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seed PRODUCTION ACROSS THE GRAVITY CONTINUUM in BRASSICA AND ARABIDOPSIS.    M.E. Musgrave¹, A. Kuang², J. Allen¹, R. Darnell¹, R. Wagers-Hughes², E. Escobedo² and J. Blasiak¹. ¹Department of Plant Science, University of Connecticut, Storrs, CT 06269, ²Biology Department, University of Texas Pan American, Edinburg, TX  78541.

   Extending our prior experiments on seed production by Brassica and Arabidopsis in microgravity, we recently investigated the effects of hypergravity on seed development using the 8-ft and 24-ft centrifuges at Ames Research Center in these same model plants.  Brassica rapa L. cv. Astroplants and Arabidopsis thaliana L. var. Columbia were 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).  Brassica siliques in tissue culture were also grown in chambers 1-3 of the PGF in a new experiment (B-POD), designed to give information about late stages of seed development not covered in the B-STIC experiment timecourse.  In Arabidopsis, seed production occurred normally at 2-g but was virtually eliminated by exposure to 4-g.  In contrast, in Brassica, equivalent numbers of seeds developed in 2-g and 4-g as in 1-g.  Hypergravity appeared to accelerate the timecourse of seed development in Brassica, with the developmentally programmed decline in starch and soluble carbohydrate reserves occurring earlier than in the stationary controls. Cytochemical localization of reserves showed that starch was retained in developing seeds longer at 1-g than at 4-g.  These results are discussed in the context of microgravity experiments that showed normal seed development in Arabidopsis in microgravity, but a retention of starch and soluble carbohydrates in Brassica seeds and a 25 – 50% reduction in total seed weight when seeds were formed in microgravity. Taken together these results demonstrate a differential reproductive response by plants across the gravity continuum, with Arabidopsis reproduction having a lower tolerance for hypergravity and a higher tolerance for microgravity than does Brassica. 

Supported by NASA grant NAG-10-329.