The Experts below are selected from a list of 282 Experts worldwide ranked by ideXlab platform
Fabrice Rappaport - One of the best experts on this subject based on the ideXlab platform.
-
the mechanism of cyclic Electron Flow
Biochimica et Biophysica Acta, 2019Co-Authors: W J Nawrocki, Benjamin Bailleul, Daniel Picot, Pierre Cardol, Fabrice Rappaport, F A Wollman, Pierre JoliotAbstract:Abstract Apart from the canonical light-driven linear Electron Flow (LEF) from water to CO2, numerous regulatory and alternative Electron transfer pathways exist in chloroplasts. One of them is the cyclic Electron Flow around Photosystem I (CEF), contributing to photoprotection of both Photosystem I and II (PSI, PSII) and supplying extra ATP to fix atmospheric carbon. Nonetheless, CEF remains an enigma in the field of functional photosynthesis as we lack understanding of its pathway. Here, we address the discrepancies between functional and genetic/biochemical data in the literature and formulate novel hypotheses about the pathway and regulation of CEF based on recent structural and kinetic information.
-
Cyclic Electron Flow in Chlamydomonas reinhardtii
bioRxiv, 2017Co-Authors: W J Nawrocki, Benjamin Bailleul, Pierre Cardol, Fabrice Rappaport, F A Wollman, Pierre JoliotAbstract:Cyclic Electron Flow (CEF), one of the major alternative Electron transport pathways to the primary linear Electron Flow (LEF) in chloroplasts has been discovered in the middle of the last century. It is defined as a return of the reductants from the acceptor side of the Photosystem I (PSI) to the pool of its donors via the cytochrome b6f, and has proven essential for photosynthesis. However, despite many efforts aimed at its characterisation, the pathway and regulation of CEF remain equivocal, and its physiological significance remains to be properly defined. Here we use novel spectroscopic approaches to measure CEF in transitory conditions in the green alga Chlamydomonas reinhardtii. We show that CEF operates at the same maximal rate regardless of the oxygen concentration, and that the latter influences LEF, rather than CEF in vivo, which questions the recent hypotheses about the CEF supercomplex formation. We further reveal that the pathways proposed for CEF in the literature are inconsistent with the kinetic information provided by our measurements. We finally provide cues on the regulation of CEF by light.
-
cyclic Electron Flow is redox controlled but independent of state transition
Nature Communications, 2013Co-Authors: Hiroko Takahashi, F A Wollman, Sophie Clowez, Olivier Vallon, Fabrice RappaportAbstract:The switch from linear to cyclic Electron Flow has long been thought to rely on the migration of antenna proteins from Photosystem II to Photosystem I. Takahashi et al. report that this is not the case and that cyclic Electron Flow is tuned by the intrachloroplastic redox power.
-
redox and atp control of photosynthetic cyclic Electron Flow in chlamydomonas reinhardtii i aerobic conditions
Biochimica et Biophysica Acta, 2010Co-Authors: Jean Alric, Jerome Lavergne, Fabrice RappaportAbstract:Abstract Assimilation of atmospheric CO2 by photosynthetic organisms such as plants, cyanobacteria and green algae, requires the production of ATP and NADPH in a ratio of 3:2. The oxygenic photosynthetic chain can function following two different modes: the linear Electron Flow which produces reducing power and ATP, and the cyclic Electron Flow which only produces ATP. Some regulation between the linear and cyclic Flows is required for adjusting the stoichiometric production of high-energy bonds and reducing power. Here we explore, in the green alga Chlamydomonas reinhardtii, the onset of the cyclic Electron Flow during a continuous illumination under aerobic conditions. In mutants devoid of Rubisco or ATPase, where the reducing power cannot be used for carbon fixation, we observed a stimulation of the cyclic Electron Flow. The present data show that the cyclic Electron Flow can operate under aerobic conditions and support a simple competition model where the excess reducing power is recycled to match the demand for ATP.
