COLLEGE STATION, Texas - Three Texas A&M University System researchers have discovered that lettuce can grow bigger in low atmospheric pressure in confinement than it can in earthlike atmospheric pressure in confinement - a finding that may apply to other plants grown in, say, greenhouses.

Dr. Fred T. Davies Jr., professor in the Texas A&M University Department of Horticultural Sciences, Dr. Chuan J. He, research scientist in the Texas Agricultural Experiment Station, and Dr. Ronald E. Lacey, professor in the Texas A&M Department of Biological and Agricultural Engineering, have grown lettuce in low-pressure chambers that are prototypes of a bioregenerative life support system for astronauts living on the moon and Mars.

Lettuce is a very sensitive plant. That it can grow so well in low atmospheric pressure, 25 percent that on Earth, in confinement encourages Davies to think other plants can too, Davies said.

"Just to demonstrate that plants can be grown in low pressure was important," he said.

The low atmospheric pressure in the chambers has slowed down so-called "dark-period" respiration, the process that yields carbon dioxide and energy from carbohydrates and oxygen in the night, in the lettuce, Davies said. The slower the dark respiration, the fewer the carbohydrates burned, the bigger the plant.

And the low atmospheric pressure has reduced the ethylene the lettuce produces, he said. Ethylene is a growth hormone in plants.

"A little bit of ethylene is good: It's needed for growth," Davies said. "But a lot of ethylene is bad."

Too much ethylene retards the growth of plants. The researchers had predicted that the low atmospheric pressure in the chambers would stress the lettuce, the lettuce would produce more and more ethylene, the chambers would trap the ethylene, and the ethylene would stunt the lettuce, Lacey said. The opposite of that has happened. And Davies, He and Lacey intend to answer why, he said, in addition to their first and foremost question.

"The real problem, the real goal is the less mass you send to space, the better," Lacey said.

The bioregenerative life support system (the lettuce is not only edible, but also produces oxygen through photosynthesis and potable water through transpiration and then condensation) that results from their prototypical low-pressure chambers may lighten the payload of a spacecraft bound for the moon or Mars, he said.

Lacey and three of his graduate students designed the chambers so that the researchers can lower atmospheric pressure by reducing carbon dioxide, oxygen and nitrogen in the chambers. The resultant life support system may require less of these atmospheric gases. The less atmospheric gases, the fewer containers of them among the payload, the lighter the payload of a spacecraft. And a lighter spacecraft will cost less to launch to outer space, Lacey said.

"Reducing the pressure is the solution - there's no alternative," he said.

NASA Advanced Life Support funds Davies, He and Lacey's research. For more information, visit Davies' and Lacey's Web sites.

For more information, contact

Source: Dr. Fred T. Davies Jr.
979/845-4524
f-davies@tamu.edu

Dr. Ronald E. Lacey
979/845-3967
ron-lacey@tamu.edu

Reporter: Susan E. Cotton
s-cotton@tamu.edu
(979) 845-7147

News Story 1348, July 7, 2006

Direct page link:
http://engineeringnews.tamu.edu/news/1348

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