BioEd Online

Stems grow up. Roots grow down. At least, that's what happens on Earth. In the microgravity environment of the International Space Station (ISS), things work a little differently. Plants do not sense “up” or “down,” so their growth can be erratic. Astronauts on long spaceflights will rely on plants as a food source, so it is important to learn how to make plants grow normally in the absence of a dominant gravity direction.

Light affects the direction in which plant roots grow. Typically, roots grow toward light sources with strong red wavelengths and away from light sources with strong blue components. These responses are referred to as phototropic (plant growth responses to light). The Plants in Space investigation examines whether white light with a strong blue component will cause plant roots to grow into their growth medium, even without gravity's directional clues “telling” them to do so.

Using similar chambers and plants as those flown on the ISS, your students will make daily observations to measure and compare plants in normal gravity with those in microgravity. Photos and videos of the space plants are available at the links below.

Four 5-day planting experiments were conducted during Fall of 2011. Experiments 1 (planted September 20, 2011) and 3 (planted October 7, 2011) looked at phototropic effects on root growth. Gel was 0.3% density. The seeds in each flask had a different orientation. From left to right in each photo of the ISS investigation, seed orientations were (1) scar side facing downward, (2) seed sideways, and (3) scar side facing upward.

Experiments 2 (planted September 29, 2011) and 4 (planted October 17, 2011) examined thigmotropism (directional growth of a plant in response to touch). Seeds in all flasks were oriented with the scar side facing downward. Each flask had two different densities of gel. From left to right in each photo from the ISS, the densities of the two layers of the gel in the flasks were .0.3 and 0.4%; 0.3 and 0.5%; and 0.3 and 0.6%.

A bonus unscheduled experiment (planted October 26, 2011) used backup experiment equipment and explored sideways-oriented seeds in the dark condition.

The two light conditions for each of the first four plantings were 24 hours of light and 24 hours of darkness. The three flasks in each condition were planted in exactly the same way.