-
involvement of state transitions in the switch between linear and cyclic Electron Flow in chlamydomonas reinhardtii
EMBO Reports, 2002Co-Authors: Giovanni Finazzi, Fabrice Rappaport, Alberto Furia, Mark Mike Fleischmann, Jeandavid Rochaix, Francesca Zito, Giorgio FortiAbstract:The energetic metabolism of photosynthetic organisms is profoundly influenced by state transitions and cyclic Electron Flow around photosystem I. The former involve a reversible redistribution of the light-harvesting antenna between photosystem I and photosystem II and optimize light energy utilization in photosynthesis whereas the latter process modulates the photosynthetic yield. We have used the wild-type and three mutant strains of the green alga Chlamydomonas reinhardtii—locked in state I (stt7), lacking the photosystem II outer antennae (bf4) or accumulating low amounts of cytochrome b6f complex (A-AUU)—and measured Electron Flow though the cytochrome b6f complex, oxygen evolution rates and fluorescence emission during state transitions. The results demonstrate that the transition from state 1 to state 2 induces a switch from linear to cyclic Electron Flow in this alga and reveal a strict cause–effect relationship between the redistribution of antenna complexes during state transitions and the onset of cyclic Electron Flow.
Giovanni Finazzi - One of the best experts on this subject based on the ideXlab platform.
-
Cyclic Electron Flow: facts and hypotheses
Photosynthesis Research, 2016Co-Authors: Giovanni Finazzi, Giles N. JohnsonAbstract:Over the last 15 years, research into the process of cyclic Electron Flow in photosynthesis has seen a huge resurgence. Having been considered by some in the early 1990s as a physiologically unimportant artefact, it is now recognised as essential to normal plant growth. Here, we provide an overview of the major developments covered in this special issue of photosynthesis research.
-
alternative photosynthetic Electron Flow to oxygen in marine synechococcus
Biochimica et Biophysica Acta, 2008Co-Authors: Shaun Bailey, Pierre Cardol, Giovanni Finazzi, Anastasios Melis, Katherine R M Mackey, Gert L Van Dijken, Gry Mine Berg, Kevin R ArrigoAbstract:Cyanobacteria dominate the world's oceans where iron is often barely detectable. One manifestation of low iron adaptation in the oligotrophic marine environment is a decrease in levels of iron-rich photosynthetic components, including the reaction center of photosystem I and the cytochrome b6f complex [R.F. Strzepek and P.J. Harrison, Photosynthetic architecture differs in coastal and oceanic diatoms, Nature 431 (2004) 689–692.]. These thylakoid membrane components have well characterised roles in linear and cyclic photosynthetic Electron transport and their low abundance creates potential impediments to photosynthetic function. Here we show that the marine cyanobacterium Synechococcus WH8102 exhibits significant alternative Electron Flow to O2, a potential adaptation to the low iron environment in oligotrophic oceans. This alternative Electron Flow appears to extract Electrons from the intersystem Electron transport chain, prior to photosystem I. Inhibitor studies demonstrate that a propyl gallate-sensitive oxidase mediates this Flow of Electrons to oxygen, which in turn alleviates excessive photosystem II excitation pressure that can often occur even at relatively low irradiance. These findings are also discussed in the context of satisfying the energetic requirements of the cell when photosystem I abundance is low.
-
redox modulation of cyclic Electron Flow around photosystem i in c3 plants
Biochemistry, 2006Co-Authors: Cecile Breyton, Pierre Joliot, Giles N. Johnson, Beena Nandha, Giovanni FinazziAbstract:We have investigated the occurrence of cyclic Electron Flow in intact spinach leaves. In particular, we have tested the hypothesis that cyclic Flow requires the presence of supercomplexes in the thylakoid membrane or other strong associations between proteins. Using biochemical approaches, we found no evidence of the presence of supercomplexes related to cyclic Electron Flow, making previous structural explanations for the modulation of cyclic Flow rather unlikely. On the other hand, we found that the fraction of photosystem I complexes engaged in cyclic Flow could be modulated by changes in the redox state of the chloroplast stroma. Our findings support therefore a dynamic model for the occurrence of linear and cyclic Electron Flow in C3 plants, based on the competition between cytochrome b6f and FNR for Electrons carried by ferredoxin. This would be ultimately regulated by the balance between the redox state of PSI acceptors and donors during photosynthesis, in a diffusing system. Photosynthesis involves the transfer of Electrons from water to NADP + via two photosystems, the so-called linear path, forming NADPH. Electron transfer also results in proton translocation across the thylakoid membrane, generat- ing a transmembrane pH gradient, which drives the synthesis of ATP. Both NADPH and ATP are then used for carbon fixation. Given that the H + /ATP efficiency of this process
-
involvement of state transitions in the switch between linear and cyclic Electron Flow in chlamydomonas reinhardtii
EMBO Reports, 2002Co-Authors: Giovanni Finazzi, Fabrice Rappaport, Alberto Furia, Mark Mike Fleischmann, Jeandavid Rochaix, Francesca Zito, Giorgio FortiAbstract:The energetic metabolism of photosynthetic organisms is profoundly influenced by state transitions and cyclic Electron Flow around photosystem I. The former involve a reversible redistribution of the light-harvesting antenna between photosystem I and photosystem II and optimize light energy utilization in photosynthesis whereas the latter process modulates the photosynthetic yield. We have used the wild-type and three mutant strains of the green alga Chlamydomonas reinhardtii—locked in state I (stt7), lacking the photosystem II outer antennae (bf4) or accumulating low amounts of cytochrome b6f complex (A-AUU)—and measured Electron Flow though the cytochrome b6f complex, oxygen evolution rates and fluorescence emission during state transitions. The results demonstrate that the transition from state 1 to state 2 induces a switch from linear to cyclic Electron Flow in this alga and reveal a strict cause–effect relationship between the redistribution of antenna complexes during state transitions and the onset of cyclic Electron Flow.
