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Krishna K. Niyogi - One of the best experts on this subject based on the ideXlab platform.
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a Thylakoid Membrane bound and redox active rubredoxin rbd1 functions in de novo assembly and repair of photosystem ii
Proceedings of the National Academy of Sciences of the United States of America, 2019Co-Authors: Jose G Garciacerdan, Ariel L. Furst, Kent L. Mcdonald, Danja Schunemann, Matthew B. Francis, Krishna K. NiyogiAbstract:Author(s): Garcia-Cerdan, Jose G; Furst, Ariel L; McDonald, Kent L; Schunemann, Danja; Francis, Matthew B; Niyogi, Krishna K | Abstract: Photosystem II (PSII) undergoes frequent photooxidative damage that, if not repaired, impairs photosynthetic activity and growth. How photosynthetic organisms protect vulnerable PSII intermediate complexes during de novo assembly and repair remains poorly understood. Here, we report the genetic and biochemical characterization of chloroplast-located rubredoxin 1 (RBD1), a PSII assembly factor containing a redox-active rubredoxin domain and a single C-terminal transMembrane α-helix (TMH) domain. RBD1 is an integral Thylakoid Membrane Protein that is enriched in stroma lamellae fractions with the rubredoxin domain exposed on the stromal side. RBD1 also interacts with PSII intermediate complexes containing cytochrome b 559 Complementation of the Chlamydomonas reinhardtii (hereafter Chlamydomonas) RBD1-deficient 2pac mutant with constructs encoding RBD1 Protein truncations and site-directed mutations demonstrated that the TMH domain is essential for de novo PSII assembly, whereas the rubredoxin domain is involved in PSII repair. The rubredoxin domain exhibits a redox midpoint potential of +114 mV and is proficient in 1-electron transfers to a surrogate cytochrome c in vitro. Reduction of oxidized RBD1 is NADPH dependent and can be mediated by ferredoxin-NADP+ reductase (FNR) in vitro. We propose that RBD1 participates, together with the cytochrome b 559, in the protection of PSII intermediate complexes from photooxidative damage during de novo assembly and repair. This role of RBD1 is consistent with its evolutionary conservation among photosynthetic organisms and the fact that it is essential in photosynthetic eukaryotes.
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a Thylakoid Membrane bound and redox active rubredoxin rbd1 functions in de novo assembly and repair of photosystem ii
Proceedings of the National Academy of Sciences of the United States of America, 2019Co-Authors: Jose G Garciacerdan, Ariel L. Furst, Kent L. Mcdonald, Danja Schunemann, Krishna K. Niyogi, Matthew B. FrancisAbstract:Photosystem II (PSII) undergoes frequent photooxidative damage that, if not repaired, impairs photosynthetic activity and growth. How photosynthetic organisms protect vulnerable PSII intermediate complexes during de novo assembly and repair remains poorly understood. Here, we report the genetic and biochemical characterization of chloroplast-located rubredoxin 1 (RBD1), a PSII assembly factor containing a redox-active rubredoxin domain and a single C-terminal transMembrane α-helix (TMH) domain. RBD1 is an integral Thylakoid Membrane Protein that is enriched in stroma lamellae fractions with the rubredoxin domain exposed on the stromal side. RBD1 also interacts with PSII intermediate complexes containing cytochrome b 559 Complementation of the Chlamydomonas reinhardtii (hereafter Chlamydomonas) RBD1-deficient 2pac mutant with constructs encoding RBD1 Protein truncations and site-directed mutations demonstrated that the TMH domain is essential for de novo PSII assembly, whereas the rubredoxin domain is involved in PSII repair. The rubredoxin domain exhibits a redox midpoint potential of +114 mV and is proficient in 1-electron transfers to a surrogate cytochrome c in vitro. Reduction of oxidized RBD1 is NADPH dependent and can be mediated by ferredoxin-NADP+ reductase (FNR) in vitro. We propose that RBD1 participates, together with the cytochrome b 559, in the protection of PSII intermediate complexes from photooxidative damage during de novo assembly and repair. This role of RBD1 is consistent with its evolutionary conservation among photosynthetic organisms and the fact that it is essential in photosynthetic eukaryotes.
