Green synthesized Fe-NPs ameliorate drought stress in Spinacia oleracea L. through improved photosynthetic capacity, redox balance, and antioxidant defense

Abstract

The global agricultural sector is under tremendous pressure due to population growth and the consequent demand for food. Drought stress is a hazardous threat to agricultural crops around the globe. Spinach (Spinacia oleracea L.) is cultivated worldwide. Spinach is a leafy vegetable and vulnerable to drought stress for having higher water content. Drought stress altered its biochemical composition and stunted its growth. The present study was designed to highlight the ameliorative role of iron nanoparticles (Fe-NPs) against drought stress. A pot experiment was performed in which three irrigation levels with 100, 50 and 25% field capacity were used. Fe-NPs were synthesized by green synthesis method using rice straw. The synthesized Fe-NPs were analyzed by various techniques including UV, SEM, FTIR, XRD and EDX. Foliar application of Fe-NPs (40 mg/L) was employed. Along with this foliar spray of iron salt (FeSO₄; 40 mg/L) was also applied for comparative analysis. Stressed-spinach plants showed a reduction in growth parameters, whereas Fe-NPs readily stimulated growth of stressed plants. Growth parameters (fresh and dry weight of root and shoot, number of leaves and leaf area), relative water content, total proteins, photosynthesis related attributes (ΦPSII, chlorophyll florescence, chlorophyll a and b and carotenoids) and nutrients uptake decreased because of drought stress. Furthermore, drought stress shows a significant increase in proline, hydrogen peroxide, malondialdehyde and enzymatic antioxidants. Application of Fe-NPs increased photosynthesis, antioxidant enzyme activity and mineral nutrient intake, which in turn improved membrane function. Moreover, it decreased the excess ROS generation brought on by drought stress. The nutritional status of plants and the generation of secondary metabolites (proline & total phenolics) was also enhanced by Fe-NPs. These findings suggest that Fe-NPs could be a helpful tool for lessening the harmful consequences of drought stress. Fe-NPs boosted growth and stimulated antioxidant defense mechanisms to mitigate the negative consequences of drought stress.