Root responses to different types of TiO2 nanoparticles and bulk counterpart in plant model system Vicia faba L.

The aim of the present work was to study, in the model system Vicia faba L., the potential stress-induced response to a commercial source of TiO2 nanoparticles (NPs) <100 nm (tetragonal crystals), to a TiO2-NPs laboratory-made sample <10 nm (spherical shape), and to the corresponding bulk material, recently classified as possibly carcinogenic to humans. The above materials were applied to V. faba seeds up to early seedling development; different endpoints were considered to estimate possible phytotoxic and genotoxic effects at ultrastructural, cyto- histological and physiological level. Oxidative stress and antioxidant response were evaluated by biochemical approach and in situ histochemical techniques. Ultrastructural studies demonstrated that the applied NPs were internalized in root plant cells but the most damages to the cellular appearance followed bulk material treatment. Our results on seed vigor index, on aberration index, on the evaluation of oxidative stress and of induced antioxidant response demonstrated that TiO2-NPs may exert specific actions at different levels of toxicity, depending on their size and shape and that the bulk counterpart seems to provoke the major adverse effects in V. faba root.