ROS mediated plant defense against abiotic stresses

Changes in the natural environment may cause stress to living organisms. This phenomenon has been widely observed in plants during abiotic stresses which include changes in temperature, pH of the soil, salinity and water content. Such stresses usually lead to the production of reactive oxygen species (ROS) in plant cells. Although ROS are generally produced inside plant cells as a by-product of different metabolic pathways including electron transport in the process of respiration, photosynthesis and several other chemical reactions, excessive production of these free radicals can lead to damage of the cell components due to oxidative stress. Other means of ROS production include external stimuli including biotic and abiotic stresses or cell lignification processes which lead to the enzymatic production of ROS. Various forms of ROS may include hydrogen peroxide (H₂O₂), hydroxyl radical (HO·), singular oxygen (¹O₂), and superoxide ion (O₂·-). These highly reactive free radicals are produced in different cellular compartments such as mitochondria, chloroplasts, peroxisome and the apoplast. Key roles for various reactive oxygen molecules include involvement in plant growth and development, programmed cell death, acclimation of stresses such as drought, salt, heat, cold, light and high frequency electromagnetic fields. In addition to involvement in stress acclimation and mitigation ROS serve as signaling molecules during biotic and abiotic stress responses. ROS are also involved in cross talk between different phytohormones, calcium signaling, antioxidant proteins, protein kinases and phosphatases and map kinase signaling network. Furthermore, ROS induce transcriptional changes show involvement of these molecules in regulating a plethora of biological processes at the transcript level. Therefore, ROS stand out as a good candidate for future research through classical as well as advanced bio-technological methods for a better understanding of plant biology.