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Auxin transport and redistribution in the gps mutants of Arabidopsis. Vijayanand Nadella¹, Gloria Muday² and Sarah Wyatt¹.  ¹Department of Environmental and Plant Biology, Ohio University, Athens, OH ²Department of Biology, Wake forest University, Winston-Salem, NC

   The inflorescence stems of the gravity persistent signal (gps) mutants of Arabidopsis have an abnormal response when gravistimulated at 4єC and returned to room temperature:  gps1 doesn’t respond, gps2 bends in the opposite direction to wildtype and gps3 over-responds curving to an angle greater than wildtype.  At 4єC auxin transport was abolished.  In gps1, an increased polar auxin transport was found after gravistimulation at 4єC and returned to room temperature, although the mutant showed no gravitropic bending under these conditions.  This nullified the hypothesis that auxin transport was disrupted in gps1 leading to a lack of response.  On the other hand, auxin transport in gps3 was not significantly different from wild type after cold gravistimulation, nullifying the hypothesis that an increase in auxin transport could provide a mechanism resulting in the exaggerated curvature seen with gps3.  gps2 also showed normal polar auxin transport as compared to wild type even though it bent in the opposite direction.  These results indicate that improper redistribution of auxin could be the basis for the phenotypes seen.  Transgenic plants have been obtain that express the auxin responsive promoter pIAA2:GUS gene fusion and tested for GUS expression in the inflorescence stem.  These plants have been crossed with each of the gps mutants, and plants selected for expression of both the GUS fusion and each gps phenotype.  Analysis of these plants is providing insight on lateral redistribution of auxin after cold gravistimulation in the mutants and given us insights into the causes of the phenotypes seen.  (Supported by The American Society of Gravitational Space Biology, the NSCORT in Plant Biology at NCSU and the USDA:  2002-35304-12333.)