CuO Nanoparticle Exposure Impairs the Root Tip Cell Walls of Arabidopsis thaliana Seedlings

Abstract

The increasing number of applications of nanoparticles (NPs) in various fields has led to negative effects on the environment. In this study, the effects of CuO nanoparticles (CuO NPs) on Arabidopsis root tips were investigated. Significant growth inhibition on Arabidopsis roots was observed after treatment with both CuO NPs (10 mg/L) and the correspondingly released Cu2+ (0.80 mg/L). Scanning electron microscope images demonstrated that NPs primarily deposited on the surface of root tips and penetrated intercellular spaces after CuO NP exposure. Light and fluorescence microscope visualization revealed that the root tips were damaged severely after CuO NP exposure, with swelling of the hair zone, splitting of the cell wall junction, and disordered cell arrangement in the root tip. Semiquantitative analysis by Fourier transform infrared spectroscopy demonstrated that the cell wall xyloglucan and esterified pectin contents in the roots were decreased. Similar but weaker effects on the roots were detected after Cu2+ treatment. Additionally, some genes related to cell wall organization were downregulated by CuO NP stress, partially contributing to the cell wall component change. The results demonstrated that CuO NPs produced phytotoxicity to the cell wall through both physical damage and biochemical disruption, causing loosening of the tethers between cellulose microfibrils in the cell wall and the disruption of cell adhesion. The phytotoxicity of CuO NPs in the plant cell wall was mainly caused by NPs and was partially related to the released Cu2+. These findings are helpful to understand better the negative effects of CuO NPs on plant regarding the cell wall.