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THREE-DIMENSIONAL RECONSTRUCTION AND ANALYSIS OF ROOT CAP STATOLITH DISTRIBUTION IN ARABIDOPSIS THALIANA.    R. Ehsanian¹,², D.K. Bruck¹, J.D. Smith³.  ¹Dept. of Biology, San Jose State University, San Jose CA; ²Lockheed Martin Space Operations, Moffett Field CA; and ³NASA Ames Research Center, Moffett Field CA.  

Living organisms have evolved mechanisms for sensing and reacting accordingly to the Earth’s gravity.  Specialized gravity-sensing cells, statocytes, serve the important function of providing higher plants with the directional cue needed for proper growth and development.  Amyloplasts in the statocytes of the root cap are redistributed due to changes in the gravitational environment leading to the hypothesis that they function as the statoliths for higher plants.  The overall focus of this research in our lab was to determine the mechanisms by which plants adapt to changes in the gravitational environment. We hypothesized that the position and size of the amyloplasts would change due to the change in the gravitational environment.  The hypergravity research facilities at NASA Ames Research Center were used to expose seedlings of Arabidopsis thaliana to chronic hypergravity stimulation.  By means of the ROSS program at the Ames Center for Bioinformatics, three-dimensional reconstructions made from electron micrographs were used to elucidate relative intracellular and intercellular positions of the amyloplasts. This method is less subjective and more accurate than traditional morphological techniques used to reconstruct and analyze ultrastructure.  The ability to visualize and measure the entire cell in a three dimensional environment helps to determine the effects of gravity on amyloplast position with much greater certainty than through traditional morphometric methods.  The results of these analyses help show how plastid position is related to size, and thus lead us to a mechanism by which higher plants adapt to changes in the gravitational environment.

This research was supported by NASA Ames Research Center.