Researchers Improve Drought Tolerance in Plants
Researchers at the University of California–Riverside have found yet another way to improve a crop's ability to survive drought, raising hope that more food can be grown in arid regions of the developing world.
"This discovery will assist farmers who depend on rainwater for their crops during those years when rainfall is low ... and should help farmers who grow crops in arid areas such as exists in many third-world countries," said Daniel R. Gallie, a biochemistry professor at the University of California–Riverside and an author of a scientific paper recently published in The Plant Cell.1
Gallie and biochemistry Professor Zhong Chen have discovered that reducing a tobacco plant's ability to recycle vitamin C causes it to scale back the amount of water that escapes from its leaves. That, in turn, allows the plant to better survive drought conditions.
Tobacco was used in the study because it's very sensitive to drought, but "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 a press release from the University of California–Riverside.2
Improving plants' ability to survive drought has long been a Holy Grail for plant researchers. And the UC–Riverside discovery is just one of several promising biotech breakthroughs.
In 2002, researchers at Cornell University in New York used a different scientific approach to develop a hardier biotech rice that can resist drought and thrive in marginal soil.
In the Cornell study, researchers took the genes that synthesize trehalose — a simple sugar that is produced in a wide variety of plants, including the resurrection plant — and inserted them into rice. The resurrection plant is a desert moss that can slow its activity to zero during a drought and completely revive with the return of water.
But the University of California–Riverside method differs in that no foreign genes were introduced into the tobacco plants to make them drought resistant.
Instead, Gallie's research team was able to use the tobacco plant's own genes to reduce the level of the enzyme dehydroascorbate reductase (DHAR), which reduces a plant's ability to recycle vitamin C. And that, in turn, signals the plant to slow the loss of water from its leaves.
"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," said Gallie. "Thus, they are better able to grow with less water and survive a drought."
Here's how it works:
Plant leaves have tiny pores called stomata that open — usually in the morning when it's cooler — to allow plants to breathe in carbon dioxide, which they need to grow. In the afternoon, when it's hotter, the stomata close to conserve water.
The stomata are controlled by guard cells that open and close the tiny pores based on the level of oxidizers such as hydrogen peroxide, whose level increases when exposed to environmental stresses such as drought. When oxidizer levels rise, the pores close.
An antioxidant such as vitamin C destroys these oxidizers in plants. By reducing the vitamin C levels, oxidizers remain high enough to keep the stomata closed. The plant is essentially tricked so it preserves water.
"Through use of this technology, we are helping crops conserve water resources," said Gallie. "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."
The ability to conserve water is becoming increasingly important — particularly in Asia where demand for more and better food is taxing natural resources.
"Already at least one in three Asians has no access to safe drinking water and fresh water will be the major limiting factor to producing more food in the future," said the "Global Environment Outlook 2000" report from the United Nations Environment Programme.3
Included in the report was a survey of 200 scientists from 50 countries who ranked freshwater scarcity as the second greatest environmental threat facing the 21st century. Only climate change ranked higher. And that, too, is affecting rainfall.
With global warming comes increasing examples of unstable weather patterns worldwide. Regions that once experienced normal rainfall — such as parts of California — are becoming semi-arid. Those places that have typically had less-than-optimal rainfall are finding the challenges of growing crops more difficult with each season.
The earth's surface temperature has risen by about 1 degree Fahrenheit in the past century, with most of the warming occurring during the past two decades, according to the U.S. Environmental Protection Agency.
"As global warming continues to play havoc with our weather patterns, some areas might receive less rain, some may receive more rain," said Gallie. "This research can address unpredictable periods of drought caused by global warming. 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."
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