Journal of Experimental Botany, Vol. 53, No. 372, pp. 0,
May 15, 2002
© 2002 Oxford University Press
Preface
Exeter
Reactive oxygen species (ROS) and the antioxidants that control them are relevant to many areas of plant biology. ROS (e.g. superoxide, hydrogen peroxide and hydroxyl radicals) are generated when metabolism interacts with oxygen. ROS can damage proteins, DNA and lipids, potentially disrupting cell function and causing mutations. Oxidative damage is also exacerbated by environmental stresses as diverse as drought, high salinity, temperature extremes, excess light, UV-B radiation, toxic metals, and air pollutants. This has spurred attempts to over-express antioxidant enzymes (including superoxide dismutase, catalase, glutathione reductase, ascorbate peroxidase and others) in transgenic plants in the hope of causing a generalized increase in stress resistance. Also, attempts are being made to increase the synthesis of small molecule antioxidants such as glutathione, 
-tocopherol (vitamin E; Grusak MA, DellaPenna D. 1999. Annual Review of Plant Physiology and Plant Molecular Biology 50, 133–161) and ascorbate (vitamin C; Smirnoff N et al. 2001. Annual Review of Plant Physiology and Plant Molecular Biology 52, 437–467) by manipulating their biosynthetic pathways. Another long-standing strand of ROS research concerns the oxidative burst that produces superoxide and hydrogen peroxide as part of plant defence against pathogens. This has some parallels with the oxidative burst used by mammalian neutrophils to kill microbes. However, much remains to be learnt about this and, on the day before writing this preface, a paper questioning the direct role of ROS in the killing activity of neutrophils was published (Reeves EP et al. 2002. Nature 416, 291–297) showing that paradigms in well-studied systems can be easily overturned.
More recently, research has begun to focus on the possible signalling role of ROS in plants, an endeavour that has lagged behind work in mammals and microbes. It is becoming increasingly clear that ROS are required for signalling (as well as for biochemical roles in lignin synthesis and cross-linking of cell wall polymers). We therefore need to view the antioxidant system as a mechanism to regulate ROS rather than to eliminate them entirely. Reviews of this area, and the related question of nitric oxide (NO) signalling, are included in this issue. Research on the signalling roles of ROS is starting to accelerate. The very recent observation that hydrogen peroxide may be involved in abscisic acid (ABA)-mediated stomatal closure (reviewed in this issue) has now been supplemented by a recent paper showing that ABI2 (a type 2C protein phosphatase that is a negative regulator of ABA action) is inactivated by hydrogen peroxide (Meinhard M et al. 2002. Planta 214, 775–782). Further interactions between ABA, calcium and ROS are suggested in studies on heat tolerance in Arabidopsis thaliana (Larkindale J, Knight MR. 2002. Plant Physiology 128, 682–695). Calcium/calmodulin activation of a plant catalase adds another dimension (Yang T, Poovaiah BW. 2002. Proceedings of the National Academy of Sciences, USA 99, 4097–4102). If one adds to this the possibility that hydroxyl radicals, generated in the cell wall, are involved in auxin-stimulated growth (Schopfer P. 2001. The Plant Journal 28, 679–688) and that differential formation of ROS across roots is associated with gravitropism (Joo JH et al. 2001. Plant Physiology 126, 1055–1060), it becomes apparent that our understanding of the role and regulation of ROS and antioxidants in plants is only just beginning. Functional genomics approaches and improved methods of measuring and localizing ROS should contribute to further advances. Hopefully, this special issue will provide a useful overview of a rapidly expanding field that has implications for many areas of plant biology.
The papers are derived from talks delivered at a symposium on Antioxidants and Reactive Oxygen Species in Plants held at the 2001 Annual Meeting of the Society for Experimental Biology (University of Kent, Canterbury, UK, April 2–3). I am grateful to the Society for Experimental Biology and its staff for providing the conference facilities and administrative backup. I am also very grateful to Professor Bill Davies, Editor of the Journal of Experimental Botany, for agreeing to the production of the special issue and for providing funds to cover the costs of speakers invited to the meeting. The staff at the Editorial Office have been extremely helpful throughout the editing of the manuscripts. Finally, I thank the speakers and authors for their enthusiastic response to the concept of the meeting and for delivering excellent talks and manuscripts.
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