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ANATOMY OF STEMS OF BRASSICA PLANTS DEVELOPED IN MICROGRAVITY R. I. Ruiz¹, A. Kuang¹, and M. E. Musgrave^{2 1}Department of Biology, The University of Texas – Pan American, Edinburgh, TX  78539; ²Biology Department, University of Massachusetts, MA  01003

    Plant stems play important roles in support, transport, and storage, but there is little information available regarding whether the microgravity environment has any influence on the structure and function of stems.  The current study compares stems of Brassica rapa L., cv. CrGC#1-33 plants grown on board the MIR space station and on the ground, in an attempt to identify microgravity effects on stem structure and function.  Brassica rapa plants (18 d-old) developed on the MIR space station and in the post-flight ground control experiment were preserved in 1% glutaraldehyde solution.  Preserved plants were dissected and stem sections between the cotyledon and the first true leaf of the preserved plants were processed and prepared for microscopy.  Cross-sections of stems were used for the measurements on their diameters, the areas of cortical, vascular and pith tissues, and cell numbers of each tissue. The ratio of each tissue region relative to the cross section area of the stem was calculated.  Starch grains in the cortex were also counted. Data analysis indicates that stems of MIR plants have a smaller diameter, reflecting smaller areas of cortical and pith tissues.  Numerous large starch grains were present in cortical cells of space plants, [while these were absent in the ground control material]. [The results suggest that in microgravity, the storage function of the stem is emphasized over the support function. This could have consequences for the nutritional value of plants that might be grown for food during spaceflight.]  

     (Supported by NASA grant NAG2-1375).