Markers of Oxidative Stress in Plants
Rashmi Shakya, Deepali
Abstract
Stresses faced by plants due to climate change are manifested at the molecular level in the form of increased production of reactive oxygen species (ROS), which comprise both free and non-free radicals. These include molecules such as hydrogen peroxide (H2O2), superoxide (O2∙−), singlet oxygen (1/2O2), and the hydroxyl radical (∙OH). Abiotic stresses lead to a reduction in photosynthetic activities and the accumulation of ROS. Oxidative stress occurs when there is a disturbance in the redox state due to increased production of free radicals and/or decreased antioxidant defense mechanisms against free radicals. Imbalance in the redox state can cause cellular injuries through DNA damage, protein oxidation, and lipid peroxidation due to the highly reactive nature of ROS. Cellular nitric oxide (NO) interacts with ROS to cause the production of several reactive nitrogen species (RNS), such as nitrogen dioxide (NO2 −), peroxynitrite (ONOO−), dinitrogen trioxide (N2O3), and nitrous acid (HNO2) that are implicated in oxidative and nitrosative damage. Furthermore, reactive iron, copper, and sulfur species also contribute to elevated ROS levels contributing to oxidative stress and impairing the redox balance. Severe oxidative stress can lead to the death of cells. Therefore, the measurement of oxidative stress markers is crucial for the proper growth and development of plants. The markers of oxidative stress can be enzymatic—such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), ascorbate peroxidase (APX), and glutathione reductase (GR)—or non-enzymatic like hydrogen peroxide (H2O2), malondialdehyde (MDA), ascorbic acid, flavonoids, phenols, and proline. Sensitive and robust assays for ROS and RNS detection, accurate quantitation, and measurements of intrinsic cell defense responses are required for measuring oxidative stress in the cell. In this chapter, an updated account of factors responsible for oxidative stress in plants is presented, followed by a detailed account of various enzymatic and non-enzymatic markers reported to date. Popular methods for their qualitative and quantitative estimation are also given. This chapter is an attempt to consolidate and enrich the knowledge base for future studies based on the significance of ROS homeostasis and regulation of oxidative stress in plants based on these markers and their interrelationships to better understand the mechanism of oxidative stress, especially in the wake of climate change.