Biogenic fabrication of zinc oxide nanoparticles for enhanced germination and early seedling establishment of rice under salinity stress

Abstract

Salinity stress restricts rice ( Oryza sativa L. ) germination and early establishment through osmotic stress, ionic toxicity, and excessive reactive oxygen species production. Although ZnO nanoparticles (ZnONPs) can enhance salinity tolerance, the influence of their biological synthesis source on nanoparticle properties and efficacy remains poorly understood. ZnONPs were synthesized using leaf extracts of sorghum (S 1 ), seaweed (S 2 ), and sugar beet (S 3 ) and compared with commercial ZnONPs (S 4 ). The nanoparticles were characterized using UV–Vis spectroscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, high-resolution transmission electron microscopy, field-emission scanning electron microscopy, and zeta-potential measurements. Rice seeds were nano-primed with ZnONPs at 25–100 ppm and evaluated under salinity stress for germination, growth, biomass, water uptake, hydrolytic enzyme activity, antioxidant responses, and lipid peroxidation. All biogenic ZnONPs exhibited characteristic crystalline ZnO structures, nanoscale dimensions, and predominantly spherical morphology. Seaweed-mediated ZnONPs showed superior physicochemical properties, including an average particle size of approximately 23.7 nm, high crystallinity, and enhanced colloidal stability (−24.85 mV). Nano-priming significantly mitigated salinity-induced inhibition of germination, seedling growth, and biomass accumulation. Seaweed-derived ZnONPs at 50–75 ppm produced physiological and biochemical responses comparable to those obtained with commercial ZnONPs at 100 ppm, demonstrating greater efficacy at lower concentrations. These treatments enhanced water uptake, hydrolytic enzyme activity, and the activities of superoxide dismutase, peroxidase, and catalase while reducing lipid peroxidation. Multivariate analyses further distinguished the effective ZnONP treatments based on coordinated improvements in germination, growth, antioxidant defence, and physiological traits. The biological synthesis source significantly influenced the physicochemical properties and functional efficacy of ZnONPs. Seaweed-derived ZnONPs were particularly effective at lower application rates and therefore represent a promising nano-priming strategy for improving early rice establishment under saline conditions.