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Checkbiotech: Researchers improve drought tolerance in plants
Posted by: DR. RAUPP & madora (IP Logged)
Date: October 05, 2004 08:18AM ;

Vitamin C provides link to a plant's ability to withstand drought conditions
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, October 2004 .

"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.17

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

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

"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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