HOW PLANTS RESPOND TO GRAVITY IS A FUNDAMENTAL BIOLOGICAL QUESTION WITH IMPORTANT IMPLICATIONS FOR SPACE FLIGHT. HERE WE PROPOSEGROUND-BASED RESEARCH DESIGNED TO LEAD TO SPACE FLIGHT IN THE AREA OF PLANT BIOLOGY. OUR EXPERIMENTAL APPROACH FOCUSES ON SEVERALFAMILIES OF PUTATIVE MECHANORECEPTORS KNOWN AS MECHANOSENSITIVE (MS) ION CHANNELS. MS ION CHANNELS HAVE BEEN PROPOSED TO PLAYA ROLE IN THE PERCEPTION OF GRAVITY IN PLANTS FOR MANY YEARS A HYPOTHESIS THAT IS SUPPORTED BY SEVERAL LINES OF EVIDENCE BUT ONE THATHAS NOT YET BEEN SYSTEMATICALLY TESTED BY MOLECULAR GENETICS. THE RESEARCH PLAN UTILIZES CONTEMPORARY METHODOLOGIES FOR THE STUDYOF THE MODEL PLANT ARABIDOPSIS THALIANA TO INTERROGATE THE BIOLOGICAL FUNCTION OF PLANT MS ION CHANNELS AND BUILDS UPON PREVIOUSNASA-FUNDED RESEARCH INTO THE RESPONSE OF PLANTS TO ALTERED GRAVITY ENVIRONMENTS. WE WILL DETERMINE THE ROLE PLAYED BY MS IONCHANNELS IN MEDIATING GRAVITY SIGNAL TRANSDUCTION THEIR PUTATIVE ROLES IN ADAPTATION TO MICROGRAVITY; AND THE MOLECULAR MECHANISMSBY WHICH THE MODEL MS ION CHANNEL MSL10 ACTIVATES STRESS-RESPONSE PATHWAYS IN PLANT CELLS. WE EXPECT THAT THESE ACTIVITIES WILL HAVETHE FOLLOWING OUTCOMES: 1) TEST THE LONG-STANDING HYPOTHESIS THAT MS ION CHANNELS FUNCTION IN GRAVITY PERCEPTION; 2) CONTRIBUTE TOOUR BASIC KNOWLEDGE REGARDING HOW PLANTS EXPLOIT MS ION CHANNELS TO SENSE AND RESPOND TO MECHANICAL STRESS; 3) PROVIDE INFORMATIONTHAT COULD BE USED ON EARTH TO IMPROVE CROP PRODUCTIVITY; AND 4) ESTABLISH A FOUNDATION OF KNOWLEDGE REQUIRED TO GENERATE MOREMECHANISTIC AND SOPHISTICATED HYPOTHESES ABOUT PLANT GRAVITY PERCEPTION THAT CAN BE TESTED IN SPACEFLIGHT USING THE EUROPEAN MODULARCULTIVATION SYSTEM AND/OR THE ABRS GFP IMAGING SYSTEM.THESE PROPOSED STUDIES DIRECTLY ADDRESS THE OBJECTIVES OF THE SOLICITATION AS THEY AIM TO ANSWER BASIC QUESTIONS ABOUT HOW PLANTS RESPOND TO CHANGES IN GRAVITY AND SHOULD LEAD TO HYPOTHESES THAT CAN BE TESTED ON FUTURE SPACEFLIGHTS.