Impact of zinc and zinc oxide nanoparticles on the physiological and biochemical processes in tomato and wheat

Abstract

In this study, the effects of various concentrations of zinc and zinc oxide nanoparticles (nZn, nZnO) were evaluated in tomato and wheat. Results showed that at lower concentrations, nZn and nZnO augmented seed germination and growth parameters, whereas with higher concentrations, the nanoparticles reduced these traits. Zn concentrations corresponding to Zn dissolved (3–23 mg Zn·L−1) from nanoparticles (NPs) did not significantly affect the germination indices in either species. Compared with the bulk counterparts of ZnO, NPs exerted more toxicity on seed germination, growth parameters, and chlorophyll and carotenoid contents, and also increased Zn bioaccumulation more. More often than not, nZnO provoked more adverse symptoms than nZn at equivalent concentrations. In both species, the Zn accumulation in roots and shoots followed the order: Zn2+ ions > nZn > nZnO > bulk ZnO > control. Exposure to 200 mg Zn·L−1 nZn and nZnO increased H2O2 accumulation and malondealdehyde (MDA) levels, which were more pronounced in tomato than wheat. The results suggested that the toxicity of NPs could be due to the particle itself, or from the Zn2+ ions dissolved from NPs. Moreover, nanotoxicity, like other stresses, caused oxidative stress in both plants, and the differences in proline accumulation and the antioxidant enzyme activities of leaves, especially APX activity, at least in part, explained the higher sensitivity of tomato to NPs than wheat.