L-Ascorbic acid in plants: from biosynthesis to its role in plant development and stress response

L-Ascorbic acid (AsA; vitamin C), is a common antioxidant in nature. In plants, it plays an important role in photosynthesis as it eliminates reactive oxygen species (ROS) generated during electron transport. Unlike animals that use D-Glucuronate as a precursor, plants produce AsA by four alternative routes using Myo-inositol, L-Gulose, D-Mannose/L-Galactose and D-Galacturonate as main precursors. Humans cannot produce AsA due to the absence of the enzyme that catalyzes the last biosynthetic step, so they need plant sources. Epidemiological studies suggest that the consumption of AsA is important for health; therefore, increasing the vitamin C content of crops could be an important goal. Many approaches have been taken to increase the vitamin C content in plants, but challenges remain. Here, we examine the biosynthesis and recycling pathways of AsA, the close connection with AsA and abiotic and biotic stresses, as well as different strategies for increasing its content in plants.