Biotube-Magnetophoretically Induced Curvature in Roots (Biotube-MICRO) - 02.25.14
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Biotube-MICRO investigates the potential for magnetic fields to orient plant roots as they grow in microgravity. Plants are not directly sensitive to magnetic fields, but starch grains, called amyloplasts, in plant cells respond to external magnetic fields. Brassica rapa seedlings will be grown in microgravity in the presence of magnets with about 50 times the strength of refrigerator magnets to see whether the orientation of the amyloplasts or other factors induce curvature in roots as they form.
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Kennedy Space Center, , FL, United States
Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
Human Exploration and Operations Mission Directorate (HEOMD)
ISS Expedition Duration
March 2014 - September 2014
Previous ISS Missions
- The goal of the experiment is to determine how plants sense and respond to gravity. The Biotube-MICRO experiment examines how directional forces affect growth in the low-gravity environment of space.
- It is unclear how a plant senses gravity and what signals a plant to distinguish up from down. The Biotube-MICRO experiment is designed to distinguish between two gravity-sensing mechanisms. When the entire content of plant cells (cytoplasm) is pulled downward by gravity, the pressure exerted on the plasma membrane might serve to identify the direction of the gravity vector. Plant cells also contain starch grains (amyloplasts) that settle in the direction of gravity. Starch grains are diamagnetic, meaning that they respond to an external magnetic field. Biotube-MICRO uses strong magnets (50 times stronger than a refrigerator magnet) to attempt to displace the starch grains. If the displacement of the starch grains is the gravity-sensing trigger, the plant root will curve away from the magnetic gradient. If pressure on the cell membrane triggers the gravity response, magnetic gradients will not induce curvature. The in-flight observations on curvature will be supplemented by postflight studies on the position of amyloplasts in columella cells, gene-expression changes that are activated in response to microgravity, and the exposure to high gradient magnetic fields. The combined data will determine how a plant senses gravity.
- The result of the proposed work will increase the understanding of the basic phenomenon of differential growth and gravity response in plants. The results could lead to the use of high gradient magnetic fields as a counter-measure to the lack of gravity signal for plants in microgravity. Additionally, as with all basic research, an improved understanding of plant growth has important implications for improving plant production on Earth.
The Biotube-MICRO experiment proposal combines morphological measurements on microgravity-germinated and grown Brassica rapa roots that are exposed to High-Gradient Magnetic Fields (HGMF) with a high-resolution spatial analysis of genes involved in gravitropism. Magnetic gradients exert a repulsive force on diamagnetic substances such as the starch in sub-cellular amyloplasts, which results in macroscopically observable gravitropic-like curvatures. The proposal is based on hardware that was developed for a previous flight experiment on STS-107. Like in the originally proposed experiment, microscopic analysis of amyloplast size and distribution are studied in the context of achieved curvature. In addition, high-resolution genetic profiling focuses on the cytoskeleton, and the distribution of the auxin and amyloplasts. The result of the proposed work will enable directional growth of seedlings and eventually mature plants under microgravity conditions using HGMF.
Three conditions are used to differentiate the effect of microgravity from uniform magnetic fields and HGMF conditions. Only HGMF is expected to influence root curvature. A uniform magnetic field serves as a ground control for possible secondary magnetic effects. This condition is compared to an inflight control without any magnetic field to determine growth rate, gene expression, and growth directionality. Root material from these experiments is used for investigations on cytoskeletal organization and the expression of starch-related genes. A second aspect of the proposed work investigates the process of gravisensing; whether it is dependent on amyloplast position, movement, or force exerted onto amyloplasts. Space experimentation is necessary to establish a threshold value for a directional magnetic force. A large focus of the experiment is on genetic changes that are activated/changed in response to microgravity, HGMF and uniform magnetic fields. The experiment advances knowledge on how cells perceive, process and transmit mechanical stimulation and how force perception affects the acto-myosin system, which is generally agreed to be the most relevant factor in mechano-transduction.
In addition to providing insight in the fundamental mechanism of the gravisensing system of plants, the data from this experiment can be used to develop technology to provide a directional, gravity-like stimulus to plants during early stages of germination. A newly developed gene extraction technology is ideally suited for gene-profiling studies and has far-reaching implications for studying gene expression, especially for confined space flight experiments.
Results from Biotube-MICRO may lead to using high-strength magnetic fields in space as a substitute for gravitational cues for growing plants. This would be important for growing food in space for long-duration missions.
An improved understanding of root growth will aid in developing advanced agricultural techniques on Earth, as well as adding to our understanding of plant growth and gravity response in general.
Downlink of images is required for a duration of 3 minutes every 2 hours beginning 20 hours after experiment start through fixation. Downlink of images is critical to the Biotube-MICRO science. In order to create a high gradient magnetic field, the distance between the root and the magnetic field source must be minimized. This results in a very small volume for root growth. The root growth rate is highly temperature dependent and could be faster or slower depending on the temperature inside the Magnetic Field Chamber. If the fixative delivery sequence begins when the roots are too short or too long, the root curvature response due to the high gradient magnetic field will be lost. Therefore, downlink of images is critical to determining the optimal experiment termination time.
To mimimize the time that the plant samples are exposed to fixative, the fixation operation must be scheduled as close as possible to the undocking of the SpaceX-4 capsule.
Return of samples is required for postflight analysis.
The payload is unpowered on ascent and transfers from the launch vehicle to the ISS. Upon reaching the ISS, Biotube-MICRO must be transferred to an EXPRESS Rack. On orbit, the experiment is activated by turning on the power and conducting an initiation sequence. This action is completed by a crewmember using a display screen and mouse. The seeds in each MFC are automatically imbibed with 0.4 mL of water from the payload water source. Ambient temperature and humidity data are recorded using internal sensors. The seeds are expected to germinate approximately twenty hours after imbibition (based on a 25-28 degrees C temperature assumption). Approximately twenty-four hours after the first imbibition, the seeds each receive an additional water volume of 0.15 mL. This action is completed automatically. The second imbibition ensures that the seedlings receive adequate moisture through the duration of the experiment. The imaging system is activated fifteen hours after the first imbibition and records images from the two magnetized MFCs. The third control MFC is not imaged. Images are taken of the distal (distal to the water delivery, proximal to the camera) seeds in two chambers in five-minute cycles for about 28 total hours of observation. This action is completed automatically and the images are recorded and downlinked. Approximately thirty minutes before the end of the observation period, 165 mL of RNALater is delivered to one of the magnetized MFCs and the non-magnetized aluminum blank control. 165 mL of 4% formaldehyde is delivered to the second magnetized MFC. All Biotube-MICRO experiment operations are complete at this time. The crew turns the power off, removes the payload from the EXPRESS Rack, and transfers it to the return vehicle. Biotube-MICRO is unpowered for return.
Ground Based Results Publications
Hasenstein KH, Scherp P, Ma Z. Gravisensing in flax roots – results from STS-107. Advances in Space Research. 2005; 36(7): 1189-1195.
Levine HG, Anderson K, Boody A, Cox DR, Kuznetsov OA, Hasenstein KH. Germination and elongation of flax in microgravity. Advances in Space Research. 2003; 31(10): 2261-2268. DOI: 10.1016/S0273-1177(03)00253-9.
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