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  • Springer  (73)
  • 1985-1989  (73)
  • 1
    Electronic Resource
    Electronic Resource
    Dependence of cell membrane conductances on bathing solution HCO 3 − /CO2 inNecturus gallbladder (1988)
    Springer
    The journal of membrane biology 102 (1988), S. 163-174 
    Details
    ISSN: 1432-1424
    Keywords: chloride transport ; equivalent circuit ; cable analysis ; fluid transport ; ouffers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The effects of bathing solution HCO 3 − /CO2 concentrations on baseline cell membrane voltages and resistances were measured inNecturus gallbladder epithelium with conventional intracellular microelectrode techniques. Gallbladders were bathed in either low HCO 3 − /CO2 Ringer's solutions (2.4mm HCO 3 − /air or 1mm HEPES/air) or a high HCO 3 − /CO2 Ringer's (10mm HCO 3 − /1% CO2). The principal finding of these studies was that the apical membrane fractional resistance (fR a) was higher in tissues bathed in the 10mm HCO 3 − /CO2 Ringer's, averaging 0.87±0.06, whereasfR a averaged 0.63±0.07 and 0.48±0.08 in 2.4mm HCO 3 − and 1mm HEPES, respectively. Intraepithelial cable analysis was employed to obtain estimates of the individual apical (R a) and basolateral membrane (R b) resistances in tissues bathed in 10mm HCO 3 − /1% CO2 Ringer's. Compared to previous resistance measurements obtained in tissues bathed in a low HCO 3 − /CO2 Ringer's, the higher value offR a was found to be due to both an increase inR a and a decrease inR b. The higher values offR a and lower values ofR b confirm the recent observations of others. To ascertain the pathways responsible for these effects, cell membrane voltages were measured during serosal solution K+ and Cl− substitutions. The results of these studies suggest that an electrodiffusive Cl− transport mechanism exists at the basolateral membrane of tissues bathed in a 10mm HCO 3 − /1% CO2 Ringer's, which can explain in part the fall inR b. The above observations are discussed in terms of a stimulatory effect of solution [HCO 3 − /PCO2 on transepithelial fluid transport, which results in adaptive changes in the conductive properties of the apical and basolateral membranes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870454
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  • 2
    Electronic Resource
    Electronic Resource
    Voltage- and time dependence of apical membrane conductance during current clamp inNecturus gallbladder epithelium (1988)
    Springer
    The journal of membrane biology 103 (1988), S. 191-204 
    Details
    ISSN: 1432-1424
    Keywords: voltage-dependent K+ channel ; TEA+ ; barium ; circuit analysis ; cable analysis ; current-voltage relationship
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The effects of short (1 sec) and long (1 min) transepithelial current clamps on membrane voltages and resistances ofNecturus gallbladder were investigated. Transepithelial and cell membrane current-voltage relationships determined from 1-sec clamps revealed that: a) depolarization of the apical membrane voltage (V mc) results in a marked decrease in apical membrane fractional resistance (fR a), whereas hyperpolarization ofV mc results in either no change infR a or a small increase, and b) the voltage-dependent changes infR a are essentially complete within 500 msec. Exposure of the tissue to 5mm TEA+ on the mucosal side caused no significant change in baselineV mc (−69±2 mV) and yet virtually abolished the voltage dependence offR a. A possible interpretation of these results is that two types of K+ channels exist in the apical membrane, with different voltage dependencies and TEA+ sensitivities. Acidification or Ba2+ addition to the mucosal solution also reduced the voltage-dependent changes infR a. The time courses of the changes infR a and in the cable properties of the epithelium were assessed during 1-min transepithelial current clamps (±200 μA/cm2). No secondary change infR a was observed with mucosa-to-serosa currents, but a slow TEA+-sensitive decrease infR a (half-time of seconds) was evident with serosa-to-mucosa currents. Cable analysis experiments demonstrated that the initial (〈500 msec) voltage-dependent decrease infR a is due to a fall in apical membrane resistance. The later decrease infR a is due to changes in both cell membrane resistances attributable to the increase in transcellular current flow resulting from a fall in paracellular conductance. The voltage dependence of the apical membrane conductance is a more significant problem in estimatingfR a than the current-induced effects on the lateral intercellular spaces. In principle, TEA+ can be used to prevent the nonlinear behavior ofR a during measurements of the voltage divider or membrane resistance ratio.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870949
