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  • 1
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Using the conventional methods of compartmental analysis has led us to recognize three main compartments in the Lemna cells: the cell-wall, cytoplasm and vacuolc. The half-times of Li+ isotopic exchange were of the order of a few minutes, a few hours and a few days, respectively. The possible existence of a 4th, small, and almost non-exchangeable compartment cannot be excluded. Despite different possible sources of uncertainty (ambiguity of the kinetic solutions, no uniformity of cell types in the plant material, uncertainties in the estimations of electric potentials), the data were consistent with i) Li+ being actively extruded from the cytoplasm, both towards the exterior and the vacuole, ii) the electrochemical potential difference of Li+ being of the order of -25 kj mol across the plasmalemma, and in the range of 5 to 10 kJ mol across the tonoplast, and iii) the passive permeability coefficients of Li+ being in the range of 10 to 10 m s both for the plasmalemma and the tonoplast.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Due to the lack of a convenient radiotracer of Li, we have used the stable isotopes, 6Li and 7Li, for unidirectional flux measurements in Lemna gibba L. (GI). Detection was performed using an ionic microanalyser. The conventional method of compartmental analysis has been improved in several ways. Growth of the plant samples has been taken into consideration. The possible non-uniqueness of the kinetic solution fitting the experimental points has been considered by numerical calculation. The derivatives and not only the direct functions have been used in order to detect whether a constant term had to be added to the first-order terms. The validity of the estimates of the characteristic parameters of transport has been checked by using efflux and influx data simultaneously. The “manipulation-shock” effects have been shown not to be negligible. The kinetic data have no simple biological significance per se, but they can serve to calculate cellular parameters of transport when combined with appropriate stereometric data. These considerations are relevant not only to our present problem, but to any type of compartmental analysis, whatever the plant sample and the absorbed substrate.
    Type of Medium: Electronic Resource
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