Zinc Oxide Nanoparticles (ZnONPs) as Nanofertilizer: Improvement on Seed Yield and Antioxidant Defense System in Soil Grown Soybean (Glycine max cv. Kowsar)
Herein, we investigated potential phytotoxicity of zinc oxide nanoparticles (ZnONPs) on seed yield, focusing on particle size-, morphology-, and concentration-dependent responses of multiple antioxidant defense biomarkers, in soil-grown soybean (Glycine max cv. Kowsar) during its lifecycle. To this end, we synthesized three types of morphologically unique ZnONPs (spherical/ 38nm, floral-like/ 59nm, and rod-like/ >500nm); all with high purity, triclinic crystal structure and negative surface charge; and compared the toxicity with Zn2+ ions. Each pot received two seeds, placed in soil inoculated with N-fixing bacteria (Rhizobium japonicum) and grown outdoor for 120 days. Our findings demonstrated a significant particle size-, morphology-, and concentration-dependent influence of ZnONPs on seed yield, lipid peroxidation, and various antioxidant biomarkers in soybean. Our spherical 38nm ZnONPs were the most protective compared to the floral-like 59nm ZnONPs, rod-like >500nm ZnONPs, and Zn2+ ions, particularly up to 160 mg/kg. However, at the highest concentration of 400 mg/kg, spherical 38nm ZnONPs elicited the highest oxidative stress responses (H2O2 synthesis, MDA, SOD, CAT, POX) in soybean compared to the other two morphologically different ZnONPs tested. The concentrationresponse curves for the three types of ZnONPs and Zn2+ ions were nonlinear (nonmonotonous) for all the endpoints evaluated. The results also suggest differential nano-specific toxicity of ZnONPs compared to ionic Zn2+ toxicity in soybean. Our higher NOAEL value of 160 mg/kg indicates the potential for ZnONPs to be used as a nanofertilizer for crops grown in Zn-deficient soils to improve crop yield, food quality and address malnutrition, globally. HighlightsO_LIParticle size-, morphology-, and concentration-dependent effects of ZnONPs tested. C_LIO_LIAll Zn compounds (ZnONPs, Zn2+) promoted seed yield up to 160 mg/kg. C_LIO_LISpherical 38nm ZnONPs elicited the least oxidative stress, except at 400 mg/kg. C_LIO_LIConcentration-response curves for all Zn compounds were non-linear. C_LIO_LIZnONPs may serve as nanofertilizer for enriching Zn-deficit soil with Zn. C_LI O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=79 SRC="FIGDIR/small/039644v1_ufig1.gif" ALT="Figure 1"> View larger version (37K): org.highwire.dtl.DTLVardef@b11794org.highwire.dtl.DTLVardef@832c45org.highwire.dtl.DTLVardef@1cf6e7borg.highwire.dtl.DTLVardef@15e5766_HPS_FORMAT_FIGEXP M_FIG TOC Art C_FIG