Chapter 14 - Regulations of reactive oxygen species in plants abiotic stress: an integrated overview

Abstract

Reactive oxygen species (ROS) is considered as an unwelcome partner in Earth’s aerobic organisms, since oxygen molecules (O2) were introduced from the atmosphere by O2-evolved photosynthetic organisms about 3 billion years ago. Unlike O2, various reactive oxygen derivatives [e.g., singlet oxygen (1O2), hydrogen peroxide (H2O2), and superoxide radical (O2• −)] under unfavorable conditions have high toxicity, thus causing oxidative stress in organism cells. In general, abiotic stress emerges when the environment deviates from optimal conditions that interfere with cellular function, which is also defined as the stress of any factor other than direct interaction with another organism. In addition, the delicate balance between the generation and removal of ROS is interfered by different types of stressors, among which the most frequently mentioned ones are drought, salinity, heavy metals, extreme temperature, excessive light, and ultraviolet radiation, as well as xenobiotic, ozone, sulfur dioxide (SO2), elevated CO2 (carbon dioxide), and nutrient deficiencies. In higher plants, those abiotic stresses usually stimulate ROS formation (a common event regardless of plant species), causing a variety of physiological variations. However, it is worth noting whether the role of ROS in cells’ functions as protection, destruction, or signal transduction, which mainly relies on the delicate equilibrium between the generation and clearance of ROS at appropriate locations and time points. Definitely, a good equilibrium exists between the signaling of ROS generation, the reactivity of ROS diffusion, the baseline of ROS metabolism, and the perception of ROS signaling in different cells’ compartments of plants throughout the evolution process (ROS network). For example, ROS induced by stress could be neutralized by plasma membrane-bound NADPH oxidases (i.e., respiratory burst oxidase homolog, rubidium hydroxides; and termed NADPH oxidases in plants) and enzymatic antioxidant systems consisting numerous scavengers, such as catalase, peroxidase, and superoxide dismutase, and nonenzymatic compounds, such as ascorbate, glutathione, and flavonoids. Under abiotic stress, redox metabolism and its corresponding signaling are often considered as a key mechanism in plants. During evolution, plants have developed a unique mechanism for active controlling of ROS overproduction and for effectively using it as a signaling molecule. To date, many signal-transduction pathways that regulated by ROS have been reported. However, the recognition of ROS-mediated signaling is discontinuous, and the specificities of ROS-signal sensing and conduction remain unresolved.