Rheological properties of living cytoplasm: endoplasm of Physarum plasmodium.
Magnetic sphere viscoelastometry, video microscopy, and the Kamiya double chamber method (Kamiya, N., 1940, Science [Wash. DC], 92:462-463.) have been combined in an optical and rheological investigation of the living endoplasm of Physarum polycephalum. The rheological properties examined were yield stress, viscosity (as a function of shear), and elasticity. These parameters were evaluated in directions perpendicular; (X) and parallel (Y) to the plasmodial vein. Known magnetic forces were used for measurements in the X direction, while the falling ball technique was used in the Y direction (Cygan, D.A., and B. Caswell, 1971, Trans. Soc. Rheol. 15:663-683; MacLean-Fletcher, S.D., and T.D. Pollard, 1980, J. Cell Biol., 85:414-428). Approximate yield stresses were calculated in the X and Y directions of 0.58 and 1.05 dyn/cm2, respectively. Apparent viscosities measured in the two directions (eta x and eta y) were found to fluctuate with time. The fluctuations in eta x and eta y were shown, statistically, to occur independently of each other. Frequency correlation with dynamoplasmograms indicated that these fluctuations probably occur independently of the streaming cycle. Viscosity was found to be a complex function of shear, indicating that the endoplasm is non-Newtonian. Plots of shear stress vs. rate of shear both parallel and perpendicular to the vein, showed that endoplasm is not a shear thinning material. These experiments have shown that living endoplasm of Physarum is an anisotropic viscoelastic fluid with a yield stress. The endoplasm appears not to be a homogeneous material, but to be composed of heterogeneous domains.
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- Viscosity
- Stress, Mechanical
- Rheology
- Physarum
- Mathematics
- Elasticity
- Developmental Biology
- Cytoplasm
- 32 Biomedical and clinical sciences
- 31 Biological sciences
Citation
Published In
DOI
ISSN
Publication Date
Volume
Issue
Start / End Page
Location
Related Subject Headings
- Viscosity
- Stress, Mechanical
- Rheology
- Physarum
- Mathematics
- Elasticity
- Developmental Biology
- Cytoplasm
- 32 Biomedical and clinical sciences
- 31 Biological sciences