Poster: Tropisms
Abs #
395: The role of the F-actin cytoskeleton in signal transduction mechanisms of gravitropism in Arabidopsis hypocotyls
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Presenter: |
Palmieri, Maria , palmiem@muohio.edu |
Authors | Palmieri, Maria (A) Kiss, John Z (A) | | Affiliations: |
(A): Botany Department, Miami University
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Gravitropism, the directed growth of a plant in response to gravity, comprises three temporal phases: perception, signal transduction, and response. In higher plants, perception occurs in specialized cells (statocytes) that contain dense, starch-filled, sedimentable amyloplasts. Signal transduction occurs when the mechanical settling of gravistimulated amyloplasts is converted into a biochemical signal. The F-actin cytoskeleton has been implicated in the signal transduction phase of gravitropism. Studies utilizing pharmacological depolymerization of F-actin with latrunculin B indicate a promotion of gravitropic curvature in hypocotyls and inflorescence stems of Arabidopsis thaliana, and in roots of Zea mays, Medicago truncatula, and Linum usitatissimum. Why gravitropic curvature is promoted when the F-actin cytoskeleton is disrupted remains unclear.
This study was undertaken to assess the relationship between amyloplast sedimentation and the F-actin cytoskeleton in the statocytes of Arabidopsis hypocotyls during gravitropism. Etiolated Arabidopsis seedlings were placed on media that either possessed or lacked latrunculin B, and then they were reoriented and cryofixed at intervals following reorientation. The specimens were further processed via freeze substitution and visualized via light microscopy. Digital images were captured and plastid position was analyzed with image analysis software. A comparison of plastid positions before and after cytoskeletal disruption demonstrates a dramatic change in the plastid sedimentation kinetics. These results help to better define the role of statoliths and their interaction with the cytoskeleton as they traverse the statocyte during gravitropism. [Supported by NASA: NCC2-1200 and NGT5-50480].
