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1.
Biochim Biophys Acta Bioenerg ; 1861(2): 148139, 2020 02 01.
Artigo em Inglês | MEDLINE | ID: mdl-31825812

RESUMO

An aerial green alga, Prasiola crispa (Lightf.) Menegh, which is known to form large colonies in Antarctic habitats, is subject to severe environmental stresses due to low temperature, draught and strong sunlight in summer. A considerable light-absorption by long-wavelength chlorophylls (LWC) at around 710 nm, which seem to consist of chlorophyll a, was detected in thallus of P. crispa harvested at a terrestrial environment in Antarctica. Absorption level at 710 nm against that at 680 nm was correlated with fluorescence emission intensity at 713 nm at room temperature and the 77 K fluorescence emission band from LWC was found to be emitted at 735 nm. We demonstrated that the LWC efficiently transfer excitation energy to photosystem II (PSII) reaction center from measurements of action spectra of photosynthetic oxygen evolution and P700 photo-oxidation. The global quantum yield of PSII excitation in thallus by far-red light was shown to be as high as by orange light, and the excitation balance between PSII and PSI was almost same in the two light sources. It is thus proposed that the LWC increase the photosynthetic productivity in the lower parts of overlapping thalli and contribute to the predominance of alga in the severe environment.


Assuntos
Clorofila A/metabolismo , Clorófitas/metabolismo , Luz , Complexo de Proteína do Fotossistema II/metabolismo , Regiões Antárticas , Complexos de Proteínas Captadores de Luz/metabolismo , Oxigênio/metabolismo , Complexo de Proteína do Fotossistema I/metabolismo , Espectrometria de Fluorescência
2.
Biochim Biophys Acta Bioenerg ; 1861(1): 148093, 2020 01 01.
Artigo em Inglês | MEDLINE | ID: mdl-31669460

RESUMO

Photosynthetic PSI-LHCI complexes from an extremophilic red alga C. merolae grown under varying light regimes are characterized by decreasing size of LHCI antenna with increasing illumination intensity [1]. In this study we applied time-resolved fluorescence spectroscopy to characterize the kinetics of energy transfer processes in three types of PSI-LHCI supercomplexes isolated from the low (LL), medium (ML) and extreme high light (EHL) conditions. We show that the average rate of fluorescence decay is not correlated with the size of LHCI antenna and is twice faster in complexes isolated from ML-grown cells (~25-30 ps) than from both LL- and EHL-exposed cells (~50-55 ps). The difference is mainly due to a contribution of a long ~100-ps decay component detected only for the latter two PSI samples. We propose that the lack of this phase in ML complexes is caused by perfect coupling of this antenna to PSI core and lack of low-energy chlorophylls in LHCI. On the other hand, the presence of the slow, ~100-ps, fluorescence decay component in LL and EHL complexes may be due to the weak coupling between PSI core and LHCI antenna complex, and due to the presence of particularly low-energy or red chlorophylls in LHCI. Our study has revealed the remarkable functional flexibility of light harvesting strategies that have evolved in the extremophilic red algae in response to harsh or limiting light conditions involving accumulation of low energy chlorophylls that exert two distinct functions: as energy traps or as far-red absorbing light harvesting antenna, respectively.


Assuntos
Complexos de Proteínas Captadores de Luz , Luz , Rodófitas/enzimologia , Complexos de Proteínas Captadores de Luz/química , Complexos de Proteínas Captadores de Luz/metabolismo , Complexo de Proteína do Fotossistema I/química , Complexo de Proteína do Fotossistema I/metabolismo , Espectrometria de Fluorescência
3.
Biochim Biophys Acta Bioenerg ; 1861(1): 148089, 2020 01 01.
Artigo em Inglês | MEDLINE | ID: mdl-31669487

RESUMO

Leaves of Arabidopsis thaliana plants grown in short days (8 h light) generate more reactive oxygen species in the light than leaves of plants grown in long days (16 h light). The importance of the two PsaE isoforms of photosystem I, PsaE1 and PsaE2, for O2 reduction was studied in plants grown under these different growth regimes. In short day conditions a mutant affected in the amount of PsaE1 (psae1-1) reduced more efficiently O2 than a mutant lacking PsaE2 (psae2-1) as shown by spin trapping EPR spectroscopy on leaves and by following the kinetics of P700+ reduction in isolated photosystem I. In short day conditions higher O2 reduction protected photosystem II against photoinhibition in psae1-1. In contrast in long day conditions the presence of PsaE1 was clearly beneficial for photosynthetic electron transport and for the stability of the photosynthetic apparatus under photoinhibitory conditions. We conclude that the two PsaE isoforms have distinct functions and we propose that O2 reduction at photosystem I is beneficial for the plant under certain environmental conditions.


Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/enzimologia , Oxigênio/metabolismo , Fotossíntese/fisiologia , Complexo de Proteína do Fotossistema I/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Transporte de Elétrons/fisiologia , Isoenzimas/genética , Isoenzimas/metabolismo , Oxirredução , Complexo de Proteína do Fotossistema I/genética
4.
J Photochem Photobiol B ; 201: 111659, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31698219

RESUMO

Stressors of different natures, including drought stress, substantially compromise the ability of plants to effectively and safely utilize light energy. We investigated the influence of water stress on the photosynthetic processes in Picea abies and Pinus sylvestris, two species with contrasting drought sensitivities. Spruce and pine seedlings were exposed to polyethylene glycol 6000-induced water deficits of different intensities and durations. The maintenance of photosystem I (PSI) oxidation in spruce required increased photosynthetic control and led to the increased reduction of the plastoquinone pool, which was not the case in pine seedlings. As a result of increased excitation pressure, photosystem II (PSII) inactivation was observed in spruce plants, whereas in pine, the decreased PSII photochemistry was likely due to sustained non-photochemical quenching. Downregulation of PSII photochemistry and maintenance of PSI in an oxidized state were linked with the prevention of oxidative stress, even under severe water deficit. The decreased photosynthetic pigment content and photosynthetic gene expression suggested the coordinated downregulation of photosynthetic apparatus components under water stress to reduce light energy absorption. In summary, the observed adaptative mechanisms of pine and spruce to water stress may be similar to the well-studied adaptative mechanisms to winter stress, which may indicate the universality of protective mechanisms under various stresses in conifers.


Assuntos
Secas , Fotossíntese , Picea/metabolismo , Pinus sylvestris/metabolismo , Peroxidação de Lipídeos , Fotossíntese/genética , Complexo de Proteína do Fotossistema I/genética , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/genética , Complexo de Proteína do Fotossistema II/metabolismo , Folhas de Planta/metabolismo , Plântula/metabolismo
5.
Biochim Biophys Acta Bioenerg ; 1860(12): 148090, 2019 12 01.
Artigo em Inglês | MEDLINE | ID: mdl-31669492

RESUMO

Photosystem I (PSI) and photosystem II (PSII) play key roles in photoinduced electron-transfer reaction in oxygenic photosynthesis. Assemblies of these PSs can be initiated by illumination of the etiolated seedlings (greening). The study aimed to identify specific fluorescence spectral components relevant to PSI and PSII assembly intermediates emerging in greening seedlings of Zea mays, a typical C4 plant. The different PSII contents between the bundle sheath (BS) and mesophyll (M) cells were utilized to spectrally isolate the precursors to PSI and PSII. The greening Zea mays leaf thin sections were observed with the cryogenic microscope combined with a spectrometer. With the aid of the singular-value decomposition analysis, we could identify four independent fluorescent species, SAS677, SAS685, SAS683, and SAS687, named after their fluorescence peak wavelengths. SAS677 and SAS685 are the dominant components after the 30-minute greening, and the distributions of these components showed no clear differences between M and BS cells, indicating immature cell differentiation in this developing stage. On the other hand, the 1-hour greening resulted in reduced distributions of SAS683 in BS cells leading us to assign this species to PSII precursors. The 2-hour greening induced the enrichment of SAS687 in BS cells suggesting its PSI relevance. Similarity in the peak wavelengths of SAS683 and the reported reaction center of PSII implied their connection. SAS687 showed an intense sub-band at around 740 nm, which can be assigned to the emission from the red chlorophylls specific to the mature PSI.


Assuntos
Complexo de Proteína do Fotossistema I/química , Complexo de Proteína do Fotossistema II/química , Espectrometria de Fluorescência , Fluorescência , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Folhas de Planta/química , Folhas de Planta/crescimento & desenvolvimento , Folhas de Planta/metabolismo , Plântula , Espectrometria de Fluorescência/métodos , Zea mays
6.
Biochim Biophys Acta Bioenerg ; 1860(11): 148079, 2019 11 01.
Artigo em Inglês | MEDLINE | ID: mdl-31518567

RESUMO

Photosynthetic pigment-protein complexes (PPCs) accomplish light-energy capture and photochemistry in natural photosynthesis. In this review, we examine three pigment protein complexes in oxygenic photosynthesis: light-harvesting antenna complexes and two reaction centers: Photosystem II (PSII), and Photosystem I (PSI). Recent technological developments promise unprecedented insights into how these multi-component protein complexes are assembled into higher order structures and thereby execute their function. Furthermore, the interfacial domain between light-harvesting antenna complexes and PSII, especially the potential roles of the structural loops from CP29 and the PB-loop of ApcE in higher plant and cyanobacteria, respectively, are discussed. It is emphasized that the structural nuances are required for the structural dynamics and consequently for functional regulation in response to an ever-changing and challenging environment.


