New Enzyme, Vitamin C Offer Potential for Sustainable Crop Yield Increase

A study by University of Exeter in the UK and Shimane University in Japan reports that a newly-identified enzyme, GDP-L-galactose phosphorylase, produces vitamin C, or ascorbate, in plants. It is widely known that vitamin C is a powerful antioxidant. In agriculture, it helps plants deal with stresses from drought to ozone and UV radiation. But until now it was not known that plants cannot grow without it.

Scientists have proved for the first time that vitamin C is essential for plant growth. This discovery may have significant implications for agriculture and for the production of vitamin C nutritional supplements.

Professor Nicholas Smirnoff of the University of Exeter, who is the lead author on the paper, has said that: "Vitamin C is the most abundant antioxidant in plants and yet its functions are poorly understood. By discovering that the new enzyme is encoded by two genes, we were able to engineer vitamin C-free plants and found that they were unable to grow."

Plants are protected by the accumulation of vitamin C against the harmful side-effects of light during the process of photosynthesis. Photosynthesis is the process through which light energy converts carbon dioxide into plant matter. The discovery of the new enzyme opens a new path to understanding how plants control the accumulation of vitamin C in response to light.

Enzymes are proteins that accelerate, or catalyze, the chemical reactions in biological cells (cells of living organisms). Enzymes are extremely selective in their substrates (molecules at the beginning of an enzymatic process) so they speed up, or catalyze, only a few specifically selected chemical reactions out of the many existing ones. The metabolic pathway, or series of chemical reactions, of a particular cell is determined by the set of enzymes available in the cell.

The discovery of enzyme GDP-L-galactose phosphorylase could pave the way for a new approach to producing vitamin C nutritional supplements. Millions of dollars are spent on vitamin C tablets each year in this country alone, making it an important and widely-used nutritional supplement. A two-step process is currently used in its manufacture: vitamin C is produced by a combination of fermentation and chemical synthesis. The new enzyme provides the potential to engineer microbes to produce vitamin C. Microbial production would be a simpler one-step process.

Microbes are organisms that are microscopic such as bacteria, archaea and fungi. They are living things that are generally unicellular, or single-celled. Microbes are critical to ecosystems because they act as decomposers. Some also have the ability to fix nitrogen in the soil and so are part of the ecological nitrogen cycle.

Regarding the discovery of the important fact that plants cannot grow without vitamin C, Professor Nicholas Smirnoff also said: "The discovery is exciting for me because it is the culmination of a long-term research programme on vitamin C in plants at the University of Exeter [UK]. It opens new opportunities to understand fundamental growth processes in plants and to improve plant resistance to stresses in a changing climate. In the longer term I hope that it will contribute to the efforts of plant scientists to improve crop yield in a sustainable manner."

The study is now published online in The Plant Journal.

Sarah Hoyle, "Study shows vitamin C is essential for plant growth," University of Exeter.