Effects of engineered aluminum and nickel oxide nanoparticles on the growth and antioxidant defense systems of Nigella arvensis L.

The effects of different concentrations (0, 50,100, 1000 and 2500 mg/L) of engineered aluminum and nickel oxide nanoparticles (Al₂O₃ and NiO NPs) on plant growth, oxidative stress and antioxidant activities in the hydroponically grown tissues of Nigella arvensis L. were investigated. The plant biomass was significantly increased under 50 and 100 mg/L of Al₂O₃ NPs or 50 mg/L of NiO NPs treatment, but was significantly decreased at higher concentrations of these nanoparticles. Assays of several enzymatic antioxidants such as ascorbate peroxidase (APX), catalase (CAT), superoxide dismutase (SOD) and peroxidase (POD) in roots and shoots indicate a general increase of activities after exposure to 50-2,500 mg/L of Al₂O₃ NPs and NiO NPs. The results are corroborated by an increased 2,2-diphenyl-1-picryl hydrazyl (DPPH) scavenging activity, total antioxidant capacity, total reducing power, total iridoids content, total saponin content, and total phenolic content in treated plants by Al₂O₃ NPs compared to the control plants. By contrast, the antioxidant activities, formation of secondary metabolites, and other related physiological parameters such as the total antioxidant capacity, DPPH scavenging activity and total saponin content were inhibited after the concentration of NiO NPs was increased to 100 mg/L. Total phenols, saponins, iridoids and total antioxidant content and DPPH scavenging activity were increased in plants treated with 100-2,500 mg/L Al₂O₃ NPs. Overall, these two nanoparticles displayed different effects in the shoots and roots of plants at different concentrations, which may be due to their physico-chemical properties.