The widespread application of copper oxide nanoparticles (CuO NPs) in agricultural production has caused growing concerns about their impact on crops. In this study, wheat root elongation was used to evaluate the toxic effect concentrations of CuO NPs in two soils with differing properties, collected from farmlands in Guangdong (GD) and Shandong (SD) provinces, China. Plant morphological and biochemical properties were also assessed to explore the toxicity mechanism of CuO NPs on wheat seedlings. The root elongation results revealed lower toxic effect concentration values in the plants grown in GD soil than in SD soil. Furthermore, the treatment with CuO NPs at 200 mg Cu kg-1 significantly reduced wheat root and shoot biomass by 35.8% and 15.8%, respectively, in GD soil. Electron microscopy showed that CuO NPs deformed wheat roots and entered leaf cells, causing deformation and damaging the cell structure. The CuO NP treatments also decreased chlorophyll content, increased antioxidant enzyme activity, and increased membrane lipid peroxidation in wheat leaves. The addition of CuO NPs significantly reduced the Zn (by 17.3%) and Fe (by 26.9%) contents in the leaves of plants grown in GD and SD soils, respectively. However, the contents of Cu, Mg, and Mn were increased by 27.4%-52.5% in GD soil and by 17.9%-71.6% in SD soil. These results suggested that CuO NPs showed greater toxicity to wheat plants grown in acidic soil than in alkaline soil and that the adverse effects of CuO NP treatments on wheat seedlings were due to a combination of CuO NPs and released Cu2+.

The damage excessive neodymium (Nd) causes to animals and plants should not be underestimated. However, there is little research on the impact of pH and associated ions on the toxicity of Nd. Here, a biotic ligand model (BLM) was expanded to predict the effects of pH and chief anions on the toxic impact of Nd on wheat root elongation in a simulated soil solution. The results suggested that Nd3+ and NdOH2+ were the major ions causing phytotoxicity to wheat roots at pH values of 4.5-7.0. The Nd toxicity decreased as the activities of H+, Ca2+, and Mg2+ increased but not when the activities of K+ and Na+ increased. The results indicated that H+, Ca2+, and Mg2+ competed with Nd for binding sites. An extended BLM was developed to consider the effects of pH, H+, Ca2+, and Mg2+, and the following stability constants were obtained: logKNdBL = 2.51, logKNdOHBL = 3.90, logKHBL = 4.01, logKCaBL = 2.43, and logKMgBL = 2.70. The results demonstrated that the BLM could predict the Nd toxicity well while considering the competition of H+, Ca2+, Mg2+ and the toxic species Nd3+ and NdOH2+ for binding sites.

Soil contamination by indium, an emerging contaminant from electronics, has a negative impact on crop growth. Inhibition of root growth serves as a valuable biomarker for predicting indium phytotoxicity. Therefore, elucidating the molecular mechanisms underlying indium-induced root damage is essential for developing strategies to mitigate its harmful effects. Our transcriptomic findings revealed that indium affects the expression of numerous genes related to cell wall composition and metabolism in wheat roots. Morphological and compositional analysis revealed that indium induced a 2.9-fold thickening and a 17.5 % increase in the content of cell walls in wheat roots. Untargeted metabolomics indicated a substantial upregulation of the phenylpropanoid biosynthesis pathway. As the major end product of phenylpropanoid metabolism, lignin significantly accumulated in root cell walls after indium exposure. Together with increased lignin precursors, enhanced activity of lignin biosynthesis-related enzymes was observed. Moreover, analysis of the monomeric content and composition of lignin revealed a significant enrichment of p-hydroxyphenyl (H) and syringyl (S) units in root cell walls under indium stress. The present study contributes to the existing knowledge of indium toxicity. It provides valuable insights for developing sustainable solutions to address the challenges posed by electronic waste and indium contamination on agroecosystems.