Glycine betaine functionalized zinc oxide nanoparticle application alleviates salinity stress through osmotic, ionic, and antioxidant regulation in Vigna radiata L.

Abstract

Soil salinity limits crop productivity by disrupting water uptake, ionic balance, and metabolism. This study evaluated the potential of glycine betaine (GB), ZnO nanoparticles (ZnO NPs), and glycine betaine-functionalized ZnO nanoparticles (GB-ZnO NPs) as seed-priming agents to mitigate salinity stress in Vigna radiata L. Characterization of GB-ZnO NPs (XRD, FTIR, TGA, DLS, SEM, AFM, XPS) confirmed high crystallinity, purity, and successful GB functionalization. Seed nanopriming with GB-ZnO NPs (5 ppm) increased seedling biomass by 174% over the hydroprimed seeds under salt stress conditions, showing improved recovery of seedling growth. Similarly, relative water content and photosynthetic pigments (chlorophyll a, chlorophyll b, and carotenoids) were improved. Ionic homeostasis was maintained through decreased sodium (Na⁺) content (64.19%) and increased potassium (K⁺) content (61.10%), resulting in a 4.49-fold higher K⁺/Na⁺ ratio compared to hydroprimed plants. There was a 103.36% increase in the concentration of Zn²⁺, whereas a reduction was observed in the concentrations of proline (41.32%) and GB (57.75%). A decline in the level of H₂O₂, O₂˙⁻, MDA, and EL, and an increase in enzymatic antioxidant activities, including CAT, APX, SOD, and GR was observed, reflecting enhanced ROS scavenging. Principal component and correlation analysis showed that GB-ZnO nanopriming is effective in coordinating various defense systems to overcome the stress of salinity in mung bean seedlings. The glycine betaine-functionalized ZnO NPs showed the highest degree of protection, outperforming ZnO NPs and GB.