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  • 1
    Electronic Resource
    Electronic Resource
    The action spectrum for chloroplast movements and evidence for blue-light-photoreceptor cycling in the alga Vaucheria (1983)
    Springer
    Planta 159 (1983), S. 267-276 
    Details
    ISSN: 1432-2048
    Keywords: Action spectrum ; Blue light ; Chloro-plast movement ; Photoreceptor cycling ; Vaucheria ; Xanthophyta
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Local stimulation of the coenocytic alga Vaucheria sessilis D.C. by blue light resulted in accumulation of chloroplasts and other organelles. The photoresponse followed a well-defined, wavelength-and fluence-rate-dependent latency period (≧10 s), and could lead to a tenfold decrease in relative cellular transmittance to 675-nm light within 5 min. Light-induced aggregation of chloroplasts was examined at eight wavelengths of light between 385 and 528 nm. A fiber-optic microphotometer was employed and the response was quantitated on the basis of the rate of 675-nm transmittance change after correcting for changes in light scattering. Chloroplast aggregation exhibited a nearly identical quantum-flux-density dependence at all eight wavelenths tested; it showed an action spectrum with a sharp maximum near 470 nm, a trough at 430 nm, and action in the near-ultraviolet spectral region. Light at 454 nm was six times less effective than 473-nm light in stimulating aggregation, a difference which could not be accounted for by chlorophyll screening alone. Beyond the latency period reciprocity did not hold for chloroplast aggregation. Instead, aggregation could be fitted to a kinetic model involving steady-state photoreceptor cycling during continuous irradiation. Chloroplast aggregation in the light was compared with three growth-associated photoresponses in Vaucheria — phototropic bending, branching and apical expansion. Time course and kinetic similarities, and the presence of a cytoplasmic fiber network in growing tips of Vaucheria, indicate that these photoresponses may be related mechanistically.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00397535
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  • 2
    Electronic Resource
    Electronic Resource
    A light-dependent current associated with chloroplast aggregation in the alga Vaucheria sessilis (1981)
    Springer
    Planta 152 (1981), S. 513-526 
    Details
    ISSN: 1432-2048
    Keywords: Actin ; Blue light ; Chloroplast aggregation ; Electrical current ; Protons ; Vaucheria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Local irradiation of the alga Vaucheria sessilis (Vauch.) D.C. with blue light, which stimulates cortical fiber reticulation and chloroplast aggregation (M.R. Blatt and W.R. Briggs, 1980, Planta 147, 355–362), also induces an outward-directed current from the irradiated region of the cell. This current appears in conjunction with cortical fiber reticulation and precedes chloroplast aggregation. The current is not photosynthetic in origin, as indicated by experiments with 3(3,4-dichlorophenyl)-1,1-dimethyl urea and carbonyl-cyanide-m-chlorophenylhydrazone (CCCP). It shows a wavelength-dependence similar to that of chloroplast aggregation and reaches a maximum of 500 nA cm-2 with saturating light intensities. The current is not dependent upon the presence of Na+, K+, or Cl- in a test medium containing only Na+, K+, Ca2+, and Cl-, but is inhibited, apparently nonspecifically, in the absence of external calcium. Both the light-induced current and chloroplast aggregation are stimulated by increases in the external KCl concentration and are inhibited by sub-micromolar concentrations of CCCP or by external pHs below approximately 5.5. We suggest that blue light stimulates the local extrusion of cations, possibly of protons, at the plasma membrane, an event which may act to destabilize the cortical fibers in Vaucheria, disrupt cytoplasmic streaming, and eventually lead to organelle aggregation in the light.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00380822
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    Paper (German National Licenses)
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