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  • 1
    Electronic Resource
    Electronic Resource
    Phyletic aspects of the distribution of 3-hydroxyretinal in the class insecta (1990)
    Springer
    Journal of molecular evolution 30 (1990), S. 72-84 
    Details
    ISSN: 1432-1432
    Keywords: Retinoids ; Chromophore ; 3-Hydroxyretinal ; Retinal ; Insect phylogeny ; Insect eyes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The distribution of 3-hydroxyretinal (R3), a recently discovered retinoid used as the visual pigment chromophore in some insects, was investigated in the class Insecta using HPLC technology. We studied 138 species in 24 orders, sampling from a wide range of taxonomic groups as well as varied habitats. In addition to groups already known to have R3, we find this retinoid in Hemiptera (suborder Heteroptera), Plecoptera, Megaloptera, and Hymenoptera. We also find retinal (R1) in Hemiptera (suborder Homoptera), Mecoptera, and Trichoptera, groups previously thought to have only R3. The pattern of R3 occurrence indicates that this retinoid cannot be considered a phylogenetic marker, having a scattered distribution in the class Insecta as well as within some orders of insects. Several environmental factors that might influence the selection of chromophore have been considered, but none correlates with its distribution. The evolutionary reasons for the pattern of occurrence of R3 therefore remain unknown.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02102454
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  • 2
    Electronic Resource
    Electronic Resource
    Electrical properties of parenchymal cell membranes in the oat coleoptile (1972)
    Springer
    Planta 102 (1972), S. 302-323 
    Details
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Parenchymal cells of oat (Avena sativa) coleoptiles had an osmotic concentration of 410 mM (determined by plasmolysis); of this only 22 mM was K+ and 1 mM Na+ (flame photometry). Cells were impaled with micropipette electrodes. Iontophoretic injection of the dye Niagara sky-blue from the micropipette showed that the tip of the electrode penetrated the vacuole. When sections of tissue were immersed in a solution of 22 mM KCl, 1 mM CaCl2, and 50 mM glucose, average membrane potential was found to be 38.5 mV inside negative specific membrane resistance was ∼510 Ω cm2, and specific membrane capacitance, ∼2 μf cm-2. The cell membranes showed 〈25% retification and no electrical excitability. Electrotonic coupling of adjacent cells could not be demonstrated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00386616
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  • 3
    Electronic Resource
    Electronic Resource
    The interpretation of intracellular measurements of membrane potential, resistance, and coupling in cells of higher plants (1978)
    Springer
    Planta 143 (1978), S. 267-274 
    Details
    ISSN: 1432-2048
    Keywords: Cells (electric properties) ; Coleoptiles ; Electrical parameters ; Intercellular coupling ; Intracellular recording ; Membrane resistance ; Microelectrodes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Results of microelectrode impalements of parenchymal cells of coleoptiles made in several different laboratories differ widely. The highest membrane potentials correlate with lower input resistance and the presence of intercellular coupling, whereas high input resistance seems to be associated with an absence of measurable coupling and possibly lower membrane potentials. In this paper we demonstrate that these results are consistent with (1) a tonoplast resistance several times greater than the input resistance of the cytoplasmic compartment, and (2) the presence of variable amounts of shunting introduced by insertion of the microelectrode through the cell membranes. The general consequences of this hypothesis are developed quantitatively. If the ideas are applicable to other tissues of higher plants-and on this point the evidence is still insufficient to judgeboth the design of experiments and the interpretation of measurements made with microelectrodes will have to be reevaluated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00391997
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  • 4
    Electronic Resource
    Electronic Resource
    Quantitative predictions for the chemiosmotic uptake of auxin (1981)
    Springer
    Planta 153 (1981), S. 25-33 
    Details
    ISSN: 1432-2048
