ABSTRACT
Ever since the introduction of molecular oxygen (O2) into our atmosphere by O2-evolving photosynthetic organisms 2.7 billion years ago, reactive oxygen species (ROS) have been the unwelcome companions of aerobic life. In contrast to O2, these partially reduced or activated derivatives of oxygen [singlet oxygen (1O2), superoxide anion (O2-), hydrogen peroxide (H2O2) and hydroxyl radical (HO)] are highly reactive and toxic, and can lead to the oxidative destruction of cells. Consequently, the evolution of all aerobic organisms has been dependent on the development of efcient ROS-scavenging mechanisms. In recent years, a new role for ROS has been identied: the control and regulation of biological processes, such as growth, cell cycle, programmed cell death, hormone signaling, biotic and abiotic stress responses, and development. These studies extend our understanding of ROS and suggest a dual role for ROS in plant biology as both toxic byproducts of aerobic metabolism and key regulators of growth, development, and defense pathways. How this dual role is controlled in plants is largely unknown. However, it is clear that the steady-state level of ROS in cells needs to be tightly regulated. In Arabidopsis, a network of more than 150 genes is involved in managing the level of ROS. This network is highly dynamic and redundant, and encodes ROS-scavenging and ROS-producing proteins. Recent studies have unraveled some of the key players in the network, but many questions related to its mode of regulation, its protective roles and its modulation of signaling networks that control growth, development and stress response remain unanswered. The hunt for ROS receptors in plants is still open. It has been suggested that plant cells sense ROS via at least three different mechanisms: (1) unidentied receptor proteins; (2) redox-sensitive transcription factors, such as NPR1 or Heat Shock Factors; and (3) direct inhibition of phosphatases by ROS. Continued genomics, proteomics and metabolomics efforts and other emerging technologies are likely to provide a more detailed picture of the networks involved in different ROS-related plant processes. Because ROS play a regulatory role
6.1 Introduction .......................................................................................................................... 140 6.2Reactive Oxygen Species ...................................................................................................... 140 6.3Drought Stress ...................................................................................................................... 141 6.4Waterlogging ......................................................................................................................... 141 6.5High Temperature ................................................................................................................. 142 6.6 Low Temperature .................................................................................................................. 143 6.7Exposure to High Light Intensities ....................................................................................... 143 6.8UV Radiation ........................................................................................................................ 144 6.9Salinity Stress ....................................................................................................................... 145 6.10Heavy Metals ........................................................................................................................ 146 6.11 Air Pollutants ........................................................................................................................ 146 6.12Conclusions ........................................................................................................................... 147 References ...................................................................................................................................... 148
in plants response and adaptation to both biotic and abiotic stress situations, new insights into the ROS gene network might also allow the identication of genes that can ultimately be exploited to modulate ROS-related plant processes that lead to the generation of better performing crop plants. (by Frank Van Breusegem and Ron Mittle)
Plants are frequently exposed to a plethora of unfavorable or even adverse conditions, called abiotic stresses, which lead to a series of morphological, physiological, biochemical, and molecular changes that prevent plants from reaching their full genetic potential, and hence limit the crop productivity. Abiotic stress is the principal cause of crop failure worldwide, dipping average yields for most major crops by more than 50% [1]. A common consequence of abiotic stresses is that they result, at some stage of stress exposure, in an increased production of ROS and subsequent oxidative stress. To maintain growth and productivity, plants must adapt themselves to stress conditions and set up specic protective mechanisms, including the protective mechanisms against oxidative stress. The chief aim of this chapter is to make a survey of protection by means of antioxidant systems against oxidative stress in plants during the action of various abiotic stresses.
