Enhancement of Antioxidants’ Enzymatic Activity in the Wheat Crop by Shewanela sp. Mediated Zinc Oxide Nanoparticles Against Heavy Metals Contaminated Wastewater

This study employed a new biological approach to synthesize Zinc oxide nanoparticles (ZnO NPs) using the bacterial strain Shewanela. Sp. This study aims to explore using zinc oxide nanoparticles to alleviate the effects of wastewater stress on plant growth and development. The synthesis of ZnO nanoparticles from Shewanela sp. involves the bioreduction of zinc salts through the metabolic processes of the bacteria, leading to the formation of ZnO nanoparticles. In this study, bacterial synthesized ZnO NPs were characterized by using scanning electron microscopy (SEM), UV/VIS Spectroscopy, X-ray diffraction (XRD), and Fourier transmission infrared spectroscopy (FTIR) analysis. The potential of these bacterial-synthesized ZnO NPs was determined by foliar application against the uptake of cadmium (Cd) and hexavalent chromium (Cr^+ 6) in wheat crops. A pot experiment was conducted for a period of 40 days to evaluate the impact of ZnO nanoparticles on wheat’s physiological and biochemical attributes. ZnO nanoparticles were applied foliarly with 4 different concentrations (0, 25, 50, and 100 mg L^− 1) at various time intervals. Results showed that the maximum growth and germination rate were observed in the treatment, where ZnO NPs were applied at 100 mg L^− 1. Maximum reduction of Cr and Cd in the roots and shoots of the plants was observed at the 100 mg L^− 1 concentration of ZnO nanoparticles. In plant shoots, the Cd decreased by 19.6%, 43.8%, and 90.9% in 25, 50, and 100 mg L^− 1 of ZnO NPs compared to control, respectively. Similarly, Cr^+ 6 concentration in plant shoot decreased by 14.6%, 39.3%, and 94.9% in 25, 50, and 100 mgL^− 1 of ZnO NPs compared to control. The foliar application of ZnO NPs boosted the chlorophyll content, total soluble sugars (TSS), total free amino acids (TFAA), ascorbic Acid (AsA) and antioxidant attributes like ascorbate peroxidase (APX), superoxide dismutase (SOD), peroxide dismutase (POD), catalase (CAT), by decreasing oxidative stress like malondialdehyde (MDA), hydrogen peroxide (H₂O₂), electrolytic leakage (EL), and superoxide radical (O₂•⁻). The foliar application of microbially synthesized ZnO NPs has the potential to enhance wheat growth and development in heavy metal-contaminated wastewater.