Plants in Space Prove Gravity Unnecessary For Normal Growth

By Breanna Draxler | December 12, 2012 9:07 am

When a seed is planted in the ground, the roots tend to grow downward in search of water and nutrients. But what happens when there is no “down” for the roots to grow? Scientists sent seeds to the International Space Station and were surprised to see what plants did without gravity to guide their roots downward.

The scientists ran their experiment on Arabidopsis plants—a go-to species for plant biologists. The control group was germinated and grown at the Kennedy Space Center (A), while the comparative group was housed on the International Space Station (B). For 15 days, researchers took pictures of the plants at six-hour intervals and compared them. Their results surprised even them: the plants in space exhibited the same growth patterns as those on Earth.

The researchers were looking for two specific patterns of root growth: waving and skewing. With waving, the root tips grow back and forth, much like waves. Skewing occurs when a plant’s roots grow at an angle, rather than straight down. Scientists don’t know exactly why these root behaviors occur, but gravity was thought to be the driving force for both.

This experiment disproved the widely accepted gravity-based theory. Although the orbiting plants grew more slowly than their terrestrial counterparts, skewing showed up equally in both groups of plants. Waving was much less pronounced in the roots of the ISS plants but still present. These results [pdf] published in BMC Plant Biology last week, demonstrate that gravity is not necessarily the key component in determining a plant’s growth pattern. In fact, gravity doesn’t even seem to be necessary for these patterns to occur at all. Scientists are now looking to other forces such as moisture, nutrients, and light avoidance to explain why roots grow the way they do.

Image courtesy of Anna-Lisa Paul et al./University of Florida, Gainesville

CATEGORIZED UNDER: Environment, Living World, Top Posts
  • Ashley Tessmer

    I don’t think that the experiment DISPROVED the widely accepted gravity-based theory, since there are gravity sensitive organs found within plants that are incredibly similar to the otoliths in humans, and have at least some effect on Earth. There is obviously some factor that is
    orienting the plants in such a way that all replicates are growing in the same direction. And as mikegtu2005 stated, do we really know the sensitivity of the gravitropism, and how do you take into account the gravitropic mutants (like Arabidopsis thaliana) here on Earth (http://www.sciencedirect.com/science/article/pii/S0168945200003095#)?

    So, the most logical next step should be to consider other factors. Something to consider is how the nutrients and light source(s) were administered? Could there have been an orienting based on the location of necessary supplements in relation to the position of the plants? Did zero gravity have an effect on the distribution of the hormone auxin throughout the plant (http://www.pnas.org/content/103/4/829.long)? There are definitely many interesting directions to continue studying the response of plants to a lack of gravity, however to dismiss the theory of gravity having an effect on plants entirely seems a bit imprudent.

  • http://www.facebook.com/gare.henderson Gare Henderson

    The role of gravity can not be determined by this experiment, since the evolution of this plant was based upon the existence of gravity. This is in many way analogus to seeing a sleeping child and concluding that he must be an angel. Run this experiment over 50 generations, with competition and environmental stresses, then we can make some conclusions about the role of gravity.

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