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  • 1
    ISSN: 1615-6102
    Keywords: Funaria protonemata ; Chara rhizoid ; Actin filament ; Phallotoxin ; Rhodamine ; Fluorescein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A simple method is introduced to visualize actin filaments in plant cells without previous aldehyde fixation and/or additional extraction procedures. The concentration dependence of differently modified phallotoxins was examined. Displacement and competition experiments were performed to demonstrate the differences between phallotoxins, unlabeled or labeled with different fluorochromes. The procedure is valid for several plant cells.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2048
    Keywords: Chara ; Graviperception ; Lepidium ; Microfilament ; Microgravity ; Statolith (reduced gravitational field)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract During five rocket flights (TEXUS 18, 19, 21, 23 and 25), experiments were performed to investigate the behaviour of statoliths in rhizoids of the green alga Chara globularia Thuill. and in statocytes of cress (Lepidium sativum L.) roots, when the gravitational field changed to approx. 10−4 · g (i.e. microgravity) during the parabolic flight (lasting for 301–390 s) of the rockets. The position of statoliths was only slightly influenced by the conditions during launch, e.g. vibration, acceleration and rotation of the rocket. Within approx. 6 min of microgravity conditions the shape of the statolith complex in the rhizoids changed from a transversely oriented lens into a longitudinally oriented spindle. The center of the statolith complex moved approx. 14 μm and 3.6 μm in rhizoids and root statocytes, respectively, in the opposite direction to the originally acting gravity vector. The kinetics of statolith displacement in rhizoids demonstrate that the velocity was nearly constant under microgravity whereas it decreased remarkably after inversion of rhizoids on Earth. It can be concluded that on Earth the position of statoliths in both rhizoids and root statocytes depends on the balance of two forces, i.e. the gravitational force and the counteracting force mediated by microfilaments.
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  • 3
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The minimum dose (dose = stimulus × time), one of three threshold values related to gravity, was determined under microgravity conditions for cress roots. Seedlings were cultivated on a 1g centrifuge in orbit and under microgravity, respectively. After continous stimulation on a threshold centrifuge, minimum doses of 20–30 gs for microgravity roots and 50–60 gs for roots grown on a 1g centrifuge were estimated, which indicated that micro-gravity roots have a higher sensitivity than 1g roots. These results do not confirm the threshold value of 12gs which was determined for cress roots using the slow rotating clinostat. Following application of intermittent stimuli to microgravity-grown roots, gravitropic responses were observed after two stimuli of 13-5 gs separated by a stimulus-free interval of 118 s. Generally, this demonstrates that higher plants are able to ‘sum up’ stimuli which are below the threshold value. Microscopic investigations of the cellular structure corresponding to stimulations in the range of the threshold value demonstrated a small displacement of statoliths in root statocytes. No significant correlation was observed between gravitropic curvature and statolith displacement. If the statolith theory is accepted, it can be concluded that stimulus transformation must occur in the cytoplasm in the near vicinity of the statoliths and that this transformation system – probably involving cytoskeletal elements – must have been affected during microgravity seedling cultivation.
    Type of Medium: Electronic Resource
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