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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 109 (1981), S. 444-444 
    ISSN: 1615-6102
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1615-6102
    Keywords: Chara ; ER aggregate ; Golgi vesicle (movement)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In tip-growingChara rhizoids, the in-vivo saltatory movements of Golgi vesicles were recorded. The movements in radial direction back and forth between the ER aggregate and the plasma membrane occurred three times more often than movements passing the ER aggregate tangentially. The mean velocity of the class of Golgi vesicles observed (0.4–1 μm in diameter) was approx. 0.3 μm/s. Higher speed of 1–1.5 μm/s occurred only in radial directions. Possibly, the ER aggregate is involved in guidance of the Golgi vesicles.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 108 (1981), S. 117-137 
    ISSN: 1615-6102
    Keywords: Chara rhizoids ; Cytoskeleton ; Microfilaments ; Statoliths ; Tension
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The behavior of statoliths in rhizoids differently oriented with respect to the gravity vector indicates that there are cytoskeleton elements which exert forces on the statoliths, mostly in the longitudinal directions. Compared to the sum of the forces acting on a statolith, the gravitational force is a relatively small component,i.e., less than 1/5 of the cytoskeleton force. The balance is disturbed by displacing the rhizoid from the normal vertical orientation. It is also reversibly disturbed by cytochalasin B such that some statoliths move against the gravity force. Phalloidin stabilizes the position of the statoliths against cytochalasin B. We infer that microfilaments are involved in controlling the position of statoliths, and that there is a considerable tension on these microfilaments. The vibration frequency of the microfilaments corresponding to this tension is in the ultrasonic range.
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  • 4
    ISSN: 1615-6102
    Keywords: Chara internodal cells ; Cytoplasmic streaming ; Graviperception ; Laser-Doppler-velocimetry ; Nitella internodal cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Velocities of cytoplasmic streaming were measured in internodal cells ofNitella flexilis L. andChara corallina Klein ex Willd. by laser-Doppler-velocimetry to investigate the possibility of non-statolith-based perception of gravity. This was recently proposed, based on a report of gravity-dependent polarity of cytoplasmic streaming. Our measurements revealed large spatial and temporal variation in streaming velocity within a cell, independent of the position of the cell with respect to the direction of gravity. In 58% of the horizontally positioned cells the velocities of acropetal and basipetal streaming, measured at opposite locations in the cell, differed significantly. In 45% of these, basipetal streaming was faster than acropetal streaming. In 60% of the vertically positioned cells however the difference was significant, downward streaming was faster in only 61% of these. When cell positions were changed from vertical to horizontal and vice versa the cells reacted variably. A significant difference between velocities in one direction, before and after the change, was observed in approx. 70% of the measurements, but the velocity was faster in the downward direction, as the second position, in only 70% of the significantly different. The ratio of basipetal to acropetal streaming velocities at opposite locations of a cell was quite variable within groups of cells with a particular orientation (horizontal, normal vertical, inverted vertical). On average, however, the ratio was close to 1.00 in the horizontal position and approx. 1.03 in the normal vertical position (basipetal streaming directed downwards), which indicates a small direct effect of gravity on streaming velocity. Individual cells, however, showed an increased, as well as a decreased, ratio when moved from the horizontal to the vertical position. No discernible effect of media (either Ca2 +-buffered medium or 1.2% agar in distilled water) on the streaming velocities was observed. The above mentioned phenomenon of graviperception is not supported by our data.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 165 (1991), S. 121-126 
    ISSN: 1615-6102
    Keywords: Chara (rhizoid) ; Cytoplasmic streaming ; Gravity (effect on streaming) ; Microfilaments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In-vivo videomicroscopy ofChara rhizoids under 10–4g demonstrated that gravity affected the velocities of cytoplasmic streaming. Both, the acropetal and basipetal streaming velocities increased on the change to microgravity. The endogenous difference in the velocities of the oppositely directed cytoplasmic streams was maintained under microgravity, yet the difference was diminished as the basipetal streaming velocity increased more than the acropetal streaming velocity. Direction and structure of microfilaments labeled by rhodamine-phalloidin had not changed after 6 min of microgravity.
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  • 6
    ISSN: 1615-6102
    Keywords: Chara rhizoid ; CB action ; Cytoplasmic streaming ; Gravity ; Polarity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Measurements of cytoplasmic streaming inChara rhizoids were made by a streak-photography method combined with dark-field illumination. The velocity of cytoplasmic streaming in the acropetal direction was faster than in the basipetal direction. The difference in the streaming velocities in both morphological directions was apparently due to endogenous forces. In addition to this, a small difference attributable to gravity was superimposed if the rhizoid was oriented parallel to the gravity vector. The difference in the endogenous forces underlying the oppositely directed streams may be as high as about 12-fold the force imposed by gravity but, on average, it is about 5-fold the gravity force. In the normal vertical position of the rhizoid, this endogenously generated difference is enhanced by the gravity effect. In contrast to the variability of streaming rate due to endogenous forces, the effect of the gravity force is relatively uniform. The difference between acropetal and basipetal streaming velocities is perpetuated over the whole range of lowered velocities after treatment with cytochalasin B. After prolonged incubation in cytochalasin B, the basipetal streaming stops earlier than the acropetal streaming. A difference in the length of filaments on both sides of the streaming machinery in rhizoids is proposed as the structural basis for the difference in velocities.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 172 (1993), S. 38-42 
    ISSN: 1615-6102
    Keywords: Actin filaments ; Chara rhizoid ; Cytochalasin ; Microgravity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Previous videomicroscopy ofChara rhizoids during parabolic flights of rockets showed that the weightless statoliths moved basipetally. A hypothesis was offered that the removal of gravity force disturbed the initial balance between this force and the basipetally acting forces generated in a dynamic interaction of statoliths with microfilaments (MFs). The prediction of this hypothesis that the statoliths would not be displaced basipetally during the microgravity phase (MG-phase) after disorganizing the MFs was tested by videomicroscopy of a rhizoid treated with cytochalasin D (CD) immediately before the flight. The prediction was fully supported by the flight experiment. Additionally, by chemical fixation of many rhizoids at the end of the MG-phase it was shown that all rhizoids treated with CD before the flight had statoliths at the same location, i.e., sedimented on the apical cell wall, while all untreated rhizoids had statoliths considerably displaced basipetally from their normal position. Thus, a dynamical interaction involving shearing forces between MFs and statoliths appears highly probable.
