Discovery heralds way for plants to survive drought

["Mark Jones" <jones118@xxxxxxxxxxx>]

Tim Radford, science editor
Thursday June 28, 2001
The Guardian

Scientists have found out how plants open and close their stomata - the tiny
pores through which they breathe. The discovery could open the way for
genetically engineered crops which could survive drought.
The "biological Morse code" used by plants to control the stomata is
described in Nature today by Gethyn Allen and Julian Schroeder from the
University of California, San Diego and colleagues from Munich and Tubingen
in Germany.

Plants soak up huge quantities of water through their roots and respire
through their stomata to cool themselves as they grow, mature and ripen. It
takes around 900 litres of water to grow 1kg of wheat. But huge areas of
farmland are becoming increasingly arid, and areas once made fertile by
irrigation are being abandoned because the soils become increasingly salty.

What has become a challenge in the developed world is already a disaster for
many poorer nations in sub-Saharan Africa, the Middle East and parts of
Asia, as crops wither before they ripen. The hunt is on for ways to develop
plants that will survive at least a period of drought, and quicken again
with the return of the rains.

"Much of the land used for agriculture is not irrigated because water is
either unavailable or too expensive," said Professor Schroeder. "So if crops
can be engineered to respond to droughts by more rapidly and effectively
closing their stomatal pores, where 95% of the water loss in plants occurs,
they could better survive drought periods by conserving water until the next
rain hits."

Calcium plays a powerful role in the machinery of the cell, and is part of
the signalling mechanism of stress. The researchers found that specialised
"guard cells" in the leaves which surround each pore, or stoma, "tune in" to
the frequency of calcium oscillations in the cell. When these oscillations
are at a particular frequency, the guard cells react, and close the stomata
for extended periods.

A study last year warned that one third of the world's population would face
"severe" water scarcity by 2025.

"We don't know how to genetically engineer a plant to hit the right
frequency to close its stomata in response to a drought," said Prof
Schroeder. "That lies in the future. But understanding the calcium code
means we can now learn more about the mechanisms that control a plant's
resistance to drought conditions."