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Unformatted text preview: ROS Regulation of Antioxidant Genes 101 Chapter 6 ROS Regulation of Antioxidant Genes Photini V. Mylona 1 * and Alexios N. Polidoros 2 ABSTRACT Over the last decade our understanding of the role of ROS has progressed from the classical view of adverse toxic metabolic by- products inadvertently associated with aerobic life to include the newly emerging role of signaling molecules regulating growth, development and coordinating responses to abiotic and biotic stress. A recent series of discoveries have given scientists new insights into ROS-dependent gene activation and the molecular mechanisms involved. The majority of information of the regulatory role of ROS on gene expression derived from experiments using: i) transgenic plants overexpressing or suppressing antioxidant genes in order to reduce or increase the intracellular ROS levels, respectively; ii) mutants impaired in ROS generation or scavenging; iii) direct application of ROS; iv) application of ROS generating compounds. Results of these experiments provided signifi cant information on ROS-dependent signaling pathways and ROS-responsive genes. A number of genes involved in defense, signal transduction, transcription, metabolism as well as cell structure have been identifi ed revealing a highly dynamic and redundant network of ROS-producing and ROS-scavenging genes. Antioxidant genes are central players in this network and their function has profound effect in controlling ROS levels and cellular redox balance. ROS, on the other 1 Agricultural Research Center of Northern Greece, NAGREF, 57001 Thermi, Greece, Fax: (+30)2310471209, E-mail: [email protected] 2 Department of Genetics and Plant Breeding, School of Agriculture, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece, Fax: (+30) 2310998654, E-mail: [email protected] *Corresponding author 102 Reactive Oxygen Species and Antioxidants in Higher Plants hand can remarkably regulate the level of antioxidant gene expression providing a feedback regulation mechanism of ROS levels, which is a critical component in modulation of signaling networks. This chapter focuses on recent developments on the role of ROS in activation of gene expression with an emphasis on ROS-scavenging enzyme systems. Introduction Oxygen supports aerobic life of land plants granting them with great energetic benefi ts but on the other hand challenges them through an endless formation of reactive oxygen species (ROS). ROS, namely singlet oxygen ( 1 O 2 ), superoxide radical (O – 2 ), hydrogen peroxide (H 2 O 2 ) and hydroxyl radical (HO . ), are by-products of the energy-generating processes of photosynthetic and respiratory electron transport chains (ETC). Consequently, chloroplasts, mitochondria and peroxisomes are the main organelles of ROS producers in plant cells. ROS are highly reactive and toxic based on their ability to react indiscriminately with almost all biomolecules provoking destructive protein modifi cations, DNA strand breaks, purine oxidations, protein-DNA...
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- ET AL, reactive oxygen species