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  • 1
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Morphometric characteristics of Lemna gibba L. cells have been estimated. The mean relative volumes of the wall, of the cytoplasm and of the vacuoles were 0.03, 0.32 and 0.65, respectively. The distribution of the individual values has been studied: for instance 29% of the cells had a mean relative volume of the vacuoles close to 0.73, 39% to 0.68, 19% to 0.61 and 13% to 0.51. The mean value and distribution of the surface areas of the tonoplast and plasmalemma were also determined. This allows us to discuss the active or passive character of the transport of various substances at the plasmalemma and at the tonoplast, according to the usual flux-ratio approach. The feasibility of such an approach in ordinary (non-giant) living cells is discussed with regard to the degree of reliability of the measurements which can be performed with such cells.
    Type of Medium: Electronic Resource
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  • 2
    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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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 56 (1982), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Plantlets of Bidens pilosus L. “remembered” a symmetry-breaking signal (the puncturing of one of the cotyledons), but expressed it only after being made permissive (by removing the apex). The mean value of the memorization index was 0.52. There was a labile short-term and a well-fixed long-term memory. The memorization process was dependent on the number of stimuli, and on the mineral status of the plant.
    Type of Medium: Electronic Resource
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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 283 (1980), S. 299-302 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Fig. 1 Lithium distribution in a mouse brain, a, Histological preparation stained by Feulgen method, b, Photograph of the corresponding detector (each small black spot which forms the shading seen corresponds to a nuclear reaction on lithium), c, Schematic representation of the brain microanatomy ...
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-2048
    Keywords: Boron ; Foliar nutrition ; Nuclear reactions ; Transport (boron) ; Trifolium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The growth of white clover (Trifolium repens L.) is severely inhibited by boron starvation, but a foliar treatment with boric acid can transitorily alleviate the deficiency symptoms. The 10B(n ,α)7 Li nuclear reaction has been used to study boron transport in the plant after foliar application. More than 98% of the boron supplied remained at the point where it was applied to the leaves, and less than 2% was useful to the growth of the treated plant. This small “efficient” portion of boron was quite mobile. It was distributed to the different parts of the plant, then was transferred from the oldest parts to the newly formed leaves. Physiological and agronomical implications of these data are discussed.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-2048
    Keywords: Axillary bud ; Bidens ; Bud (axillary) ; Memorization ; Morphogenesis (memorization)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Plantlets of Bidens pilosus L., considered to be basically symmetrical, can be “lateralized” (A/B) by being administered a “symmetry-breaking” signal such as puncturing one of the plant cotyledons. The induced asymmetry remains latent as long as the plants have not been made “permissive”, i.e. as long as the plant apex is left functioning. When the apex has been removed (plant “decapitation”), the latent asymmetry is expressed by one of the cotyledonary buds (a/b) statistically beginning to elongate before the other. The interval of time between delivering the “symmetry-breaking” signal and making the plant “permissive” is the “memorization-time”, Δt. Memorization can be quantified by using a “precedence index”, q, the values of which range from 0 (no detectable asymmetry with regard to bud growth) to ±1 (bud growth perfectly asymmetric in favour of either bud b or a). Even for memorization times, Δt, up to 14 d, q-values up to 0.4 (or even larger) are observed. Various experimental characteristics (e.g. light, temperature, presence or absence of the root system) but not the plant age can affect the q-values, at the moment when the treatments are performed, at least in the range of 6 to 25 d. Combining several puncturing treatments either increases or decreases the q-values, depending on the nature of these treatments and the time-intervals, δt, between them. Symmetrically removing both cotyledons in the minutes following the puncturing of one of them does not significantly alter the results, which means that the “symmetry-breaking” message is rapidly transported and memorized within the plant. Non-traumatic asymmetrical treatments (droplets of saline solutions, light-gradients) can also act as symmetry-breaking signals and be memorized. Plants other than Bidens are likely to possess similar memorization ability, although the q-values observed up to now have not been very large.
    Type of Medium: Electronic Resource
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