) seedlings were studied in the experiment. The flight and ground control groups each contained 30 seedlings.
Mouse-ear cress is a flowering herb widely used for research in plant genetics because its genome size and short life cycle (45 days) make it an ideal candidate for gene mapping studies. The species was also chosen because its small size fits easily into the experiment hardware.
The plants were flown in the Plant Growth Unit (PGU). The Atmospheric Exchange System (AES) accompanied the PGU to provide slow purging of the Plant Growth Chambers with filtered cabin air. For general descriptions of the PGU and the AES, see CHROMEX-01.
Operations
Preflight
Thirty seeds were sown on agar 13 days prior to loading into the chambers so that plants would be developing flowers at launch time. The chambers were loaded into the PGU and then into the Shuttle middeck.
Inflight
A 48-hour delayed synchronous ground control experiment was conducted in the Orbiter Environmental Simulator (OES). For a general description of the OES, see CHROMEX-01. The flight plants initiated flowering shoots while on orbit. The only procedure the crew performed was a daily verification of proper hardware function.
Postflight
The PGU was retrieved from the Shuttle two to three hours after landing, and the reproductive material of the plants was immediately processed. Gas samples were taken from the chambers before the plant specimens were retrieved. The processed plant tissue was subjected to in vivo observations of pollen viability, pollen tube growth, and esterase activity in the stigma, or fixed for later microscopy.
Results
Under the conditions of this flight, the space-grown plants had reproductive development comparable to that of the ground controls, and immature seeds were produced. These results represent the first report of successful plant reproduction on the Space Shuttle.
Additional Reading
NASA. STS-68 Press Kit, August 1994. Contained in NASA Space Shuttle Launches Web site:
http://www.ksc.nasa.gov/shuttle/missions/missions.html.