Convergence of Pathways Towards Ascorbate–Glutathione for Stress Mitigation

In plants, exposure to temperature extremes, heavy metal-contaminated soils, drought, air pollutants, and pathogens results in the generation of reactive oxygen species (ROS) that alter the intracellular redox environment, which in turn influences signaling pathways and cell fate. As part of their response to these stresses, plants produce ascorbate and glutathione. Since ascorbate is an essential metabolite implicated in vital cell functions, it is surprising that the pathway of ascorbate synthesis in plants remains to be fully established which involve various intermediates, namely GDP-mannose, GDP-l-galactose, l-galactose, and l-galactono-1,4-lactone. On the other hand, glutathione acts as an antioxidant by quenching ROS and is involved in the ascorbate–glutathione cycle that eliminates damaging peroxides. Two enzymes catalyze glutathione synthesis: glutamate-cysteine ligase and glutathione synthetase. Here, we explore the biosynthesis/functions of ascorbate and glutathione not only in relation to stress conditions, but also in the wider contexts of plant development and environmental responses.