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Rob Welschen - One of the best experts on this subject based on the ideXlab platform.
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midday depression of net photosynthesis in the tropical rainforest tree eperua grandiflora contributions of stomatal and internal conductances respiration and rubisco functioning
Tree Physiology, 2003Co-Authors: Thijs L Pons, Rob WelschenAbstract:Summary High midday temperatures can depress net photosynthesis. We investigated possible mechanisms underlying this phenomenon in leaves of Eperua grandiflora (Aubl.) Benth. saplings. This tropical tree establishes in small gaps in the rainforest canopy where direct sunlight can raise midday temperatures markedly. We simulated this microclimate in a growth chamber by varying air temperature between 28 and 38 °C at constant vapor pressure. A decrease in stomatal conductance in response to an increase in leaf-to-air vapor pressure difference (∆W ) caused by an increase in leaf temperature (Tleaf) was the principal reason for the decrease in net photosynthesis between 28 and 33 °C. Net photosynthesis decreased further between 33 and 38 °C. Direct effects on mesophyll functioning and indirect effects through ∆W were of similar magnitude in this temperature range. Mitochondrial respiration during photosynthesis was insensitive to Tleaf over the investigated temperature range; it thus did not contribute to midday depression of net photosynthesis. Internal conductance for CO2 diffusion in the leaf, estimated by combined gas exchange and chlorophyll fluorescence measurements, decreased slightly with increasing Tleaf. However, the decrease in photosynthetic rate with increasing Tleaf was larger and thus the difference in CO2 partial pressure between the Substomatal Cavity and chloroplast was smaller, leading to the conclusion that this factor was not causally involved in midday depression. Carboxylation capacity inferred from the CO2 response of photosynthesis increased between 28 and 33 °C, but remained unchanged between 33 and 38 °C. Increased oxygenation of ribulose-1,5-bisphosphate relative to its carboxylation and the concomitant increase in photorespiration with increasing Tleaf were thus not compensated by an increase in carboxylation capacity over the higher temperature range. This was the principal reason for the negative effect of high midday temperatures on mesophyll functioning.
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midday depression of net photosynthesis in the tropical rainforest tree eperua grandiflora contributions of stomatal and internal conductances respiration and rubisco functioning erratum 2004 may v 24 no 5 p 599
Tree Physiology, 2003Co-Authors: Thijs L Pons, Rob WelschenAbstract:High midday temperatures can depress net photosynthesis. We investigated possible mechanisms underlying this phenomenon in leaves of Eperua grandiflora (Aubl.) Benth. saplings. This tropical tree establishes in small gaps in the rainforest canopy where direct sunlight can raise midday temperatures markedly. We simulated this microclimate in a growth chamber by varying air temperature between 28 and 38 °C at constant vapor pressure. A decrease in stomatal conductance in response to an increase in leaf-to-air vapor pressure difference (deltaW) caused by an increase in leaf temperature (Tleaf) was the principal reason for the decrease in net photosynthesis between 28 and 33 °C. Net photosynthesis decreased further between 33 and 38 °C. Direct effects on mesophyll functioning and indirect effects through deltaW were of similar magnitude in this temperature range. Mitochondrial respiration during photosynthesis was insensitive to Tleaf over the investigated temperature range; it thus did not contribute to midday depression of net photosynthesis. Internal conductance for CO2 diffusion in the leaf, estimated by combined gas exchange and chlorophyll fluorescence measurements, decreased slightly with increasing Tleaf. However, the decrease in photosynthetic rate with increasing Tleaf was larger and thus the difference in CO2 partial pressure between the Substomatal Cavity and chloroplast was smaller, leading to the conclusion that this factor was not causally involved in midday depression. Carboxylation capacity inferred from the CO2 response of photosynthesis increased between 28 and 33 °C, but remained unchanged between 33 and 38 °C. Increased oxygenation of ribulose-1,5-bisphosphate relative to its carboxylation and the concomitant increase in photorespiration with increasing Tleaf were thus not compensated by an increase in carboxylation capacity over the higher temperature range. This was the principal reason for the negative effect of high midday temperatures on mesophyll functioning.
Thijs L Pons - One of the best experts on this subject based on the ideXlab platform.
