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.