Reactive Oxygen Species in Plants: From Source to Sink

Abstract

Reactive oxygen species (ROS, partial reduction or derivatives of free radicals) are highly reactive, dangerous and can cause oxidative cell death. In addition to their role as toxic by-products of aerobic metabolism, ROS play a role in the control and regulation of biological processes such as growth, the cell cycle, programmed cell death, hormone signaling, biotic and abiotic stress reactions and development. ROS always arise in plants as a by-product of several metabolic processes that are located in different cell compartments, or as a result of the inevitable escape of electrons to oxygen from the electron transport activities of chloroplasts, mitochondria and plasma membranes. These reactive species are formed in chloroplasts, mitochondria, plasma membranes, peroxisomes, apoplasts, the endoplasmic reticulum and cell walls. The action of many non-enzymatic and enzymatic antioxidants present in tissues is required for efficient scavenging of ROS generated during various environmental stressors. The current review provides an in-depth look at the fate of ROS in plants, a beneficial role in managing stress and other irregularities. The production sites are also explained with their negative effects. In addition, the biochemical properties and sources of ROS generation, capture systems, the influence of ROS on cell biochemistry and the crosstalk of ROS with other signaling molecules/pathways are discussed.

Keywords: cell death; production; reactive oxygen species; signaling; stress.

Figure 1

ROS signaling, the activation of the MAPK cascade and redox ROS homeostasis in the cell. In biotic and abiotic stressors, the reactive oxygen species (ROS) signaling pathway is regulated by mitogen-activated protein kinases (MAPK). ROS is a common messenger that is produced in response to both the stress response and the MAPK cascade. Despite having a similar MAPK signaling regulator, the plant’s reaction to both stressors is distinct.

Figure 2

Effects of oxidative stresses on plant parts and different defense mechanisms. In plants, ROS cause serious damage to the cells by inhibiting proteins, DNA and other metabolic pathways. Conversely, the defense system is activated in the plants against ROS to regulate its functional activity by activating different enzymatic and non-enzymatic antioxidant agents.

Figure 3

Atmospheric oxygen is shown to undergo excitation or reduction to form different ROS and reactive nitrogen species; super oxide dismutase is shown to form hydrogen peroxide (H₂O₂), which in turn reacts with Fe²⁺ to form hydroxyl radicals (OH⁻) via the Fenton reaction.

Figure 4

Integration of ROS and redox biology in cellular processes. Different cell organelles, including mitochondria, chloroplasts, peroxisomes and cell-wall-bound peroxidases (PER) and respiratory burst oxidase homologs (RBOHs), produce ROS that accumulate in the form of hydrogen peroxide (H₂O₂), resulting in the mediation of cell-to-cell signaling pathways. However, the presence of Fe²⁺ ions can cause cellular oxidative stress via hydroxyl radicals. These processes must be balanced and are crucial for redox biology for the regulation of the metabolism and other physiological and cellular functions.