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  • 1
    Electronic Resource
    Electronic Resource
    Evidence for a K+ channel in bovine chromaffin granule membranes: single-channel properties and possible bioenergetic significance (1994)
    Springer
    European biophysics journal 23 (1994), S. 263-275 
    Details
    ISSN: 1432-1017
    Keywords: K+ channel ; Chromaffn granule ; Membrane reconstitution ; Planar bilayer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract A K+ channel was incorporated into voltage-clamped planar lipid bilayers from bovine chromaffin granules and resealed granule membranes (“ghosts”). It was not incorporated from plasma membrane-rich fractions from the adrenal medulla. The channel had a conductance of ∼ 400 pS in symmetric 450 mM KCI, with the permeability sequence K+ 〉 Rb+ 〉 Cs+ 〉 Na+ 〉 Li+, and was insensitive to both Ca2+ and charybdotoxin. It exhibited complex gating kinetics, consistent with the presence of multiple open and closed states, and its gating was voltage-dependent. The channels appeared to incorporate into bilayers with the same orientation, and were blocked from one side (the side of vesicle addition) by 0.2-1 mM TEA'. The block was slightly voltage-dependent. Acidification of resealed granule membranes in response to external ATP (which activated the vacuolartype ATPase) was significantly reduced in the presence of 1 mM intralumenal TEACI (with 9 mM KCl), and parallel measurements with the potential-sensitive dye Oxonol V showed that such vesicles tended to develop higher internal-positive membrane potentials than control vesicles containing only 10 mM KCI. 1 mM TEA+ had no effect on proton-pumping activity when applied externally, and did not directly affect either the proton-pumping or ATP hydrolytic activity of the partially-purified ATPase. These results suggest that chromaffin granule membranes contain a TEA+-sensitive K+ channel which may have a role in regulating the vesicle membrane potential.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00213576
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  • 2
    Electronic Resource
    Electronic Resource
    Stomatal resistance of three potato cultivars as influenced by soil water status, humidity and irradiance (1997)
    Springer
    Potato research 40 (1997), S. 47-57 
    Details
    ISSN: 1871-4528
    Keywords: minimum stomatal resistance ; soil water ; Solanum tuberosum L. ; photosynthetic photon flux density ; vapour pressure deficit
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Leaf stomatal resistance varies considerably in response to changes in environmental conditions. Understanding cultivar differences in the response of stomata to these conditions is important for effectively simulating water-use and growth. In this study the stomatal resistance of three field grown potato (Solanum tuberosum L.) cultivars Atlantic. Monona and Norchip was observed in response to photosynthetic photon flux density, leaf to air vapour pressure difference and root zone available soil water. Substantial variation in stomatal resistance was accounted for by functions of the environmental variables for both Monona and Norchip. The explained variation for Atlantic was considerably less. Light saturation occurred near 500 μmol m−2 s−1. Increasing stomatal resistance above 1000 μmol m−2s−1 was also observed but is likely an artifact of stomatal closure on days in which mid-day leaf water potentials dropped below critical levels. Although the leaf presumably insufficient to obtain substantial effects. The soil water status was partially linked to the average 1000 h to 1500 h stomatal resistance on clear, sunny days. Significant differences were observed among the cultivars in the response of stomata to changes in the available soil water.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02407561
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  • 3
    Electronic Resource
    Electronic Resource
    Estimating potato leaf area index for specific cultivars (1997)
    Springer
    Potato research 40 (1997), S. 251-266 
    Details
    ISSN: 1871-4528
    Keywords: LAI ; canopy expansion ; radiation use efficiency ; Solanum tuberosum L. ; soil water
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The growth and duration of crop leaf area determines the amount of solar radiation intercepted by the canopy and therefore influences the extent of photosynthesis, evaporation, transpiration and final dry matter yield. The objective of this study was to develop cultivar specific relationships to estimate the daily leaf area index (LAI) for the potato crop (Solanum tuberosum L.) that included the effects of available soil water. The model is divided into three LAI growth stages, the durations of which are partially related to potato heat units (PHU). The LAI in the first stage is estimated from a cultivar specific leaf area-based radiation use efficiency index with a soil water reduction factor. The second stage involves the maintenance of a constant LAI with the duration related to both PHU and a soil water index that can accelerate senescence. The final stage includes a decrease in the LAI from a maximum to zero in response to a cultivar specific PHU accumulation. Model simulations compared favourably with independent LAI measurements obtained with a LI-COR plant canopy analyzer over two seasons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02358007
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