Biostimulants and the modulation of plant antioxidant systems and properties

Plant antioxidant systems, both enzymatic and nonenzymatic, are central to plant innate tolerance to abiotic and biotic stressors via the maintenance of redox and osmotic homeostasis. Reactive species formation is closely associated with stress-response elicitation and this results in the accumulation, beyond physiological levels, of hyperreactive molecules that are cytotoxic. Plant antioxidant systems employ physiological and biochemical mechanisms to scavenge reactive oxygen species and keep cellular and tissue ROS levels within the nontoxic range, thereby maintaining redox homeostasis. Plant biostimulants are organic or inorganic substances that can alleviate the adverse effects of stressors and improve plant productivity. They mediate vigorous growth, development, and the amelioration of stress-induced injury by regulating plant antioxidant systems. Here, we bring into perspective the current understanding of biostimulant-mediated elicitation and control of plant antioxidant systems in fostering stress tolerance. We also highlight aspects that require research attention and hold promises in providing applicable knowledge for crop improvement programs.