The hydroxyl radical in plants: from seed to seed

Abstract

The hydroxyl radical (OH(•)) is the most potent yet short-lived of the reactive oxygen species (ROS) radicals. Just as hydrogen peroxide was once considered to be simply a deleterious by-product of oxidative metabolism but is now acknowledged to have signalling roles in plant cells, so evidence is mounting for the hydroxyl radical as being more than merely an agent of destruction. Its oxidative power is harnessed to facilitate germination, growth, stomatal closure, reproduction, the immune response, and adaptation to stress. It features in plant cell death and is a key tool in microbial degradation of plant matter for recycling. Production of the hydroxyl radical in the wall, at the plasma membrane, and intracellularly is facilitated by a range of peroxidases, superoxide dismutases, NADPH oxidases, and transition metal catalysts. The spatio-temporal activity of these must be tightly regulated to target substrates precisely to the site of radical production, both to prevent damage and to accommodate the short half life and diffusive capacity of the hydroxyl radical. Whilst research has focussed mainly on the hydroxyl radical's mode of action in wall loosening, studies now extend to elucidating which proteins are targets in signalling systems. Despite the difficulties in detecting and manipulating this ROS, there is sufficient evidence now to acknowledge the hydroxyl radical as a potent regulator in plant cell biology.

Metabolic Processes During Seed Germination

“…Interaction between phytohormones and H 2 O 2 can be antagonistic or synergistic. Signaling processes trigger interactions are not developed only between particular phytohormones but also between phytohormones and other signaling molecules such as NO [148], H 2 S [149], ·OH [150] and H 2 O 2 [151], which is believed to play a central role in signaling processes during plant development and stress responses [152]. GA treatment enhanced ROS production namely superoxide and H 2 O 2 in radish plants [153] and Arabidopsis [154].…”

Role of Reactive Oxygen Species during Cell Expansion in Leaves

“…1). The O 2 2 dismutates into H 2 O 2 , which can cause cross-linking of the cell wall or is converted into the cell wall loosening _ OH (Richards et al, 2015). During biotic stress, NADPH oxidases produce an oxidative burst to eliminate invading pathogens and send stress signals (Suzuki et al, 2011); during abiotic stress, they appear to mainly act as stress signal amplifiers to promote adaptive responses.…”

Antioxidant evaluation and inhibitory activity of Chromolaena odorata leaf extract on hydrogen peroxide-induced erythrocyte hemolysis

“…The hydroxyl radical is the most harmful one because of its high and non-selective reactivity [23,24]. The results revealed the extract scavenged hydroxyl radicals which was concentration-dependent (Figure 4).…”