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  • 1
    Electronic Resource
    Electronic Resource
    Water stress provokes a generalized increase in phosphatidylcholine turnover in barley leaves (1982)
    Springer
    Planta 155 (1982), S. 493-501 
    Details
    ISSN: 1432-2048
    Keywords: Betaine biosynthesis ; Glycinebetaine ; Hordeum (stress) ; Phospholipid turnover ; Water stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Water and salt stress promote betaine accumulation in leaves of barley (Hordeum vulgare L.) by accelerating the de-novo synthesis of betaine, via choline. Previous radiotracer kinetic studies have implicated stress-enhanced turnover of the choline moiety of phosphatidylcholine (PC) as a major source of choline for betaine synthesis. Two approaches have therefore been followed to show whether stress-induced PC turnover is a cellor organelle-specific phenomenon, or a generalized one. In the first approach, [3H]ethanolamine of high specific activity was supplied to second leaves of unstressed and water-stressed barley plants; after 1 h, paired sections of tissue were excised from each leaf, one for extraction and analysis of [3H]metabolites and the other for autoradiography. The3H-activity remaining in the leaf tissue after washing out the water-soluble3H-metabolites during preparation for autoradiography was taken to be mainly in phospholipids. In unstressed leaves, [3H]phosphatidylethanolamine (PE) was the major labeled phospholipid, whereas there were approximately equal amounts of [3H]PE and [3H]PC in stressed leaves. At the light-microscope level, silver grains were associated with all living cells in both unstressed and stressed leaves; grains were concentrated in the cytoplasmic regions of highly vacuolate mesophyll cells, and were distributed throughout densely cytoplasmic vascular parenchyma. At the electron-microscope level, silver grains were not confined to any particular types of membranes in unstressed or stressed leaves. In the second approach, second leaves of stressed plants received a 1-h pulse of [14C]ethanolamine, and were then homogenized. The brei was subjected to sucrose density gradient centrifugation. The specific radioactivity of [14C]PC was quite similar in the gradient fractions, whether they contained microsomes or mitochondrial plus chloroplast membranes. We infer that stress does not enhance the turnover of any structurally discrete class of PC, but rather stimulates PC turnover in several or all classes of membranes in most cells of the leaf.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01607573
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  • 2
    Electronic Resource
    Electronic Resource
    Light stimulation of proline synthesis in water-stressed barley leaves (1979)
    Springer
    Planta 145 (1979), S. 45-51 
    Details
    ISSN: 1432-2048
    Keywords: Glutamate ; Hordeum ; Light (photosynthesis) ; Proline ; Water stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effect of light on [14C]glutamate conversion to free proline during water stress was studied in attached barley (Hordeum vulgare L.) leaves which had been trimmed to 10 cm in length. Plants at the three-leaf stage were stressed by flooding the rooting medium with polyethylene glycol 6000 (osmotic potential-19 bars) for up to 3 d. During this time the free proline content of 10-cm second leaves rose from about 0.02 to 2 μmol/leaf while free glutamate content remained steady at about 0.6 μmol/leaf. In stressed leaves, the amount of [14C]glutamate converted to proline in a 3-h period of light or darkness was taken to reflect the in-vivo rate of proline biosynthesis because the following conditions were met: (a) free-glutamate levels were not significantly different in light and darkness; (b) both tracer [14C]-glutamate and [14C]proline were rapidly absorbed; (c) rates of [14C]proline oxidation and incorporation into protein were very slow. As leaf water potential fell, more [14C]glutamate was converted to proline in both light and darkness, but at any given water potential in the range-12 to-20 bars, illuminated leaves converted twice as much [14C]glutamate to proline.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00379926
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  • 3
    Electronic Resource
    Electronic Resource
    Translocation and metabolism of glycine betaine by barley plants in relation to water stress (1980)
    Springer
    Planta 150 (1980), S. 191-196 
    Details
    ISSN: 1432-2048
    Keywords: Betaine ; Hordeum ; Water stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The glycine betaine which accumulated in shoots of young barley plants (Hordeum vulgare L.) during an episode of water stress did not undergo net destruction upon relief of stress, but its distribution among plant organs changed. During stress, betaine accumulated primarily in mature leaves, whereas it was found mainly in young leaves after rewatering. Well-watered, stressed, and stressed-rewatered plants were supplied with [methyl-14C]betaine (8.5 nmol) via an abraded spot on the second leaf blade, and incubated for 3 d. In all three treatments the added 14C migrated more or less extensively from the second leaf blade, but was recovered quantitatively from various plant organs in the form of betaine; no labeled degradation products were found in any organ. When 0.5 μmol of [methyl-14C]betaine was applied via an abraded spot to the second leaf blades of well-watered, mildly-stressed, and stressed-rewatered plants, 14C was translocated out of the blades at velocities of about 0.2–0.3 cm/min which were similar to velocities found for applied [14C]sucrose. Heat-girdling of the sheath prevented export of [14C]betaine from the blade. When 0.5 μmol [3H]sucrose and 0.5 μmol [14C]betaine were suppled simultaneously to second leaf blades, the 3H/14C ratio in the sheath tissue was the same as that of the supplied mixture. After supplying tracer [14C]betaine aldehyde (the immediate precursor of betaine) to the second leaf blade, the 14C which was translocated into the sheath was in the form of betaine. Thus, betaine synthesized by mature leaves during stress behaves as an inert end product and upon rewatering is translocated to the expanding leaves, most probably via the phloem. Accordingly, it is suggested that the level of betaine in a barley plant might serve as a useful cumulative index of the water stress experienced during growth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00390825
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    Paper (German National Licenses)
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