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  • 1
    Electronic Resource
    Electronic Resource
    In vitro identification of rhodopsin in the green alga Chlamydomonas (1991)
    s.l. : American Chemical Society
    Biochemistry 30 (1991), S. 3692-3697 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00229a014
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  • 2
    Electronic Resource
    Electronic Resource
    Rhodopsin-regulated calcium currents in Chlamydomonas (1991)
    [s.l.] : Nature Publishing Group
    Nature 351 (1991), S. 489-491 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The green alga Chlamydomonas responds to bright flashes of green light by means of two distinct ion current components which we have recorded in cell wall-deficient mutants using the suction pipette technique7'8 (Fig. 1). The photocurrents are transient and occur in a time range of 0.5 to 50 ms ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/351489a0
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Vision in microalgae (1997)
    Springer
    Planta 203 (1997), S. 265-274 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Algal eye ; Calcium current ; Flagellum (beating) ; Green-light receptor ; Phototaxis ; Rhodopsin ; Vision
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Flagellate green algae such as Chlamydomonas and related genera are guided by their eyes to places where light conditions are optimal for photosynthetic growth. These eyes constitute the simplest and most common visual system found in nature. The eyes contain optics, photoreceptors and the elementary components of a signal-transduction chain. Rhodopsin serves as the photoreceptor, as it does in animal vision. Upon light stimulation, its all-trans-retinal chromophore isomerizes into 13-cis and activates a photoreceptor channel which leads to a rapid Ca2+ influx into the eyespot region. At low light levels, the depolarization activates small flagellar currents which induce in both flagella small but slightly different beating changes resulting in distinct directional changes. In continuous light, Ca2+ fluxes serve as the molecular basis for phototaxis. In response to flashes of higher energy the larger photoreceptor currents trigger a massive Ca2+ influx into the flagella which causes the well-known phobic response. The identification of proteins contributing to this signalling system has just begun with the isolation and cloning of the opsins from Chlamydomonas and Volvox. These plant opsins are highly charged, are not typical seven-helix receptors, and are believed to form a protein complex with the photoreceptor channel. In Spermatozopsis, a G-protein has been found which interacts either directly with the rhodopsin or with the rhodopsin-ion channel complex. By using insertional mutagenesis, genes coding for proteins that are involved in signalling have been tagged. One of them is connected to the flagellar channel and crucial for the flagellar action potential. Elucidation of photoreception in flagellated algae will provide deeper insight into the development of visual systems, starting from single-celled organisms and moving up through higher animals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050191
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  • 4
    Electronic Resource
    Electronic Resource
    Adaptation of Chlamydomonas phototaxis: I. A light-scattering apparatus for measuring the phototactic rate of microorganisms with high time resolution (1990)
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 15 (1990), S. 230-244 
    Details
    ISSN: 0886-1544
    Keywords: photomovement ; population method ; stop response ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Phototaxis of the unicellular alga Chlamydomonas was studied with subsecond time resolution by using a newly developed taxigraph. The taxigraph determines the cell density in a particular volume element of a cuvette by measuring the amount of scattered light originating from the cells in this region. When the cell density is kept below 106/ml, a linear relationship exists between the scattered photon irradiance and the number of scattering particles. Time-dependent scattering changes can be used to determine direction and extent of phototactic activity as well as the time course of various adaptation processes. This communication describes design and performance of the taxigraph in detail and compares results obtained from Chlamydomonas cell populations with those obtained from single-cell analysis by using a computer-aided motion analysis system.The high time resolution of the taxigraph permits the study of rapid adaptational processes. Chlamydomonas strain 806 cells, which have been reported to show exclusively negative phototaxis, were found to turn transiently towards the light upon a rapid change in irradiance, before eventually moving away from it. The duration of the initial positive phototactic response was critically dependent on the magnitude of the irradiance increment. Adaptation to a step-up stimulus was consistently faster than to a step-down stimulation. The statistical nature of the switch from positive to negative phototaxis is demonstrated by single-cell observation.Different adaptation levels were characterised by stimulus-response curves, either in the presence of a constant background or following a defined delay after long previous irradiation. To describe the observed behaviour the existence of two adaptation processes, occurring on a vastly different time scale, must be anticipated: a rapid (seconds) background adaptation and a slow desensitisation in steady light which is completed in 30-40 min.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cm.970150406
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  • 5
    Electronic Resource
    Electronic Resource
    Light-induced stop response in Chlamydomonas reinhardtii: Occurrence and adaptation phenomena (1989)
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 14 (1989), S. 501-515 
    Details
    ISSN: 0886-1544
    Keywords: phototaxis ; motion analysis system ; photoreception ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: In darkness Chlamydomonas cells swim forward with a helical motion of low amplitude. When cells are exposed to light conditions they are not adapted to, they perform direction changes or stop responses depending on how far the stimulant irradiance is shifted from the former adaptation level. Here we present the utility of a commercially available motion analysis system for the analysis of the Chlamydomonas stop response.Chlamydomonas cells stop in darkness only occasionally with a random temporal distribution but with a highly increased frequency after a flash or a step-up light stimulation. The delay time, tD, defined as the minimal time difference between flash and a light-induced stop, was below 50 ms. The reaction time, tR, defined as the time difference between flash and the maximal probability for a cell to stop was found to be 140 ms. During a stop the cells swim revers for some 300 ms with 20% of the forward swimming speed.To a given stimulation program cells adapt with a first-order kinetic. In the case of a single step-up or step-down stimulation this adaptation consists of a single stop response followed by direction changes which decrease in frequency to a certain steady-state level. To repetitive light pulses the cells respond with a gradual disappearance of step-up stop responses and a concurrent appearance of step-down responses.External calcium influences the stop response in a multifunctional way. For stop responses to occur 300 nM calcium are required. At increasing calcium concentrations the duration of a stop response is extended. Besides light, calcium regulates the time course of light-adaption and the absolute adaptation level.A kinetic model for the description of adaptation is presented.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cm.970140408
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