Ascorbic Acid: An Antioxidant for Plant Stress Mitigation

Plants are continuously exposed to a range of abiotic and biotic stresses that compromise their growth, development, and productivity. These stresses, including drought, salinity, extreme temperatures, heavy metals, and pathogen attacks, commonly lead to an excessive accumulation of reactive oxygen species (ROS). While ROS act as signaling molecules at low concentrations, their uncontrolled build-up causes oxidative damage to proteins, lipids, and nucleic acids, severely affecting plant metabolism. To counteract oxidative stress, plants have evolved a complex antioxidant defense system comprising enzymatic and non-enzymatic antioxidants. Among these, ascorbic acid (AsA), or vitamin C, is one of the most abundant, versatile, and effective molecules in plants. Ascorbic acid plays multiple roles: it directly scavenges ROS, regenerates other antioxidants, regulates redox signaling, and participates in hormone biosynthesis and stress signaling cascades. Its biosynthesis primarily occurs through the L-galactose (Smirnoff–Wheeler) pathway, though alternative pathways also contribute under specific conditions. The ascorbate–glutathione cycle further enhances the efficiency of AsA by recycling it in reduced form. Through these mechanisms, AsA protects photosynthetic machinery, stabilizes membranes, and supports cellular homeostasis under diverse stress conditions. Beyond its endogenous functions, exogenous application of AsA through foliar sprays or seed priming has been demonstrated to alleviate stress-induced damage and improve crop performance. Advances in biotechnology, including transgenic approaches and CRISPR/Cas-mediated genome editing, offer novel opportunities to enhance AsA levels in crops for improved resilience against climate change-induced stressors. This chapter provides a comprehensive overview of the biochemical, physiological, and molecular roles of ascorbic acid in stress mitigation, with emphasis on its biosynthesis, metabolism, interaction with other antioxidants and hormones, and its potential application in sustainable crop improvement strategies.