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  • 8
    ISSN: 1432-2048
    Keywords: Electric potential (extracellular) ; Extracellular electric potential ; Leaf (electric potential) ; Light and electric potential ; Signal transmission
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Extracellular recordings of electrical potential in leaves of different species by means of band-pass amplifiers showed the occurrence of fast, small changes (spikes) with an amplitude below 1 mV. Local illumination of leaves induced temporal patterns of spikes outside the illuminated region. The light-induced patterns recorded by a given electrode in a particular experimental setup were similar for successive illuminations. The patterns recorded at different sites on the same leaf were different. Locally repetitive patterns of spikes at the electrode outside the illuminated region indicate the occurrence of some signals transmitted from this region to the cells in the neighborhood of the electrode.
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  • 9
    ISSN: 1432-2048
    Keywords: Actin filament ; Cytochalasin D ; Graviperception ; Intracellular potential ; Lepidium root ; Statocyte
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Two glass microelectrodes were inserted from opposite sides of the root cap into statocytes of Lepidium sativum L. immersed in medium with or without cytochalasin D (CD). Intracellular potentials (Eis) of statocytes were measured with reference to an earthed electrode in the bathing solution. In the absence of CD, Ei values were −160 ±2 mV (n = 52) in vertical roots. During the recording of EiS, the roots were tilted from the vertical by 45° so that in a tilted root one electrode was on the upper side and the other on the lower side; after 5 min the roots were returned to the vertical. At approximately 64 s after tilting (lasting 5–15 s) there was a transient lowering of E i (more negative) by an average of 4.7 mV on both the upper and lower sides (n = 52). In some cases, this decrease in Ei was preceded by a transitory increase. Returning the roots to the vertical resulted in a response similar to that obtained by tilting. In roots treated with CD at a concentration of 3 μM for 1 h, the initial Ei was -145 ±2 mV (n = 43), and the lowering of Ei on position change (tilting or returning) was smaller (2.0 mV) in some statocytes (n = 50) and higher (8.1 mV) in others (n = 14) compared to control roots (without and with DMSO). A higher concentration (10 μM) of CD and longer treatment (2 h) further reduced the decrease in Ei (1.1 mV) on position change (n = 26). The observed effects of CD support the hypothesis that statoliths in statocytes are anchored by actin filaments to the plasma membrane and/or to the cortical endoplasmic reticulum. Movement of statoliths during the first step of graviperception may lead to stress changes in actin filaments, affecting the transmembrane potential and also the Ei.
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  • 10
    ISSN: 1432-2048
    Keywords: Key words: Chara– Cytoplasmic streaming – Gravity effect – Laser-Doppler-velocimetry – Protonema – Rhizoid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract.  The spatial pattern of acropetal and basipetal cytoplasmic streaming velocities has been studied by laser-Doppler-velocimetry (LDV) in the positively gravitropic (downward growing) rhizoids of Chara globularis Thuill. and for the first time in the negatively gravitropic (upward growing) protonemata. The LDV method proved to be precise and yielded reproducible results even when tiny differences in velocities were measured. In the apical parts of the streaming regions of both cell types, acropetal streaming was faster than basipetal streaming. Starting at the apical reversal point of streaming, the velocity increased basipetally with the distance from that point and became fairly constant close to the basal reversal point; subsequently, the velocity decreased slightly acropetally as the apical reversal point was again approached. There was no change in velocity at the basal reversal point. However, at the apical reversal point there was an abrupt decrease in velocity. The pattern of the ratio of acropetal to basipetal streaming velocity (VR) was a function of the relative distance of the site of measurement from the apical reversal point rather than a function of the absolute distance. Upon inversion of the rhizoids, the VR decreased on average by 3.8% (±0.4%), indicating that the effect of gravity on the streaming velocity was merely physical and without a physiological amplification. Rhizoids that had developed on the slowly rotating horizontal axis of a clinostat, and had never experienced a constant gravity vector, were similar to normally grown rhizoids with respect to VR pattern. In protonemata, the VR pattern was not significantly different from that in rhizoids although the direction of growth was inverse. In rhizoids, oryzalin caused the polar organization of the cell to disappear and nullified the differences in streaming velocities, and cytochalasin D decreased the velocity of basipetal streaming slightly more than that of acropetal streaming. Cyclopiazonic acid, known as an inhibitor of the Ca2+-ATPase of the endoplasmic reticulum, also reduced the streaming velocities in rhizoids, but had slightly more effect on the acropetal stream. It is possible that the endogenous difference in streaming velocities in both rhizoids and protonemata is caused by differences in the cytoskeletal organization of the opposing streams and/or loading of inhibitors (like Ca2+) from the apical/subapical zone into the basipetally streaming endoplasm.
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