The Dual Role of Reactive Oxygen Species as Signals that Influence Plant Stress Tolerance and Programmed Cell Death

Reactive oxygen species (ROS) are molecules and radicals which are continuously made by the redox cascades of aerobic metabolism in plants. They may even act as a signal by altering the redox equilibrium of the cell, which can change how specific proteins work or how genes are expressed and respond to biotic and abiotic stress. The network of redox signals controls metabolism to regulate how energy is produced and utilized at every stage of plant growth by interfering with the main signaling molecules (hormones) to adapt to environmental changes. In normal conditions, plants have many ways to fight ROS, but when they are stressed, ROS starts building up and causes oxidative stress. This duality can only be achieved by strictly regulating ROS generation and consumption by the antioxidant defense system within cells. Indeed, ROS are involved in a wide variety of redox-governing actions within cells, which are necessary for maintaining cellular homeostasis. However, its excess synthesis has been linked to oxidative stress, a potentially harmful process that damages biomolecules and cellular structures and contributes to programmed cell death (PCD). The chapter provides a concise view of the dual role of ROS signaling in plant acclamatory defense processes and PCD.