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  • 1
    Digitale Medien
    Digitale Medien
    Enzymatic Regulation of Photosynthetic CO2, Fixation in C3 Plants (1988)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Plant Physiology and Plant Molecular Biology 39 (1988), S. 533-594 
    Details
    ISSN: 1040-2519
    Quelle: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Thema: Biologie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1146/annurev.pp.39.060188.002533
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  • 2
    Digitale Medien
    Digitale Medien
    Isotopic heterogeneity of water in transpiring leaves: identification of the component that controls the δ18O of atmospheric O2 and CO2 (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 17 (1994), S. 0 
    Details
    ISSN: 1365-3040
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Two direct but independent approaches were developed to identify the average δ18O value of the water fraction in the chloroplasts of transpiring leaves. In the first approach, we used the δ18O value of CO2 in isotopic equilibrium with leaf water to reconstruct the δ18O value of water in the chloroplasts. This method was based on the idea that the enzyme carbonic anhydrase facilitates isotopic equilibrium between CO2 and H2O predominantly in the chloroplasts, at a rate that is several orders of magnitude faster than the non-catalysed exchange in other leaf water fractions. In the second approach, we measured the δ18O value of O2 from photosynthetic water oxidation in the chloroplasts of intact leaves. Since O2 is produced from chloroplast water irreversibly and without discrimination, the δ18O value of the O2 should be identical to that of chloroplast water. In intact, transpiring leaves of sunflower (Helianthus annuus cv. giant mammoth) under the experimental conditions used, the average δ18O value of chloroplasts water was displaced by 3—10 % (depending on relative humidity and atmospheric composition) below the value predicted by the conventional Craig & Gordon model. Furthermore, this δ18O value was always lower than the δ18O value that was measured for bulk leaf water. Our results have implications for a variety of environmental studies since it is the δ18O value of water in the chloroplasts that is the relevant quantity in considering terrestrial plants influence on the δ18O values of atmospheric CO2 and O2, as well as in influencing the δ18O of plant organic matter.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-3040.1994.tb00267.x
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  • 3
    Digitale Medien
    Digitale Medien
    Asymmetric patchy stomatal closure for the two surfaces of Xanthium strumarium L. leaves at low humidity (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 16 (1993), S. 0 
    Details
    ISSN: 1365-3040
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Images of chlorophyll fluorescence were used to demonstrate patchy stomatal closure at low humidities in leaves of well-watered Xanthium strumarium plants. The pattern and extent of patchy stomatal closure were shown to be different for the two surfaces of amphistomatous leaves by taking images of leaves with CO2 available to only one leaf was exposed to low humidity, patchiness was more extensive on that surface. Gas-exchange experiments were also conducted to determine the apparent photosynthetic capacity of the mesophyll (photosynthesis rate at constant ci when it was supplied with CO2 through both surfaces or through each surface alone. These experiments showed declines in the apparent photosynthetic capacity of the mesophyll at low humidities that were consistent with patchy stomatal closure on one or both surfaces. The results suggest that patchy stomatal closure can be a factor in the steady-state reponses of stomata to humidity. In amphistomatous leaves this is further complicated by the fact that patches on one epidermis may not coincide with those of the other surface.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-3040.1993.tb00841.x
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  • 4
    Digitale Medien
    Digitale Medien
    Control of photosynthetic carbon dioxide fixation by the boundary layer, stomata and ribulose 1,5-biphosphate carboxylase/oxygenase (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 13 (1990), S. 0 
    Details
    ISSN: 1365-3040
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Abstract Coefficients describing the sensitivity of the rate of photosynthetic carbon dioxide fixation to small changes in the stomatal conductance and boundary layer conductance are derived. These sensitivity or ‘control’ coefficients, together with those for the carboxylase and oxygenase activities of ribulose 1,5-bisphosphate carboxylase/oxygenase, are calculated from standard gas exchange data and apply under conditions where leaf temperature and water vapour concentration at the leaf surface remain largely constant. It is shown that the magnitude of the control coefficients depends on conditions such as photon flux density, ambient CO2 concentration and relative humidity at the leaf surface. The extension of this analysis to encompass the sensitivity of the photosynthetic fluxes to changes in enzyme concentrations and kinetic properties is also discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-3040.1990.tb02137.x
