How does light facilitate vitamin C biosynthesis in leaves?

Plants store ascorbate in high concentrations, particularly in their leaves. Ascorbate is an excellent antioxidant that acts as an indispensable photoprotectant. The d-mannose/l-galactose pathway is responsible for ascorbate biosynthesis in plants. Light facilitates ascorbate biosynthesis in a light intensity-dependent manner to enhance ascorbate pool size in leaves, and photosynthesis is required for this process. Light- and photosynthesis-dependent activation of the rate-limiting enzyme GDP-l-galactose phosphorylase (GGP) plays a critical role in ascorbate pool size regulation. In addition, the tight regulation of ascorbate biosynthesis by ascorbate itself has been proposed. Ascorbate represses GGP translation in a dose-dependent manner through the upstream open reading frame in the 5 '-untranslated regions of the gene, which may compete with the light-dependent activation of ascorbate biosynthesis. This review focuses on ascorbate biosynthesis based on past and latest findings and critically discusses how light activates this process.

Automated summary

Plants store high concentrations of ascorbate, especially in their leaves, which acts as an excellent antioxidant and photoprotectant. The d-mannose/l-galactose pathway is responsible for ascorbate biosynthesis in plants, which is facilitated by light intensity and requires photosynthesis. The activation of the rate-limiting enzyme GGP by light and photosynthesis plays a critical role in regulating ascorbate pool size. Ascorbate itself also regulates its biosynthesis by repressing GGP translation in a dose-dependent manner.