Phytotoxicity Of Engineered CuO Nanoparticles And Their Upwards Translocation In Maize

In recent years, with the rapid development of nanotechnology, engineered nanoparticles (NPs) have been more and more widely used in textiles, electronics, pharmaceuticals, ceramics, paints, cosmetics, agriculture, environmental remediation and other industries. The large-scale application of NPs is due to their unique mechanical properties, catalytic activity, optical properties and electrical conductivity and so on. However, in the production, use and disposal process of nano-products, NPs will inevitably enter into the environment, and their own unique properties will bring the organism and the environment unpredictable impacts. Well-known international journals Science and Nature published articles several times, pointing out that NPs may have a potentially negative impact on the environment. Plant is the primary producer of ecosystem and the starting point of bioaccumulation. NPs will be released into the atmosphere, water and soil by various means, taken up by plants, and then eventually enter into human body through the food chains, constituting the potential risks to human health. Currently, the impact of nanoparticles on plant has attracted the attention of the scientific community. Nanoparticles could penetrate into the plants and be translocated and transported in plants, also, cause toxic effects to plants. However, the mechanism of uptake, translocation and accumulation of nanoparticles by plants is still unknown, and the mechanism of toxicity of nanoparticles to plants is also not clear. The purpose of this study is, by means of hydroponic experiments, to study the impacts of CuO nanoparticles on seed germination and seedling growth of plants, revealing the toxic effects of nanoparticles on the growth of higher plants and trying to explore the mechanism of phytotoxicity of nanoparticles. Simultaneously, we aim to study the uptake, translocation and accumulation of nanoparticles by plant, try to understand the possible pathways of nanoparticles penetrating into plants and the distribution and bioaccumulation of nanoparticles in plants, to provide the basic data for further understanding the phytotoxicity mechanism of CuO nanoparticles on higher plants and the rules of translocation and transportmigration of nanoparticles in plants.Ecotoxicity data regarding CuO nanoparticles are just emerging and no information about effects of CuO nanoparticles on higher plants has been reported. Here, the effects of CuO nanoparticles on maize seed germination, root elongation and the growth of maize seedlings were firstly studied, and uptake and upwards translocation of nanoparticles by maize seedlings were investigated. Results showed seed germination rate was not significantly affected but seed germination process was retarded and root elongation was significantly inhibited. CuO nanoparticles were toxic to the growth of maize seedlings, causing reduced biomass, aberrant root morphology, decreased plant water content and loss of plasma membrane integrity. Cupric ion and bulk CuO did't show similar impacts on the growth of maize, indicating that the toxic effects of CuO nanoparticles on maize seedlings resulted from the nanoparticles themselves and hardly had something to do with their released Cu²⁺ in this study. Further research also shows that Cu content in maize seedling exposed to CuO nanoparticles was far higher than that of control, cupric ion treatment and bulk CuO treatment. After maize seedlings were exposed to 100mg/L CuO nanoparticles for 15 days, the translocation factor of Cu from root to shoot was about 0.13. Futhermore, with the method of TEM-EDS, CuO nanoparticles were observed in the cell wall of epidermal cells, the apoplast and protoplast of cortical cells, and even in exylem sap extracted from the stem of maize seedlings, suggesting that CuO nanoparticles could be taken up by plant root and translocated upwards through the vascular system by maize.