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  • Stomatal control  (3)
  • Osmotic potential  (2)
  • (+)-Menthyllithium, stereoselective metallation with  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Poor stomatal control of water balance and the abscission of green needles from a declining stand of spruce trees [Picea abies (L.) Karst.] from the northern Alps (1995)
    Springer
    Trees 10 (1995), S. 63-73 
    Details
    ISSN: 1432-2285
    Keywords: Forest decline ; Osmotic potential ; Picea abies ; Stomatal control ; Water potential
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract On a site on the west slope of the Wank in the northern Alps changes in water potential, osmotic potential and transpiration rate were measured in spruce trees during the dry summer months of 1991. The pattern of decrease in water potential and osmotic potential on days of varying evaporative demand from trees of widely different decline conditions was used to describe the relative ability of the trees to withstand drought stress. Stress diagrams served as a tool for interpreting the state of health of each tree. The criterion is independent of the water situation of the tree and the other external conditions of the respective experiment. These diagrams clearly show that the foliage of spruces with high needle losses reaches the limit of endurance relatively early. For equal evaporative demand much lower turgor levels were observed in spruces with high needle loss compared to undamaged trees. Associated with the occurrence of low turgor values was the shedding of green needles. The abscission zone was shown in sections. The accumulation of highly fluorescent substances in the bundle sheath cells of the same material was described. Incomplete to non-existent stomatal control over water loss was attributed to modifications in the cell walls of the stomata which appear to alter the ability of the guard cells to sense changes in either atmospheric or cellular hydration. Our studies point to the following situation: air pollution directly affects stomatal control, the loss of stomatal control changes the drought avoidance abilities of the foliage and, as a consequence, low turgor levels occur and premature needle abscission is induced. As site water balance decreases, either due to a dry year or to poor moisture holding abilities of the soil, these conditions become apparent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00192185
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Experiments on the water balance of individual attached twigs of Picea abies (L .) Karst. in pure and ozone-enriched air (1997)
    Springer
    Trees 11 (1997), S. 229-239 
    Details
    ISSN: 0931-1890
    Keywords: Key words Ozone ; Picea abies ; Stomatal control ; Water potential ; Xylem sap flow
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Rates of transpiration and xylem sap flow were continuously measured in individual twigs in the upper crown of an 18-year-old spruce. Two gas exchange chambers were run simultaneously under identical conditions. One of two equivalent twigs was exposed to pure air whereas the other received the ozone-enriched air of the site. A third gas exchange chamber in mid-crown ran independently with normal outside air and was used for basic experiments. At certain times needles were sampled for water potential measurements. Chamber humidity was reduced step by step and the transpiration and xylem sap flow rates were permanently compared. It turned out that sap flow keeps up with transpiration without lagging as long as chamber humidity is high and the twigs outside the chamber are not subject to substantial evaporative demand. However, in warm summer weather and with high flow rates sap flow is no longer sufficient. As the balance quotient (uptake/release) of 0.8 was reached the stomata began to close and water balance improved. The flux quotient increased far above 1.0 without water potential of the needles, which had decreased before, increasing significantly. The balance quotient of the twig in ozone-enriched air fell to relatively low values and only increased again correspondingly slowly due to lagging stomatal closure. Despite increased water uptake after the light phase, the ozone-treated twig ran into a water deficit in the daily balance during the course of an uninterrupted drought period. Water deficit increased from day to day and only disappeared with the next rainfall. For providing insight into the ozone effect shown in this study it was thought necessary to discuss comprehensively the controversial views of the stomatal control mechanism. The results show that the stomata react to small scale changes in water status as expected for an effective negative feedback system. The less sensitive reaction of the stomata under the influence of ozone confirms earlier results. Increased severity and duration of the daily drought stress loads were attributed to a lag in adjustment due to poor stomatal control. The demonstrated function mechanism shows that the detrimental effect of ozone is dependent on weather conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00009669
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  • 3
    Electronic Resource
    Electronic Resource
    Experiments on the water budget of densely and sparsely needled spruces [Picea abies (L.) Karst.] in a declining stand (1991)
    Springer
    Trees 5 (1991), S. 164-170 
    Details
    ISSN: 1432-2285