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a thioredoxin like β propeller Protein maintains the efficiency of light harvesting in arabidopsis
Proceedings of the National Academy of Sciences of the United States of America, 2013Co-Authors: Matthew D Brooks, Krishna K. Niyogi, Emily Sylakglassman, Graham R FlemingAbstract:The light-harvesting complexes of plants have evolved the ability to switch between efficient light harvesting and quenching forms to optimize photosynthesis in response to the environment. Several distinct mechanisms, collectively termed “nonphotochemical quenching” (NPQ), provide flexibility in this response. Here we report the isolation and characterization of a mutant, suppressor of quenching 1 (soq1), that has high NPQ even in the absence of photosystem II subunit S (PsbS), a Protein that is necessary for the rapidly reversible component of NPQ. The formation of NPQ in soq1 was light intensity-dependent, and it exhibited slow relaxation kinetics and other characteristics that distinguish it from known NPQ components. Treatment with chemical inhibitors or an uncoupler, as well as crosses to mutants known to affect other NPQ components, showed that the NPQ in soq1 does not require a transThylakoid pH gradient, zeaxanthin formation, or the phosphorylation of light-harvesting complexes, and it appears to be unrelated to the photosystem II damage-and-repair cycle. Measurements of pigments and chlorophyll fluorescence lifetimes indicated that the additional NPQ in soq1 is the result of a decrease in chlorophyll excited-state lifetime and not pigment bleaching. The SOQ1 gene was isolated by map-based cloning, and it encodes a previously uncharacterized Thylakoid Membrane Protein with thioredoxin-like and β-propeller domains located in the lumen and a haloacid-dehalogenase domain exposed to the chloroplast stroma. We propose that the role of SOQ1 is to prevent formation of a slowly reversible form of antenna quenching, thereby maintaining the efficiency of light harvesting.
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photo oxidative stress in a xanthophyll deficient mutant of chlamydomonas
Journal of Biological Chemistry, 2004Co-Authors: Krishna K. Niyogi, Irene Baroli, Benjamin L Gutman, Heidi K Ledford, Jai W Shin, Brian L Chin, Michel HavauxAbstract:Abstract When there is an imbalance between the light energy absorbed by a photosynthetic organism and that which can be utilized in photosynthesis, photo-oxidative stress can damage pigments, Proteins, lipids, and nucleic acids. In this work we compared the wild type and a xanthophyll-deficient mutant of Chlamydomonas reinhardtii in their response to high amounts of light. Wild-type Chlamydomonas cells were able to acclimate to high amounts of light following transfer from low light conditions. In contrast, the npq1 lor1 double mutant, which lacks protective xanthophylls (zeaxanthin and lutein) in the chloroplast, progressively lost viability and photosynthetic capacity along with destruction of Thylakoid Membrane Protein-pigment complexes and accumulation of reactive oxygen species and Membrane lipid peroxides. Loss of viability was partially rescued by lowered oxygen tension, suggesting that the high sensitivity of the mutant to light stress is caused by the production of reactive oxygen species in the chloroplast. Cell death was not prevented by the addition of an organic carbon source to the growth medium, demonstrating that the photo-oxidative damage can target other essential chloroplast processes besides photosynthesis. From the differential sensitivity of the mutant to exogenously added pro-oxidants, we infer that the reactive oxygen species produced during light stress in npq1 lor1 may be singlet oxygen and/or superoxide but not hydrogen peroxide. The bleaching phenotype of npq1 lor1 was not due to enhanced photodamage to photosystem II but rather to a less localized phenomenon of accumulation of photo-oxidation products in chloroplast Membranes.
Danja Schunemann - One of the best experts on this subject based on the ideXlab platform.