Pierre Joliot - One of the best experts on this subject based on the ideXlab platform.
-
the mechanism of cyclic Electron Flow
Biochimica et Biophysica Acta, 2019Co-Authors: W J Nawrocki, Benjamin Bailleul, Daniel Picot, Pierre Cardol, Fabrice Rappaport, F A Wollman, Pierre JoliotAbstract:Abstract Apart from the canonical light-driven linear Electron Flow (LEF) from water to CO2, numerous regulatory and alternative Electron transfer pathways exist in chloroplasts. One of them is the cyclic Electron Flow around Photosystem I (CEF), contributing to photoprotection of both Photosystem I and II (PSI, PSII) and supplying extra ATP to fix atmospheric carbon. Nonetheless, CEF remains an enigma in the field of functional photosynthesis as we lack understanding of its pathway. Here, we address the discrepancies between functional and genetic/biochemical data in the literature and formulate novel hypotheses about the pathway and regulation of CEF based on recent structural and kinetic information.
-
Cyclic Electron Flow in Chlamydomonas reinhardtii
bioRxiv, 2017Co-Authors: W J Nawrocki, Benjamin Bailleul, Pierre Cardol, Fabrice Rappaport, F A Wollman, Pierre JoliotAbstract:Cyclic Electron Flow (CEF), one of the major alternative Electron transport pathways to the primary linear Electron Flow (LEF) in chloroplasts has been discovered in the middle of the last century. It is defined as a return of the reductants from the acceptor side of the Photosystem I (PSI) to the pool of its donors via the cytochrome b6f, and has proven essential for photosynthesis. However, despite many efforts aimed at its characterisation, the pathway and regulation of CEF remain equivocal, and its physiological significance remains to be properly defined. Here we use novel spectroscopic approaches to measure CEF in transitory conditions in the green alga Chlamydomonas reinhardtii. We show that CEF operates at the same maximal rate regardless of the oxygen concentration, and that the latter influences LEF, rather than CEF in vivo, which questions the recent hypotheses about the CEF supercomplex formation. We further reveal that the pathways proposed for CEF in the literature are inconsistent with the kinetic information provided by our measurements. We finally provide cues on the regulation of CEF by light.
-
regulation of cyclic and linear Electron Flow in higher plants
Proceedings of the National Academy of Sciences of the United States of America, 2011Co-Authors: Pierre Joliot, Giles N. JohnsonAbstract:Cyclic Electron Flow is increasingly recognized as being essential in plant growth, generating a pH gradient across thylakoid membrane (ΔpH) that contributes to ATP synthesis and triggers the protective process of nonphotochemical quenching (NPQ) under stress conditions. Here, we report experiments demonstrating the importance of that ΔpH in protecting plants from stress and relating to the regulation of cyclic relative to linear Flow. In leaves infiltrated with low concentrations of nigericin, which dissipates the ΔpH without significantly affecting the potential gradient, thereby maintaining ATP synthesis, the extent of NPQ was markedly lower, reflecting the lower ΔpH. At the same time, the photosystem (PS) I primary donor P700 was largely reduced in the light, in contrast to control conditions where increasing light progressively oxidized P700, due to down-regulation of the cytochrome bf complex. Illumination of nigericin-infiltrated leaves resulted in photoinhibition of PSII but also, more markedly, of PSI. Plants lacking ferredoxin (Fd) NADP oxidoreductase (FNR) or the polypeptide proton gradient regulation 5 (PGR5) also show reduction of P700 in the light and increased sensitivity to PSI photoinhibition, demonstrating that the regulation of the cytochrome bf complex (cyt bf) is essential for protection of PSI from light stress. The formation of a ΔpH is concluded to be essential to that regulation, with cyclic Electron Flow playing a vital, previously poorly appreciated role in this protective process. Examination of cyclic Electron Flow in plants with a reduced content of FNR shows that these antisense plants are less able to maintain a steady rate of this pathway. This reduction is suggested to reflect a change in the distribution of FNR from cyclic to linear Flow, likely reflecting the formation or disassembly of FNR–cytochrome bf complex.
