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internal atmosphere and seed storage reserves: Exploring the role of gravity in seed development. M.E. Musgrave, J. Blasiak, and J. Allen.  Department of Plant Science, University of Connecticut, Storrs, CT 06269.

   To understand gravity effects on seed development, we will conduct a series of experiments on the ISS-Test Bed (ISS-TB) and 24-ft centrifuges at Ames Research Center.  Data from experiments at 2-g and 4-g will be compared with our existing data on seed development in microgravity and at 1-g. We have hypothesized that the changes in seed development occurring in microgravity may be caused by lack of convective air movement within the developing seed pod (silique). Because buoyancy-driven convection is gravity dependent, we expect to enhance internal gas mixing by subjecting plants to hypergravity treatments.  Brassica rapaL. cv. Astroplants and Arabidopsis thaliana L. var. Columbia will be grown in the Plant Growth Facility (PGF) and Plant Growth Unit (PGU) respectively, according to the experiment conditions on STS-87 (B-STIC) and STS-68 (CHROMEX-5), during summer 2006.  Brassica siliques growing in tissue culture will also be included.  During a 16-d time-course, these siliques will be destructively sampled to determine the composition of their internal atmosphere and the biochemical composition of the developing seeds. At the end of the B-STIC experiment, comparable data will be gathered from siliques developing on the plants. Our ground-based experiments have optimized sampling strategies for the siliques. To quantify internal atmosphere, Brassica siliques are ruptured in helium contained within a gas-tight syringe, and the component gases are quantified by gas chromatography.  High variance results when multiple siliques are sampled from individual plants. The implications of this finding for gas transport within the plant as well as for experimental design are discussed.  Micro-analytical techniques elucidate the patterns of protein, carbohydrate and lipid accumulation in Brassica seed samples recovered from the ruptured siliques over the time-course of development. The results form a baseline for comparison for our upcoming studies at 2-g and 4-g. Supported by NASA grant NAG-10-329.