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a Thylakoid Membrane bound and redox active rubredoxin rbd1 functions in de novo assembly and repair of photosystem ii
Proceedings of the National Academy of Sciences of the United States of America, 2019Co-Authors: Jose G Garciacerdan, Ariel L. Furst, Kent L. Mcdonald, Danja Schunemann, Matthew B. Francis, Krishna K. NiyogiAbstract:Author(s): Garcia-Cerdan, Jose G; Furst, Ariel L; McDonald, Kent L; Schunemann, Danja; Francis, Matthew B; Niyogi, Krishna K | Abstract: Photosystem II (PSII) undergoes frequent photooxidative damage that, if not repaired, impairs photosynthetic activity and growth. How photosynthetic organisms protect vulnerable PSII intermediate complexes during de novo assembly and repair remains poorly understood. Here, we report the genetic and biochemical characterization of chloroplast-located rubredoxin 1 (RBD1), a PSII assembly factor containing a redox-active rubredoxin domain and a single C-terminal transMembrane α-helix (TMH) domain. RBD1 is an integral Thylakoid Membrane Protein that is enriched in stroma lamellae fractions with the rubredoxin domain exposed on the stromal side. RBD1 also interacts with PSII intermediate complexes containing cytochrome b 559 Complementation of the Chlamydomonas reinhardtii (hereafter Chlamydomonas) RBD1-deficient 2pac mutant with constructs encoding RBD1 Protein truncations and site-directed mutations demonstrated that the TMH domain is essential for de novo PSII assembly, whereas the rubredoxin domain is involved in PSII repair. The rubredoxin domain exhibits a redox midpoint potential of +114 mV and is proficient in 1-electron transfers to a surrogate cytochrome c in vitro. Reduction of oxidized RBD1 is NADPH dependent and can be mediated by ferredoxin-NADP+ reductase (FNR) in vitro. We propose that RBD1 participates, together with the cytochrome b 559, in the protection of PSII intermediate complexes from photooxidative damage during de novo assembly and repair. This role of RBD1 is consistent with its evolutionary conservation among photosynthetic organisms and the fact that it is essential in photosynthetic eukaryotes.
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a Thylakoid Membrane bound and redox active rubredoxin rbd1 functions in de novo assembly and repair of photosystem ii
Proceedings of the National Academy of Sciences of the United States of America, 2019Co-Authors: Jose G Garciacerdan, Ariel L. Furst, Kent L. Mcdonald, Danja Schunemann, Krishna K. Niyogi, Matthew B. FrancisAbstract:Photosystem II (PSII) undergoes frequent photooxidative damage that, if not repaired, impairs photosynthetic activity and growth. How photosynthetic organisms protect vulnerable PSII intermediate complexes during de novo assembly and repair remains poorly understood. Here, we report the genetic and biochemical characterization of chloroplast-located rubredoxin 1 (RBD1), a PSII assembly factor containing a redox-active rubredoxin domain and a single C-terminal transMembrane α-helix (TMH) domain. RBD1 is an integral Thylakoid Membrane Protein that is enriched in stroma lamellae fractions with the rubredoxin domain exposed on the stromal side. RBD1 also interacts with PSII intermediate complexes containing cytochrome b 559 Complementation of the Chlamydomonas reinhardtii (hereafter Chlamydomonas) RBD1-deficient 2pac mutant with constructs encoding RBD1 Protein truncations and site-directed mutations demonstrated that the TMH domain is essential for de novo PSII assembly, whereas the rubredoxin domain is involved in PSII repair. The rubredoxin domain exhibits a redox midpoint potential of +114 mV and is proficient in 1-electron transfers to a surrogate cytochrome c in vitro. Reduction of oxidized RBD1 is NADPH dependent and can be mediated by ferredoxin-NADP+ reductase (FNR) in vitro. We propose that RBD1 participates, together with the cytochrome b 559, in the protection of PSII intermediate complexes from photooxidative damage during de novo assembly and repair. This role of RBD1 is consistent with its evolutionary conservation among photosynthetic organisms and the fact that it is essential in photosynthetic eukaryotes.
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interaction studies between the chloroplast signal recognition particle subunit cpsrp43 and the full length translocase alb3 reveal a Membrane embedded binding region in alb3 Protein
Journal of Biological Chemistry, 2011Co-Authors: Beatrix Dunschede, Thomas Bals, Silke Funke, Danja SchunemannAbstract:Abstract Posttranslational targeting of the light-harvesting chlorophyll a,b-binding Proteins depends on the function of the chloroplast signal recognition particle, its receptor cpFtsY, and the translocase Alb3. The Thylakoid Membrane Protein Alb3 of Arabidopsis chloroplasts belongs to the evolutionarily conserved YidC/Oxa1/Alb3 Protein family; the members of this family facilitate the insertion, folding, and assembly of Membrane Proteins in bacteria, mitochondria, and chloroplasts. Here, we analyzed the interaction sites of full-length Alb3 with the cpSRP pathway component cpSRP43 by using in vitro and in vivo studies. Bimolecular fluorescence complementation and Alb3 proteoliposome studies showed that the interaction of cpSRP43 is dependent on a binding domain in the C terminus of Alb3 as well as an additional Membrane-embedded binding site in the fifth transMembrane domain (TMD5) of Alb3. The C-terminal binding domain was mapped to residues 374–388, and the binding domain within TMD5 was mapped to residues 314–318 located close to the luminal end of TMD5. A direct binding between cpSRP43 and these binding motifs was shown by pepspot analysis. Further studies using blue-native gel electrophoresis revealed that full-length Alb3 is able to form dimers. This finding and the identification of a Membrane-embedded cpSRP43 binding site in Alb3 support a model in which cpSRP43 inserts into a dimeric Alb3 translocation pore during cpSRP-dependent delivery of light-harvesting chlorophyll a,b-binding Proteins.