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  • 3
    Electronic Resource
    Electronic Resource
    Pseudocopulation of an orchid by male ants: a test of two hypotheses accounting for the rarity of ant pollination (1987)
    Springer
    Oecologia 73 (1987), S. 522-524 
    Details
    ISSN: 1432-1939
    Keywords: Ant pollination ; Orchid ; Pseudocopulation ; Metapleural gland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The orchid Leporella fimbriata is pollinated by pseudocopulation with winged males of the ant Myrmecia urens. This recently studied interaction provides a unique opportunity to examine the two current hypotheses concerning the apparent rarity of ant pollination systems worldwide. The first hypothesis requires a series of specialized growth forms and floral characteristics regarded as adaptations to ant pollination. L. fimbriata does not possess them. The second considers the pollenicidal effects of secretions from the metapleural gland of ants. These glands are absent in M. urens males and it may be that the occurrence of ant pollination requires the absence of metapleural glands in the vector.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00379410
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  • 4
    Electronic Resource
    Electronic Resource
    Plant stress and insect behavior: cottonwood, ozone and the feeding and oviposition preference of a beetle (1988)
    Springer
    Oecologia 76 (1988), S. 51-56 
    Details
    ISSN: 1432-1939
    Keywords: Plagiodera versicolora ; Populus deltoides ; Clones ; Damage distribution ; Community structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Adults and larvae of the beetle Plagiodera versicolora preferred to feed on and consumed more of cottonwood, Populus deltoides, plant material that had been previously exposed to an acute dose of ozone (0.20 ppm, 5 h), compared to controls in choice experiments. However, females preferred to oviposit on the unexposed controls. Results were consistent for 2 cottonwood clones over 3 years in disc, leaf and whole-plant choice tests. The differential feeding and oviposition response of this insect to stressed plants could have at least 3 unexpected consequences: 1. An immediate increase in damage to stressed trees, but a subsequent decrease in damage. 2. A subsequent increase in damage to unstressed adjacent trees. 3. Changes in the insect and pathogen communities of both stressed and unstressed trees. These complex scenarios show that predicting outcomes of plant stress on plant-insect interactions will require comprchensive examination of behavioral, growth and reproductive responses of insects to stressed plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00379599
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  • 5
    Electronic Resource
    Electronic Resource
    Plant stress and insect performance: cottonwood, ozone and a leaf beetle (1988)
    Springer
    Oecologia 76 (1988), S. 57-61 
    Details
    ISSN: 1432-1939
    Keywords: Plagiodera versicolora ; Plant stress ; Populus deltoides ; Ozone effects ; Insect fitness
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Leaf area consumption rates, development rates, survivorship, and fecundity of the imported willow leaf beetle (Plagiodera versicolora Laich) were examined on two clones of eastern cottonwood which were previously exposed to ozone or charcoal-filtered air. P. versicolora consumed more ozone treated foliage, but were more fecund when reared on charcoal-filtered air treated plants. Beetle development rates and survivorship were not significantly different on treated and control cottonwoods. We concluded that: 1) Ozone fumigation of cottonwood reduced foliage quality, and the reproductive success and overall performance of P. versicolora. 2) increased foliage consumption by beetles was probably a mechanism compensating for decreases in foliage quality. 3) Reductions in beetle fecundity were due to an initial reduction in oviposition rates. 4) Beetle feeding preference did not correlate with the suitability of foliage for beetle performance. These results are discussed in relation to the impact of air pollution on plant-insect interactions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00379600
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  • 6
    Electronic Resource
    Electronic Resource
    Effects of multiple stresses on radish growth and resource allocation (1989)
    Springer
    Oecologia 81 (1989), S. 124-131 
    Details
