１．Experiment Title
Enhanced effects of gravity by biological self-organizing processes

２．Principal Investigator
Yoshihiro Mogami
Graduate School of Humanities and Sciences, Ochanomizu University

３．Outline of Experiment
　We proposed a research aiming to reveal a new concept concerning the effect of terrestrial gravity on the biological systems. Gravity has been considered as a kind of restrictive force which provides the mechanical limits of growth and morphology of the organisms. In the proposed research we would like to reveal the possibility for gravity to develop new functions of the biological systems through self-organizing processes between the elements of the system. Self-organizing processes, which are ubiquitous in nature, and the resultant dynamic instability of the system itself are known to have an ability to amplify the subtle effects of external forces, such as that of gravity on the biological event of the cellular dimensions.
　We are stressing the bioconvective pattern formation as a research model for our proposal. Bioconvection is an example of self-organization including the collective interactions of negative gravitactic microorganisms. When the top-heavy density gradient caused by gravitactic migration of microorganisms grows sufficiently large, an overturning convection occurs.
　This leads to a formation of characteristic two-dimensional pattern of the scale much larger than that of microorganism itself. The bioconvective patterns which involve highly concentrated aggregation of cells then develop into three-dimensional structures.
　Previous studies have shown that bioconvective pattern is not only sensitive to changes in gravitational acceleration but also is inherent with an instability to undergo an abrupt transition of spatial property.
　Main target of our space experiment is to compare the threshold of the effect of gravity on the self-organizing pattern formation with that of the gravitactic behavior of individual microorganisms. On the basis of the analysis of the pattern formation under altered gravity in space and physical effects on the fluid which compete with gravity on earth and thus enhanced only in space, the crucial roles of gravity will be clarified on the self-organizing events which may lead to develop new properties of biological systems.