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the Thylakoid Membrane Protein alb3 associates with the cpsecy translocase in arabidopsis thaliana
Biochemical Journal, 2002Co-Authors: Eva Klostermann, Imke Droste Gen Helling, Jeanpierre Carde, Danja SchunemannAbstract:The integration of light-harvesting chlorophyll Proteins (LHCPs) into the Thylakoid Membrane requires the integral Thylakoid Membrane Protein ALB3, a homologue of the bacterial cytoplasmic Membrane Protein YidC. In bacteria, YidC is associated with the SecY-translocase and facilitates the integration of Sec-dependent Proteins into the plasma Membrane. In addition, it is also involved in the insertion of Sec-independent Proteins. In the present study we demonstrate, in Arabidopsis thaliana, that most ALB3 is a constituent of an oligomeric complex of approx. 180 kDa. In addition, we detected ALB3 in several higher-molecular-mass complexes (up to 700 kDa). Furthermore, we show that most ALB3 co-fractionates with cpSecY during gel-filtration analysis and blue native gel electrophoresis, suggesting an association of ALB3 with the cpSecY complex. A direct interaction of ALB3 with the cpSecY complex was demonstrated by co-immunoprecipitation experiments using digitonin-solubilized Thylakoid Membrane Proteins and anti-cpSecY or anti-ALB3 antibodies. This result was further confirmed by electron microscopic co-immunolocalization of ALB3 and cpSecY. In addition, an association of ALB3 with the cpSecY complex was demonstrated directly by cross-linking experiments using the chemical cross-linker disuccinimidyl suberate.
Matthew B. Francis - One of the best experts on this subject based on the ideXlab platform.
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a Thylakoid Membrane bound and redox active rubredoxin rbd1 functions in de novo assembly and repair of photosystem ii
Proceedings of the National Academy of Sciences of the United States of America, 2019Co-Authors: Jose G Garciacerdan, Ariel L. Furst, Kent L. Mcdonald, Danja Schunemann, Matthew B. Francis, Krishna K. NiyogiAbstract:Author(s): Garcia-Cerdan, Jose G; Furst, Ariel L; McDonald, Kent L; Schunemann, Danja; Francis, Matthew B; Niyogi, Krishna K | Abstract: Photosystem II (PSII) undergoes frequent photooxidative damage that, if not repaired, impairs photosynthetic activity and growth. How photosynthetic organisms protect vulnerable PSII intermediate complexes during de novo assembly and repair remains poorly understood. Here, we report the genetic and biochemical characterization of chloroplast-located rubredoxin 1 (RBD1), a PSII assembly factor containing a redox-active rubredoxin domain and a single C-terminal transMembrane α-helix (TMH) domain. RBD1 is an integral Thylakoid Membrane Protein that is enriched in stroma lamellae fractions with the rubredoxin domain exposed on the stromal side. RBD1 also interacts with PSII intermediate complexes containing cytochrome b 559 Complementation of the Chlamydomonas reinhardtii (hereafter Chlamydomonas) RBD1-deficient 2pac mutant with constructs encoding RBD1 Protein truncations and site-directed mutations demonstrated that the TMH domain is essential for de novo PSII assembly, whereas the rubredoxin domain is involved in PSII repair. The rubredoxin domain exhibits a redox midpoint potential of +114 mV and is proficient in 1-electron transfers to a surrogate cytochrome c in vitro. Reduction of oxidized RBD1 is NADPH dependent and can be mediated by ferredoxin-NADP+ reductase (FNR) in vitro. We propose that RBD1 participates, together with the cytochrome b 559, in the protection of PSII intermediate complexes from photooxidative damage during de novo assembly and repair. This role of RBD1 is consistent with its evolutionary conservation among photosynthetic organisms and the fact that it is essential in photosynthetic eukaryotes.
