Abstract
Reactive oxygen species (ROS) are signaling molecules essential for plant responses to abiotic and biotic stimuli as well as for multiple developmental processes. They are produced as byproducts of aerobic metabolism and are affected by adverse environmental conditions. The ROS content is controlled on the side of their production but also by scavenging machinery. Antioxidant enzymes represent a major ROS-scavenging force and are crucial for stress tolerance in plants. Enzymatic antioxidant defense occurs as a series of redox reactions for ROS elimination. Therefore, the deregulation of the antioxidant machinery may lead to the overaccumulation of ROS in plants, with negative consequences both in terms of plant development and resistance to environmental challenges. The transcriptional activation of antioxidant enzymes accompanies the long-term exposure of plants to unfavorable environmental conditions. Fast ROS production requires the immediate mobilization of the antioxidant defense system, which may occur via retrograde signaling, redox-based modifications, and the phosphorylation of ROS detoxifying enzymes. This review aimed to summarize the current knowledge on signaling processes regulating the enzymatic antioxidant capacity of plants.
Highlights
Reactive oxygen species (ROS), as unavoidable byproducts of metabolism, have important signaling roles in living organisms under optimal and adverse environmental conditions (Apel and Hirt, 2004; Baxter et al, 2014; Waszczak et al, 2018)
ROS are produced from atmospheric oxygen by its partial monovalent reduction, which occurs in the presence of electron donors
Apoplastic ROS are produced by plasma membrane-localized NADPH oxidase [NOX, in plants encoded by RESPIRATORY BURST OXIDASE HOMOLOG (RBOH) genes; Sagi and Fluhr, 2006], oxalate oxidase (Voothuluru and Sharp, 2013), or by the degradation of spermidine by polyamine oxidase (Geilfus et al, 2015)
Summary
Reactive oxygen species (ROS), as unavoidable byproducts of metabolism, have important signaling roles in living organisms under optimal and adverse environmental conditions (Apel and Hirt, 2004; Baxter et al, 2014; Waszczak et al, 2018). Plant ROS are generated mainly by electron transport chains in chloroplasts (Pospíšil, 2016; Foyer, 2018) and mitochondria (Gleason et al, 2011) as well as during photorespiration in peroxisomes (del Río et al, 2006; del Río and López-Huertas, 2016). Apoplastic ROS are produced by plasma membrane-localized NADPH oxidase [NOX, in plants encoded by RESPIRATORY BURST OXIDASE HOMOLOG (RBOH) genes; Sagi and Fluhr, 2006], oxalate oxidase (Voothuluru and Sharp, 2013), or by the degradation of spermidine by polyamine oxidase (Geilfus et al, 2015). Four ROS, namely singlet oxygen (1O2), superoxide (O2·−), hydrogen peroxide (H2O2), and hydroxyl radical (OH·), are more abundant and stable. They quickly interconvert, providing a high level of functional variability.
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