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Graviperception and graviorientation in flagellates.

D P Hader1, R Hemmersbach

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

Planta
|September 7, 2001
PubMed
Summary
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Gravitaxis in Euglena gracilis is an active response, not passive. Cell density, not organelles, mediates this response, involving ion channels and membrane potential changes.

Area of Science:

  • Cellular Biology
  • Biophysics
  • Space Biology

Background:

  • Gravitaxis, the orientation of organisms in response to gravity, is crucial for many life forms.
  • Understanding gravitaxis mechanisms in single-celled organisms like Euglena gracilis provides insights into fundamental biological processes.

Purpose of the Study:

  • To investigate the physiological mechanisms underlying gravitaxis in Euglena gracilis.
  • To determine the threshold and saturation levels of gravitaxis response under varying accelerations.
  • To explore the role of cellular components and membrane dynamics in graviception.

Main Methods:

  • Space flight experiment on the American shuttle Columbia with controlled accelerations (0-1.5 g).
  • Density manipulation using Ficoll medium to assess the role of cell body as statolith.

Related Experiment Videos

  • Inhibitor studies using gadolinium, ion-channel blockers, ionophores, and ATPase inhibitors.

    • Main Results:

    • Gravitaxis is an active physiological response, not passive cell alignment.
    • Response threshold: 0.08-0.16 g; saturation: 0.32-0.64 g.
    • The entire cell body acts as a statolith; cytoplasm pressure on the membrane activates stretch-sensitive ion channels.
    • Early sensory transduction involves modulation of membrane potential; inhibitors block gravitaxis without affecting motility.

    Conclusions:

    • Euglena gracilis exhibits an active, receptor-mediated gravitaxis.
    • Cellular density and membrane ion channels are key components of the graviception pathway.
    • No adaptation to microgravity was observed during the mission.