Poster: Tropisms
Abs #
656: In vivo viscosity measurements of cytoplasm in Chara rhizoids
We microinjected magnetic beads of known mass, density and size to determine the viscosity of cytoplasm of intact, living Chara rhizoids. By application of a magnetic field, we moved the beads to the apical dome, statoliths, nucleus, and the zone of cytoplasmic streaming and measured their velocity. The velocity was compared with that of beads in 20 different glucose and sucrose solutions of viscosity ranging from 1.023 to 80 Pa.s. The beads were moved either parallel or perpendicular to the rhizoid axis for 5 to 35 mm. The values from intact rhizoids were compared with those that were treated with latrunculin B and/or oryzalin (depolymerizers of f-actin and microtubules, respectively). In all measured areas the viscosity varied with the direction of movement with longitudinal displacement being faster than the displacement in the transverse direction. The viscosity in the area of cytoplasmic streaming (1.1 Pa.s) was significantly lower than in the adjacent cytoplasm (40 - 45 Pa.s) . The viscosity in the vicinity of the plasma membrane was ca. 28 Pa.s, indicating interactions with membrane-bound elements. The zone of the highest measured viscosity (>80 Pa.s) was detected in the vicinity of the statoliths, 15 - 40 mm from the tip. The lower longitudinal viscosity in this area compared with transverse displacement are likely to affect statolith sedimentation. We hypothesize that this polar viscosity acts as a noise-reduction system that contributes to statolith-based gravisensing. Our data represent the first mapping of viscosity in a living plant cell. Supported by NASA grant NAG 2-1423.
