Hormone–ROS Interactions in Plants: A Molecular Framework for Stress Resilience

Reactive oxygen species (ROS) are inevitable by-products of aerobic metabolism in plants and serve as essential signalling molecules under both optimal and stress conditions. However, excessive accumulation of ROS leads to oxidative stress, causing cellular injury through lipid peroxidation, protein oxidation, and nucleic acid damage, ultimately compromising plant growth and productivity. Phytohormones, including abscisic acid (ABA), salicylic acid (SA), jasmonates (JA), ethylene (ET), auxins (IAA), cytokinins (CK), gibberellins (GA), and brassinosteroids (BR), function as central regulators of plant stress responses and play crucial roles in maintaining redox homeostasis. These hormones modulate ROS levels through multiple mechanisms: stimulation of apoplastic ROS production as secondary messengers, induction of antioxidant enzyme systems such as superoxide dismutase, catalase, and ascorbate peroxidase, and regulation of non-enzymatic antioxidant metabolites like ascorbate and glutathione. Recent evidence highlights that hormonal interactions with ROS are highly context-dependent, with certain hormones simultaneously promoting ROS as signalling intermediates while also enhancing scavenging mechanisms to prevent cellular damage. Hormone crosstalk adds another layer of complexity, as synergistic or antagonistic interactions among ABA, SA, JA, BR, and other hormones finely tune antioxidant responses according to stress type, tissue, and developmental stage. Advances in molecular biology and omics approaches have revealed key signaling nodes, including NADPH oxidases, MAP kinases, and redox-sensitive transcription factors, that act as integrators of hormone–ROS networks. Furthermore, priming strategies with exogenous hormone application demonstrate potential for improving stress resilience by preparing antioxidant systems for rapid activation under adverse conditions. This review synthesises recent progress on the mechanistic roles of phytohormones in oxidative stress regulation, emphasising their dual functions as inducers of ROS signalling and enhancers of antioxidant capacity. We discuss how hormone-regulated ROS balance influences stomatal regulation, chloroplast function, pathogen defence, and growth trade-offs. We also highlight translational opportunities for crop improvement through targeted manipulation of hormone pathways, alongside current limitations such as dose sensitivity, species-specific responses, and field-level variability. By identifying knowledge gaps and proposing integrative research directions, this review underscores the central role of hormones in redox biology and their potential in guiding sustainable agricultural practices under increasingly variable climate conditions.