    ISSN: 1432-1939
    Keywords: Plant stress ; Raphanus sativus X raphanistrum ; Air pollution effects ; Plant nutrition ; Physiological responses
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Acclimation of wild radish plants to a simultaneous combination of SO2 fumigation and decreasing nitrate availability was investigated. Plants were grown for 24 d under continuous daytime (10h) exposure to 0 or 0.4 ppm SO2 and were grown in a nutrient solution with stable nitrate concentrations of 100 μM for the first 15 d, 50 μM from day 15 to day 19, and 25 μM from day 19 to day 24. Analysis of relative growth rates (RGR) showed that radish plants responded rapidly to changes in nitrate availability and that SO2 treatment affected those responses. Shoot RGR of plants from both treatments and root RGR of control plants showed rapid declines and subsequent recoveries in response to decreasing nitrate availability. Root RGR of SO2-treated plants declined rapidly in response to decreased nitrate availability, but did not recover as quickly or completely as root RGR of control plants. Analysis of specific leaf weights and tissue nitrogen concentrations showed that control plants had significantly higher amounts of nitrogen in tissues after nitrate availability was lowered, and had higher rates of nitrate uptake in comparison to SO2-treated plants; especially when nitrate availability was highest. Furthermore, control plants had temporarily higher rates of root respiration in comparison to SO2-treated plants, suggesting that control plants temporarily allocated more resources to physiological processes occurring in roots, such as nutrient uptake. Although SO2-induced changes in growth and resource allocation of plants were relatively small, it was probable that SO2 treatment of radish plants affected plant nitrogen balance, and subsequently affected the ability of plants to respond to decreased nitrate availibility, by affecting resource partitioning to nitrate uptake and root growth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00377021
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  • 7
    Electronic Resource
    Electronic Resource
    Foraging behavior of cackling Canada Goose goslings: implications for the roles of food availability and processing rate (1988)
    Springer
    Oecologia 75 (1988), S. 119-124 
    Details
    ISSN: 1432-1939
    Keywords: Canada Goose ; Digestion ; Foraging ; Grazing ; Tundra
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Time spent foraging (and in other activities), rate of pecking at food items and length of foraging and nonforaging periods were studied in cackling Canada goose (Branta canadensis minima) goslings during brood-rearing on the Yukon-Kuskokwim Delta, Alaska in 1978 and 1979. Brood density on the study area was twice as high in 1978 (23 broods) as in 1979 (12 broods) owing in part to annual variation in nesting density and success. Peck-rates were lower in meadows during 1978 than in 1979. There was no between-year difference in time spent foraging prior to the adult molt (59% of daylight hours) but during molt, goslings spent more time feeding in 1978 (70%) than in 1979 (56%). Prior to the adult molt, 12.2 and 11.9 hours were spent feeding each day in 1978 and 1979 respectively, whereas goslings fed for 13.4 and 10.6 hours daily, in the two years during molting and fledging. Increased foraging time during the molt in 1978 completely compensated for lower peck rates so that total number of pecks per day during this period were similar in 1978 (62,800 pecks/d) and 1979 (57,900 pecks/d). Elsewhere, we reported that cackling geese significantly reduced the availability of their preferred food in 1979 and this food comprised a smaller proportion of the diet in 1978 than 1979. This variation in diet suggests that preferred foods were less available at higher brood densities, resulting in annual variation in foraging behavior. Lengths of foraging periods increased during brood-rearing in both years but were longer on average in 1978. There was no seasonal or between year variation in the length of nonforaging periods. The alternating pattern of foraging and nonforaging periods suggests that rate of processing limits rate of food intake because a relatively constant period of time was regularly required to empty the esophagus before foraging could be resumed. The restriction of food intake by digestive processes increased the importance of dietary nutrient concentrations because low nutrient concentrations could not be compensated for by higher rates of food intake.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00378824
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  • 8
