The ascorbate-glutathione cycle coming of age

Concepts, regarding the operation of the ascorbate/glutathione cycle and the associated water/water cycle in the processing of metabolically-generated hydrogen peroxide and other forms of reactive oxygen species (ROS), are well established in the literature. However, our knowledge of functions of these cycles and their component enzymes continues to grow and evolve. Recent insights include participation in the intrinsic environmental and developmental signaling pathways that regulate plant growth, development and defense. In addition to ROS processing, the enzymes of the two cycles not only support the functions of ascorbate and glutathione, they also have "moonlighting" functions. They are subject to post-translational modifications and have an extensive interactome, particularly with other signaling proteins. In this assessment of current knowledge, we highlight the central position of the ascorbate/glutathione cycle in the network of cellular redox systems that underpin the energy-sensitive communication within the different cellular compartments and integrate plant signalling pathways.