title: Roles of the reactive oxygen species-generating peroxidase reactions in plant defense and growth induction.
abstract: Extracellularly secreted plant peroxidases (POXs) are considered to catalyze the generation of reactive oxygen species (ROS) coupled to oxidation of plant hormone indole-3-acetic acid (IAA) and defense-related compounds salicylic acid (SA), aromatic monoamines (AMAs) and chitooligosaccharides (COSs). This review article consists of two parts, which describe H(2)O(2)-dependent and H(2)O(2)-independent mechanisms for ROS generation, respectively. Recent studies have shown that plant POXs oxidize SA, AMAs and COSs in the presence of H(2)O(2) via a conventional POX cycle, yielding the corresponding radical species, such as SA free radicals. These radical species may react with oxygen, and superoxide (O(2)(.-)) is produced. Through the series of reactions 2 moles of O(2)(.-) can be formed from 1 moles of H(2)O(2), thus leading to oxidative burst. It has been revealed that the ROS induced by SA, AMAs and COSs triggers the increase in cytosolic Ca(2+) concentration. Actually POXs transduce the extracellular signals into the redox signals that eventually stimulate the intracellular Ca(2+) signaling required for induction of defense responses. On the other hand, IAA can react with oxygen and plant POXs in the absence of H(2)O(2), by forming the ternary complex enzyme-IAA-O(2), which readily dissociates into enzyme, IAA radicals and O(2)(.-). This article covers the recent reports showing that extracellularly produced hydroxy radicals derived from O(2)(.-) mediate the IAA-induced cell elongation. Here a novel model for IAA signaling pathway mediated by extracellular ROS produced by cell-wall POXs is proposed. In addition, possible controls of the IAA-POX reactions by a fungal alkaloid are discussed.
authors.affiliation: Graduate School of Environmental Engineering, The University of Kitakyushu, 1-1 Hibikino, Wakamatsu-Ward, 808-0135, Kitakyushu, Japan. kawanotom@env.kitakyu-u.ac.jp
authors.forename: T
authors.initials: T
authors.lastname: Kawano
mesh_terms: D010544:Peroxidases / Q000378:metabolism*; D063245:Plant Development; D018521:Plant Physiological Phenomena; D010944:Plants / Q000201:enzymology*; D017382:Reactive Oxygen Species
chemical_list: D017382:Reactive Oxygen Species; D010544:Peroxidases