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Measuring a Plant's Response to Gravity

Judy Day, with the Science House, a NC State University K-12 science outreach program, has developed an activity investigating a plant’s response to gravity. Judy uses a ProScope USB digital microscope to record changes over time in a plant that has been placed on its side. For best results, Judy recommends using an Arabidopsis thaliana (the wild variety) having an inflorescence stem at least 10 cm long. Here is a brief description of Judy’s procedure:

Changes in stem height in response to gravity
Changes in stem height in response to gravity

Before starting the experiment, place the plant upright, in a dark place for several hours to allow the stem to straighten. Gently mark one centimeter increments on the stem to allow tracking of the changes and to have known reference distances to use for video analysis. Bring the plant to the video location, and with the plant in its upright position, prepare to start the video. Using the time lapse feature of the video software, capture video images every three minutes for a 60 minute period. Gently lay the plant on its side, start the video, and watch the changes. Note: since the plant is sensitive to movement, move as little as possible during the setup.

Once you have your video, use the video analysis features in Logger Pro to measure the changes in the plant as it responds to gravity. The sample graph shows data that Judy obtained. Note the relatively uniform change in stem height over time.

Quicktime time-lapse movie of the plant's growth
Quicktime time-lapse movie of the plant’s growth

Judy also sent us some suggested extensions to try:

  • Compare various points on the stem for movement.
  • If the plant has multiple stems, trim the top of one stem and leave the other alone.
  • Compare length of stem with range of movement.
  • Compare other plants for rates of movement.
  • Place the plant in a 4°C environment on its side for an hour; then move the plant to room temperature in an upright position. Record observations of movements of the plant.

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