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IN VITRO GROWTH OF BRASSICA SILIQUES – A NOVEL MODEL FOR THE STUDY OF SEED DEVELOPMENT AND MATURATION IN SPACEFLIGHT CONDITIONS.  A. Kuang¹, J. Blasiak², M. E. Musgrave², ¹Department of Biology, University of Texas – Pan American, Edinburg, TX; ²Biology Department, University of Massachusetts, 221 Morrill Science Center, Amherst, MA 01003

    Our previous study reported that cell ultrastructure and storage reserves in Brassica seeds  had changed during maturation in spaceflight on Mir. Understanding how reserve deposition is affected during seed development in the spaceflight environment is our goal.  However, study of seed development and maturation in microgravity is impeded by limitation of supply of materials caused by the small size of plant growth chambers currently available and limited access to long-duration spaceflight exposure. To solve this problem of limited study materials, we use a “tissue culture” method for seed development in vitro and collect developing seeds from siliques cultured on agar medium instead of siliques from growing plants.  Siliques of Brassica are removed from growing plants 10-12 days post-pollination.  After surface sterilization of the siliques with 10% Chlorox solution, their cut ends are inserted 3-4 mm into the sterilized MS agar medium containing basic nutrients.  Time to silique ripening in culture was comparable to time to ripening on the plant.  Seeds from those siliques grown in agar medium and from the plants were fixed for light and electron microscopy observation.  The microscopy observation of cell structure and storage reserves shows no differences between seeds from siliques cultured on agar medium and from growing plants.  Dry seeds collected from siliques grown on medium geminate normally and seedlings are vigorous.   There is no difference between the germination rate of these seeds and that of the seeds harvested from growing plants.  The tissue culture method could provide plenty of seeds at late developmental stages for both microscopy observation and biochemical analysis, thus solving the problem of the limitation of material supply caused by the current lack of facilities needed to grow plants full-term under spaceflight conditions.

(Supported by NASA grant NAG2 – 1375.)

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