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  • 5
    Digitale Medien
    Digitale Medien
    Effects of light on respiration and oxygen isotope fractionation in soybean cotyledons (2000)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 23 (2000), S. 0 
    Details
    ISSN: 1365-3040
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Light effects on electron flow through the cyanide-resistant respiratory pathway, oxygen isotope fractionation and total respiration were studied in soybean (Glycine max L.) cotyledons. During the first 12 h of illumination there was an increase in both electron partitioning through the alternative pathway and oxygen isotope fractionation by the alternative oxidase. The latter probably indicates a change in the properties of the alternative oxidase. There was no engagement of the alternative oxidase in darkness and its fractionation was 27‰. In green cotyledons 60% of the respiration flux was through the alternative pathway and the alternative oxidase fractionation was 32‰. Exposing previously illuminated tissue to continuous darkness induced a decrease in the electron partitioning through the alternative pathway. However, this decrease was not directly linked with the low cellular sugar concentration resulting from the lack of light because 5 min of light every 12 h was sufficient to keep the alternative pathway engaged to the same extent as plants grown under control conditions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-3040.2000.00607.x
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  • 6
    Digitale Medien
    Digitale Medien
    Dynamics of patchy stomatal movements, and their contribution to steady-state and oscillating stomatal conductance calculated using gas-exchange techniques (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 17 (1994), S. 0 
    Details
    ISSN: 1365-3040
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Patchy stomatal movements were induced in leaves of Helianthus annuus L. and Xanthium strumarium L. by increasing Δw and decreasing light in a gas-exchange cuvette. The dynamics of the patchy movements were recorded and analysed using images of chlorophyll fluorescence, and the influence of heterogeneous stomatal activity on gas-exchange measurements of whole-leaf stomatal conductance was explored. Image series and gas-exchange measurements from two contrasting 100 min experiments are presented. One series of images, taken using Helianthus annuus, was characterized by strongly oscillating stomatal conductance induced by a decrease in light at high Δw. Fluorescence analysis revealed that individual patches of the leaf displayed a variety of behaviours (from static to strongly oscillating fluorescence), which, when averaged, matched the time dependence of the oscillating stomatal conductance measured by gas-exchange techniques. During the second series of images, taken using Xanthium strumarium, stomatal conductance (measured with gas exchange) declined slightly after an increase in Δw, and then maintained a steady state. Again, some patches in this leaf showed highly dynamic qNP, although on the whole qNP varied without any obvious pattern or frequency. When all patch activity in this series was averaged, it paralleled the steady whole-leaf stomatal conductance determined by gas-exchange measurements. It is clear from this work that coordinated patchy stomatal movements can contribute significantly to the dynamics of whole-leaf stomatal conductance, and, in contrast, that dynamic but uncoordinated patchy movements can average to produce a steady gas-exchange trace.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-3040.1994.tb02033.x
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  • 7
    Digitale Medien
    Digitale Medien
    The relationship between the Rubisco reaction mechanism and models of photosynthesis (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 13 (1990), S. 0 
    Details
    ISSN: 1365-3040
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Abstract. A new model of photosynthesis published recently in this journal (H. Farazdaghi & G. E. Edwards, Plant, Cell and Environment (1988) 11, 789–798; 799–809) clams to have a more complete mechanistic basis than currently used models based on the paper of G. D. Farquhar, S. von Caemmerer & J. A. Berry (Planta (1980) 149, 78–90). In this paper, we examine the validity of the new kinetic expression for the rate of CO2 fixation by Rubisco, and the derivation of an equation for photosynthetic CO2 assimilation as a function of light intensity and CO2 concentration presented in the new model. In addition, we compare measured response curve of photosynthesis to CO2 and light with simulated curves using alternative models. We conclude that the new model is mechanistically misleading and, empirically, overestimates the extent to which light and CO2 co-limit the rate of photosynthesis under most physiological conditions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-3040.1990.tb01306.x
