TiO 2 nanoparticles may alleviate cadmium toxicity in co-treatment experiments on the model hydrophyte Azolla filiculoides.

The hydrophyte Azolla filiculoides can be a useful model to assess if TiO ₂ NPs may in some way alleviate the Cd injuries and improve the ability of the plant to cope with this metal. With this mechanistic hypothesis, after a pre-treatment with TiO ₂ NPs, A. filiculoides plants were transferred to cadmium-contaminated water with or without TiO ₂ nanoparticles. After 5 days of treatment, cadmium uptake, morpho-anatomical, and physiological aspects were studied in plants. The continuous presence of TiO ₂ nanoparticles, though not increasing the uptake of cadmium in comparison with a priming treatment, induced a higher translocation of this heavy metal to the aerial portion. Despite the translocation factor was always well below 1, cadmium contents in the fronds, generally greater than 100 ppm, ranked A. filiculoides as a good cadmium accumulator. Higher cadmium contents in leaves did not induce damages to the photosynthetic machinery, probably thanks to a compartmentalization strategy aimed at confining most of this pollutant to less metabolically active peripheral cells. The permanence of NPs in growth medium ensured a better efficiency of the antioxidant apparatus (proline and glutathione peroxidase and catalase activities) and induced a decrease in H ₂ O ₂ content, but did not suppress TBARS level.