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  • 1
    Electronic Resource
    Electronic Resource
    Regulation of malic-acid metabolism in Crassulacean-acid-metabolism plants in the dark and light: In-vivo evidence from 13C-labeling patterns after 13CO2 fixation (1988)
    Springer
    Planta 175 (1988), S. 184-192 
    Details
    ISSN: 1432-2048
    Keywords: Carbon dioxide fixation (dark) ; Crassulacean acid metabolism ; Fumarase ; Malic acid ; Phosphoenolpyruvate carboxylase ; Ribulose-1,5-bisphosphate carboxylase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The labeling patterns in malic acid from dark 13CO2 fixation in seven species of succulent plants with Crassulacean acid metabolism were analysed by gas chromatography-mass spectrometry and 13C-nuclear magnetic resonance spectrometry. Only singly labeled malic-acid molecules were detected and on the average, after 12–14 h dark 13CO2 fixation the ratio of [4-13C] to [1-13C] label was 2:1. However the 4-C carboxyl contained from 72 to 50% of the label depending on species and temperature. The 13C enrichment of malate and fumarate was similar. These data confirm those of W. Cockburn and A. McAuley (1975, Plant Physiol. 55, 87–89) and indicate fumarase randomization is responsible for movement of label to 1-C malic acid following carboxylation of phosphoenolpyruvate. The extent of randomization may depend on time and on the balance of malic-acid fluxes between mitochondria and vacuoles. The ratio of labeling in 4-C to 1-C of malic acid which accumulated following 13CO2 fixation in the dark did not change during deacidification in the light and no doubly-labeled molecules of malic acid were detected. These results indicate that further fumarase randomization does not occur in the light, and futile cycling of decarboxylation products of [13C] malic acid (13CO2 or [1-13C]pyruvate) through phosphoenolpyruvate carboxylase does not occur, presumably because malic acid inhibits this enzyme in the light in vivo. Short-term exposure to 13CO2 in the light after deacidification leads to the synthesis of singly and multiply labeled malic acid in these species, as observed by E.W. Ritz et al. (1986, Planta 167, 284–291). In the shortest times, only singly-labeled [4-13C]malate was detected but this may be a consequence of the higher intensity and better detection statistics of this ion cluster during mass spectrometry. We conclude that both phosphoenolpyruvate carboxylase (EC 4.1.1.32) and ribulose-1,5-biphosphate carboxylase (EC 4.1.1.39) are active at this time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00392426
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  • 2
    Electronic Resource
    Electronic Resource
    Control of photosynthesis by the carbohydrate level in leaves of the C4 plant Amaranthus edulis L. (1989)
    Springer
    Planta 177 (1989), S. 515-525 
    Details
    ISSN: 1432-2048
    Keywords: Amaranthus ; Carbohydrate accumulation ; Chilling treatment ; Sucrose inhibition of photosynthesis ; Phloem translocation ; Photosynthesis (C4 plant)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Photosynthesis was studied in relation to the carbohydrate status in intact leaves of the C4 plant Amaranthus edulis. The rate of leaf net CO2 assimilation, stomatal conductance and intercellular partial pressure of CO2 remained constant or showed little decline towards the end of an 8-h period of illumination in ambient air (340 μbar CO2, 21% O2). When sucrose export from the leaf was inhibited by applying a 4-h cold-block treatment (1°C) to the petiole, the rate of photosynthesis rapidly decreased with time. After the removal of the cold block from the petiole, further reduction in photosynthetic rate occurred, and there was no recovery in the subsequent light period. Although stomatal conductance declined with time, intercellular CO2 partial pressure remained relatively constant, indicating that the inhibition of photosynthesis was not primarily caused by changes in stomatal aperture. Analysis of the leaf carbohydrate status showed a five- to sixfold increase in the soluble sugar fraction (mainly sucrose) in comparison with the untreated controls, whereas the starch content was the same. Leaf osmotic potential increased significantly with the accumulation of soluble sugars upon petiole chilling, and leaf water potential became slightly more negative. After 14 h recovery in the dark, photosynthesis returned to its initial maximum value within 1 h of illumination, and this was associated with a decline in leaf carbohydrate levels overnight. These data show that, in Amaranthus edulis, depression in photosynthesis when translocation is impaired is closely related to the accumulation of soluble sugars (sucrose) in source leaves, indicating feedback control of C4 photosynthesis. Possible mechanisms by which sucrose accumulation in the leaf may affect the rate of photosynthesis are discussed with regard to the leaf anatomy of C4 plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00392620
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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