title: Production, amplification and systemic propagation of redox messengers in plants? The phloem can do it all!
abstract: Rapid long-distance signalling is an emerging topic in plant research, and is particularly associated with responses to biotic and abiotic stress. Systemic acquired resistance (SAR) to pathogen attack is dependent on nitric oxide (NO) and reactive oxygen species (ROS) such as hydrogen peroxide (H2O2). By comparison, systemic wound responses (SWRs) and systemic acquired acclimation (SAA) to abiotic stress encounters are triggered by rapid waves of H2O2, calcium and electrical signalling. Efforts have been made to decipher the relationship between redox messengers, calcium and other known systemic defence signals. Less is known about possible routes of signal transduction throughout the entire plant. Previously, the phloem has been suggested to be a transport conduit for mobile signals inducing SAR, SWR and SAA. This review highlights the role of the phloem in systemic redox signalling by NO and ROS. A not yet identified calcium-dependent NO source and S-nitrosoglutathione reductase are candidate regulators of NO homeostasis in the phloem, whereas ROS concentrations are controlled by NADPH oxidases and the H2O2-scavenging enzyme ascorbate peroxidase. Possible amplification mechanisms in phloem-mediated systemic redox signalling are discussed.
authors.affiliation: Institute of Biochemical Plant Pathology, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, D-85764, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Gaupels
authors.affiliation: Institute of Biochemical Plant Pathology, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, D-85764, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Durner
authors.affiliation: Institute of Phytopathology, Research Center for BioSystems, Land Use and Nutrition, Justus Liebig University Gießen, Gießen, D-35392, Germany.
authors.forename: Karl-Heinz
authors.initials: KH
authors.lastname: Kogel
mesh_terms: D009569:Nitric Oxide / Q000378:metabolism; D010084:Oxidation-Reduction; D052585:Phloem / Q000378:metabolism*; D010944:Plants / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D017382:Reactive Oxygen Species; D009569:Nitric Oxide
keywords: abiotic stress; calcium; hydrogen peroxide (H2O2); nitric oxide (NO); pathogen resistance; phloem; systemic signalling; wound response