By looking into the plant world, researchers are expanding human appreciation of ascorbic acid -- vitamin C. There is no doubt that this vitamin is key to human health or that people get it from the foods they eat, but researchers at Boyce Thompson Institute for Plant Research Inc. at Cornell University have new information to explain why plants make this important anti-oxidant.

Humans are among the few species that do not produce their own vitamin C and must rely on eating the right foods to obtain it. Researchers at the Boyce Thompson Institute created mutant plants that have no capacity to make vitamin C, and they then subjected the plants to strenuous environmental factors such as high levels of ozone and ultraviolet light.

"We grew our Arabidopsis thaliana plants in elevated levels of ozone. For a normal plant, this is not a problem. They naturally detoxify themselves to get rid of the free radicals," said Robert L. Last, plant molecular biologist at the Boyce Thompson Institute and Cornell adjunct associate professor of genetics. Free radicals are atoms with unpaired electrons that are bad for the human immune system. "But our mutants lacking vitamin C had shriveled leaves. When grown in an ozone-contained environment, those plants, the ones with shriveled leaves, were not able to cope with environmental stress."

Their study, "Environmental stress sensitivity of an ascorbic acid-deficient Arabidopsis mutant," in the Proceedings of the National Academy of Sciences, was reported by Last, Patricia L. Conkin, a postdoctoral fellow with Boyce Thompson and Elizabeth H. Williams, a Cornell undergraduate student. The research was funded by the National Science Foundation Presidential Young Investigator grant and an American Cancer Society postdoctoral fellowship grant.

"The big picture is this: We are very much like the plant mutants. Humans cannot make vitamin C, while most of the rest of the animal world can make their own," Last said. The way in which plant cells make vitamin C is now the topic of a project funded by the U.S. Dept. of Agriculture.

The study of the vitamin C deficient plants also showed that they were hypersensitive to sulfur dioxide and ultraviolet B radiation. The plants that did not lack vitamin C stood firm against those environmental stresses, much like humans stand up well against external stresses when they consume vitamin C. Last believes this research shows that ascorbic acid acts as a key free-radical scavenger and participates in important enzyme reactions.

"That's why ascorbic acid is thought to play a variety of critical roles in plants and animals," he said.

Last indicated that an important goal of this research is to continually improve crop foods, some of which do not contain much ascorbic acid.

"Although [it is] an important part of the diet, there is little vitamin C in important food staples like wheat or rice," Last said. "With information like this, we can use the tools of modern genetics to increase the nutritional value of food crops."