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  • 1980-1984  (2)
  • 1975-1979  (1)
  • 1
    ISSN: 1432-2048
    Schlagwort(e): Caffeine ; Coffea ; Leaf development ; Photosynthesis ; Purine alkaloids and light ; Purine alkaloids and temperature
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract In the leaves of Coffea arabica L., purine alkaloid formation was estimated by analyzing the theobromine and caffeine content and by measuring the methylation rate of [2-14C]theobromine to [2-14C]caffeine in short-term experiments (6–24 h). At the same time, growth (in terms of dry weight and area), net photosynthesis (NPS), and dark respiration were determined. During leaf development, which was considered to be terminated when NPS was at a maximum (60–80 μmol g-1 s-1) and dark respiration at a minimum (5–7.5 μmol g-1 s-1), the content of theobromine and the velocity of caffeine formation were both found to decrease by a factor of more than 100. The close correlation between the theobromine content and the methylation rate is suspended when purine alkaloid formation is influenced by factors other than leaf development. Among these factors, temperature is the most effective: the velocity of caffeine biosynthesis is increased by raising the temperature and vice versa. Although the plants were well irrigated, a drastic decrease of NPS in the afternoon was observed under all environmental conditions tested. Light saturation was reached between 170–360 μmol m-2 s-1. The temperature optimum of NPS was shown to be very broad (24–33°C)m provided the adaptation time was sufficiently long.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Plant cell reports 2 (1983), S. 33-35 
    ISSN: 1432-203X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Suspension cultures of Coffea arabica L. are a useful source for methyltransferase preparations of high activity catalysing the transfer of methylgroups from S-adenosyl-L-methionine to 7-methylxanthine and to theobromine producing theobromine and caffeine respectively. Surprisingly, these enzyme activities are not correlated with the availability of precursors during a culture cycle. They are highest in the growth phase when supply of precursors is reduced. Mixed substrate experiments and time dependent changes in the enzyme activity ratio provide indirect evidence for the existence of two separate enzymes catalysing the final methylations in caffeine biosynthesis.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    ISSN: 1432-1106
    Schlagwort(e): Visual cortex damage ; Recovery mechanisms ; Lateral suprasylvian cortex neurons ; Cats
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Damage to visual cortical areas 17, 18, and 19 in the cat produces severe and long-lasting deficits in performance of form and pattern discriminations. However, with extensive retraining the animals are able to recover their ability to discriminate form and pattern stimuli. Recent behavioral experiments from this laboratory have shown that a nearby region of cortex, the lateral suprasylvian visual area (LS area), plays an important role in this recovery (Wood et al., 1974; Baumann and Spear, 1977b). The present experiment investigated the underlying neurophysiological mechanisms of the recovery by recording from single neurons in the LS area of cats which had recovered from long-term visual cortex damage. Five adult cats received bilateral removal of areas 17, 18, and 19. They were then trained to criterion on two-choice brightness, form, and pattern discriminations. Recording from LS area neurons was carried out after the behavioral training, from 3 to 7 months after the visual cortex lesions. The properties of these neurons were compared to those of LS area neurons in normal cats (Spear and Baumann, 1975) and in cats with acute or short-term visual cortex damage and no behavioral recovery (Spear and Baumann, 1979). The results showed that all of the changes from normal which were produced by acute visual cortex damage were also present after the behavioral recovery. Moreover, all of the response properties of LS area neurons which remain after acute visual cortex damage were present in similar form after the behavioral recovery. There was no evidence for any functional reorganization in the LS area concomitant with its role in the behavioral recovery. These results suggest that functional reorganization plays little or no role in recovery from visual cortex damage in adult cats. Rather, the recovery of form and pattern discrimination ability appears to be based upon the functioning of residual neural processes in the LS area which remain after the visual cortex damage.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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