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  • 1
    Electronic Resource
    Electronic Resource
    On Petri's analysis of the linear system of quadrics through a canonical curve (1973)
    Springer
    Mathematische Annalen 206 (1973), S. 157-175 
    Details
    ISSN: 1432-1807
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01430982
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  • 2
    Electronic Resource
    Electronic Resource
    Influence of electric fields on photophobic reactions in blue-green algae (1977)
    Springer
    Archives of microbiology 114 (1977), S. 83-86 
    Details
    ISSN: 1432-072X
    Keywords: Blue-green algae ; Electric fields ; Phormidium uncinatum ; Photophobic reaction ; Sensory transduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effect of external electric fields on photoaccumulations of Phormidium uncinatum in light traps has been studied. 1. In direct current fields the phobic reaction of trichoms leaving the light field is not impaired if a voltage of 2.5 V is not exceeded. With voltages between 3 and 7 V the trichoms are motile, but phobic reactions are cancelled, provided the organisms are oriented more or less parallel to the electric field lines. Higher voltages cause the algae to die within minutes. 2. Only alternating current fields of very low frequencies (≤10-3 Hz) have similar effects. Sine waves are more effective than triangular ones, but less than square waves. A hypothesis is proposed according to which sensory transduction of photophobic reactions in blue-green algae is mediated by changes in the endogenous membrane potential. This potential might be interfered with by the application of an external electric field, thus inhibiting photophobic reactions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00429635
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  • 3
    Electronic Resource
    Electronic Resource
    Extracellular and intracellular determination of light-induced potential changes during photophobic reactions in blue-green algae (1978)
    Springer
    Archives of microbiology 119 (1978), S. 75-79 
    Details
    ISSN: 1432-072X
    Keywords: Blue-green algae ; Light-induced potential changes ; Phormidium uncinatum ; Photophobic response ; Sensory transduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Light-induced potential changes have been measured in the filamentous blue-green alga Phormidium uncinatum both intracellularly and between the two ends of a trichome. There is evidence that these potential changes are correlated with photophobic reactions in this organism. 1. The potential changes follow the light-dark regime with a lag phase of about 10 s. The photophobic reaction time has been found to be about the same length of time. 2. The action spectra of both externally and internally measured light-induced potential changes correspond with the photophobic action spectrum, indicating the participation of the main photosynthetic pigments of Phormidium, chlorophyll a and phycobilins. A hypothesis is being discussed according to which sensory transduction between photoreceptor and motor apparatus of the cell is mediated by light-induced electrical potential changes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00407931
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  • 4
    Electronic Resource
    Electronic Resource
    Step-up photophobic response in the ciliate, Stentor coeruleus (1980)
    Springer
    Archives of microbiology 126 (1980), S. 181-186 
    Details
    ISSN: 1432-072X
    Keywords: Hypericin ; Ionophores ; Light-induced membrane potential ; Photophobic response ; Stentor ; Uncouplers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The avoidance by Stentor coeruleus of a light trap is caused by a step-up photophobic response. The phobic response invariably consists of a delay of about 200 ms, a stop response, a turn to one side, and resumption of swimming in the new direction. After this the cells enter a refractory period of 1–3 s following a phobic response, during which they will not give a second response. Phobic responses can be elicited by spatial and temporal increases in light intensity. The action spectrum for the step-up photophobic response resembles the absorption spectrum of stentorin, the proposed photoreceptor pigment, and of its chromophore, hypericin. The phobic response is specifically inhibited by the protonophorous uncouplers TPMP+ and FCCP but not by the ionophores gramicidin and A23187. Since the uncouplers block light-induced membrane potential changes at the same concentrations, it has been proposed that the primary photoreception causes a light-induced potential change, which in turn, induces a motor response.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00511225
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of inhibitors on photomovement in desmids (1981)
    Springer
    Archives of microbiology 129 (1981), S. 168-172 
    Details
    ISSN: 1432-072X
    Keywords: Desmids ; Inhibitors ; Microvideography ; Photokinesis ; Photophobic response ; Photosynthetic electron transport ; Phototaxis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effects of the inhibitors of the photosynthetic electron transport chain, 3-(3′,4′-dichlorophenyl) 1,1-dimethylurea (DCMU) and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB), on the three phtoomovement responses known in the desmid Cosmarium cucumis have been studied. Both inhibitors block photokinesis very effectively in their respective specific concentration range. Most of the impairment of phototaxis and the photophobic response observed in population techniques seems to be due to a reduced motility of the cells, since microvideographic analysis of the cell movement indicated that the inhibitors do not affect the phobic response at all and that there is only partial inhibition of phototaxis. Both the fraction of motile cells and the duration of motility periods are affected by the inhibitors. The results demonstrate that, though all three photoresponses are mediated by chlorophyll acting as photoreceptor, at least the phobic response is independent of the photosynthetic electron transport chain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00455356
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  • 6
    Electronic Resource
    Electronic Resource
    Phototaxis in the flagellates, Euglena gracilis and Ochromonas danica (1981)
    Springer
    Archives of microbiology 130 (1981), S. 78-82 
    Details
    ISSN: 1432-072X
