Minisymposium: Tropisms
Abs #
28001: Induction of curvature in Chara rhizoids by magnetic beads
Gravisensing in Chara depends on the interaction between dense, sedimenting statoliths and the actin cytoskeleton in the rhizoid apex. Because the apical cell of the rhizoid contains both the gravity receptor and response mechanism, the rhizoid represents a model system for the study of gravitropism. Although the statoliths respond to gravity or other forces (e.g., high-gradient magnetic fields or optical tweezers) such manipulation precludes identifying the statoliths as pressure-causing signal provider or as F-actin-tethered pendulums. The latter scenario would identify the cytoskeletal protein as the actual gravisensor. To study the effect of particle displacement we injected magnetic beads (1 mm in diameter) close to the statoliths of the rhizoid in the presence of an external osmoticum to offset excessive turgor pressure. After full recovery of the rhizoid (closure of the puncture, re-established turgor and cytoplasmic streaming) displacement of the injected beads was induced by application of an external magnetic field. In order to investigate the response of the rhizoid in a (natural) vertical position, we set up a horizontal long working distance microscope that allows the positioning of magnets close to the microinjected cell. Video microscopy revealed that an external magnet is able to displace a subset of the magnetic particles but not the cells’ own statoliths and that curvature is a function of the magnetic field strength. Therefore, gravisensing does not necessarily depend on cell own statoliths but can be mimicked by particles that are similar in size. Work is in progress to quantify the response, and utilize antibody or ligand coating of the beads to study the interaction with the actin cytoskeleton and its function in statolith positioning and gravisensing. Supported by NASA grant NAG 2-1423.
