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Physical characterization of gravitaxis in Euglena gracilis
1Friedrich-Alexander-Universitat, Institut fur Botanik und Pharmazeutische Biologie, Erlangen.
Journal of Plant Physiology
|September 7, 2001
Summary
Gravitaxis in Euglena gracilis is explained by cell density and sedimentation forces. A 5-second integration period precedes reorientation, suggesting a novel signal transduction model.
Area of Science:
- Microbiology
- Biophysics
- Cell Biology
Background:
- Gravitaxis, the orientation response to gravity, is a known phenomenon in microorganisms like Euglena gracilis.
- The prevailing model attributes gravitaxis to the density difference between the cell and its medium.
Purpose of the Study:
- To investigate the physical basis of gravitaxis in Euglena gracilis.
- To test the current model's feasibility and explore the signal transduction mechanisms involved.
Main Methods:
- Determined the specific density of Euglena gracilis cultures under varying conditions.
- Measured cell size and gravitaxis kinetics in parallel.
- Analyzed stimulus-response curves and compared energy requirements for reorientation.
Main Results:
- Specific density ranged from 1.046 to 1.054 g mL-1.
- A linear relationship was observed between applied force and gravitaxis kinetics.
- An integration period of approximately 5 seconds was identified before gravitactic reorientation.
- Gravitaxis kinetics showed similarity at 1 x gn and 0.12 x gn.
Conclusions:
- The current density-based model requires refinement, with evidence for signal amplification and integration.
- A hypothesis involving an integration period and an all-or-none reaction explains gravitaxis kinetics across different gravity levels.