Methionine-coated nano zinc oxide: A novel nanopriming agent to enhance antioxidant defence, and agronomic traits in arsenic-stressed rice

Arsenic contamination significantly affects rice yield and production. Recent studies have highlighted the potential of nanoparticles to mitigate heavy metal stress in cereals, although concerns about their phytotoxicity in agricultural systems have emerged. Coating nanoparticles may enhance their biocompatibility and reduce toxicity. In this study, we synthesized nano zinc oxide (ZnONPs) and methionine-coated nano zinc oxide (Met-ZnONPs), characterizing their properties using UV-Vis spectroscopy and transmission electron microscopy (TEM). Met-ZnONPs exhibited a blue shift and quantum confinement when characterized through UV-Vis and TEM. We aimed to compare the effects of seed priming with ZnONPs and Met-ZnONPs, hypothesizing that methionine coatings would enhance efficacy. Rice seeds were primed for 24 hours with either ZnONPs or Met-ZnONPs before sowing under both arsenic stress and non-stress conditions. We monitored intrinsic arsenic levels in soil and irrigation water and assessed arsenic content in rice grains post-harvest. Priming with 25 ppm Met-ZnONPs increased plant height, fresh weight, and activities of key antioxidant enzymes (ascorbate peroxidase, glutathione reductase, monodehydroascorbate reductase, and dehydroascorbate reductase) by 13.73%, 19.36%, 19.57%, 25.19%, 17.17%, and 14.4% respectively, compared to increases of 10.24%, 3.82%, 3.63%, 11.26%, 16.35%, 9.94%, and 7.06% for 50 ppm ZnONPs. Furthermore, 50 ppm Met-ZnONPs resulted in a 47.89% reduction in grain arsenic and a 36% decrease in hydrogen peroxide levels, while ZnONPs alone showed reductions of 22.28% in grain arsenic and 32% in hydrogen peroxide. These findings suggest that coating nanoparticles can enhance crop production by improving their biocompatibility and mitigating phytotoxic effects.