Stress Response and Tolerance of Zea mays to CeO2 Nanoparticles: Cross Talk among H2O2, Heat Shock Protein, and Lipid Peroxidation

The rapid development of nanotechnology will inevitably release nanoparticles (NPs) into the environment with unidentified consequences. In addition, the potential toxicity of CeO2 NPs to plants and the possible transfer into the food chain are still unknown. Corn plants (Zea mays) were germinated and grown in soil treated with CeO2 NPs at 400 or 800 mg/kg. Stress-related parameters, such as H2O2, catalase (CAT), and ascorbate peroxidase (APX) activity, heat shock protein 70 (HSP70), lipid peroxidation, cell death, and leaf gas exchange were analyzed at 10, 15, and 20 days post-germination. Confocal laser scanning microscopy was used to image H2O2 distribution in corn leaves. Results showed that the CeO2 NP treatments increased accumulation of H2O2, up to day 15, in phloem, xylem, bundle sheath cells and epidermal cells of shoots. The CAT and APX activities were also increased in the corn shoot, concomitant with the H2O2 levels. Both 400 and 800 mg/kg CeO2 NPs triggered the up-regulation of the HSP70 in roots, Indicating a systemic stress response. None of the CeO2 NPs increased the level of thiobarbituric acid reacting substances, Indicating that no lipid peroxidation occurred. CeO2 NPs, at both concentrations, did not induce Ion leakage in either roots or shoots, suggesting that membrane integrity was not compromised. Leaf net photosynthetic rate, transpiration, and stomatal conductance were not affected by CeO2 NPs. Our results suggest that the CAT, APX, and HSP70 might help the plants defend against CeO2 NP-induced oxidative injury and survive NP exposure.