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The Role of Phytochromes in the Gravitropic and Phototropic Responses of Inflorescence Stems of Arabidopsis thaliana. M.A. Schwind and J.Z. Kiss. Department of Botany, Miami University, Oxford, OH.

   Plants actively respond to light and gravity changes through phototropic and gravitropic pathways, respectively.  A number of recent studies have increasingly shown that the pigment phytochrome plays a key role in adaptations to light and gravity. To further study the role of phytochromes in tropisms, we studied gravitropism and phototropism in inflorescence stems of Arabidopsis phytochrome mutants. Mutant strains tested included phyA, phyB, phyD, phyE, phyAB, and phyABD.  Inflorescence stems were grown on Rockwell cubes for 26-30 days until they were between 2 and 8cm tall.  For gravitropism experiments, the cubes were reoriented 90° in the dark.  During phototropism experiments, plants were exposed to unilateral blue light.  Preliminary results indicate an accelerated response rate to gravity changes in phyAB and more so in phyABD mutants; however, no significant difference in curvature was found in the single phytochrome mutants. These results suggest phytochromes A, B and D interact to play a role in inflorescence stem gravitropism. In addition, we will report experiments for blue light phototropic responses. Since most work to date has been with seedlings, these experiments should provide insight into the role of phytochromes in tropistic responses in stems of mature plants.

(Supported by NASA and the Miami U. Undergraduate Summer Scholars Program).