Mechanism of Reactive Oxygen Species Regulation in Plants

Reactive oxygen species (ROS) are the products of physiological metabolism in various cellular compartments such as mitochondria, peroxisomes, and chloroplasts. Under biotic and abiotic stress, ROS are significantly accumulated and can progressively induce oxidative damage and ultimately lead to cell death. Moreover, ROS generation is a fundamental process in plants to transmit and transport the signal toward the nucleus to increase tolerance against diverse conditions. The defense system against ROS not only consists of a scavenging system but is also comprised of an enzymatic and non-enzymatic defense system against various environmental issues. The enzymatic defense system against ROS includes various enzymes such as peroxidase (POD), superoxide dismutase (SOD), polyphenol oxidase (PPO), ascorbate peroxidase (APX), glutathione peroxidase (GPX), and catalase (CAT). This chapter covers a detailed study of the organelle-specific generation of ROS and existing enzymatic systems to balance the redox state. Moreover, the role of non-enzymatic and low-molecular-weight antioxidants in ROS detoxification and retrograde signaling will also be discussed. Plants have also evolved several interconnected signaling pathways to control the expression of different transcriptional factors and stress-responsive genes for producing various classes of proteins that result in stress regulation. More importantly, the relationship between ROS and epigenetic modifications to regulate gene expression will be precisely discussed in this chapter. Excess ROS accumulation can lead to the activation of cell death processes such as apoptosis which is crucial for plant development and survival. The role of apoptosis in maintaining normal cellular homeostasis under stress conditions is discussed in detail. In this chapter, the different mechanisms involved in ROS regulation that will offer a new platform for the improvement of abiotic stress tolerance in crops are summarized.