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The Effect of Microgravity on the Arrangement of Amyloplasts in Hypcotyl Endodermal Cells.   D. Cirelli and J.Z. Kiss, Department of Botany, Miami University, Oxford, OH 45056.

   The overarching goal of this project is to study the effects of microgravity (µg) on the development of plant cells. Specifically, the structure of gravity-perceiving endodermal cells of hypocotyls will be studied by morphometric analyses in wild-type, a reduced-starch mutant, and a starchless mutant of Arabidopsis thaliana grown in µg (F-µg) and compared to ground 1g (G-1g) and flight 1g (F-1g) controls. These experiments were performed as part of the Shuttle-to-Mir Biorack missions, where an incubator with an on-board reference centrifuge was included. Studies are in progress to assess the appropriate software for modeling the position of statolithic amyloplasts in endodermal cells during the various gravity treatments provided during the spaceflight experiments. Our results with hypocotyls will be compared to studies on the columella cells of the root cap. In addition, we plan to test the hypothesis that changing gravity stimulation can elicit feedback control over statolith mass by changing the size, number, and grouping of amyloplasts. Plastid grouping and position is also of particular interest since some organisms display a programmed pre-grouping while others show a seemingly random disposition in µg.