    Keywords: Forest decline ; Osmotic potential ; Picea abies ; Water content ; Water potential
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The osmotic potentials of needles were compared from numerous trees that had been classified according to needle loss along an altitude profile. With the increasing degree of damage of the trees, the maximum and minimum values deviated more strongly above and below the common mean of all samples. The level of water content of the needles unequivocally reflected the vitality of the trees. Experiments covering a whole vegetation period were performed on a tree pair selected from a natural stand. They were designed to demonstrate differences in water balance between the “healthy” and “damaged” state of the trees. For the “damaged” tree, measurements of the water potentials of single needles showed a greater reduction of potential during the course of the day compared to the “healthy” tree. Recovery in the evenings was slower and often incomplete. The osmotic potentials of “damaged” and “healthy” shoots measured in individual needles also differed both predawn and especially after transpiration stress. Depending on weather and soil desiccation, the differences were more or less pronounced. In the “damaged” tree, the rises in potential after saturation of the twigs fell far short of the “healthy” tree. Reduction of water potential, osmotic potential and relative water content under comparable stress conditions suggest a reduced tolerance of drought by damaged trees. In the context of earlier experiments this result was ascribed to a lack of stomatal control, and long-term pollution effects were thus explained as a specific disturbance of hydroregulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00204339
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  • 4
    Electronic Resource
    Electronic Resource
    The effect of air pollution on the mechanism of stomatal control (1992)
    Springer
    Trees 7 (1992), S. 12-25 
    Details
    ISSN: 1432-2285
    Keywords: Air pollution ; Drought stress ; Forest decline ; Gas exchange measurements ; Stomatal control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary A long-term field experiment permanently measuring gas exchange in the top of a 70-year-old spruce, continued for through the 1990 growing season. Two gas exchange chambers were run simultaneously under identical climatic conditions. One of two similar twigs was exposed to ambient air whereas the other received pure air. These experiments aimed to examine the ability of the stomata to control water balance, comparing pure and ambient air. This was done not only in natural climatic conditions but also in experimental, specifically maintained stress situations. Special care was taken to ensure that only steady state values of stomatal responses are related to the environmental stimuli. During a drought period lasting several weeks, overshooting transpiration values were documented for the ambient air. The two twigs do not merely differ in their control capacity, but the behaviour of the stomata in ambient air deviates from the “norm”. The increasingly uncontrolled water losses during the drought period have a negative effect on photosynthetic capacity. The influence of water deficit on stomatal response to other environmental factors (light, CO2) is shown. Due to deficient control quality of the stomata lower stress tolerance in the face of drought is suggested in ambient air as compared with pure air. By tracing dysfunctions to structural changes in the cell walls of the stomatal apparatus, a mechanism is described explaining forest decline under the combined influence of air pollutants and drought stress.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00225227
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  • 5
    Electronic Resource
    Electronic Resource
    Studien zur enantio- und diastereoselektiven α-Metallierung prochiraler Sulfoxide mit (+)-Menthyllithium (1991)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 124 (1991), S. 2489-2498 
    Details
    ISSN: 0009-2940
    Keywords: (+)-Menthyllithium, stereoselective metallation with ; Prochiral sulfoxides, enantio- and diastereoselective α-deprotonation of ; 2-Bornyllithium, content of isobornyllithium in ; Racemization, mechanism by intermolecular transmetallation ; e.e., temperature dependence of ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantio- and Diastereoselective α-Metallation of Prochiral Sulfoxides by (+)-MenthyllithiumSix out of ten prochiral dialkyl sulfoxides 3 with diastereotopic α methylene protons were stereoselectively metallated by (+)-menthyllithium (11) to yield two diastereomeric pairs of enriched enantiomers 29 after the reaction with benzophenone. The maximum e.e. was 40%. Dicyclohexyl sulfoxide (3c) was deprotonated enantioselectively with an e.e. of 30%. 2-Bornyllithium (21) was unsuccessful as a chiral base and was shown for the first time to contain 4% of isobornyllithium (22). The reactions were performed in pentane at - 80°C; in diethyl ether and THF the e.e.'s were only slightly higher, and at higher temperatures the selectivity was rapidly decreasing. It was shown that racemization takes place by an intermolecular transmetallation reaction. The structure of 29f [n = 3] was elucidated by an X-ray analysis.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19911241120
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