| 1. |
- Wieloch, Thomas, 1979-, et al.
(author)
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A model of photosynthetic CO2 assimilation in C3 leaves accounting for respiration and energy recycling by the plastidial oxidative pentose phosphate pathway
- 2023
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In: New Phytologist. - : John Wiley & Sons. - 0028-646X .- 1469-8137. ; 239:2, s. 518-532
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Journal article (peer-reviewed)abstract
- Recently, we reported estimates of anaplerotic carbon flux through the oxidative pentose phosphate pathway (OPPP) in chloroplasts into the Calvin–Benson cycle. These estimates were based on intramolecular hydrogen isotope analysis of sunflower leaf starch. However, the isotope method is believed to underestimate the actual flux at low atmospheric CO2 concentration (Ca).Since the OPPP releases CO2 and reduces NADP+, it can be expected to affect leaf gas exchange under both rubisco- and RuBP-regeneration-limited conditions. Therefore, we expanded Farquhar-von Caemmerer–Berry models to account for OPPP metabolism. Based on model parameterisation with values from the literature, we estimated OPPP-related effects on leaf carbon and energy metabolism in the sunflowers analysed previously.We found that flux through the plastidial OPPP increases both above and below Ca ≈ 450 ppm (the condition the plants were acclimated to). This is qualitatively consistent with our previous isotope-based estimates, yet gas-exchange-based estimates are larger at low Ca.We discuss our results in relation to regulatory properties of the plastidial and cytosolic OPPP, the proposed variability of CO2 mesophyll conductance, and the contribution of day respiration to the A/Ci curve drop at high Ca. Furthermore, we critically examine the models and parameterisation and derive recommendations for follow-up studies.
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| 2. |
- Wieloch, Thomas, 1979-, et al.
(author)
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Anaplerotic flux into the Calvin-Benson cycle. Integration in carbon and energy metabolism of Helianthus annuus
- 2024
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Other publication (other academic/artistic)abstract
- Plants assimilate carbon primarily via the Calvin-Benson cycle. Two companion papers report evidence for anaplerotic carbon flux into this cycle. To estimate flux rates in Helianthus annuus leaves based on gas exchange measurements, we here expanded Farquhar-von Caemmerer-Berry photosynthesis models by terms accounting for anaplerotic respiration and energy recycling. In line with reported isotope evidence (companion papers), we found relative increases in anaplerotic flux as intercellular CO2 concentrations, Ci, decrease below a change point. At Ci=136 and 202 ppm, we found absolute rates of 2.99 and 2.39 μmol Ru5P m−2 s−1 corresponding to 58.3 and 28.2% of net CO2 assimilation, 13.1 and 10.7% of ribulose 1,5-bisphosphate regeneration, and 22.2 and 15.8% of Rubisco carboxylation (futile carbon cycling), respectively. Anaplerotic respiration governs total day respiration with contributions of 81.3 and 77.6%, and anaplerotic relative to photorespiratory CO2 release amounts to 63.9 and 67%, respectively. Furthermore, anaplerotic flux significantly increases absolute ATP demands and ATP-to-NADPH demand ratios of photosynthesis and may explain increasing sucrose-to-starch carbon partitioning ratios with decreasing Ci. We propose that anaplerotic flux can occur under both Rubisco and RuBP-limited growth conditions. Overall, our work introduces the anaplerotic pathway as central component in carbon and energy metabolism of C3 plants.
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| 3. |
- Wieloch, Thomas, 1979-, et al.
(author)
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Anaplerotic flux into the Calvin-Benson cycle. Isotope evidence for in vivo occurrence in Helianthus annuus
- 2024
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Other publication (other academic/artistic)abstract
- - As the central carbon uptake pathway in photosynthetic cells, the Calvin-Benson cycle is among the most important biochemical cycles for life on Earth. Recently, anaplerotic carbon flux (through the chloroplast-localised oxidative branch of the pentose phosphate pathway) into this cycle was proposed.- Here, we measured intramolecular deuterium abundances in leaf starch of Helianthus annuus grown at varying ambient CO2 concentrations, Ca. Additionally, we modelled deuterium fractionations expected for the anaplerotic pathway and compared modelled with measured fractionations.- We report deuterium fractionation signals at starch glucose H1 and H2. Below a response change point, these signals increase with decreasing Ca consistent with modelled fractionations by anaplerotic flux. Under normal growth conditions (Ca≥450 ppm corresponding to intercellular CO2 concentrations, Ci, ≥328 ppm), we estimate negligible anaplerotic flux. At Ca=180 ppm (Ci=140 ppm), we estimate that of the glucose 6-phosphate entering the starch biosynthesis pathway more than 11.5% is diverted into the anaplerotic pathway.- In conclusion, we report evidence consistent with anaplerotic carbon flux into the Calvin-Benson cycle in vivo. We propose the flux may help to (i) maintain high levels of ribulose 1,5-bisphosphate under source-limited growth conditions to facilitate photorespiratory nitrogen assimilation required to build-up source strength and (ii) counteract oxidative stress.
