http://science.nasa.gov/headlines/y2...reenhouses.htm

Greenhouses for Mars
NASA Science News
February 25, 2004

hen humans go to the moon or Mars, they'll probably take plants with them.
NASA-supported researchers are learning how greenhouses work on other
planets.

February 25, 2004: Confused? Then you're just like plants in a greenhouse on
Mars.

No greenhouses exist there yet, of course. But long-term explorers, on Mars,
or the moon, will need to grow plants: for food, for recycling, for
replenishing the air. And plants aren't going to understand that off-earth
environment at all. It's not what they evolved for, and it's not what
they're expecting.

But in some ways, it turns out, they're probably going to like it better!
Some parts of it, anyway.

"When you get to the idea of growing plants on the moon, or on Mars,"
explains molecular biologist Rob Ferl, director of Space Agriculture
Biotechnology Research and Education at the University of Florida, "then you
have to consider the idea of growing plants in as reduced an atmospheric
pressure as possible."

There are two reasons. First, it'll help reduce the weight of the supplies
that need to be lifted off the earth. Even air has mass.

Second, Martian and lunar greenhouses must hold up in places where the
atmospheric pressures are, at best, less than one percent of Earth-normal.
Those greenhouses will be easier to construct and operate if their interior
pressure is also very low -- perhaps only one-sixteenth of Earth normal.

The problem is, in such extreme low pressures, plants have to work hard to
survive. "Remember, plants have no evolutionary preadaption to hypobaria,"
says Ferl. There's no reason for them to have learned to interpret the
biochemical signals induced by low pressure. And, in fact, they don't. They
misinterpret them.

Low pressure makes plants act as if they're drying out.

In recent experiments, supported by NASA's Office of Biological and Physical
research, Ferl's group exposed young growing plants to pressures of
one-tenth Earth normal for about twenty-four hours. In such a low-pressure
environment, water is pulled out through the leaves very quickly, and so
extra water is needed to replenish it.

But, says Ferl, the plants were given all the water they needed. Even the
relative humidity was kept at nearly 100 percent. Nevertheless, the plants'
genes that sensed drought were still being activated. Apparently, says Ferl,
the plants interpreted the accelerated water movement as drought stress,
even though there was no drought at all.

That's bad. Plants are wasting their resources if they expend them trying to
deal with a problem that isn't even there. For example, they might close up
their stomata -- the tiny holes in their leaves from which water escapes. Or
they might drop their leaves altogether. But, those responses aren't
necessarily appropriate.

Fortunately, once the plants' responses are understood, researchers can
adjust them. "We can make biochemical alterations that change the level of
hormones," says Ferl. "We can increase or decrease them to affect the
plants' response to its environment."

And, intriguingly, studies have found benefits to a low pressure
environment. The mechanism is essentially the same as the one that causes
the problems, explains Ferl. In low pressure, not only water, but also plant
hormones are flushed from the plant more quickly. So a hormone, for example,
that causes plants to die of old age might move through the organism before
it takes effect.

Astronauts aren't the only ones who will benefit from this research. By
controlling air pressure, in, say, an Earth greenhouse or a storage bin, it
may be possible to influence certain plant behaviors. For example, if you
store fruit at low pressure, it lasts much longer. That's because of the
swift elimination of the hormone ethylene, which causes fruit to ripen, and
then rot. Farm produce trucked from one coast to the other in low pressure
containers might arrive at supermarkets as fresh as if it had been picked
that day.

Much work remains to be done. Ferl's team looked at the way plants react to
a short period of low pressure. Still to be determined is how plants react
to spending longer amounts of time -- like their entire life -- in hypobaric
conditions. Ferl also hopes to examine plants at a wider variety of
pressures. There are whole suites of genes that are activated at different
pressures, he says, and this suggests a surprisingly complex response to low
pressure environments.

To learn more about this genetic response, Ferl's group is bioengineering
plants whose genes glow green when activated. In addition they are using DNA
microchip technology to examine as many as twenty-thousand genes at a time
in plants exposed to low pressures.

Plants will play an extraordinarily important role in allowing humans to
explore destinations like Mars and the moon. They will provide food, oxygen
and even good cheer to astronauts far from home. To make the best use of
plants off-Earth, "we have to understand the limits for growing them at low
pressure," says Ferl. "And then we have to understand why those limits
exist."

Ferl's group is making progress. "The exciting part of this is, we're
beginning to understand what it will take to really use plants in our life
support systems." When the time comes to visit Mars, plants in the
greenhouse might not be so confused after all.