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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 177 (1995), S. 1-19 
    ISSN: 1432-1351
    Keywords: Colour preference ; Flower colouration ; Flower visitation ; Visual signals ; Innate behaviour
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Freshly emerged flower visitors exhibit colour preferences prior to individual experience with flowers. The understanding of innate colour preferences in flower visitors requires a detailed analysis, as, on the one hand, colour is a multiple-signal stimulus, and, on the other hand, flower visits include a sequence of behavioural reactions each of which can be driven by a preferential behaviour. Behavioural reactions, such as the distant approach, the close-range orientation, the landing, and the extension of mouthparts can be triggered by colour stimuli. The physiological limitations of spectral sensitivity, the neuro-sensory filters, and the animals' different abilities to make use of visual information such as brightness perception, wavelength-specific behaviour and colour vision shape colour preferences. Besides these receiverbased factors, there are restrictions of flower colouration due to sender-based factors such as the absorption properties of floral pigments and the dual function of flower colours triggering both innate and learned behaviour. Recordings of the spectral reflection of coloured objects, which trigger innate colour preferences, provide an objective measure of the colour stimuli. Weighting the spectral reflection of coloured objects by the spectral composition of the ambient light and the spectral sensitivity of the flower visitors' photoreceptors allows the calculation of the effective stimuli. Perceptual dimensions are known for only a few taxa of flower visitors.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1617-4623
    Keywords: Key words Hemolysin secretion ; HlyD mutants ; HlyD/HlyB suppressor mutants ; TolC ; Vancomycin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The glycopeptide antibiotic vancomycin blocks cell wall synthesis in Escherichia coli only when it can reach its target site in the periplasm. In vivo, sensitivity to vancomycin is enhanced in the presence of the hemolysin (hly) determinant of E. coli or its translocator portion hlyBD. Two different mutations in hlyD alter the cell's susceptibility to vancomycin: mutations in the tolC-homologous region of hlyD increase vancomycin resistance, whereas mutations at the 3′-terminus of hlyD lead to hypersensitivity to vancomycin and to the accumulation of large periplasmic and cytoplasmic pools of this antibiotic in E. coli. These effects are only observed in the presence of functional HlyB and TolC, the two other components of the hemolysin secretion machinery. A defect in TolC causes hyperresistance to vancomycin, even when present together with a mutant HlyD protein which in the presence of TolC renders E. coli hypersensitive to vancomycin. Lipid bilayer experiments in vitro revealed specific interactions between TolC and vancomycin or HlyD protein. Second-site suppressor mutations in hlyD and hlyB were obtained, which abolish the hypersensitive phenotype caused by the 3′-terminal mutations in hlyD. Our results are compatible with the idea that (a) TolC, together with the TolC-homologous part of HlyD, forms a pore in the outer membrane through which hemolysin is released and vancomycin taken up; and (b) the C-terminal sequence of HlyD interacts with periplasmic loop(s) of HlyB to form a closed channel spanning the periplasm.
    Type of Medium: Electronic Resource
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