Plants in space: Gravity not needed to orient root growth

Plant growth is not as dependent on gravity as previously thought, according to new research from the University of Florida.

In a study published in the current issue of the journal BMC Plant Biology, researchers found for the first time that roots display normal movements used to get around rocks and obstacles even when there is no gravity.

The movements, known as waving and skewing, were thought to be due to gravity pulling on roots as they sample their growing surface with touch, said Anna-Lisa Paul, one of the study’s lead authors and a UF horticultural sciences research associate professor.

“The skewing and waving of roots has always been thought to dependent on gravity, but as the images from our experiment started to come down from the International Space Station in early 2010, it was clear that gravity was not required after all,” said Paul, a member of UF’s Institute of Food and Agricultural Sciences.

“Roots in space make these same kinds of movements and choices that you see on the ground,” she said.

The findings are important, said Rob Ferl, the study’s other lead author and a UF/IFAS horticultural sciences professor, because they provide fundamental insight into how roots interact with their environment and suggest that plants could likely be cultivated in reduced-gravity environments, such as space stations or the moon.

“As space agriculturalists, we really want to know that when we move to the moon, when we move to Mars, which don’t have the same amount of gravity that we have, can we still grow plants? Will their roots still work right in a fractional gravity environment?” Ferl said. “And the answer is yes, definitely.”

For the study, the researchers grew Wassilweskija and Columbia varieties of Arabidopsis thaliana, plants related to mustard that scientists often use as model plants for research, on both the ISS in zero gravity and on Earth.

The plants were grown in a nutrient-rich agar solution in specialized chambers developed by Kennedy Space Center engineers that allowed a high-resolution camera to photograph plant growth every six hours. For the plants in space and on Earth, images were transmitted to the researchers for real-time analysis.

The chamber housing the plants on the ground was set to provide the same temperature and environmental conditions experienced by the plants in orbit.

Although differences in root growth were recorded between the plants on Earth and the plants in space, overall, root growth behaviors were generally similar.

Both varieties demonstrated growth away from the seed and typical patterns of skewing, which means to grow at a slant away from a purely vertical direction, and waving, which means to grow in tight, alternating curves. For example, Wassilweskija roots skewed strongly to the right in space while Columbia roots slightly skewed to the left, just as they do on Earth.

Paul said in the absence of gravity, perhaps the plant is responding to another directional cue, such as the overhead light source.

“The space flight environment is absolutely outside the evolutionary experience of any organism on the face of the planet,” Paul said. “It was very intriguing for to us to realize there is an evolutionary adaptation for roots to grow away from the seed to find the nutrients and water the plant needs to survive in the absence of gravity.”

The experiments were launched in 2010 and returned on space shuttle Endeavour on June 1, 2011.

NASA funded the research. Claire E. Amalfitano, who was a biological scientist in Ferl’s lab, is also an author of the study.

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