Applications of Physical and Biological Techniques In the Study of Gravisensing and Response System of Plants
The BioTube/Magnetic Field Apparatus (MFA) research is designed to provide insight into the organization and operation of the gravity sensing systems of plants and other small organisms. This experiment on STS-107 uses magnetic fields to manipulate sensory cells in plant roots, thus using magnetic fields as a tool to study gravity-related phenomena. The experiment will be located in the SPACEHAB module and is about the size of a household microwave oven.
The goal of the experiment is to improve our understanding of the basic phenomenon of how plants respond to gravity. The BioTube/MFA experiment specifically examines how gravitational forces serve as a directional signal for growth in the low-gravity environment of space. This study will contribute to an improved understanding of how plants grow and will have important implications for improving plant growth and productivity on Earth.
Image to right: Flax root growing in Magnetic Field Chamber hardware.
In BioTube/MFA, magnetic fields will be used to determine whether the distribution of subcellular starch grains, called amyloplasts, within plant cells predicts the direction in which roots will grow and curve in microgravity.
Image to right: Bioube/MFA in locker.
On Earth amyloplasts in plant cells accumulate in the direction of gravity causing a change in the cell. This essentially translates to a signal indicating which direction is “up” or “down”. The BioTube/MFA experiment utilizes high-gradient magnetic fields to change the distribution of amyloplasts in flax roots. The magnetic field is concentrated at a specific point which produces magnetic gradient. As the root grows, it approaches the wedge and moves into the magnetic gradient. The starch grains are then repelled by the magnetic gradient, causing the roots to curve in the direction of the displaced starch grains.
The BioTube/MFA experiment contains dry flax seeds (also known as Linum usitatissimum) that will germinate in space. The seeds will be watered and the roots will begin to grow across the highgradient magnetic field wedges in two Magnetic Field Chambers. A third Magnetic Field Chamber will provide a uniform (non-gradient) magnetic field for the roots as a comparison to the highgradient magnetic field. Time-lapse imagery will record pictures of the roots as they grow. Approximately 48 hours after seed watering, a chemical fixative will preserve the flax specimens for microscopic analysis and the experiment will end.
The science objectives of the BioTube/MFA experiment address three major questions: 1.) Are amyloplasts the organelles in plant cells that perceive gravity? 2.) Does the position or movement of the amyloplasts (sedimentation on earth, or, response to a high gradient magnetic field in orbit) affect the root growth direction? 3.) Does gravity exert an effect on the deposition of cell wall material and the organization of plant cells organelles?
These goals will provide insight into the fundamental organization and operation of the gravity response system of plants and determine if, other than the root cap, other parts of the plant require cues for directional growth.
Image to right: The leftmost portion of the panel depicts the random orientation of amyloplasts in a simulated spaceflight experiment. The rightmost portion of the panel shows the effect of a magnetic force displacing amyloplasts to the left.
The leftmost portion of the panel belongs to a normal root with the amyloplasts sedimented to the root cap region. Center panel shows a root cap with a lateral high-gradient magnetic field displacing amyloplasts to the left. Rightmost portion of the panel shows a gravitationally affected root with amyloplasts sedimented left.
Astronauts will turn on the BioTube/MFA experiment three days prior to landing. All experiment operations will be complete within a 48 hour period. The BioTube/MFA software automatically controls a series of events that will deliver water to the seeds, take images of the growing roots and deliver a chemical fixative which preserves the roots for later analysis. The astronaut crew will periodically check on the equipment as the experiment progresses and will turn the power off following chemical fixation.
Science Discipline Supported
The BioTube/MFA research primarily addresses Fundamental Space Biology, but applies to other disciplines. Similar flight experiments could be conducted on the International Space Station to increase the knowledge of how biological processes are affected by microgravity.