Nano-selenium spraying during reproductive growth enhances antioxidant capacity, source-sink coordination and grain...

Selenium (Se) biofortification of staple crops is an effective strategy to alleviate global dietary Se deficiency; however, the physiological mechanisms linking Se application to yield formation and grain quality remain insufficiently understood, particularly for nanoscale Se fertilizers. Here, a field experiment was conducted to investigate how foliar-applied nano-selenium (Nano-Se) at two concentrations (10 and 20 mg L^-1) and four growth stages (mid-tillering, stem elongation, heading, and grain-filling) regulate antioxidant defense, photosynthetic capacity, grain filling, and Se accumulation in rice. Nano-Se markedly enhanced leaf antioxidant enzyme activities (SOD, POD, CAT) and glutathione content while reducing H₂O₂ and malondialdehyde levels, especially when applied at heading and grain-filling stages. These physiological improvements were accompanied by increased chlorophyll content, soluble sugars, and proteins, indicating sustained photosynthetic function and metabolic activity during reproductive growth. Consequently, Nano-Se significantly increased grain yield by 2.8%-14.6%, mainly through higher grain-filling rate and 1000-grain weight, with the strongest effects observed at the heading stage. Grain quality was concurrently improved, as reflected by reduced chalkiness, higher head rice rate, and enhanced amylose and fat contents. Nano-Se substantially promoted Se accumulation in grains, predominantly in organic forms, while also increasing beneficial mineral elements (K, Ca, Mg, Mn, Cu, Zn) and reducing the accumulation of toxic metals (As, Cd, Cr, Pb). Overall, foliar application of Nano-Se at appropriate concentrations during reproductive stages optimizes antioxidant protection and source-sink coordination, enabling simultaneous improvements in yield, grain quality, and nutritional safety.