concentration-dependent manner (10, 100, and 1000 mg/L). For this reason, we used the highest tested concentration (1000 mg/L) to verify if the plant cells developed defense mechanisms against the TiO(2)NPs and evaluated other evidences of TiO(2)NP genotoxicity. Nucleolar alterations and plant defense responses (i.e., increased lytic vacuoles, oil bodies and NP phase change) were observed in meristematic cells exposed to TiO(2)NP at 1000 mg/L. In summary, TiO(2)NPs can damage the genetic material of plants; however, plants displayed defense mechanisms against the deleterious effects of these NPs. In addition, A. cepa was found to be a suitable test system to evaluate the cyto- and genotoxicity of NPs.