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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 114 (1977), S. 83-86 
    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
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 119 (1978), S. 75-79 
    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.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 130 (1981), S. 83-86 
    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.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 110 (1976), S. 301-303 
    ISSN: 1432-072X
    Keywords: Blue-green algae ; Electron pool hypothesis ; Photophobic reaction ; Photosystems ; Phormidium uncinatum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In continuation of experiments with photo-system II inhibitors [3-(3,4-dichlorophenyl)-1,1-dimethylurea and 2,5-dibromo-3-methyl-6-isopropylbenzoquinone] the effect of photosystem I inhibitors was studied. 1. Neither the plastocyanin inhibitor, potassium cyanide, nor the ferredoxin antagonist, disalicyliden propandiamin, markedly affected those phobic reactions which are mediated by the electron transport via photosystem II into the electron pool. 2. On the other hand those phobic reactions, which are triggered by an increased flow of electrons out of the pool, are specifically inhibited by both substances. These results are regarded as further evidence that there is only one electron pool, the level of which triggers photophobic reactions and is located in the linear electron transport chain near photosystem II.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 118 (1978), S. 115-119 
    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 The correlation between photophobic responses and light-induced electric potential changes has been studied in the blue-green alga Phormidium uncinatum. 1. The photophobic reaction time depends on both length of preillumination and presentation time of stimulus. Under optimal conditions a reaction time of about 10 s has been determined. 2. Light-induced potential changes can be measured by means of external electrodes with a small gap between them bridged by a population of perpendicularly oriented trichomes. These potential changes follow a light-dark cycle with a lag phase of about 10 s. 3. The amplitude of these light-induced potential changes increases with light intensity until it reaches a saturation value of about 12 mV at 10000 lx. The action spectrum resembles the photophobic action spectrum with peaks in the absorption region of C-phycoerythrin and chlorophyll a. The significance of light-induced potential changes as a means of sensory transduction for photophobic responses in blue-green algae is being discussed.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 131 (1982), S. 77-80 
    ISSN: 1432-072X
    Keywords: Amplification ; Blue-green algae ; Cations ; Gating channels ; Ionophores ; Phobic response ; Phormidium uncinatum ; Photomovement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The sensory transduction chain of photophobic responses in the blue-green alga, Phormidium uncinatum seems to involve a gating cation transport through membrane bound ion channels which provides an effective amplification. The calcium conducting ionophore A23187 inhibits the photophobic response totally and induces frequent reversals which resemble phobic responses but occur without any light stimulation. This indicates that the electrogenic ion conductance may depend on a gradient of divalent cations, esp. calcium. The calcium conductance during a photophobic response is further confirmed by the inhibitory effect of ruthenium red and lanthanum, blockers of the electrogenic calcium transport. In the case of lanthanum this inhibition is found at a concentration at which neither the number of motile filaments nor the average speed of movement is impaired. Incorporation of ionophores for monovalent cations (gramicidin and valinomycin) only partially impairs the response. Similarly, inhibition of the Na+/K+ pump by ouabain is less effective. Thus, the existence of a countercurrent of monovalent cations during the response, which has been described for e.g. ciliates, is yet obscure in blue-green algae.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Journal of mathematical biology 10 (1980), S. 257-269 
    ISSN: 1432-1416
    Keywords: Blue-green algae ; Light trap ; Mathematical model ; Phobic response ; Phormidium uncinatum ; Photoaccumulation ; Photomovement ; Phototaxis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract A mathematical model has been developed to evaluate the contribution of phototactic responses in light-induced accumulations. A set of differential equations describes the organism density inside and outside of the light trap as well as on its border. The model predicts that organisms first occupy the rim of the light trap and then gradually fill the interior. This has been substantiated experimentally. Computer simulations of light-induced accumulations in a light trap agree with the measured values. The distance from the trap within which organisms respond phototactically depends on the organism density, which determines the amount of stray light, and on the zero threshold for both phototaxis and photophobic response.
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