The Fundamental Role of Reactive Oxygen Species in Plant Stress Response.

Chemical, physical, and biotic factors continuously vary in the natural environment. Such parameters are considered as stressors if the magnitude of their change exceeds the current acclimation norm of the plant. Activation of genetic programs allows for conditional expansion of the acclimation norm and depends on specific sensing mechanisms, intracellular communication, and regulation. The redox and reactive oxygen species (ROS) network plays a fundamental role in directing the acclimation response. These highly reactive compounds like H2O2 are generated and scavenged under normal conditions and participate in realizing a basal acclimation level. Spatial and temporal changes in ROS levels and redox state provide valuable information for regulating epigenetic processes, transcription factors (TF), translation, protein turnover, metabolic pathways, and cross-feed, e.g., into hormone-, NO-, or Ca2+-dependent signaling pathways. At elevated ROS levels uncontrolled oxidation reactions compromise cell functions, impair fitness and yield, and in extreme cases may cause plant death.