Reactive Oxygen Species in Plant Cell Walls

Plant cell walls are dynamic structures composed of polysaccharides, phenolics, and proteins. The plant cell wall is important not only for maintaining cell shape, but it also responds to endogenous and environmental clues through the release of signaling molecules, such as H2O2, which may act following autocrine and paracrine pathways. However, the primary function of reactive oxygen species (ROS) production in the plant cell wall is to modify cell wall components by processes of cell wall stiffening/softening, which, in the last intance, control plant growth and morphogenesis. Four possible enzymatic machineries could explain how this H2O2 is produced: NADPH oxidases (NOX), peroxidases, poly(di)amine oxidases, and oxalate oxidases, but most of the molecular evidence, particularly in epidermal, vascular, and suberizing tissues, supports the exclusive participation of NOX in this process. Given the limited efficacy of the ROS-scavenging systems in plant cell walls, it may be concluded that ROS accumulation in the cell walls of these tissues is only the static image of their high redox state and large oxidative metabolism.