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Plants respond to gravity (gravitropism) and light (phototropism). Typically,
plant shoots will grow away from the direction of gravity and grow towards a light
source. Some plants are primarily gravitropic while others are primarily phototropic.
The moss, Ceratodon, is comprised of long chains of cells that grow from the filament
tips. On earth, heavy particles in these tip cells fall toward gravity, causing
the moss to grow away from the direction of gravity. When exposed to the microgravity
environment of space, gravitropic forces no longer affect the moss. Due to decreased
gravity, heavy particles don’t fall out in the same manner. The resulting
random particle distribution will cause changes in growth characteristics. Light
direction is not altered in microgravity so the plant will still grow phototropically
(towards light) just like on earth.
For STS–107, the BRIC–14 experiment expands on the previous results with three major objectives. 1. Determine the age or developmental stage at which moss grows in a non-random pattern when exposed to microgravity conditions; 2. Determine the minimum illumination level required to impose a phototropic response on the growth pattern of the moss in the absence of gravity; and 3. Understand how microgravity affects the distribution of cell substructures. Background Information: To address the first objective of this flight experiment, selected moss colonies
will be grown while exposed to a directional light for six days before launch.
Once in space, the lights will be turned off and the moss will continue to grow
in darkness. This moss will be compared to moss that is grown without any exposure
to light but has had similar exposure time to microgravity. This part of the experiment
will help determine the age and developmental growth stage of the moss at which
non-random spiral growth is exhibited.
The third objective is to understand how the nonrandom distribution of cell substructure takes place in space. Scientists have known for quite some time that fibers inside cells are responsible for the organization of subcellular components called organelles. An unexpected finding from STS–87 is that these heavy organelles, which are affected by gravity on earth, form non-random groups within the cells. The investigators hypothesize that this grouping is organized by these same fibers, although normally, the fibers don’t cause grouping on earth. To test this theory, chemicals will be applied that breakdown the fibers. If the fibers play a role, then the organelles should become randomly distributed inside the cells during spaceflight. This experiment will provide information about how the positions of heavy organelles are controlled and organized inside cells on earth.
Above: Cellular substructure distribution (from the STS–87 experiment). The astronauts will check the temperature and verify that the flight hardware
is functioning each day. They will also switch the growth lights on and off at
various locations in the flight hardware and will use a specialized tool to apply
chemicals to the moss. These chemicals, called fixatives, will stop the growth
process of the moss and preserve the specimens for analysis after the mission
has ended. Science Discipline SupportedThis research primarily addresses Fundamental Space Biology, but can also be related to other disciplines. Similar flight experiments can be conducted on the International Space Station to increase knowledge of how natural processes react to space and enrich life on Earth through people living and working in space. Principal Investigator: Dr. Fred Sack, Co-investigator: Dr. Volker Kern, Project Manager: Guy Etheridge, Project Engineer: Dave Reed, ResourcesVisit BRIC-14 for a printable PDF version of this research. Visit http://spaceresearch.nasa.gov/sts-107/overview.html to learn more about the other OBPR investigations flying on STS-107. See Florida Today for a news article on this subject.
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