Vitamin C is an essential nutrient in the human diet and it has been long known that plants are an excellent source of this important antioxidant. Prolonged absence of vitamin C in the diet leads to scurvy, a disease prevalent amongst early marine explorers who had little access to fresh fruit and vegetables.
The biosynthetic pathway for vitamin C in animals was discovered many years ago and it was found that several groups of animals including humans, guinea pigs and teleost fish have lost the last enzyme in this pathway, preventing them from making their own vitamin C. Humans are therefore primarily reliant on plants as a source of vitamin C, although the route through which plants make vitamin C was discovered much more recently.
In 1998 Dr Glen Wheeler (now an MBA Senior Research Fellow) and Professor Nicholas Smirnoff at the University of Exeter identified that plants make vitamin C through an entirely different route to animals. This pathway became known as the D-mannose/L-galactose pathway or the Smirnoff-Wheeler pathway.
A special issue of the Journal of Experimental Botany has now been published to celebrate 25 years since the discovery of this pathway, highlighting the substantial progress that has been made in our understanding of vitamin C biosynthesis in plants. These studies have revealed the critical role that vitamin C plays in plant metabolism and have enabled biotechnological approaches to increase the vitamin C content of crop plants for improved stress resistance and nutritional content.
Subsequent research has also shed light on the evolution of vitamin C biosynthesis, indicating that green and red seaweeds use a similar pathway to plants, but many other marine algae use a third pathway that combines the animal pathway with the last enzyme in the plant pathway.
A Darwin Review has been published within the special issue summarising these findings (Smirnoff and Wheeler, J Exp Bot, 2024). Whilst huge progress has been made in understanding how vitamin C is synthesised by plants and algae, it is clear that much remains to be learnt about the different cellular roles of this enigmatic metabolite.