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a Thylakoid Membrane bound and redox active rubredoxin rbd1 functions in de novo assembly and repair of photosystem ii
Proceedings of the National Academy of Sciences of the United States of America, 2019Co-Authors: Jose G Garciacerdan, Ariel L. Furst, Kent L. Mcdonald, Danja Schunemann, Krishna K. Niyogi, Matthew B. FrancisAbstract:Photosystem II (PSII) undergoes frequent photooxidative damage that, if not repaired, impairs photosynthetic activity and growth. How photosynthetic organisms protect vulnerable PSII intermediate complexes during de novo assembly and repair remains poorly understood. Here, we report the genetic and biochemical characterization of chloroplast-located rubredoxin 1 (RBD1), a PSII assembly factor containing a redox-active rubredoxin domain and a single C-terminal transMembrane α-helix (TMH) domain. RBD1 is an integral Thylakoid Membrane Protein that is enriched in stroma lamellae fractions with the rubredoxin domain exposed on the stromal side. RBD1 also interacts with PSII intermediate complexes containing cytochrome b 559 Complementation of the Chlamydomonas reinhardtii (hereafter Chlamydomonas) RBD1-deficient 2pac mutant with constructs encoding RBD1 Protein truncations and site-directed mutations demonstrated that the TMH domain is essential for de novo PSII assembly, whereas the rubredoxin domain is involved in PSII repair. The rubredoxin domain exhibits a redox midpoint potential of +114 mV and is proficient in 1-electron transfers to a surrogate cytochrome c in vitro. Reduction of oxidized RBD1 is NADPH dependent and can be mediated by ferredoxin-NADP+ reductase (FNR) in vitro. We propose that RBD1 participates, together with the cytochrome b 559, in the protection of PSII intermediate complexes from photooxidative damage during de novo assembly and repair. This role of RBD1 is consistent with its evolutionary conservation among photosynthetic organisms and the fact that it is essential in photosynthetic eukaryotes.
Jose G Garciacerdan - One of the best experts on this subject based on the ideXlab platform.
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a Thylakoid Membrane bound and redox active rubredoxin rbd1 functions in de novo assembly and repair of photosystem ii
Proceedings of the National Academy of Sciences of the United States of America, 2019Co-Authors: Jose G Garciacerdan, Ariel L. Furst, Kent L. Mcdonald, Danja Schunemann, Matthew B. Francis, Krishna K. NiyogiAbstract:Author(s): Garcia-Cerdan, Jose G; Furst, Ariel L; McDonald, Kent L; Schunemann, Danja; Francis, Matthew B; Niyogi, Krishna K | Abstract: Photosystem II (PSII) undergoes frequent photooxidative damage that, if not repaired, impairs photosynthetic activity and growth. How photosynthetic organisms protect vulnerable PSII intermediate complexes during de novo assembly and repair remains poorly understood. Here, we report the genetic and biochemical characterization of chloroplast-located rubredoxin 1 (RBD1), a PSII assembly factor containing a redox-active rubredoxin domain and a single C-terminal transMembrane α-helix (TMH) domain. RBD1 is an integral Thylakoid Membrane Protein that is enriched in stroma lamellae fractions with the rubredoxin domain exposed on the stromal side. RBD1 also interacts with PSII intermediate complexes containing cytochrome b 559 Complementation of the Chlamydomonas reinhardtii (hereafter Chlamydomonas) RBD1-deficient 2pac mutant with constructs encoding RBD1 Protein truncations and site-directed mutations demonstrated that the TMH domain is essential for de novo PSII assembly, whereas the rubredoxin domain is involved in PSII repair. The rubredoxin domain exhibits a redox midpoint potential of +114 mV and is proficient in 1-electron transfers to a surrogate cytochrome c in vitro. Reduction of oxidized RBD1 is NADPH dependent and can be mediated by ferredoxin-NADP+ reductase (FNR) in vitro. We propose that RBD1 participates, together with the cytochrome b 559, in the protection of PSII intermediate complexes from photooxidative damage during de novo assembly and repair. This role of RBD1 is consistent with its evolutionary conservation among photosynthetic organisms and the fact that it is essential in photosynthetic eukaryotes.
