Astronaut Jeffrey Williams, Expedition 22 commander, working on the payload Advanced Plant Experiments on Orbit-Cambium - Transgenic Arabidopsis Gene Expression System (APEX-TAGES) in the pressurized Japanese Experiment Module aboard space station. (NASA)
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Crew image of the Advanced Plant Experiments on Orbit - Transgenic Arabidopsis Gene Expression System (APEX-TAGES) study during Expedition 23. (NASA)
View large image The Transgenic Arabidopsis Gene Expression System (TAGES) study conducted in November 2009 aboard the International Space Station, showed plant roots grow in different directions in space just as they do on Earth. This is an unexpected result researchers say will influence the way seeds and plants will be handled on space missions that could call on space-grown food to feed astronauts.
The finding "Plant growth strategies are remodeled by spaceflight" was published in BMC Plant Biology 2012.
"It shows us that gravity just isn't essential in root orientation, and that is something that is novel for the scientific community in general," said Anna-Lisa Paul, Ph.D., a researcher at the University of Florida and one of the principal investigators of the experiment team. "We've always thought that these kinds of movements of plants depended on gravity."
Roots provide nutrients and stability to plants on Earth. Varieties of plants, from fruit-bearing vines to tall trees, grow their root systems differently. It was thought, Paul said, gravity was the primary influence on plant cells to tell them how to change direction. It turns out that's not the case, the research found.
"The ability to get away from where you are sown so you can go out and find the nutrients you need is something that's inherent in the programming of the plant, and that programming works just fine even when you don't have a gravity to drive it," Paul said.
Paul worked with University of Florida colleague Robert Ferl, Ph.D., on the experiment, which used different varieties of Arabidopsis - a mustard-like plant - grown in an enclosure NASA calls the Advanced Biological Research System (ABRS) aboard the space station for several weeks. A camera documented the root growth of the plants, and the researchers compared the growth to that of identical plants kept inside the Orbital Environment Simulator in the Space Life Sciences Laboratory at NASA's Kennedy Space Center in Florida.
The scientists were surprised to find that the root patterns were basically identical for the two groups of plants. Whether the plants grew in space or in a facility on Earth, the traits matched all the conditions of the space station, except for the weightlessness.
"These patterns of root growth, usually referred to as skewing and waving, have been well characterized on Earth as growth strategies the plant uses to avoid objects as it grows," Paul said. "It was always thought that the patterns were generated through a combination of a touch response between the root tip and whatever it is running into (a rock, a hard surface, etc.) and the force of gravity pulling on the root tip. So, the fact you can see those same patterns and behaviors on orbit, where there is no gravity to pull on the root, was very intriguing. This gives us, and the scientific community in general, fundamental insights into how plant roots work - insights you could not get on the ground, as the natural force of gravity overwhelms the inherent response signals."
Paul, who has flown numerous investigations on shuttle and station, said the results show that mission planners can count on plants growing in space or possibly on other worlds.
"The better we are at making the spaceflight hardware in which we grow plants a benign habitat, the better gardeners in space we become," Paul said. "The fact that we have less and less impediment to growing plants on orbit makes it easier and easier to envision growing things either on long interplanetary trips or on other planetary surfaces."
As explorers head into deep space in the coming years, Paul said it is inevitable that they will take plants with them potentially as a food source.
"When we leave Earth's orbit, we're going to take plants with us," Paul said. "We are explorers; it's what we do as a species, and it's exciting to be a part of it."