AUTHOR=Cuypers Ann , Hendrix Sophie , Amaral dos Reis Rafaela , De Smet Stefanie , Deckers Jana , Gielen Heidi , Jozefczak Marijke , Loix Christophe , Vercampt Hanne , Vangronsveld Jaco , Keunen Els TITLE=Hydrogen Peroxide, Signaling in Disguise during Metal Phytotoxicity JOURNAL=Frontiers in Plant Science VOLUME=7 YEAR=2016 URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2016.00470 DOI=10.3389/fpls.2016.00470 ISSN=1664-462X ABSTRACT=

Plants exposed to excess metals are challenged by an increased generation of reactive oxygen species (ROS) such as superoxide (O2•-), hydrogen peroxide (H₂O₂) and the hydroxyl radical (^•OH). The mechanisms underlying this oxidative challenge are often dependent on metal-specific properties and might play a role in stress perception, signaling and acclimation. Although ROS were initially considered as toxic compounds causing damage to various cellular structures, their role as signaling molecules became a topic of intense research over the last decade. Hydrogen peroxide in particular is important in signaling because of its relatively low toxicity, long lifespan and its ability to cross cellular membranes. The delicate balance between its production and scavenging by a plethora of enzymatic and metabolic antioxidants is crucial in the onset of diverse signaling cascades that finally lead to plant acclimation to metal stress. In this review, our current knowledge on the dual role of ROS in metal-exposed plants is presented. Evidence for a relationship between H₂O₂ and plant metal tolerance is provided. Furthermore, emphasis is put on recent advances in understanding cellular damage and downstream signaling responses as a result of metal-induced H₂O₂ production. Finally, special attention is paid to the interaction between H₂O₂ and other signaling components such as transcription factors, mitogen-activated protein kinases, phytohormones and regulating systems (e.g. microRNAs). These responses potentially underlie metal-induced senescence in plants. Elucidating the signaling network activated during metal stress is a pivotal step to make progress in applied technologies like phytoremediation of polluted soils.