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| 4. |
- Wieloch, Thomas, 1979-, et al.
(author)
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Anaplerotic flux into the Calvin–Benson cycle: hydrogen isotope evidence for in vivo occurrence in C 3 metabolism
- 2022
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In: New Phytologist. - : John Wiley & Sons. - 0028-646X .- 1469-8137. ; 234:2, s. 405-411
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Journal article (peer-reviewed)abstract
- As the central carbon uptake pathway in photosynthetic cells, the Calvin–Benson cycle is among the most important biochemical cycles for life on Earth. A carbon flux of anaplerotic origin (i.e. through the chloroplast-localized oxidative branch of the pentose phosphate pathway) into the Calvin–Benson cycle was proposed recently.Here, we measured intramolecular deuterium abundances in leaf starch of Helianthus annuus grown at varying ambient CO2 concentrations, Ca. Additionally, we modelled deuterium fractionations expected for the anaplerotic pathway and compared modelled with measured fractionations.We report deuterium fractionation signals at H1 and H2 of starch glucose. Below a Ca change point, these signals increase with decreasing Ca consistent with modelled fractionations by anaplerotic flux. Under standard conditions (Ca = 450 ppm corresponding to intercellular CO2 concentrations, Ci, of 328 ppm), we estimate negligible anaplerotic flux. At Ca = 180 ppm (Ci = 140 ppm), more than 10% of the glucose-6-phosphate entering the starch biosynthesis pathway is diverted into the anaplerotic pathway.In conclusion, we report evidence consistent with anaplerotic carbon flux into the Calvin–Benson cycle in vivo. We propose the flux may help to: maintain high levels of ribulose 1,5-bisphosphate under source-limited growth conditions to facilitate photorespiratory nitrogen assimilation required to build-up source strength; and counteract oxidative stress.
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| 5. |
- Wieloch, Thomas, 1979-, et al.
(author)
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Metabolism is a major driver of hydrogen isotope fractionation recorded in tree‐ring glucose of Pinus nigra
- 2022
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In: New Phytologist. - : John Wiley & Sons. - 0028-646X .- 1469-8137. ; 234:2, s. 449-461
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Journal article (peer-reviewed)abstract
- Stable isotope abundances convey valuable information about plant physiological processes and underlying environmental controls. Central gaps in our mechanistic understanding of hydrogen isotope abundances impede their widespread application within the plant and biogeosciences.To address these gaps, we analysed intramolecular deuterium abundances in glucose of Pinus nigra extracted from an annually resolved tree-ring series (1961–1995).We found fractionation signals (i.e. temporal variability in deuterium abundance) at glucose H1 and H2 introduced by closely related metabolic processes. Regression analysis indicates that these signals (and thus metabolism) respond to drought and atmospheric CO2 concentration beyond a response change point. They explain ≈ 60% of the whole-molecule deuterium variability. Altered metabolism is associated with below-average yet not exceptionally low growth.We propose the signals are introduced at the leaf level by changes in sucrose-to-starch carbon partitioning and anaplerotic carbon flux into the Calvin–Benson cycle. In conclusion, metabolism can be the main driver of hydrogen isotope variation in plant glucose.
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| 6. |
- Wieloch, Thomas, 1979-, et al.
(author)
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Metabolism is the major driver of hydrogen isotope fractionation recorded in tree-ring glucose of Pinus nigra
- 2021
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Other publication (other academic/artistic)abstract
- - Stable isotope abundances convey valuable information about plant physiological processes and underlying environmental controls. Central gaps in our mechanistic understanding of hydrogen isotope abundances impede their widespread application within the plant and Earth sciences.- To close these gaps, we analysed intramolecular deuterium abundances in glucose of Pinus nigra extracted from an annually resolved tree-ring series (1961 to 1995).- We found fractionation signals at glucose H1 and H2 introduced by closely related metabolic processes. These signals (and thus metabolism) respond to drought and atmospheric CO2 concentration beyond a response change point. They explain ≈60% of the whole-molecule deuterium variability. Altered metabolism is associated with below-average yet not exceptionally low growth.- We propose the signals are introduced at the leaf-level by changes in sucrose-to-starch carbon partitioning and anaplerotic carbon flux into the Calvin-Benson cycle. In conclusion, metabolism can be the main driver of hydrogen isotope variation in plant glucose.
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