Biosynthesis of L-ascorbic acid in plants: new pathways for an old antioxidant

The biosynthetic pathway of L-ascorbic acid (vitamin C) in plants has been established for several years. However, recent reports describe alternative pathways, revealing a more complex picture of L-ascorbic acid biosynthesis than had been expected. GDP-L-gulose and myo-inositol are proposed as new intermediates in L-ascorbic acid biosynthesis, indicating that part of the animal pathway might also be operating in plants. Enzymatic studies on the GDP-mannose- 3',5'-epimerase and L-galactono-1,4-lactone dehydrogenase suggest that they are important regulatory steps for L-ascorbic acid biosynthesis.