Enhancing rice (Oryza sativa L.) yield and quality by improving photosynthesis with foliar application of zinc oxide nanoparticles

Zinc (Zn) is a critical co-factor for enzymes involved in photosynthesis, delaying leaf senescence and enhancing photosynthetic efficiency. Supplementing rice leaves with Zn can improve yield, quality, and Zn content in edible parts, addressing food security and micronutrient deficiencies. In this study, we evaluated the effects of spraying Zn oxide nanoparticles (ZnO NPs) (0, 5, 10, and 20 mg L-1) at the rice panicle initiation stage on photosynthesis, yield, and grain quality through a two-year field experiment. Results showed that foliar application of ZnO NPs at the panicle initiation stage increased the leaf area index, net photosynthetic rate, and photosynthetic potential, leading to a 1.5-6.4% increase in grain yield through a higher grain filling rate and 1000-grain weight. ZnO NPs also delayed leaf senescence and prolonged the duration of active photosynthesis, which significantly contributed to higher biomass production and improved grain filling, further enhancing yield. Additionally, the enhancement in photosynthetic efficiency and delayed senescence promoted the production of high-quality grains. ZnO NPs improved rice appearance quality by reducing the chalkiness grain rate and degree. The rice tasting value increased by 3.3-7.0%, reflecting improvements in appearance, viscosity, and balance, along with reductions in hardness. ZnO NPs raised peak viscosity and breakdown values while lowering setback values. Furthermore, ZnO NPs significantly increased Zn content in brown and milled rice by 13.8-56.0% and 20.1-78.6%, respectively, and improved Zn bioavailability by reducing the phytate-to-zinc molar ratio. These findings highlight the potential of ZnO NPs as a sustainable nanotechnology-based approach to simultaneously improve rice productivity, quality, and nutritional value, offering a promising solution for addressing food security and micronutrient deficiency in rice-based diets.