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Gravitaxis and graviperception in Euglena gracilis.

D P Hader1, M Lebert, P Richter

  • 1Institut fur Botanik and Pharmazeutische Biologie der Friedrich-Alexander-Universitat, Erlangen, Germany.

Advances in Space Research : the Official Journal of the Committee on Space Research (COSPAR)
|September 7, 2001
PubMed
Summary

Euglena gracilis uses an active receptor for gravitaxis, not passive alignment. Gravitational response shows a threshold and saturation, with no adaptation to weightlessness observed during spaceflight.

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Area of Science:

  • Cell Biology
  • Biophysics
  • Space Biology

Background:

  • Gravitaxis, the ability of organisms to sense and respond to gravity, is crucial for many life forms.
  • The flagellate Euglena gracilis exhibits gravitaxis, but the underlying mechanism remains incompletely understood.

Purpose of the Study:

  • To investigate the mechanism of gravitactic orientation in Euglena gracilis.
  • To determine the role of active physiological processes versus passive physical forces in cell orientation.

Main Methods:

  • Space flight experiment on the space shuttle Columbia with varying acceleration levels (0-1.5 x g).
  • Computerized real-time image analysis for tracking cell orientation.
  • Terrestrial experiments manipulating medium density and using ion channel blockers.

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Main Results:

  • Gravitactic orientation dependence on acceleration followed a sigmoidal curve with a threshold (< or = 0.16 x g) and saturation (approx. 0.32 x g).
  • No adaptation to weightlessness was observed during a 12-day space mission.
  • Gravitaxis was eliminated by matching medium and cell density, and reversed at higher densities, suggesting cytoplasmic pressure on membranes.
  • Gadolinium, a calcium channel inhibitor, affected gravitaxis, implicating calcium ion channels.
  • Ion channel blockers, ionophores, and ATPase inhibitors impaired graviperception, suggesting a role for membrane potential modulation.

Conclusions:

  • Gravitaxis in Euglena gracilis is mediated by an active physiological receptor system.
  • The mechanism likely involves stretch-sensitive calcium ion channels and modulation of membrane potential.
  • The findings provide insights into the biophysical and molecular basis of gravity sensing in microorganisms.