The Effects of Gravity on Plant Growth and Development

<p>Mary Musgrave, professor of plant physiology, with a model of the space shuttle in her office.  Photo by Peter Morenus</p>

Mary Musgrave, professor of plant physiology, with a model of the space shuttle in her office. Photo by Peter Morenus

Mary Musgrave has been known to stand in her backyard and watch her experiments fly overhead across the night sky.

Musgrave, professor and head of the Department of Plant Science and Landscape Architecture in the College of Agriculture and Natural Resources, has spent much of her career studying the physiology of plants in space. Although she has never traveled to space herself, she has sent plants for voyages on space shuttles and to space stations to investigate how weightlessness affects plant growth and reproduction.

Her research has received continuous funding from NASA for two decades.

Plants in Space

NASA’s interest in plant development in space arises from the expectation that astronauts will one day spend months, or even years, on long-term expeditions to the moon, Mars, or deeper into outer space. On such lengthy journeys, astronauts could potentially sustain themselves with plants grown as food onboard space shuttles or in extraterrestrial habitats.

“If a crew is gone for more than six months,” says Musgrave, “it is more cost-effective to launch all that you need to grow food than to launch all the food you’re going to be eating.”

Sending food into space would be costly, she adds. “Let’s say you take a hamburger with you to space. How much does it cost in terms of fuel to bring that up? It’s $3,000 for your quarter-pounder. It’s expensive to lift weight up into orbit.”

Plants also can serve as convenient traveling companions. Taking in carbon dioxide and releasing oxygen, they offer a useful means of recycling water and air for astronauts on the spacecraft with them.

In NASA’s initial space biology experiments, however, successfully reproducing plants in space proved difficult. In weightlessness, plants cannot be watered with, for instance, a watering can. Scientists also found that plants in space suffered from waterlogging. Rather than filtering down through the soil, water encased the plants’ roots, killing them before they had flowered. Without flowers, Musgrave knew, plants cannot produce seeds and reproduce – leaving astronauts without life support.

Musgrave and fellow researchers have solved many growth and reproductive challenges confronting plants in space. “The bulk of my research was actually about seed production in space,” she says, “but we had to go through many problem-solving steps to have the plants survive, flower, and produce seeds.”

Experimenting with plants related to crops like canola, broccoli, and cabbage, they designed tubes that ran through the plants’ roots, releasing water only when necessary. To improve drainage, they replaced conventional soil with a special porous clay. Engineers also devised a system that circulated air from the space shuttle’s main cabin through the chambers where the plants grew, enhancing their exposure to the carbon dioxide they needed. Adopting these modifications, NASA discovered that plants could thrive in space.

The Effects of Hypergravity

With funding for spaceflight experiments having waned since the Columbia disaster in 2003, NASA has more recently supported Musgrave’s research involving plants grown on the other end of the gravity continuum – in high gravity, or hypergravity. Placing plants in an enormous centrifuge, Musgrave subjects plants for up to 16 days to constant gravitational forces as high as 4-g, more than the force you might encounter on a high-intensity roller coaster.

<p>A pair of test tubes holding simple callus (cell culture) systems for studying how gravity controls flavor and nutraceutical compounds in plants. Photo by Peter Morenus</p>

A pair of test tubes holding simple callus (cell culture) systems for studying how gravity controls flavor and nutraceutical compounds in plants. Photo by Peter Morenus

Observing the effects of high gravity on these plants, Musgrave has determined that plants, and the composition of their seeds, are altered when grown at different gravity levels. For one, the compounds within the plants that control flavor changes, so the plants tend to taste different.

Seeds produced at various gravity levels also possess different nutritional qualities than seeds produced on Earth. “This is important to NASA as they think futuristically about how they’ll feed the crew, based on food that astronauts would be growing themselves,” she says. “If they used the nutritional characteristics of seeds that we know here on Earth, they wouldn’t be the same when they’re being produced in space.”

Experimenting with plants in both space and hypergravity offers Musgrave a framework by which she can begin to predict plant physiology for all points in between, allowing her to theorize about how plants might fare if grown in extraterrestrial environments that are not quite weightless, such as the moon.

“As you look at how things change across the gravity continuum,” she says, “you can ask questions … that would be important if you were trying to think ahead to what people would be experiencing in very different environments. It gives you basic information. Otherwise, everything is wild speculation.”

Seeds produced at various gravity levels also possess different nutritional qualities than seeds produced on Earth. “This is important to NASA as they think futuristically about how they’ll feed the crew, based on food that astronauts would be growing themselves,” she says. “If they used the nutritional characteristics of seeds that we know here on Earth, they wouldn’t be the same when they’re being produced in space.”

Experimenting with plants in both space and hypergravity offers Musgrave a framework by which she can begin to predict plant physiology for all points in between, allowing her to theorize about how plants might fare if grown in extraterrestrial environments that are not quite weightless, such as the moon.

“As you look at how things change across the gravity continuum,” she says, “you can ask questions … that would be important if you were trying to think ahead to what people would be experiencing in very different environments. It gives you basic information. Otherwise, everything is wild speculation.”