The Interplay Between Salicylic Acid and Reactive Oxygen Species During Cell Death in Plants

Abstract

There is increasing interest in the interactive role between salicylic acid (SA), reactive oxygen species (ROS) and other plant signalling molecules in regulating cell death in plants. Initial evidence suggested that SA was a potent inhibitor of heme-containing enzymes such as catalase and ascorbate peroxidase, thus capable of stimulating ROS accumulation during various biotic and abiotic stress conditions. However, others suggested that the mode of action of SA may in fact be related to its ability to prime the defense response, by increasing the levels of various defense compounds. SA was also proposed as both a potent inducer of the NADPH-oxidase and an inhibitor of the alternative oxidase, thus capable of indirect regulation of the redox status of plant cells. This role in regulating the redox status has been linked to the programmed cell death (PCD) typically observed during the hypersensitive response (HR) but also during development (leaf laces, tracheary elements, root cap, germinationl) and some abiotic stress responses (salt and heavy metal stress, anoxia). Today, an interplay between SA, ROS and other signalling molecules is proposed in the regulation of PCD in plants. The present chapter reviews the evidence that has accumulated on the interactive nature of the relationship between ROS and SA and addresses this love-hate relationship in view of cell death in plants.