Formation and Functional Role of Reactive Oxygen Species (ROS)
In the following chapters we will focus on the role of ROS as a messenger product and substrate in contributing to communication and feedback in hierarchical networks. The next two chapters provide an overview on recent developments and current knowledge about monitoring, generation and the functional role of reactive oxygen species (ROS) - H2O2,
HO2, HO*, OH-, Ю2 and O- in both oxidative degradation and signal transduction in photosynthetic organisms. We further describe microscopic techniques for ROS detection and controlled generation. Reaction schemes elucidating formation, decay, monitoring and signaling of ROS in cyanobacteria and eukaryotes are discussed. The discussion further targets the rapidly growing field of regulatory effects of ROS on nuclear gene expression.
The excess of ROS under unfavorable stress conditions causes a shift in the balance of oxidants/antioxidants towards oxidants, which leads to the intracellular oxidative stress. Formation of ROS (the production rate) as well as decay of ROS (the decay rate) with the latter one determining the lifetime of ROS finally determines the actual concentration distribution of the ROS pool. The activity of antioxidant enzymes, superoxide dis- mutase (SOD), catalase, peroxidases, and several others, as well as the content of low molecular weight antioxidants, such as ascorbic acid, glutathione, tocopherols, carotenoids, anthocyanins, play a key role in regulation of the level of ROS and products of lipid peroxidation (LP) in cells (Apel and Hirt, 2004; Biel et al., 2009; Pradedova et al., 2011; Kreslavski et al., 2012b).
The exact mechanisms of neutralization and the distribution of ROS have not all been clarified so far. Especially the involvement of organelles, cells and up to the whole organism, summarizing the complicated network of ROS signalling are still far from being completely understood (Swanson and Gilroy, 2010; Kreslavski et al., 2013a; Schmitt et al., 2014a).
It is obvious that ROS exert deleterious effects. Oxidative destruction by ROS is known and has been studied for decades. However, ROS also act as important signaling molecules with regulatory functions. ROS were found to play a key role in the transduction of intracellular signals and in control of gene expression and activity of antioxidant systems (Apel and Hirt, 2004; Desikan et al., 2001, 2003; Mori and Schroeder, 2004; Galvez- Valdivieso and Mullineaux, 2010; Foyer and Shigeoka, 2011; Schmitt et al., 2014a). Being implicated in reactions against pathogens, (e.g. by respiratory bursts) and by the active participation in signaling, ROS have a protective role in plants (Bolwell et al., 2002; Dmitriev, 2003).
ROS contribute to acclimation and protection of plants, regulate processes of polar growth, stomatal activity, light-induced chloroplast movements, and plant responses to biotic and abiotic environmental factors (Mullineaux at al., 2006; Pitzschke and Hirt, 2006; Miller et al., 2007; Swanson and Gilroy, 2010; Vellosillo et al., 2010). In animals, recent studies have established that physiological H2O2 signaling is essential for stem cell proliferation, as illustrated in neural stem cell models, where it can also influence subsequent neurogenesis (Dickinson and Chang, 2011). The following book chapters will describe generation and decay of ROS and their monitoring in cells (chapter 3). Additionally the rapidly growing field of regulatory effects and pathways of ROS will be described (chapter 4) although a complete description of the multitude of roles of ROS from nonphotochemical quenching (NPQ) to genetic signaling is impossible. However, these two chapters provide an overview about the existing knowledge aiming to include the most important original literature and reviews. The following two book chapters are based on the review of (Schmitt et al., 2014a), however, they are significantly broadened to connect the research to overall top down and bottom up signaling in hierarchic networks as it is the aim of this book.