    Keywords: Euglena ; Flagellates ; Microvideography ; Ochromonas ; Photomovement ; Phototaxis ; Statistical analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Oriented movement with respect to laterally impinging white light of the flagellates Euglena gracilis and Ochromonas danica has been analyzed in an individual cell study with a microvideographic technique. Using the deviation of track segments (in given time intervals of 1 s) from the light direction as raw data allowed a computer based analysis of the direction distribution. A number of statistical methods employed to test the significance of the obtained results demonstrated an obvious phototactic orientation in Ochromonas which was positive (toward the light source) in low illuminance (1.25 lx=5.3×10-3 Wm-2) and negative in higher illuminance (〉12.5 lx=5.3×10-2 Wm-2). Since in this flagellate the threshold for negative phototaxis is much lower than that for the step-up photophobic response, the hypothesis that negative phototaxis may be brought about by repetitive step-up phobic responses can be rejected for at least this organism. In Euglena positive phototaxis was observed in ≤50 lx (=0.21 Wm-2), while an illuminance of 500 lx (=2.1 Wm-2) caused a negative phototaxis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00527076
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  • 7
    Electronic Resource
    Electronic Resource
    Participation of two photosystems in the photo-phobotaxis ofPhormidium uncinatum (1974)
    Springer
    Archives of microbiology 96 (1974), S. 255-266 
    Details
    ISSN: 1432-072X
    Keywords: Cyanophyceae ; Phototaxis ; Phobotaxis ; Photosynthesis ; Electron Transport Chain ; Inhibitors ; Action Spectra
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract 1. A hypothesis based on the Hill-Bendall-model of photosynthetic electron transport is proposed to explain positive and negative photo-phobotaxis inPhormidium uncinatum. In the non-cyclic electron chain a pool is located into which photosystem II (e. g. by absorption by C-phycoerythrin, 561 nm) feeds electrons while photosystem I (e.g. 723 nm) drains electrons out of it. 2. Interruption of the electron flow into the pool causes a sudden decrease of the pool size and thus a positive phobic response. This happens e.g. when an organism leaves a trap which is illuminated by a wavelength absorbed by photosystem II pigments (e. g. 561 nm). 3. A negative reaction takes place when electrons are suddenly drained out of the pool; again the pool size decreases. This is the case when an organism enters a light trap illuminated by photosystem I light (723 nm). 4. The net flow of electrons into or out of the pool—and thus the reaction sense—can be manipulated by the relative excitation of the two photosystems or by blocking the electron influx by DCMU.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00590181
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  • 8
    Electronic Resource
    Electronic Resource
    Inhibition of aggregation by light in the cellular slime mold Dictyostelium discoideum (1979)
    Springer
    Archives of microbiology 123 (1979), S. 281-285 
    Details
    ISSN: 1432-072X
    Keywords: Aggregation ; Amoebae ; Dictyostelium ; Light inhibition ; Photoreceptor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Aggregation of Dictyostelium amoebae is inhibited by light. White light intensities ≥102 μW · cm-2 cause an inhibition which reaches a saturation at 2 · 103 μW · cm-2. The action spectrum, based on photon fluence-response curves, shows a major peak around 405 nm and extends through most of the visible spectrum with a secondary maximum at about 530 nm. The action spectrum of the inhibition of aggregation resembles the action spectrum of accumulations of amoebae in light traps and the action spectrum of photodispersal from light traps; it does not resemble the action spectrum of phototaxis in pseudoplasmodia.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00406662
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  • 9
    Electronic Resource
    Electronic Resource
    Dependence of the photophobic response of the blue-green alga, Phormidium uncinatum, on cations (1982)
    Springer
    Archives of microbiology 132 (1982), S. 345-348 
    Details
    ISSN: 1432-072X
    Keywords: Blue-green alga ; Calcium ions ; Cations ; Ion fluxes ; Phormidium ; Photophobic response
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract It is suggested that photophobic responses caused by a sudden step-down in light intensity require the presence of cations in the blue-green alga, Phormidium uncinatum. Drastic removal of cations abolishes the phobic response, which recovers after addition of Ca2+ ions. Calcium can be substituted for partially by other cations with an effectivity following the sequence Ca〉Mg〉Na〉Ba〉Co=0. During the photophobic response there is a 25% increase in 45Ca binding by the cells related to a step-down in light intensity. Three seconds after a light-dark transition there is a sharp increase in the binding of labelled calcium, followed by a subsequent release. Flushing the filaments with high cation concentrations, esp. calcium causes a reversal of movement in the absence of a light stimulus similar to a photophobic reversal. This stimulus could trigger the same sequence of events in the transduction chain bypassing the primary photoresponse.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00413387
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  • 10
    Electronic Resource
    Electronic Resource
    Electrical and proton gradients in the sensory transduction of photophobic responses in the blue-green alga, Phormidium uncinatum (1981)
    Springer
    Archives of microbiology 130 (1981), S. 83-86 
    Details
    ISSN: 1432-072X
    Keywords: Blue-green algae ; Electric fields ; pH jump ; Phormidium uncinatum ; Photophobic response ; Sensory transduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The gliding filaments of the blue-green alga Phormidium uncinatum stop their movement almost instantaneously when transfered from their growth pH of 7.2 into a buffer ≤4.5 or ≥12.5. A pH jump into the range between 5.6 and 12.0 induces no visible response while in the range between 4.9 and 5.5 the organisms reverse the direction of their movement. The pH jump is believed to simulate an early step during the sensory transduction chain of the photophobic response which eventually results in a reversal of movement. One of the subsequent steps is the inversion of an electric potential gradient existing between the front and rear ends of a filament which dictates the direction of movement. A similar reversal of the naturally existing potential gradient can be provoked by switching on an external do field when the filaments move towards the anode or switching it off when the filaments glide in the opposite direction. Implications of these results on the current model of sensory transduction of the photophobic response in Phormidium uncinatum are being discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00527077
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