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Arabidopsis thaliana — a model organism for space research  Klaus Palme, University of Freiburg, Schдnzlestr. 1, D-79104 Freiburg, Germany

   Gravitational force is one of the few constants in the evolution of life on Earth which played an important role in the development of flora and fauna on Earth. Although there is a huge and obvious difference between animals and plants, they share a broad basis of genetic material related to developmental and physiological processes. This makes plants the perfect research object for the effects of gravity on living beings: they can't move, the effect of gravity can be more easily monitored. Though it is clear that the gravitational force has a crucial influence on a number of biological processes, little is known about the molecular mechanism with which plants perceive gravity and about how gravity influences the substances that transmit the information within the organism. To find out more about this mechanism, research was done on Arabidospis thaliana (thale cress). This plant was chosen because of its many advantages for large scale molecular research: Short generation time, large number of offspring, mutants in literally every gene and a small, fully sequenced genome make it an ideal research object. Not surprising, this plant has become a major model for molecular plant research. Molecularly exploring signal transduction pathways is now starting to shed light on the major pathways that affect gravity signal transduction. An important 'plant hormone' - auxin - controls the curving of plants in response to light and gravity. The physical signals of gravity build up 'messenger substances' or hormones - and spread them throughout the plant. Research results show that the plants only curve, if auxin is clustered in certain regions. We have identified an important group of transmitters, named PIN proteins, which ship the auxin to these regions. Information will be provided on this protein family and the role its members play in auxin transport and action. We will also provide an overview on signalling pathways important for gravity mediated growth. Understanding these signal transduction pathways is likely to provide important markers for breeding and help to improve resistance towards a variety of other environmental factors including touch, light, gradients in temperature, humidity, ions, chemicals, and oxygen. Breeding hardier, more resistant varieties of important crops is not only a priority for agricultural research but also important for the growth of plants under weightlessness.