UCLA and Dartmouth University scientists who normally work on genes involved in aging and cancer in animals, said the discovery came while they were studying a gene in worms.

"We uncovered the last unknown enzyme in the synthesis of vitamin C in plants," said Charles Brenner of the Dartmouth Medical School's Norris Cotton Cancer Center.

Humans have lost the ability to make vitamin C -- well known as an antioxidant and enzyme cofactor -- and need to take it up from dietary sources, particularly from plants.

Only in 1998 was a biosynthetic pathway proposed to explain how plants make vitamin C. Research since then confirmed much of the pathway, although the gene responsible for the seventh step of the proposed 10-step pathway from glucose to vitamin C remained unknown.

The new research by Brenner and UCLA's Steven Clarke led to the discovery.

The findings are detailed in the Journal of Biological Chemistry.