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a Thylakoid Membrane bound and redox active rubredoxin rbd1 functions in de novo assembly and repair of photosystem ii
Proceedings of the National Academy of Sciences of the United States of America, 2019Co-Authors: Jose G Garciacerdan, Ariel L. Furst, Kent L. Mcdonald, Danja Schunemann, Krishna K. Niyogi, Matthew B. FrancisAbstract:Photosystem II (PSII) undergoes frequent photooxidative damage that, if not repaired, impairs photosynthetic activity and growth. How photosynthetic organisms protect vulnerable PSII intermediate complexes during de novo assembly and repair remains poorly understood. Here, we report the genetic and biochemical characterization of chloroplast-located rubredoxin 1 (RBD1), a PSII assembly factor containing a redox-active rubredoxin domain and a single C-terminal transMembrane α-helix (TMH) domain. RBD1 is an integral Thylakoid Membrane Protein that is enriched in stroma lamellae fractions with the rubredoxin domain exposed on the stromal side. RBD1 also interacts with PSII intermediate complexes containing cytochrome b 559 Complementation of the Chlamydomonas reinhardtii (hereafter Chlamydomonas) RBD1-deficient 2pac mutant with constructs encoding RBD1 Protein truncations and site-directed mutations demonstrated that the TMH domain is essential for de novo PSII assembly, whereas the rubredoxin domain is involved in PSII repair. The rubredoxin domain exhibits a redox midpoint potential of +114 mV and is proficient in 1-electron transfers to a surrogate cytochrome c in vitro. Reduction of oxidized RBD1 is NADPH dependent and can be mediated by ferredoxin-NADP+ reductase (FNR) in vitro. We propose that RBD1 participates, together with the cytochrome b 559, in the protection of PSII intermediate complexes from photooxidative damage during de novo assembly and repair. This role of RBD1 is consistent with its evolutionary conservation among photosynthetic organisms and the fact that it is essential in photosynthetic eukaryotes.
Toshiharu Shikanai - One of the best experts on this subject based on the ideXlab platform.
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pgr5 is involved in cyclic electron flow around photosystem i and is essential for photoprotection in arabidopsis
Cell, 2002Co-Authors: Yuri Munekage, Masaya Hojo, Jorg Meurer, Tsuyoshi Endo, Masao Tasaka, Toshiharu ShikanaiAbstract:During photosynthesis, plants must control the utilization of light energy in order to avoid photoinhibition. We isolated an Arabidopsis mutant, pgr5 (proton gradient regulation), in which downregulation of photosystem II photochemistry in response to intense light was impaired. PGR5 encodes a novel Thylakoid Membrane Protein that is involved in the transfer of electrons from ferredoxin to plastoquinone. This alternative electron transfer pathway, whose molecular identity has long been unclear, is known to function in vivo in cyclic electron flow around photosystem I. We propose that the PGR5 pathway contributes to the generation of a Delta(pH) that induces thermal dissipation when Calvin cycle activity is reduced. Under these conditions, the PGR5 pathway also functions to limit the overreduction of the acceptor side of photosystem I, thus preventing photosystem I photoinhibition.
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pgr5 is involved in cyclic electron flow around photosystem i and is essential for photoprotection in arabidopsis
Cell, 2002Co-Authors: Yuri Munekage, Masaya Hojo, Jorg Meurer, Tsuyoshi Endo, Masao Tasaka, Toshiharu ShikanaiAbstract:Abstract During photosynthesis, plants must control the utilization of light energy in order to avoid photoinhibition. We isolated an Arabidopsis mutant, pgr5 ( proton gradient regulation ), in which downregulation of photosystem II photochemistry in response to intense light was impaired. PGR5 encodes a novel Thylakoid Membrane Protein that is involved in the transfer of electrons from ferredoxin to plastoquinone. This alternative electron transfer pathway, whose molecular identity has long been unclear, is known to function in vivo in cyclic electron flow around photosystem I. We propose that the PGR5 pathway contributes to the generation of a ΔpH that induces thermal dissipation when Calvin cycle activity is reduced. Under these conditions, the PGR5 pathway also functions to limit the overreduction of the acceptor side of photosystem I, thus preventing photosystem I photoinhibition.