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  • 8
    Digitale Medien
    Digitale Medien
    The relation between membrane lipid phase separation and frost tolerance of cereals and other cool climate plant species (1982)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 5 (1982), S. 0 
    Details
    ISSN: 1365-3040
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Abstract. The temperatures at which liposomes prepared from membrane phospholipids begin to phase separate were compared to the temperatures at which intact plants were damaged. Woody perennials tolerated temperatures below which their membrane phospholipids began to phase separate. By contrast, rye and wheat seedlings were damaged about 25°C above their phase separation temperature. Differences in tolerance among cultivars pre-hardened to frost were reflected by changes of the phase separation temperature. The results support the notion that alterations in membrane lipid composition are associated with frost hardening. A correlation between the temperature of phase separation and frost tolerance suggests that lipid properties may influence freezing tolerance of cereals; however, the lethal event is apparently not phase separation of the membrane phospholipids.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/1365-3040.ep11572449
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  • 9
    Digitale Medien
    Digitale Medien
    A portable system for measuring carbon dioxide and water vapour exchange of leaves (1982)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 5 (1982), S. 0 
    Details
    ISSN: 1365-3040
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Abstract. The apparatus described here is a fully portable, steady-state gas exchange system for simultaneous measurements of the CO2 exchange and transpiration of single, attached leaves. The leaf cuvette provides temperature, humidity, and CO2-concentration control. The system is suitable for either surveys or detailed studies of photosynthetic and stomatal responses to environmental variables. Representative data demonstrate the response time characteristics of the system and constitute the first field evidence of stomatal behaviour consistent with a recent hypothesis concerning the optimum pattern of stomatal conductance for the maximization of water-use-efficiency.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/1365-3040.ep11571607
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  • 10
    Digitale Medien
    Digitale Medien
    Functional diversity of photosynthesis during drought in a model tropical rainforest – the contributions of leaf area, photosynthetic electron transport and stomatal conductance to reduction in net ecosystem carbon exchange (2004)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 27 (2004), S. 0 
    Details
    ISSN: 1365-3040
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: The tropical rainforest mesocosm within the Biosphere 2 Laboratory, a model system of some 110 species developed over 12 years under controlled environmental conditions, has been subjected to a series of comparable drought experiments during 2000–2002. In each study, the mesocosm was subjected to a 4–6 week drought, with well-defined rainfall events before and after the treatment. Ecosystem CO2 uptake rate (Aeco) declined 32% in response to the drought, with changes occurring within days and being reversible within weeks, even though the deeper soil layers did not become significantly drier and leaf-level water status of most large trees was not greatly affected. The reduced Aeco during the drought reflected both morphological and physiological responses. It is estimated that the drought-induced 32% reduction of Aeco has three principal components: (1) leaf fall increased two-fold whereas leaf expansion growth of some canopy dominants declined to 60%, leading to a 10% decrease in foliage coverage of the canopy. This might be the main reason for the persistent reduction of Aeco after rewatering. (2) The maximum photosynthetic electron transport rate at high light intensities in remaining leaves was reduced to 71% for three of the four species measured, even though no chronic photo-inhibition occurred. (3) Stomata closed, leading to a reduced ecosystem water conductance to water vapour (33% of pre-drought values), which not only reduced ecosystem carbon uptake rate, but may also have implications for water and energy budgets of tropical ecosystems. Additionally, individual rainforest trees responded differently, expressing different levels of stress and stress avoiding mechanisms. This functional diversity renders the individual response heterogeneous and has fundamental implications to scale leaf level responses to ecosystem dynamics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-3040.2004.01231.x
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