Reducing Enzyme Involved in Recycling Vitamin C Increases a Plant’s Responsiveness to Drought Conditions

University of California, Riverside researchers reported the development of technology that increases crop drought tolerance by decreasing the amount of an enzyme that is responsible for recycling vitamin C.

Biochemist Daniel R. Gallie (photo), a professor of biochemistry at the University of California, Riverside together with Zhong Chen of his research group reported their findings in the May issue of The Plant Cell .

In the study, the authors reasoned that decreasing the amount of the enzyme dehydroascorbate reductase or DHAR would reduce the ability of plants to recycle vitamin C, making them more drought tolerant through improved water conservation. The researchers accomplished this by using the plant's own gene to decrease the amount of the enzyme three fold.

Researchers used tobacco as a model for crops that are highly sensitive to drought conditions.

“However, our discovery should be applicable to most if not all crop species as the role of vitamin C is highly conserved among plants,” said Gallie.
In work published last year in the Proceedings of the National Academy of Sciences, Gallie and his research team reported that the level of vitamin C could be boosted by increasing the amount of this same enzyme.

The U.S. Department of Agriculture and California Agricultural Experiment Station funded the six years of research that led to the current findings.

Vitamin C serves as an important antioxidant in plants as it does in humans and among its many functions in both, it destroys reactive oxygen species that can otherwise damage or even kill cells. “Once used, vitamin C must be regenerated otherwise it is irrevocably lost. The enzyme dehydroascorbate reductase, or DHAR, plays a critical role in this recycling process,” explained Gallie.

Reactive oxygen species are produced in plants typically following exposure to environmental conditions such as drought, cold, or air pollution. Plants sense drought conditions by the buildup in reactive oxygen species and then respond by reducing the amount of water that escapes from their leaves. Reducing the amount of DHAR decreases the ability of the plant to recycle vitamin C, thus reducing the ability to eliminate the buildup in reactive oxygen species that occurs with the onset of a drought.

“This reduction in vitamin C recycling causes plants to be highly responsive to dry growth conditions by reducing the rate of water that escapes from their leaves. Thus, they are better able to grow with less water and survive a drought,” said Gallie.

“Through use of this technology, we are helping crops to conserve water resources. In a way, we are assisting them to be better water managers, which is important for crops growing in areas that can experience erratic rainfall,” he added. “This discovery will assist farmers who depend on rainwater for their crops during those years when rainfall is low. It will also assist farmers who irrigate their crops to conserve water, which is important in a state like California where rapid population growth continues to increase the demand on this scare resource. Finally, this discovery should help farmers who grow crops in arid areas, such as exists in many third-world countries.”

The onset of global warming is another development that adds impact to Gallie’s research findings. The U.S. Environmental Protection Agency Web site states that the Earth's surface temperature has risen by about one degree Fahrenheit in the past century, with most of the warming occurring during the past two decades. The EPA suggests that most of the warming over the last 50 years can be attributed to human activities, but cautions that uncertainties remain about exactly how earth’s climate is responding.

“Increasing drought tolerance in crops is highly valuable to U.S. and world agriculture now and will be even more critical as our environment continues to change as a consequence of global warming,” said Gallie.

Related Links:
Daniel Gallie's Web page
EPA Web site on global warming

The University of California, Riverside is a major research institution and a national center for the humanities. Key areas of research include nanotechnology, genomics, environmental studies, digital arts and sustainable growth and development. With a current undergraduate and graduate enrollment of nearly 17,000, the campus is projected to grow to 21,000 students by 2010. Located in the heart of inland Southern California, the nearly 1,200-acre, park-like campus is at the center of the region's economic development.