-
redox modulation of cyclic Electron Flow around photosystem i in c3 plants
Biochemistry, 2006Co-Authors: Cecile Breyton, Pierre Joliot, Giles N. Johnson, Beena Nandha, Giovanni FinazziAbstract:We have investigated the occurrence of cyclic Electron Flow in intact spinach leaves. In particular, we have tested the hypothesis that cyclic Flow requires the presence of supercomplexes in the thylakoid membrane or other strong associations between proteins. Using biochemical approaches, we found no evidence of the presence of supercomplexes related to cyclic Electron Flow, making previous structural explanations for the modulation of cyclic Flow rather unlikely. On the other hand, we found that the fraction of photosystem I complexes engaged in cyclic Flow could be modulated by changes in the redox state of the chloroplast stroma. Our findings support therefore a dynamic model for the occurrence of linear and cyclic Electron Flow in C3 plants, based on the competition between cytochrome b6f and FNR for Electrons carried by ferredoxin. This would be ultimately regulated by the balance between the redox state of PSI acceptors and donors during photosynthesis, in a diffusing system. Photosynthesis involves the transfer of Electrons from water to NADP + via two photosystems, the so-called linear path, forming NADPH. Electron transfer also results in proton translocation across the thylakoid membrane, generat- ing a transmembrane pH gradient, which drives the synthesis of ATP. Both NADPH and ATP are then used for carbon fixation. Given that the H + /ATP efficiency of this process
Jean Alric - One of the best experts on this subject based on the ideXlab platform.
-
Cyclic Electron Flow around photosystem I in unicellular green algae
Photosynthesis Research, 2010Co-Authors: Jean AlricAbstract:Cyclic Electron Flow around PSI, or cyclic photophosphorylation, is the photosynthetic process which recycles the reducing equivalents produced by photosystem I in the stroma towards the plastoquinone pool. Through the activity of cytochrome b _6 f , which also transfers protons across the membrane, it promotes the synthesis of ATP. The literature dealing with cyclic Electron Flow in unicellular algae is far less abundant than it is for plants. However, in the chloroplast of algae such as Chlorella or Chlamydomonas, an efficient carbohydrate catabolism renders the redox poise much more reducing than in plant chloroplasts. It is therefore worthwhile highlighting the specific properties of unicellular algae because cyclic Electron Flow is highly dependent upon the accumulation of these stromal reducing equivalents. Such an increase of reducing power in the stroma stimulates the reduction of plastoquinones, which is the limiting step of cyclic Electron Flow. In anaerobic conditions in the dark, this reaction can lead to a fully reduced plastoquinone pool and induce state transitions, the migration of 80% of light harvesting complexes II and 20% of cytochrome b _6 f complex from the PSII-enriched grana to the PSI-enriched lamella. These ultrastructural changes have been proposed to further enhance cyclic Electron Flow by increasing PSI antenna size, and forming PSI-cyt b _6 f supercomplexes. These hypotheses are discussed in light of recently published data.
-
redox and atp control of photosynthetic cyclic Electron Flow in chlamydomonas reinhardtii i aerobic conditions
Biochimica et Biophysica Acta, 2010Co-Authors: Jean Alric, Jerome Lavergne, Fabrice RappaportAbstract:Abstract Assimilation of atmospheric CO2 by photosynthetic organisms such as plants, cyanobacteria and green algae, requires the production of ATP and NADPH in a ratio of 3:2. The oxygenic photosynthetic chain can function following two different modes: the linear Electron Flow which produces reducing power and ATP, and the cyclic Electron Flow which only produces ATP. Some regulation between the linear and cyclic Flows is required for adjusting the stoichiometric production of high-energy bonds and reducing power. Here we explore, in the green alga Chlamydomonas reinhardtii, the onset of the cyclic Electron Flow during a continuous illumination under aerobic conditions. In mutants devoid of Rubisco or ATPase, where the reducing power cannot be used for carbon fixation, we observed a stimulation of the cyclic Electron Flow. The present data show that the cyclic Electron Flow can operate under aerobic conditions and support a simple competition model where the excess reducing power is recycled to match the demand for ATP.