    Keywords: Auxin (cellular uptake models, carriers, cotransport, symport) ; Chemiosmotic model for weak acid uptake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract 1. The predictions of a general kinetic model for the chemiosmotic uptake of auxin and other weak acids are compared with experimental results for the auxin indoleacetic acid. The proposed mechanism involves diffusional flux of undissociated acid, a saturable, voltage-sensitive flux of anion (A-), and a carrier-mediated symport of H+ and A-, all operating in parallel. During much of uptake, the electrochemical gradients are such that the net symport and the net anion flux are in opposition: the symport contributes more to influx; the anion path, to efflux. The voltage-sensitive flux of A- therefore constitutes a “leak”. 2. The presence of a symport, whose carrier can distribute across the membrane in response to the internal and external concentrations of auxin, can speed the rate of uptake, but does not by itself alter the accumulation of auxin at equilibrium. 3. The accumulation ratio at equilibrium is less at low concentrations of auxin than at higher concentrations, indicating the presence of a saturable anion path. The concentration dependence of the transition depends on several factors, and is not a reliable indicator of the A--carrier binding constant. 4. Observed uptake near neutral pH appears larger than is consistent with a voltage-sensitive anion flux being the only carrier-mediated path across the membrane. This observation provides indirect evidence for the presence of an auxin-proton symport in addition to a saturable A- carrier. 5. The change in kinetics of uptake of [3H]indole-3-acetic acid (IAA), observed as the total concentration of IAA is raised from 0.1 to 100 μM, is consistent with either (i) a symport that saturates at low concentrations, or (ii) activation of an A- efflux by intermediate concentrations of auxin. 6. The data on the concentration dependence of uptake of auxin are not consistent with a multi-proton symport.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00385314
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  • 5
    Electronic Resource
    Electronic Resource
    Dark adaptation, sensitivity, and rhodopsin level in the eye of the lobster,Homarus (1977)
    Springer
    Journal of comparative physiology 120 (1977), S. 143-159 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Dark adaptation of living lobsters was measured by recording the ERG at several temperatures in the range 5–20 °C following adapting flashes that convert about 70% of the rhodopsin to metarhodopsin. Recovery of log threshold is rapid, and at 10–20° is nearly complete in 10 min. Only at 5 °C is dark adaptation significantly slowed. Comparison of dark adaptation with data on regeneration of pigment (Bruno et al., 1977) is consistent with the hypothesis that as rhodopsin concentration rises and falls, its only effect on sensitivity is to alter the probability of quantum catch. This interpretation is further bolstered by observations on winter lobsters that have a 70% deficiency of rhodopsin without the concomitant increase in metarhodopsin that accompanies light adaptation. No effect of metarhodopsin on sensitivity was detected. These experiments support the growing body of evidence indicating that the relationship between rhodopsin concentration and log threshold is fundamentally different in the rhabdomeric photoreceptors of invertebrates and the rods and cones of vertebrates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00619311
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  • 6
    Electronic Resource
    Electronic Resource
    Discrimination of colors by the black-chinned hummingbird,Archilochus alexandri (1979)
    Springer
    Journal of comparative physiology 130 (1979), S. 209-220 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The color vision of a population of black-chinned hummingbirds was studied by behavioral methods. Birds were attracted to feeders equipped with tungsten lamps and interference filters. Results are based on counts of approximately 5700 visits by 92 ± 5 birds. Population size was estimated by mistnetting and marking 29 hummingbirds, 22 of which could be recognized individually during the course of the experiments. Following experience with red (620 nm) at all feeders, the birds showed a modest tendency to visit red (620 nm, 650 nm) and blue (490 nm) rather than intermediate greens and yellows. When sugar was presented at only one wavelength, however, choices became much sharper. When positions of the feeders were randomized, trained birds selected feeders on the basis of hue. Brightness was not used as a significant cue. This finding thus provides a more rigorous demonstration of color vision in hummingbirds than has heretofore been available. Either position or color could be learned in several hours (6–22 visits). Red (620 nm) and green (546 nm) were learned at the same rate. Two different (and opposing) color associations could be learned simultaneously at sites approximately 30 m apart. Discrimination of hue was measured following training to each of four wavelengths: 620, 590, 546, and 480 nm. Light from interference filters with transmission maxima at 546 and 550 nm were differentiated by the birds to a statistically significant extent. 546 and 590 nm appear to lie near the boundaries of hues; a boundary near 540 nm is found in pigeon but not human color vision.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00614607
