Seeking the Light
Development of Gravity Sensitive Plant Cells in Microgravity
All living things sense gravity like humans might sense light or sound. The
Biological Research In Canisters (BRIC14) experiment, explores how moss
cells sense and respond to gravity and light.
This experiment studies how gravity influences the internal structure of moss
cells and seeks to understand the influences of the spaceflight environment on
cell growth. This knowledge will help researchers understand the role of gravity
in the evolution of cells and life on earth.
Left: Moss Sample in Petri Dish.
Above: Effects of Phototropism.
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 dont 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.
The scientists original hypothesis was that both random cell structure
and cell growth would occur in space. The objectives for BRIC14 experiment
were developed from the knowledge gained during a previous shuttle flight, STS87.
Unexpectedly, moss specimens grown on STS87 showed non-random subcellular
component distribution and spiral growth.
Above: Non-random spiral growth after phototropically
induced directional growth
For STS107, the BRIC14 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.
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 second objective of the experiment is to determine the illumination intensity
required to induce a phototropic response in the absence of gravity. This part
of the experiment will expose moss to three different levels of light and observe
at which light intensity samples respond. The moss will grow in the dark for seven
days in space prior to the lights turning on. This will allow the moss time to
establish a random growth pattern prior to exposure to a directional light source.
Above: Moss from STS87, showing spiral growth
patterns developed in the dark in microgravity.
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 STS87 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 dont 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
Above: Cellular substructure distribution (from the
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
Science Discipline Supported
This 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,
Ohio State University
Co-investigator: Dr. Volker Kern,
Ames Research Center
Project Manager: Guy Etheridge,
Kennedy Space Center
Project Engineer: Dave Reed,
Kennedy Space Center Moss
Visit BRIC-14 for a
printable PDF version of this research.
to learn more about the other OBPR investigations flying on STS-107.
See Florida Today for a news article on this subject.