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  • desiccation  (2)
  • Heat budget  (1)
  • Phase transitions  (1)
  • membrane  (1)
  • 1
    ISSN: 1573-6881
    Keywords: Phase transitions ; phospholipids ; water ; desiccation ; dehydration ; anhydrobiosis ; imbibition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract Dry phospholipid bilayers are known to undergo transient changes in permeability during rehydration. In this review, we present evidence from which we suggest that this permeability change is due to a gel to liquid-crystaline phase transition accompanying rehydration. If the transition is avoided, as in lipids that remain in gel phase whether dry or rehydrated, the problem of leakage during rehydration is obviated, at least in part. Further, the evidence that the transition temperature for dry bilayers can be depressed by certain sugars is discussed. Finally, we show that these principles can be extended to intact cells. Using pollen grains as a model, we have measured the transition temperature for membrane phospholipids and show that the transition is correlated with physiological measurements including permeability changes and subsequent germination. From theT m values taken from pollen grains at different water contents, we have constructed a phase diagram for the intact pollen that has high predictive value for physiological properties.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-5176
    Keywords: Cyanobacteria ; Nostoc commune ; glycan ; phase transition ; membrane ; desiccation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cells of the cyanobacterium Nostoc commune secrete a complex, high molecular weight, extracellular polysaccharide (EPS) which accumulates to more than 60% of the dry weight of colonies. The EPS was purified from the clonal isolate N. commune DRH1. The midpoint of the membrane phase transition (Tm) of desiccated cells of N. commune CHEN was low (Tm dry = 8 °C) and was comparable to the Tm of rehydrated cells((Tm)H20 = 6 °C). The EPS was not responsible for the depression of Tm. However, the EPS, at low concentrations, inhibited specifically the fusion of phosphatidylcholine membrane vesicles when they were dried in vitro at0% relative humidity (−400 MPa). Low concentrations of a trehalose:sucrose mixture, in a molar ratio which corresponded with that present in cells in vivo, together with small amounts of the EPS, were efficient in preventing leakage of carboxyfloroscein (CF) from membrane vesicles. Freeze-fracture electron microscopy resolved complex changes in the structure of the EPS and the outer membrane in response to rehydration of desiccated cells. The capacity of the EPS to prevent membrane fusion, the maintenance of a low Tm dry in desiccated cells, and the changes in rheological properties of the EPS in response to water availability, constitute what are likely important mechanisms for desiccation tolerance in this cyanobacterium.
    Type of Medium: Electronic Resource
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  • 3
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Publication Date: 2017-01-04
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 1981
    Description: The equatorial Pacific heat flow low, a major oceanic geothermal anomaly centered on the equatorial sediment bulge, was investigated using deeply penetrating heat flow probes (6-11 meters penetration) within three detailed surveys (400 km2) and along over 10,000 km of continuous seismic profiles (CSP). Previous heat flow measurements in this region defined a broad region characterized by a heat flux well below 1 HFU. We report 98 new measurements collected during cruises PLEIADES 3 and KNORR 73-4 that verify the anomalous nature of the heat flux and also define non-linear temperature gradients (concave down). Temperature field disturbances due to perturbations of a purely conductive heat transport regime are incapable of suitably explaining either of these observations . A simple model incorporating heat transport by both conduction and fluid convection through the sediments fits the observations. A volume flux of (hydrothermal) fluid in the range of 10-6 to 10-5 cm3/sec/cm2 (0.1 liter/yr/cm2) is required. The sense of the flow for all measurements exhibiting non-linear gradients is upward out of the sediment column; no evidence for the recharging of the system was observed. Investigation of a well-defined boundary of the low zone at 4°N and 114°W showed a transition from low and variable heat flow to values compatible with thermal models that correlated with a change in the nature of the basement from rough to smooth. A few outcrops occur in the area of rough basement, but otherwise the region is well-sedimented (greater than 200 meters). Measurements within a detailed survey centered at this transition showed a dramatic increase in heat flow from 1.21 HFU to values greater than 3 HFU over a horizontal distance of 10km. A similar transition from non-linear to linear temperature gradients was not observed as nearly every measurement was non-linear. Heat flow measurements located in well-sedimented, outcrop-free areas (A environments) were associated with linear gradients and a heat flux greater than 1 HFU, however, several of these values were well below the theoretical heat flow for the appropriate age crust. Values measured in environments other than A exhibited variable heat flow and non-linear gradients. The average value of measurements located in A environments within the equatorial Pacific heat flow low was 1.37±0.27 HFU. The previously reported average was 0.92±0.48 HFU based on several measurements from L-DGO cruise VEMA 24-3. The average heat flow measured at a survey located outside the low heat flow zone on crust of 55 ±5 m.a. was 1.76 ±0.30 HFU which is in good agreement with the theoretical value of 1.60. The measurements in this survey were not located in A environments suggesting that crustal convection has ceased or is greatly attenuated within crust of this age. Error analysis of the geothermal data reduction using the convective/conductive heat transport model suggests that the volume flux parameter is sensitive to temperature measurement errors greater than a few millidegrees. Volume fluxes less than 10-7 cm/sec are difficult to distinguish from the purely conductive case assuming instrumental accuracies of 0.001°C. Resolution of the volume flux deteriorates as heat flow decreases and is poor for values less than 0.5 HFU. A detailed survey located within the low zone confirmed previous measurements of low heat flow, however, due to the low value of heat flow (about 0.5 HFU) the small-scale variability could not be clearly defined.
    Keywords: Geothermal resources ; Heat budget ; Ocean circulation ; Ocean bottom ; Marine geophysics ; Pleides (Ship) Cruise 3 ; Knorr (Ship : 1970-) Cruise KN73-4
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
    Format: application/pdf
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