The dual effect of Selenium nanoparticles in rice seedlings: From increasing antioxidant activity to inducing oxidative stress

Selenium deficiency has been a worldwide concern because it can pose a risk to human health. Selenium nanoparticles (SeNPs) are in general less toxic and more bioavailable than ionic Se and, therefore, their use for biofortification of food crops has attracted attention. Rice is a staple food consumed by half of the world's population. Indeed, studies on SeNPs' impacts on oxidative stress and antioxidant responses in rice seedlings are scarce. Herein, the effect of different concentrations of SeNPs on growth, antioxidant enzyme activity, reactive oxygen species, and nitric oxide metabolites in rice germinating seeds were investigated. Results revealed a dual effect of SeNPs on seedling growth. At low concentrations (0.5 mg L−1), the nanoparticles did not affect seedling growth, while at higher concentrations root elongation was significantly decreased. Soaking rice seeds with SeNPs at 0.5 mg L−1 effectively improved the activity of ascorbate peroxidase, catalase, and superoxide dismutase enzymes. However, a decrease in antioxidant enzyme activity was observed with increasing SeNPs concentrations. All treatments decreased S-nitrosothiols and nitrite concentrations compared to the control. Hydrogen peroxide concentrations also decreased for concentrations higher than 5 mg L−1, compared to the control. Our results suggest a beneficial effect of SeNPs at the optimal concentration of 0.5 mg L−1 on stimulating antioxidant metabolism and mitigating reactive oxygen species in plant tissues without affecting the physiological parameters.