Reactive oxygen species as integrators of stress signalling and developmental regulation in plants

Abstract

Reactive oxygen species (ROS) serve as both critical signalling molecules and potent cytotoxins. Generated predominantly in chloroplasts, mitochondria, peroxisomes, and the apoplast, ROS arise as by-products of aerobic metabolism and are further induced under environmental stresses. This dual nature positions ROS at the interface of plant stress responses, development, and immunity. At low concentrations, ROS act as secondary messengers regulating processes such as seed germination, root hair elongation, stomatal closure, and systemic acquired acclimation. They mediate complex interactions with phytohormones, including abscisic acid (ABA), ethylene (ET), auxins (IAA), and cytokinins, modulating developmental and stress responses. Conversely, excessive ROS accumulation under drought, salinity, extreme temperatures, or pathogen attack leads to oxidative damage, impairing macromolecules and triggering programmed cell death. Plants counteract this through robust antioxidant systems comprising enzymatic (SOD, CAT, APX) and non-enzymatic (ascorbate, glutathione, carotenoids) components. Beyond localized responses, ROS can function as systemic signals through self-propagating RBOH-dependent ROS waves, coordinating whole-plant acclimation and defence, while MAPK cascades act as intracellular effectors that transduce ROS signals into transcriptional and physiological responses. This review elucidates the multifaceted roles of ROS in plant physiology, emphasizing their context-dependent effects as either beneficial regulators or detrimental agents, thus underscoring their identity as both boon and bane. ROS are double-edged molecules vital for signalling, yet harmful at high levels. ROS hormone crosstalk fine-tunes growth, stress responses, and developmental transitions. ROS guides key processes like seed germination, root growth, and programmed cell death. ROS waves enable systemic stress signalling, integrating MAPK, calcium, and retrograde pathways. Antioxidant systems maintain ROS balance, safeguarding plant health under stress. ROS are double-edged molecules vital for signalling, yet harmful at high levels. ROS hormone crosstalk fine-tunes growth, stress responses, and developmental transitions. ROS guides key processes like seed germination, root growth, and programmed cell death. ROS waves enable systemic stress signalling, integrating MAPK, calcium, and retrograde pathways. Antioxidant systems maintain ROS balance, safeguarding plant health under stress.