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In plants, reactive oxygen species (ROS) can be generated by various processes occurring in different cellular compartments. Under physiological steady-state conditions, ROS are scavenged by different antioxidative components, but the balance between production and scavenging of ROS may be perturbed by a number of adverse environmental factors, giving rise to rapid increases in intracellular ROS levels. Although high concentrations of ROS can cause irreversible damage and cell death, they can also influence signaling and gene expression, indicating that cells have evolved strategies to utilize ROS to control various biological programs (Apel and Hirt, 2004). Being small and able to diffuse over short distances, ROS are ideally suited to act as signaling molecules. Among different ROS, only hydrogen peroxide (H2O2) can cross plant membranes and can therefore directly function in cell-to-cell signaling. Plant cells possess still-unidentified specific ROS sensors that process and translate this information into respective biological output programs. In several systems, various pathways, particularly those involving mitogen-activated protein kinases (MAPKs), are modulated by ROS and will be the focus of this review.
Pitzschke et al. (Thu,) studied this question.