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Evaluation of the Effects of Low Atmospheric Pressure on the Ultrastructure of Radish (Raphanus sativa cv. Cherry Bomb II).    A.A. Brinley1, J.T. Richards2 Christine Simone2, Gary Stutte2, Mike Dixon3   1Kalamazoo College, Kalamazoo, MI 2Dynamac Corporation, Kennedy Space Center, FL 3 CESRF, University of Guelph, Guelph, Ontario, Canada.

   Plant growth at reduced atmospheric pressures will be highly beneficial for long duration space missions as it may reduce launch and resupply costs, increase nutritional and psychological benefits to astronauts, and allow for recirculation of water and air in a spacecraft.  In order to assess the physiology of plants grown under reduced atmospheric pressures, radishes (Raphanus sativa cv. Cherry Bomb II) were grown at total atmospheric pressures of 33 kPa, 66 kPa, and 95 kPa at the University of Guelph’s Controlled Environmental Systems Research Facility (CESRF).  In order to reduce the effect of inherent reduction of O2 at low atmospheric pressure, the O2 partial pressure was kept at 20.9 kPa throughout all pressure treatments.  Carbon dioxide partial pressure was also kept constant at 0.1 kPa throughout the experiment.  Twenty-one days after planting tissue was immediately excised from the leaves and hypocotyl, placed in a fixative (FAA), and sent to Kennedy Space Center for ultrastructural analysis.  The tissue samples were prepared with a dehydration series, a clearing series, embedding in paraffin, and finally, thin sectioning for detailed examination.  Tissue sections were then stained and evaluated for leaf thickness, starch localization, and cell density.  Statistical analysis of the data revealed that reduced atmospheric pressure had no significant effect on the ultrastructure of radish.