Plant growth and resilience require balancing an inherently oxidative metabolism with powerful antioxidant systems that help maintain homeostasis. When the environment changes, reactive oxygen species are potent indicators of that change, allowing adaptation through re-balancing metabolism and antioxidant systems. A large body of evidence supports the use of exogenously applied antioxidants to improve both plant growth and their resilience to stress. Notably, some phenotypic effects are similar upon the application of chemically diverse antioxidants, while others are distinct. In this review, we analyze research from antioxidant treatment experiments and highlight the similarities in their practical applications and their effects on plant stress tolerance, photosynthesis, native antioxidant systems, and phytohormones. We also briefly cover the specific effects of individually applied antioxidants and what is known about their potential modes of action. Given the strong potential of antioxidant applications, we discuss research needed to promote their agricultural use. Finally, we identify outstanding questions about how the exogenous application of antioxidants mechanistically affects plant growth.

Many microbes accumulate energy storage molecules such as triglycerides and starch during nutrient limitation. In eukaryotic green algae grown under nitrogen limiting conditions, triglyceride accumulation is coupled with chlorosis and growth arrest. In this study we show that accumulation of reactive oxygen species (ROS) under nitrogen limitation in the microalga Chlorella sorokiniana is involved in thylakoid membrane remodeling, leading to chlorosis. We show that ROS accumulation under nitrogen limitation is an active process involving downregulation of expression of ROS-quenching enzymes, such as superoxide dismutases, catalase, peroxiredoxin, and glutathione peroxidase-like, and upregulation of enzymes involved in generating ROS, such as NADPH oxidase, xanthine oxidase and amine oxidases. Expression of enzymes involved in ascorbate and glutathione metabolism are also affected under these conditions. We also show that calcium influx plays a putative role in activation of NADPH oxidases, leading to ROS generation and membrane remodeling. Quenching ROS under nitrogen limitation reduces TAG accumulation, adding additional evidence for the role of ROS signaling in the process.