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  • 1
    Electronic Resource
    Electronic Resource
    Changes in photosynthetic capacity, carboxylation efficiency, and CO2 compensation point associated with midday stomatal closure and midday depression of net CO2 exchange of leaves of Quercus suber (1984)
    Springer
    Planta 162 (1984), S. 193-203 
    Details
    ISSN: 1432-2048
    Keywords: Carboxylation efficiency ; Compensation point (CO2) ; Photosynthesis (temperature, humidity) ; Quercus ; Sclerophyll
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The carbon-dioxide response of photosynthesis of leaves of Quercus suber, a sclerophyllous species of the European Mediterranean region, was studied as a function of time of day at the end of the summer dry season in the natural habitat. To examine the response experimentally, a “standard” time course for temperature and humidity, which resembled natural conditions, was imposed on the leaves, and the CO2 pressure external to the leaves on subsequent days was varied. The particular temperature and humidity conditions chosen were those which elicited a strong stomatal closure at midday and the simultaneous depression of net CO2 uptake. Midday depression of CO2 uptake is the result of i) a decrease in CO2-saturated photosynthetic capacity after light saturation is reached in the early morning, ii) a decrease in the initial slope of the CO2 response curve (carboxylation efficiency), and iii) a substantial increase in the CO2 compensation point caused by an increase in leaf temperature and a decrease in humidity. As a consequence of the changes in photosynthesis, the internal leaf CO2 pressure remained essentially constant despite stomatal closure. The effects on capacity, slope, and compensation point were reversed by lowering the temperature and increasing the humidity in the afternoon. Constant internal CO2 may aid in minimizing photoinhibition during stomatal closure at midday. The results are discussed in terms of possible temperature, humidity, and hormonal effects on photosynthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00397440
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Sequential histamine inhalations cause increased bronchial histamine reactivity in guinea pigs: Role of platelets, thromboxanes and prostacyclin (1984)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 327 (1984), S. 148-155 
    Details
    ISSN: 1432-1912
    Keywords: Acetylsalicylic acid ; Bronchial obstruction ; Guinea pigs ; Histamine aerosol ; Histamine receptor antagonists ; Prostacyclin aerosol ; Platelets ; Thromboxane synthetase inhibitors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Groups of 6–15 guinea pigs sensitized to ovalbumin were challenged by repeated inhalations of a constant histamine dose at time 0, 10, 20, 60 and 70 min. Bronchial obstruction was measured by whole body plethysmography. The degree of bronchial obstruction increased from one challenge to the other reaching maximal values after 70 min. This increase of bronchial responsiveness to histamine after repeated histamine challenges was reduced by pretreatment with clemastine (histamine H1-receptor antagonist, 0.12 mg/kg i.p., n=7, P〈0.05) and more effectively by combined clemastine/cimetidine pretreatment (combined H1-H2-receptor antagonists, 0.12 resp. 10 mg/kg, n=7, P〈0.001); pretreatment with acetylsalicyclic acid (10 mg/kg orally) accelerated the increase of bronchial responsiveness to histamine (n=9, P〈0.01 at the second challenge), inhalation of prostacyclin (1 μg) prior to each histamine inhalation prevented the increase of bronchial histamine sensitivity totally (n=10, P〈0.001), whereas inhibition of thromboxane biosynthesis (imidazol, 10 mg/kg i.p., n=6; 4-[2-(1H-imidazol-1-yl)ethoxy]benzoic acid, 10 mg/kg i.p., n=9; imidazo(1,5-a)pyridine-5-hexanoic acid, 1 mg/kg i.p., n=8) as well as immunologic platelet depletion were ineffective in our test system. We conclude that prostacyclin inhibits the increase of bronchial responsiveness to histamine after sequential histamine inhalation challenges by a platelet independent mechanism. 1-(3-phenyl-2-propenyl)-1H-imidazol, the fourth type of thromboxane synthetase inhibitor tested (10 mg/kg i.p., n=15) showed specific effects which may be attributed to antihistamine functions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00500910
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    Paper (German National Licenses)
    Fulltext
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