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  • Photophobic response  (8)
  • Blue-green algae  (7)
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  • 1
    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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  • 2
    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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  • 3
    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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  • 4
    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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  • 5
    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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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Further evidence for the electron pool hypothesis (1976)
    Springer
    Archives of microbiology 110 (1976), S. 301-303 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00690242
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of inhibitors and uncouplers on light-induced potential changes triggering photophobic responses (1979)
    Springer
    Archives of microbiology 120 (1979), S. 57-60 
    Details
    ISSN: 1432-072X
    Keywords: Inhibitors ; Membrane potential changes ; Phormidium uncinatum ; Photophobic response ; Sensory transduction ; Uncouplers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effects of inhibitors and uncouplers on light-induced potential changes have been studied to determine the mechanisms involved in sensory transduction in photophobic responses of the filamentous blue-green alga, Phormidium uncinatum. 1. DCMU and DBMIB, inhibitors of the photosynthetic electron transport chain, impair light-induced potential changes at about the same concentrations at which they inhibit photophobic responses. They seem to act by decreasing the photosynthetic electron flow rate and they do not decrease the resting potental of the cell. 2. The lipophilic cation TPMP+ which acts as an uncoupler with protonophorous properties blocks both photophobic responses and light-induced potential changes. TPMP+ inhibits the resting potential apparently through penetration of membranes causing a breakdown of the generated potentials. 3. Application of a small electric de field enhances the effect of an inhibitor, which indicates that both measures impair light-induced potential changes. These results support the hypothesis that sensory transduction in photophobic responses of blue-green algae is mediated by light-induced potential changes, the generations of which can be explained by the Mitchell chemiosmotic hypothesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00413274
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  • 9
    Electronic Resource
    Electronic Resource
    Evidence of electrical potential changes in photophobically reacting blue-green algae (1978)
    Springer
    Archives of microbiology 118 (1978), S. 115-119 
    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 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00406083
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  • 10
    Electronic Resource
    Electronic Resource
    Gated ion fluxes involved in photophobic responses of the blue-green alga, Phormidium uncinatum (1982)
    Springer
    Archives of microbiology 131 (1982), S. 77-80 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00451502
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