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estimating mesophyll conductance to co2 methodology potential errors and recommendations
Journal of Experimental Botany, 2009Co-Authors: Thijs L Pons, Susanne Von Caemmerer, John R. Evans, Jaume Flexas, Bernard Genty, Miquel Ribascarbo, Enrico BrugnoliAbstract:The three most commonly used methods for estimating mesophyll conductance (gm) are described. They are based on gas exchange measurements either (i) by themselves; (ii) in combination with chlorophyll fluorescence quenching analysis; or (iii) in combination with discrimination against 13 CO2. To obtain reliable estimates of gm, the highest possible accuracy of gas exchange is required, particularly when using small leaf chambers. While there may be problems in achieving a high accuracy with leaf chambers that clamp onto a leaf with gaskets, guidelines are provided for making necessary corrections that increase reliability. All methods also rely on models for the calculation of gm and are sensitive to variation in the values of the model parameters. The sensitivity to these factors and to measurement error is analysed and ways to obtain the most reliable gm values are discussed. Small leaf areas can best be measured using one of the fluorescence methods. When larger leaf areas can be measured in larger chambers, the online isotopic methods are preferred. Using the large CO2 draw-down provided by big chambers, and the isotopic method, is particularly important when measuring leaves with high gm that have a small difference in [CO2] between the Substomatal Cavity and the site of carboxylation in the chloroplast (Ci2Cc gradient). However, equipment for the fluorescence methods is more easily accessible. Carbon isotope discrimination can also be measured in recently synthesized carbohydrates, which has its advantages under field conditions when large number of samples must be processed. The curve-fitting method that uses gas exchange measurements only is not preferred and should only be used when no alternative is available. Since all methods have their weaknesses, the use of two methods for the estimation of gm, which are as independent as possible, is recommended.
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midday depression of net photosynthesis in the tropical rainforest tree eperua grandiflora contributions of stomatal and internal conductances respiration and rubisco functioning
Tree Physiology, 2003Co-Authors: Thijs L Pons, Rob WelschenAbstract:Summary High midday temperatures can depress net photosynthesis. We investigated possible mechanisms underlying this phenomenon in leaves of Eperua grandiflora (Aubl.) Benth. saplings. This tropical tree establishes in small gaps in the rainforest canopy where direct sunlight can raise midday temperatures markedly. We simulated this microclimate in a growth chamber by varying air temperature between 28 and 38 °C at constant vapor pressure. A decrease in stomatal conductance in response to an increase in leaf-to-air vapor pressure difference (∆W ) caused by an increase in leaf temperature (Tleaf) was the principal reason for the decrease in net photosynthesis between 28 and 33 °C. Net photosynthesis decreased further between 33 and 38 °C. Direct effects on mesophyll functioning and indirect effects through ∆W were of similar magnitude in this temperature range. Mitochondrial respiration during photosynthesis was insensitive to Tleaf over the investigated temperature range; it thus did not contribute to midday depression of net photosynthesis. Internal conductance for CO2 diffusion in the leaf, estimated by combined gas exchange and chlorophyll fluorescence measurements, decreased slightly with increasing Tleaf. However, the decrease in photosynthetic rate with increasing Tleaf was larger and thus the difference in CO2 partial pressure between the Substomatal Cavity and chloroplast was smaller, leading to the conclusion that this factor was not causally involved in midday depression. Carboxylation capacity inferred from the CO2 response of photosynthesis increased between 28 and 33 °C, but remained unchanged between 33 and 38 °C. Increased oxygenation of ribulose-1,5-bisphosphate relative to its carboxylation and the concomitant increase in photorespiration with increasing Tleaf were thus not compensated by an increase in carboxylation capacity over the higher temperature range. This was the principal reason for the negative effect of high midday temperatures on mesophyll functioning.
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midday depression of net photosynthesis in the tropical rainforest tree eperua grandiflora contributions of stomatal and internal conductances respiration and rubisco functioning erratum 2004 may v 24 no 5 p 599
Tree Physiology, 2003Co-Authors: Thijs L Pons, Rob WelschenAbstract:High midday temperatures can depress net photosynthesis. We investigated possible mechanisms underlying this phenomenon in leaves of Eperua grandiflora (Aubl.) Benth. saplings. This tropical tree establishes in small gaps in the rainforest canopy where direct sunlight can raise midday temperatures markedly. We simulated this microclimate in a growth chamber by varying air temperature between 28 and 38 °C at constant vapor pressure. A decrease in stomatal conductance in response to an increase in leaf-to-air vapor pressure difference (deltaW) caused by an increase in leaf temperature (Tleaf) was the principal reason for the decrease in net photosynthesis between 28 and 33 °C. Net photosynthesis decreased further between 33 and 38 °C. Direct effects on mesophyll functioning and indirect effects through deltaW were of similar magnitude in this temperature range. Mitochondrial respiration during photosynthesis was insensitive to Tleaf over the investigated temperature range; it thus did not contribute to midday depression of net photosynthesis. Internal conductance for CO2 diffusion in the leaf, estimated by combined gas exchange and chlorophyll fluorescence measurements, decreased slightly with increasing Tleaf. However, the decrease in photosynthetic rate with increasing Tleaf was larger and thus the difference in CO2 partial pressure between the Substomatal Cavity and chloroplast was smaller, leading to the conclusion that this factor was not causally involved in midday depression. Carboxylation capacity inferred from the CO2 response of photosynthesis increased between 28 and 33 °C, but remained unchanged between 33 and 38 °C. Increased oxygenation of ribulose-1,5-bisphosphate relative to its carboxylation and the concomitant increase in photorespiration with increasing Tleaf were thus not compensated by an increase in carboxylation capacity over the higher temperature range. This was the principal reason for the negative effect of high midday temperatures on mesophyll functioning.