    Electronic Resource
    Electronic Resource
    Residues of chlorinated phenols and phenoxy acid herbicides in the urine of Arkansas children (1989)
    Springer
    Archives of environmental contamination and toxicology 18 (1989), S. 469-474 
    Details
    ISSN: 1432-0703
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Medicine
    Notes: Abstract Urine samples from 197 Arkansas children were analyzed for eight chlorinated phenols and four chlorinated phenoxy herbicides by using a new procedure that combined gas chromatography with tandem mass spectrometry. With the detection limit of 1 part per billion (ppb), six of these pesticides were detected in more than 10% of the samples. 2,5-Dichlorophenol (a metabolite ofp-dichlorobenzene), and pentachlorophenol were detected in 96% and 100%, respectively, of the children's urine at median concentrations of 9 ppb and 14 ppb, respectively. 2,4,5-Trichlorophenol was detected in 54% of the children's urine at a median concentration of 1 ppb. One trichlorophenol and three other dichlorophenols were found in 3% to 27% of the samples. The herbicide 2,4-dichlorophenoxyacetic acid was observed in 20% of all samples. The concentrations of all analytes are reported as background or reference levels for use in future studies. The finding of 2,5-dichlorophenol as a ubiquitous contaminant merits further study.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01055011
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  • 9
    Electronic Resource
    Electronic Resource
    The origin of mutant cells: mechanisms by whichSaccharomyces cerevisiae produces cells homoplasmic for new mitochondrial mutations (1985)
    Springer
    Current genetics 9 (1985), S. 627-640 
    Details
    ISSN: 1432-0983
    Keywords: Mitochondria ; Mutation ; Yeast ; Selection ; Random drift
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Haploid yeast cells have about 50 copies of the mitochondrial genome, and a mutational event is unlikely to affect more than one of these at a time. This raises the question of how such cells, or their progeny, become fixed (homoplasmic) for the mutant alele. We have tested the roles of six hypothetical mechanisms in producing erythromycin-resistant mutant cells: (i) random partitioning of mitochondrial genomes at cell division; (ii) intracellular selection for mtDNA molecules of one genotype; (iii) intracellular random drift of mitochondrial allele frequencies; (iv) intercellular selection for cells of a particular mitochondrial genotype; (v) induction of mitochondrial gene mutations by the antibiotic used to select mutants; and (vi) reduction in the number of mitochondrial genomes per cell by the antibiotic. Our experiments indicate that intracellular selection plays the major role in producing erythromycin-resistant mutant cells in the presence of the antibiotic. In the absence of the antibiotic, the combined effects of random drift and random partitioning are most important in determining the fate of new mutations, most of which are lost rather than fixed. Our experiments provide no evidence for mutation induction or ploidy reduction by erythromycin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00449815
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  • 10
    Electronic Resource
    Electronic Resource
    A method to create simplified versions of existing habitat suitability index (HSI) models (1988)
    Springer
    Environmental management 12 (1988), S. 79-83 
    Details
    ISSN: 1432-1009
    Keywords: Habitat evaluation procedures ; Habitat quality ; Habitat suitability index models ; Impact assessment ; Wildlife management
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The habitat evaluation procedures (HEP), developed by the US Fish and Wildlife Service, are widely used in the United States to determine the impacts of major construction projects on fish and wildlife habitats. HEP relies heavily on habitat suitability index (HSI) models that use measurements of important habitat characteristics to rate habitat quality for a species on a scale of 0 (unsuitable) to 1.0 (optimal). This report describes a method to simplify existing HSI models to reduce the time and expense involved in sampling habitat variables. Simplified models for three species produced HSI values within 0.2 of those predicted by the original models 90% of the time. Simplified models are particularly useful for rapid habitat inventories and evaluations, wildlife management, and impact assessments in extensive areas or with limited time and personnel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01867379
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