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  • 7
    Electronic Resource
    Electronic Resource
    Responses of crayfish photoreceptor cells following intense light adaptation (1986)
    Springer
    Journal of comparative physiology 158 (1986), S. 35-42 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary After intense orange adapting exposures that convert 80% of the rhodopsin in the eye to metarhodopsin, rhabdoms become covered with accessory pigment and appear to lose some microvillar order. Only after a delay of hours or even days is the metarhodopsin replaced by rhodopsin (Cronin and Goldsmith 1984). After 24 h of dark adaptation, when there has been little recovery of visual pigment, the photoreceptor cells have normal resting potentials and input resistances, and the reversal potential of the light response is 10–15 mV (inside positive), unchanged from controls. The log V vs log I curve is shifted about 0.6 log units to the right on the energy axis, quantitatively consistent with the decrease in the probability of quantum catch expected from the lowered concentration of rhodopsin in the rhabdoms. Furthermore, at 24 h the photoreceptors exhibit a broader spectral sensitivity than controls, which is also expected from accumulations of metarhodopsin in the rhabdoms. In three other respects, however, the transduction process appears to be light adapted: (i) The voltage responses are more phasic than those of control photoreceptors. (ii) The relatively larger effect (compared to controls) of low extracellular Ca++ (1 mmol/1 EGTA) in potentiating the photoresponses suggests that the photoreceptors may have elevated levels of free cytoplasmic Ca++. (iii) The saturating depolarization is only about 30% as large as the maximal receptor potentials of contralateral, dark controls, and by that measure the log V-log I curve is shifted downward by 0.54 log units. The gain (change in conductance per absorbed photon) therefore appears to have been diminished.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00614518
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  • 8
    Electronic Resource
    Electronic Resource
    The visual pigment and visual cycle of the lobster,Homarus (1977)
    Springer
    Journal of comparative physiology 120 (1977), S. 123-142 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The visual pigment of the American lobster,Homarus americanus, has been studied in individual isolated rhabdoms by microspectrophotometry. Lobster rhodopsin has λmax at 515 nm and is converted by light to a stable metarhodopsin with λmax at 490 nm. These figures are in good agreement with corresponding values obtained by Wald and Hubbard (1957) in digitonin extracts. Photoregeneration of rhodopsin to metarhodopsin is also observed. The absorbance spectrum of lobster metarhodopsin is invariant with pH in the range 5.4–9, indicating that even after isomerization of the chromophore fromcis totrans, the binding site of the chromophore remains sequestered from the solvent environment. Total axial density of the lobster rhabdom to unpolarized light is about 0.7. As described for several other Crustacea, aldehyde fixation renders the metarhodopsin susceptible to photobleaching, a process that is faster at alkaline than at neutral or acid pH. Small amounts of a photoproduct with λmax at 370 nm are occasionally seen. A slower dark bleaching of lobster rhabdoms (τ1/2−2 h) also occurs, frequently through intermediates with absorption similar to metarhodopsin. The molar extinction coefficient of metarhodopsin is about 1.2 times greater than that of rhodopsin, each measured at their respective λmax. Isomerization of the chromophore fromcis totrans is accompanied by a change in the orientation of the absorption vector of about 3°. The absorption vector of metarhodopsin is either tilted more steeply into the membrane or is less tightly oriented with respect to the microvillar axes. When living lobsters are kept at room temperature, light adaptation does not result in an accumulation of metarhodopsin. At 4 °C, however, the same adapting lights cause a reduction of rhodopsin and an increase in metarhodopsin. There is thus a temperature-sensitive regeneration mechanism that supplements photoregeneration. Following 1 ms, 0.1 joule xenon flashes that convert about 70% of the rhodopsin to metarhodopsin in vivo, dark regeneration occurs in the living eye with half-times of about 25 and 55 min at 22 °C and 15 °C respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00619310