Alain Pugin - One of the best experts on this subject based on the ideXlab platform.
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Stomatal deregulation in plasmopara viticola-infected grapevine leaves
New Phytologist, 2007Co-Authors: Mathilde Allegre, Sophie Trouvelot, Xavier Daire, Marielle Adrian, Marie-claire Héloir, Laurence Mercier, Alain PuginAbstract:In grapevine, the penetration and sporulation of Plasmopara viticola occur via stomata, suggesting functional relationships between guard cells and the pathogen. This assumption was supported by our first observation that grapevine (Vitis vinifera cv. Marselan) cuttings infected by P. viticola wilted more rapidly than healthy ones when submitted to water starvation. • Here, complementary approaches measuring stomatal conductance and infrared thermographic and microscopic observations were used to investigate stomatal opening/closure in response to infection. • In infected leaves, stomata remained open in darkness and during water stress, leading to increased transpiration. This deregulation was restricted to the colonized area, was not systemic and occurred before the appearance of symptoms. Cytological observations indicated that stomatal lock-open was not related to mechanical forces resulting from the presence of the pathogen in the Substomatal Cavity. In contrast to healthy leaves, stomatal closure in excised infected leaves could not be induced by a water deficit or abscisic acid (ABA)treatment. However, ABA induced stomatal closure in epidermal peels from infected leaves, indicating that guard cells remained functional. • These data indicate that the oomycete deregulates guard cell functioning, causing significant water losses. This effect could be attributed to a nonsystemic compound, produced by the oomycete or by the infected plant, which inhibits stomatal closure or induces stomatal opening; or a reduction of the back-pressure exerted by surrounding epidermal cells. Both hypotheses are under investigation.
Mathilde Allegre - One of the best experts on this subject based on the ideXlab platform.
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Stomatal deregulation in plasmopara viticola-infected grapevine leaves
New Phytologist, 2007Co-Authors: Mathilde Allegre, Sophie Trouvelot, Xavier Daire, Marielle Adrian, Marie-claire Héloir, Laurence Mercier, Alain PuginAbstract:In grapevine, the penetration and sporulation of Plasmopara viticola occur via stomata, suggesting functional relationships between guard cells and the pathogen. This assumption was supported by our first observation that grapevine (Vitis vinifera cv. Marselan) cuttings infected by P. viticola wilted more rapidly than healthy ones when submitted to water starvation. • Here, complementary approaches measuring stomatal conductance and infrared thermographic and microscopic observations were used to investigate stomatal opening/closure in response to infection. • In infected leaves, stomata remained open in darkness and during water stress, leading to increased transpiration. This deregulation was restricted to the colonized area, was not systemic and occurred before the appearance of symptoms. Cytological observations indicated that stomatal lock-open was not related to mechanical forces resulting from the presence of the pathogen in the Substomatal Cavity. In contrast to healthy leaves, stomatal closure in excised infected leaves could not be induced by a water deficit or abscisic acid (ABA)treatment. However, ABA induced stomatal closure in epidermal peels from infected leaves, indicating that guard cells remained functional. • These data indicate that the oomycete deregulates guard cell functioning, causing significant water losses. This effect could be attributed to a nonsystemic compound, produced by the oomycete or by the infected plant, which inhibits stomatal closure or induces stomatal opening; or a reduction of the back-pressure exerted by surrounding epidermal cells. Both hypotheses are under investigation.
Heinz W. Gäggeler - One of the best experts on this subject based on the ideXlab platform.
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Tracing uptake and assimilation of NO2 in spruce needles with 13N
Journal of Experimental Botany, 1995Co-Authors: Markus Ammann, Michael Stalder, Marianne Suter, Christian Brunold, Urs Baltensperger, D. T. Jost, Andreas Türler, Heinz W. GäggelerAbstract:For the first time, spruce shoots (Picea abies [L.] Karst.) were fumigated in vivo with 13 N-labelled NO 2 with the aim of elucidating the mechanism of NO 2 -trapping in the apoplast of the Substomatal Cavity. Uptake by the needles could be monitored on-line, and a quantitative analysis of the activity records delivered a deposition velocity in agreement with the common dry deposition estimates and ruled out rapid export processes. A fast extraction procedure was applied which revealed that NO 2 did not produce any detectable traces of nitrite. In needles in which the enzymes of nitrate reduction were not induced by prior fumigation with NO 2 , incorporation of NO 2 was partially inhibited as compared to the fully induced shoots which took up and assimilated NO 2 as expected from a constant influx. The only labelled inorganic species found in the extracts was nitrate (60%), whereas the rest of the label (40%) was assimilated organic nitrogen. A quantitative analysis of the data shows that the reaction of NO 2 in the apoplast yields at least three times more nitrate than nitrite, so that the existing models about the apoplastic trapping reaction, disproportionation or antioxidant scavenging, which both postulate substantial production of nitrite, have to be reconsidered.
