Synthesis of calcium-based nanofertilizer and its efficacy towards reduction of oxidative stress and fluoride uptake in rice (Oryza sativa L.)

The phytotoxicity of fluoride and its build-up in agricultural plants and subsequently the entry into the food chain is a serious threat to human health. The present study highlighted the green synthesis of calcium oxide nanoparticles (CaO NPs) and characterization using UV-Vis spectrophotometer, TEM, SEM, EDX, XRD, and FTIR. Further, synthesized CaO NPs (0, 10, and 50 mg/L) were applied on fluoride-stressed (10 mg/L) rice seedlings to check its possible ameliorative effects towards growth and fluoride accumulation in different parts of rice seedlings. Characterization revealed that nanoparticles were crystalline (46.72 %) and spherical in shape, with an average diameter of 20–25 nm. Results of the seedling growth analysis revealed that CaO NPs inhibited the translocation of fluoride in rice plants, which in turn decreased the phytotoxicity caused by fluoride, including lipid peroxidation and chlorosis, and enhanced the overall growth of seedlings. The co-exposure of CaO NPs with fluoride also showed a reduction in the fluoride-induced oxidative stress, as demonstrated by lower MDA, O₂^•- contents, and activity of antioxidant enzymes (CAT, SOD, and POD) as compared to fluoride treatment alone. The application of CaO NPs also restored potassium content in seedlings grown under fluoride stress. Furthermore, the highest reduction of fluoride accumulation by 65 and 76 % in roots and shoots was recorded at 50 mg/L of CaO NPs treatment, respectively. Therefore, the present study clearly indicated the ameliorative potential of CaO NPs towards fluoride stress in rice. However, a field study is needed to establish the social acceptance of this valuable nanofertilizer in fluoride-contaminated areas.