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  • 9
    Electronic Resource
    Electronic Resource
    Photosensitivity of retinular cells in white-eyed crayfish (Procambarus clarkii) (1977)
    Springer
    Journal of comparative physiology 122 (1977), S. 273-288 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. The eyes of a white-eyed mutant of the crayfishProcambarus clarkii have been examined by several techniques. The white phenotype is due to the absence of the distal and retinular screening pigments. The accessory pigments, around the basal ends of the rhabdoms, are still present. As in the wild-type, the accessory pigments are white in reflected light and brown in transmitted light. 2. Animals kept in darkness for several days have normal rhabdoms. Difference spectra for total bleaches have λmax at 531 nm, and the metarhodopsin has λmax at 515 nm. These pigments are spectrally indistinguishable from the rhodopsin and metarhodopsin of wild-type crayfish. 3. Several days exposure to normal indoor lighting causes extensive atrophy of the rhabdom and loss of visual pigment, as well as a 70-fold decrease in sensitivity. 4. Spectral sensitivity of the eye (ERG) has λmax at about 560 nm (close to the wild-type) after several days in darkness, but shifts to 546 nm as the rhabdoms atrophy. Neither curve is displaced by adaptation with blue light. Both values are red-shifted from the λmax of the pigment of the rhabdom, most likely by the accessory screening pigment. The shift is smaller when the screening pigment is separated from the (atrophied) rhabdom by several μm. 5. If the distal screening pigments of the wild-type are removed surgically and precautions are taken to stabilize the effects of remaining screening pigments, intracellular recordings have λmax at 562 nm and show much less variation than has previously been reported. 6. The mutant, like the wild-type, has violet receptors whose contribution to the ERG is unmasked by long wavelength adaptation. Their λmax is at 440 nm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00611895
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  • 10
    Electronic Resource
    Electronic Resource
    Microspectrophotometry of the visual pigment of the spider crab Libinia emarginata (1969)
    Springer
    Journal of comparative physiology 65 (1969), S. 218-232 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Description / Table of Contents: Zusammenfassung Die isolierten, dunkeladaptierten Rhabdome von Libinia emarginata wurden mikrospektrophotometrisch untersucht, um die Sehfarbstoffe und ihre lichtempfindlichen Eigenschaften zu entdecken. Die Rhabdome enthalten ein einziges Pigment (λmax 493 nm). Nach einer Bestrahlungszeit von 1 min mit hellem orangem Licht entsteht ein lichtfestes Photoprodukt mit beinahe dem gleichen λmax wie das ursprüngliche Pigment, aber mit etwas größerer Absorption gegen die langwellige Seite des Absorptionsmaximums hin. Das Pigment von Libinia-Rhabdomen bleicht langsam aus, wenn man es orangem oder gelbem Licht in Gegenwart von 5% Glutaraldehyd aussetzt. Werden richtig orientierte Rhabdome von der Seite belichtet, so zeigt das lichtempfindliche Pigment teils Isotropismus teils Dichroismus. Im ersten Fall sind die Mikrovilli parallel zur Richtung des Meßstrahles orientiert, im zweiten Fall stehen sie senkrecht dazu. Das größte Dichroismus-Verhältnis liegt bei 2. Man erhält die größte Absorption, wenn die Polarisationsrichtung parallel zur Achse der Mikrovilli steht.
    Notes: Summary Isolated dark-adapted rhabdoms from the spider crab Libinia emarginata were examined by microspectrophotometry to determine the visual pigments present and their light-sensitive characteristics. The rhabdoms contain a single pigment with λmax=493 nm. Upon one minute irradiation with bright orange light this pigment forms a light-stable photoproduct with nearly the same λmax as the parent pigment but with slightly greater absorption to the long wavelength side of the absorption peak. On exposure to orange or yellow light in the presence of 5% glutaraldehyde, however, the pigment of Libinia rhabdoms bleaches slowly. The photosensitive pigment of properly oriented, transversely illuminated rhabdoms shows isotropic and dichroic regions, corresponding to layers of the rhabdom in which the microvilli are respectively parallel and perpendicular to the direction of propagation of the measuring beam. The maximum dichroic ratio is about 2, with most absorption when the plane of polarization is parallel to the microvillar axes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00297684
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