Gravitaxis in the Flagellate Euglena gracilisis Controlled by an Active Gravireceptor

Dp, Häder; Rosum, Andreas; Schäfer, Jochen; Hemmersbach, Ruth

doi:10.1016/s0176-1617(11)82011-0

Cited by 56 publications

(14 citation statements)

References 18 publications

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“…A threshold value of 0.14g is in the same range as was determined by microgravity experiments for other gravisensitive cell types, i.e. ciliates (Hemmersbach et al, 1996), flagellates (Häder et al, 1995), and higher plant statocytes (Brown et al, 1995). In conclusion, the mechanisms of gravity sensing might be overbuilt (Bjö rkman, 1988;Sack, 1997); however, only a high sensitivity ensures that the sensing system can operate efficiently and can correct even the smallest deviations from the gravitropic set-point angle.…”

Section: Gravisensitivity Is Determined By Molecular Interactions Betmentioning

confidence: 55%

How to Activate a Plant Gravireceptor. Early Mechanisms of Gravity Sensing Studied in Characean Rhizoids during Parabolic Flights

et al. 2005

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Early processes underlying plant gravity sensing were investigated in rhizoids of Chara globularis under microgravity conditions provided by parabolic flights of the A300-Zero-G aircraft and of sounding rockets. By applying centrifugal forces during the microgravity phases of sounding rocket flights, lateral accelerations of 0.14g, but not of 0.05g, resulted in a displacement of statoliths. Settling of statoliths onto the subapical plasma membrane initiated the gravitropic response. Since actin controls the positioning of statoliths and restricts sedimentation of statoliths in these cells, it can be calculated that lateral actomyosin forces in a range of 2 3 10 214 N act on statoliths to keep them in place. These forces represent the threshold value that has to be exceeded by any lateral acceleration stimulus for statolith sedimentation and gravisensing to occur. When rhizoids were gravistimulated during parabolic plane flights, the curvature angles of the flight samples, whose sedimented statoliths became weightless for 22 s during the 31 microgravity phases, were not different from those of in-flight 1g controls. However, in ground control experiments, curvature responses were drastically reduced when the contact of statoliths with the plasma membrane was intermittently interrupted by inverting gravistimulated cells for less than 10 s. Increasing the weight of sedimented statoliths by lateral centrifugation did not enhance the gravitropic response. These results provide evidence that graviperception in characean rhizoids requires contact of statoliths with membrane-bound receptor molecules rather than pressure or tension exerted by the weight of statoliths.

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Section: Gravisensitivity Is Determined By Molecular Interactions Betmentioning

confidence: 55%

How to Activate a Plant Gravireceptor. Early Mechanisms of Gravity Sensing Studied in Characean Rhizoids during Parabolic Flights

et al. 2005

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“…Clinostats-one or two axes running fast and constantly in one direction A clinostat is a device in which samples are rotated to prevent the biological system from perceiving the gravitational acceleration vector. Different configurations exist with respect to the number of rotation axes, the speed, and the direction of rotation (Briegleb, 1992;Hä der et al, 1995;Klaus et al, 1997;Klaus, 2001). Clinostats with one rotation axis, which runs perpendicular to the direction of the gravity vector, are called 1-D (seldom) or 2-D clinostats (more common).…”

Section: Microgravity Simulatorsmentioning

confidence: 99%

Ground-Based Facilities for Simulation of Microgravity: Organism-Specific Recommendations for Their Use, and Recommended Terminology

et al. 2013

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Research in microgravity is indispensable to disclose the impact of gravity on biological processes and organisms. However, research in the near-Earth orbit is severely constrained by the limited number of flight opportunities. Ground-based simulators of microgravity are valuable tools for preparing spaceflight experiments, but they also facilitate stand-alone studies and thus provide additional and cost-efficient platforms for gravitational research. The various microgravity simulators that are frequently used by gravitational biologists are based on different physical principles. This comparative study gives an overview of the most frequently used microgravity simulators and demonstrates their individual capacities and limitations. The range of applicability of the various ground-based microgravity simulators for biological specimens was carefully evaluated by using organisms that have been studied extensively under the conditions of real microgravity in space. In addition, current heterogeneous terminology is discussed critically, and recommendations are given for appropriate selection of adequate simulators and consistent use of nomenclature.

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“…Exposing Euglena and Paramecium to real microgravity conditions (drop tower, parabolic flights of aircrafts, or rockets) results within seconds in a loss of gravitaxis and gravikinesis (e.g., Hemmersbach-Krause et al, 1993a, 1993bHäder et al, 1995Häder et al, , 1996.…”

Section: Magnetic Levitation Versus Real Microgravity-the Biological mentioning

confidence: 99%

Impact of a High Magnetic Field on the Orientation of Gravitactic Unicellular Organisms—A Critical Consideration about the Application of Magnetic Fields to Mimic Functional Weightlessness

Hemmersbach

Simon²,

Waßer³

et al. 2014

Astrobiology

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The gravity-dependent behavior of Paramecium biaurelia and Euglena gracilis have previously been studied on ground and in real microgravity. To validate whether high magnetic field exposure indeed provides a groundbased facility to mimic functional weightlessness, as has been suggested earlier, both cell types were observed during exposure in a strong homogeneous magnetic field (up to 30 T) and a strong magnetic field gradient. While swimming, Paramecium cells were aligned along the magnetic field lines; orientation of Euglena was perpendicular, demonstrating that the magnetic field determines the orientation and thus prevents the organisms from the random swimming known to occur in real microgravity. Exposing Astasia longa, a flagellate that is closely related to Euglena but lacks chloroplasts and the photoreceptor, as well as the chloroplast-free mutant E. gracilis 1F, to a high magnetic field revealed no reorientation to the perpendicular direction as in the case of wild-type E. gracilis, indicating the existence of an anisotropic structure (chloroplasts) that determines the direction of passive orientation. Immobilized Euglena and Paramecium cells could not be levitated even in the highest available magnetic field gradient as sedimentation persisted with little impact of the field on the sedimentation velocities. We conclude that magnetic fields are not suited as a microgravity simulation for gravitactic unicellular organisms due to the strong effect of the magnetic field itself, which masks the effects known from experiments in real microgravity.

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Gravitaxis in the Flagellate Euglena gracilisis Controlled by an Active Gravireceptor

Cited by 56 publications

References 18 publications

How to Activate a Plant Gravireceptor. Early Mechanisms of Gravity Sensing Studied in Characean Rhizoids during Parabolic Flights

How to Activate a Plant Gravireceptor. Early Mechanisms of Gravity Sensing Studied in Characean Rhizoids during Parabolic Flights

Ground-Based Facilities for Simulation of Microgravity: Organism-Specific Recommendations for Their Use, and Recommended Terminology

Impact of a High Magnetic Field on the Orientation of Gravitactic Unicellular Organisms—A Critical Consideration about the Application of Magnetic Fields to Mimic Functional Weightlessness

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