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  • Crassulacean acid metabolism  (2)
  • Cell & Developmental Biology  (1)
  • LEVI-CIVITA SOLUTION  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Crassulacean acid metabolism in tropical dicotyledonous trees of the genusClusia (1987)
    Springer
    Trees 1 (1987), S. 238-247 
    Details
    ISSN: 1432-2285
    Keywords: Citric acid ; Clusia ; Crassulacean acid metabolism ; Malic acid ; Tropics ; Venezuela
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The performance of crassulacean acid metabolism (CAM) by dicotyledonous trees of the genusClusia sampled at three sites in the state of Falcon in northern Venezuela is characterized.Clusia leaves have a somewhat succulent appearance. Unlike leaves of many other CAM plants, which are uniformly built up of very large isodiametric cells, there are distinct layers of palisade and spongy mesophyll, with individual cells being smaller. There is no specialized water storage tissue. δ13C values indicate thatC. multiflora in the elfin-cloud forest on top of Cerro Santa Ana, at ∼800 m altitude, performs C3 photosynthesis (δ13 −27.1‰). However,C. rosea in the tall cloud forest on Cerro Santa Ana (∼600m altitude), andC. rosea andC. alata in the dry forest on Serrania San Luis (∼900 m altitude) perform CAM (δ13C −14.1 to −19.2‰). InC. alta andC. rosea there were large day-night changes in the levels of malic and citric acids ranging from 63 to 240 mmol 1−1 for malid acid and from 35 to 112 mmol 1−1 for citric acid. The sum of the changes in malate and citrate levels accounts for the changes of titratable protons measured. With a day-night change of titratable protons of 768 mmol 1−1 in one of the analyses,C. rosea showed the highest value yet encountered in a CAM plant. Oscillations of free sugars (fructose, glucose, sucrose) and of starch were also analysed in the CAM performingClusia species. Carbon skeletons of the precursors involved in nocturnal malate and citrate synthesis largely derive from free sugars and not from polyglucan. Unlike some other CAM plants, there is no clear and quantitative correlation between day-night changes of organic acid levels and cell sap osmolality.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01816822
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  • 2
    Electronic Resource
    Electronic Resource
    Crassulacean acid metabolism (CAM) in leaves of Aloe arborescens mill (1979)
    Springer
    Planta 145 (1979), S. 357-363 
    Details
    ISSN: 1432-2048
    Keywords: Aloe ; Crassulacean acid metabolism ; CO2 fixation ; Phosphoenolpyruvate-carboxylase ; Water tissue
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In the succulent leaves of Aloe arborescens Mill diurnal oscillations of the malic acid content, being indicative of Crassulacean Acid Metabolism (CAM), were exhibited only by the green mesophyll. In contrast, the malic acid level of the central chloroplast-free water-storing tissue remained constant throughout the day-night cycle. Apart from malate, the green tissue contained high amounts of isocitrat which was lacking in the water tissue. There was no significant transfer from the green mesophyll to the water tissue of 14C fixed originally via dark 14CO2 fixation in the mesophyll. Both isolated mesophyll and water tissue were capable of dark CO2 fixation yielding mainly malate as the first stable product. Both tissues have phosphoenolpyruvate carboxylase. However, the enzymes derived from the both sources could be distinguished by their molecular weights and by their kinetic properties, suggesting different phosphoenolpyruvate carboxylase proteins. The conclusion drawn from the experiments is that in a. arborescens the CAM cycle proceeds exclusively in the green mesophyll and that the water tissue, though capable of malate synthesis via β-carboxylation of phosphoenolpyruvate, behaves as an independent metabolic system where CAM is lacking. This view is supported by the finding that the cell walls bordering the green mesophyll from the water tissue lack plasmodesmata, hence conveniant pathways of metabolite transport.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00388361
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  • 3
    Electronic Resource
    Electronic Resource
    Two Counter-moving Light Beams (1999)
    Springer
    General relativity and gravitation 31 (1999), S. 349-356 
    Details
    ISSN: 1572-9532
    Keywords: CYLINDRICALLY SYMMETRIC STATIC NULL DUST ; LEVI-CIVITA SOLUTION
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The cylindrically symmetric field of two beamsof light shining in opposite directions is studied. Wepresent four static or stationary exact solutions of thecorresponding field equations and compare their properties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026640727307
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  • 4
    Electronic Resource
    Electronic Resource
    Regulation of polyamine transport by polyamines and polyamine analogs (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 155 (1993), S. 399-407 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Regulation of polyamine transport in murine L1210 leukemia cells was characterized in order to better understand its relationship to specific intracellular polyamines and their analogs and to quantitate the sensitivity by which it is controlled. Up-regulation of polyamine uptake was evaluated following a 48-hr treatment with a combination of biosynthetic enzyme inhibitors to deplete intracellular polyamine pools. The latter declined gradually over 48 hr and was accompanied by a steady increase in spermidine (SPD) and spermine (SPM) transport as indicated by rises in Vmax to levels ∼4.5 times higher than control values. Restoration of individual polyamine pools during a 6-hr period following inhibitor treatment revealed that SPD and SPM uptake could not be selectively affected by specific pool changes. The effectiveness of individual polyamines in reversing inhibitor-induced stimulation of uptake was as follows: putrescine 〈 SPD 〈 SPM = the SPM analog, N1, N12-bis(ethyl)spermine (BESPM). In contrast to stimulation of transport, down-regulation by exogenous polyamines or analogs occurred rapidly and in response to subtle increases in intracellular pools. Following a 1-hr exposure to 10 μM BESPM, Vmax values for SPD and SPM fell by 70%, whereas the analog pool increased to only 400-500 pmol/106 cells - about 15-20% of the total polyamine pool (∼2.8 nmol/106 cells). SPM produced nearly identical regulatory effects on transport kinetics. Both BESPM and SPM were even more effective at down-regulating transport that had been previously stimulated four to fivefold by polyamine depletion achieved with enzyme inhibitors. A dose response with BESPM at 48 hr revealed a biphasic effect on uptake whereby concentrations of analog 〈 3 μM produced an increase in SPD and SPM Vmax values, whereas concentrations 3 μM and higher produced a marked suppression of these values. Cells treated with 3 μM BESPM for 2 hr and placed in analog-free medium recovered transport capability in only 3 hr. Thus, whereas stimulation of polyamine transport is a relatively insensitive and slowly responsive process that tends to parallel polyamine depletion, down-regulation of polyamine transport by exogenous polyamines and analogs and its reversal are rapidly responsive events that correlate with relatively small (i.e., 15-20%) changes in intracellular polyamine pools.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041550222
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    Paper (German National Licenses)
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