Biochemical Response of Oakleaf Lettuce Seedlings to Different Concentrations of Some Metal(oid) Oxide Nanoparticles

Nanoparticles (NPs) significantly modify the physiological functions and metabolome of plants. The purpose of the study was to investigate the effect of CeO_2, Fe₂O₃, SnO₂, TiO₂, and SiO₂ nanoparticles, applied in foliar spraying of oakleaf lettuce at concentrations 0.75% to 6%, on the antioxidant enzyme activity and content of non-enzymatic antioxidants, chlorophyll pigments, fresh weight (FW) and dry weight (DW). It was found that 3% Fe₂O₃-NPs caused a 27% decrease in fresh weight compared to control plants. Fe₂O₃-NPs caused an increase in dry weight (g 100 g⁻¹ FW) when compared to the control for all concentrations, but total DW (g per plant) was similar for all NPs treatments. Significant increases in chlorophyll <i>a</i> + <i>b</i> content after treatment with 1.5% and 6% SiO₂-NPs, 3% Fe₂O₃-NPs, and 3% TiO₂-NPs were noted. Fe₂O₃-NPs caused a significant increase in the activity of ascorbate peroxidase, guaiacol peroxidase, and catalase (only for 3% Fe₂O₃-NPs). SnO₂-NPs decreased ascorbate peroxidase (APX) and guaiacol peroxidase (GPOX) activity (for all tested concentrations) but increased catalase (CAT) activity when a 3% suspension of these NPs was applied. The level of glutathione (GSH) increased due to application of all metal/metalloid oxides, with the exception of SnO₂-NPs. When all concentrations of TiO₂-NPs were applied, L-ascorbic acid increased significantly, as well as increasing at higher concentrations of SiO₂-NPs (3% and 6%) and at 0.75% and 3% Fe₂O₃-NPs. SiO₂-NPs and TiO₂-NPs significantly elevated the carotenoid and total phenolic content in treated plants compared to the control. The total antioxidant capacity of plants treated with 3% CeO₂-NPs was almost twice as high as that of the control.