Positive Interaction of Selenium Nanoparticles and Olive Solid Waste on Vanadium-Stressed Soybean Plant

The purpose of the current study was to determine the possible improvement in soybean
plants’ tolerance against vanadium-induced stress in response to the application of olive solid waste
(OSW) and selenium nanoparticles (Se-NPs), by assessing metabolites and plant defense systems.
Drawing upon this aim, a pot experiment was performed where the soybean plants were grown
with a fertilization treatment (including, control, OSW, Se-NPs, and Se-NPs + OSW) under vanadium stress (including non-stress and 350 mg sodium orthovanadate per kg of soil). Enhancement
of hydrogen peroxide (H2O2) and malondialdehyde (MDA) accumulation in vanadium-stressed
plants confirmed the oxidative damage in unfertilized plants. Results indicated the positive effects
of the combined treatment (Se-NPs + OSW) in improving the plant stress tolerance by causing a
balance in the produced ROS and detoxified ROS in the plant. It was mainly stimulated through the
improvement of the photosynthetic parameters, anthocyanin metabolism pathway, phenylpropanoid pathway, non-enzymatic antioxidant metabolites (tocopherols, malondialdehyde, polyphenols, and flavonoids), antioxidant enzymes, and biochemical components involved in the ASC/GSH
cycle (ascorbate, ascorbate peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase, glutathione, glutathione reductase, and glutathione peroxidase), and antioxidant direct scavenging enzymes (peroxidase, catalase, and superoxide dismutase), which finally resulted in higher
plant biomass. In conclusion, the simultaneous application of OSW and Se-NPs treatments provided
a reliable protection for soybean plants in vanadium-contaminated soils through the activation of
antioxidant and non-antioxidant defense mechanisms.