Hydrogen peroxide, ascorbate, and glutathione: building the Foyer-Halliwell-Asada pathway.

Ascorbate and glutathione are water-soluble compounds that are found at high concentrations in many plant tissues. A close association between the two molecules has been noted almost since the time Planta was founded, 100 years ago. Although both have many functions, much attention has been paid to their influence as antioxidants. One of the conceptual turning-points regarding the significance of these compounds in plants occurred in the second half of the 1970s, when the ascorbate-glutathione pathway was first characterized as a chloroplastic antioxidative process. Now known as the Foyer-Halliwell-Asada pathway, this sequence of reactions notably links reduction of HO, catalysed by ascorbate peroxidase, to oxidation of NADH or NADPH, catalysed by monodehydroascorbate reductase and glutathione reductase. One of the papers that laid the foundation stones of the pathway was Foyer and Halliwell (Planta 133:21-25, 1976). This perspective takes a look back at the contributions of this and related work in the context of plant biology research at the time, and considers the importance of the pathway within our current understanding of reactive oxygen species biology and redox homeostasis and signalling. Emphasis is placed on the advances in our knowledge of the genes and proteins involved and the potential metabolic flexibility of the pathway, as well as its place within the highly intricate plant network of HO-metabolising systems.