Giles N. Johnson - One of the best experts on this subject based on the ideXlab platform.
-
Cyclic Electron Flow: facts and hypotheses
Photosynthesis Research, 2016Co-Authors: Giovanni Finazzi, Giles N. JohnsonAbstract:Over the last 15 years, research into the process of cyclic Electron Flow in photosynthesis has seen a huge resurgence. Having been considered by some in the early 1990s as a physiologically unimportant artefact, it is now recognised as essential to normal plant growth. Here, we provide an overview of the major developments covered in this special issue of photosynthesis research.
-
regulation of cyclic and linear Electron Flow in higher plants
Proceedings of the National Academy of Sciences of the United States of America, 2011Co-Authors: Pierre Joliot, Giles N. JohnsonAbstract:Cyclic Electron Flow is increasingly recognized as being essential in plant growth, generating a pH gradient across thylakoid membrane (ΔpH) that contributes to ATP synthesis and triggers the protective process of nonphotochemical quenching (NPQ) under stress conditions. Here, we report experiments demonstrating the importance of that ΔpH in protecting plants from stress and relating to the regulation of cyclic relative to linear Flow. In leaves infiltrated with low concentrations of nigericin, which dissipates the ΔpH without significantly affecting the potential gradient, thereby maintaining ATP synthesis, the extent of NPQ was markedly lower, reflecting the lower ΔpH. At the same time, the photosystem (PS) I primary donor P700 was largely reduced in the light, in contrast to control conditions where increasing light progressively oxidized P700, due to down-regulation of the cytochrome bf complex. Illumination of nigericin-infiltrated leaves resulted in photoinhibition of PSII but also, more markedly, of PSI. Plants lacking ferredoxin (Fd) NADP oxidoreductase (FNR) or the polypeptide proton gradient regulation 5 (PGR5) also show reduction of P700 in the light and increased sensitivity to PSI photoinhibition, demonstrating that the regulation of the cytochrome bf complex (cyt bf) is essential for protection of PSI from light stress. The formation of a ΔpH is concluded to be essential to that regulation, with cyclic Electron Flow playing a vital, previously poorly appreciated role in this protective process. Examination of cyclic Electron Flow in plants with a reduced content of FNR shows that these antisense plants are less able to maintain a steady rate of this pathway. This reduction is suggested to reflect a change in the distribution of FNR from cyclic to linear Flow, likely reflecting the formation or disassembly of FNR–cytochrome bf complex.
-
redox modulation of cyclic Electron Flow around photosystem i in c3 plants
Biochemistry, 2006Co-Authors: Cecile Breyton, Pierre Joliot, Giles N. Johnson, Beena Nandha, Giovanni FinazziAbstract:We have investigated the occurrence of cyclic Electron Flow in intact spinach leaves. In particular, we have tested the hypothesis that cyclic Flow requires the presence of supercomplexes in the thylakoid membrane or other strong associations between proteins. Using biochemical approaches, we found no evidence of the presence of supercomplexes related to cyclic Electron Flow, making previous structural explanations for the modulation of cyclic Flow rather unlikely. On the other hand, we found that the fraction of photosystem I complexes engaged in cyclic Flow could be modulated by changes in the redox state of the chloroplast stroma. Our findings support therefore a dynamic model for the occurrence of linear and cyclic Electron Flow in C3 plants, based on the competition between cytochrome b6f and FNR for Electrons carried by ferredoxin. This would be ultimately regulated by the balance between the redox state of PSI acceptors and donors during photosynthesis, in a diffusing system. Photosynthesis involves the transfer of Electrons from water to NADP + via two photosystems, the so-called linear path, forming NADPH. Electron transfer also results in proton translocation across the thylakoid membrane, generat- ing a transmembrane pH gradient, which drives the synthesis of ATP. Both NADPH and ATP are then used for carbon fixation. Given that the H + /ATP efficiency of this process