Assuntos
Complexos de Proteínas Captadores de Luz/metabolismo , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Cianobactérias , Complexos de Proteínas Captadores de Luz/química , Fotossíntese/fisiologia , Complexo de Proteína do Fotossistema I/química , Complexo de Proteína do Fotossistema II/química , Plantas , Rodófitas
7.
J Plant Res ; 132(6): 867-880, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31541373

RESUMO

Mosses are one of the earliest land plants that diverged from fresh-water green algae. They are considered to have acquired a higher capacity for thermal energy dissipation to cope with dynamically changing solar irradiance by utilizing both the "algal-type" light-harvesting complex stress-related (LHCSR)-dependent and the "plant-type" PsbS-dependent mechanisms. It is hypothesized that the formation of photosystem (PS) I and II megacomplex is another mechanism to protect photosynthetic machinery from strong irradiance. Herein, we describe the analysis of the PSI-PSII megacomplex from the model moss, Physcomitrella patens, which was resolved using large-pore clear-native polyacrylamide gel electrophoresis (lpCN-PAGE). The similarity in the migration distance of the Physcomitrella PSI-PSII megacomplex to the Arabidopsis megacomplex shown during lpCN-PAGE suggested that the Physcomitrella PSI-PSII and Arabidopsis megacomplexes have similar structures. Time-resolved chlorophyll fluorescence measurements show that excitation energy was rapidly and efficiently transferred from PSII to PSI, providing evidence of an ordered association of the two photosystems. We also found that LHCSR and PsbS co-migrated with the Physcomitrella PSI-PSII megacomplex. The megacomplex showed pH-dependent chlorophyll fluorescence quenching, which may have been induced by LHCSR and/or PsbS proteins with the collaboration of zeaxanthin. We discuss the mechanism that regulates the energy distribution balance between two photosystems in Physcomitrella.


Assuntos
Bryopsida/genética , Complexos de Proteínas Captadores de Luz/genética , Complexo de Proteína do Fotossistema I/genética , Complexo de Proteína do Fotossistema II/genética , Proteínas de Plantas/genética , Bryopsida/enzimologia , Eletroforese em Gel de Poliacrilamida , Complexos de Proteínas Captadores de Luz/metabolismo , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Proteínas de Plantas/metabolismo
8.
Plant Sci ; 287: 110166, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31481226

RESUMO

In angiosperms, cyclic electron flow (CEF) around photosystem I (PSI) is more important for photoprotection under fluctuating light than under constant light. However, the underlying mechanism is not well known. In the present study, we measured the CEF activity, P700 redox state and electrochromic shift signal upon a sudden transition from low to high light in wild-type plants of Arabidopsis thaliana and Bletilla striata (Orchidaceae). Within the first 20 s after transition from low to high light, P700 was highly reduced in both species, which was accompanied with a sufficient proton gradient (ΔpH) across the thylakoid membranes. Meanwhile, the level of CEF activation was elevated. After transition from low to high light for 60 s, the plants generated an optimal ΔpH. Under such condition, PSI was highly oxidized and the level of CEF activation decreased to the steady state. Furthermore, the CEF activation was positively correlated to the P700 reduction ratio. These results indicated that upon a sudden transition from low to high light, the insufficient ΔpH led to the over-reduction of PSI electron carriers, which in turn stimulated the CEF around PSI. This transient stimulation of CEF not only favored the rapid ΔpH formation but also accepted electrons from PSI, thus protecting PSI at donor and acceptor sides. These findings provide new insights into the important role of CEF in regulation of photosynthesis under fluctuating light.


Assuntos
Arabidopsis/metabolismo , Transporte de Elétrons , Orchidaceae/metabolismo , Complexo de Proteína do Fotossistema I/metabolismo , Arabidopsis/efeitos da radiação , Clorofila/metabolismo , Relação Dose-Resposta à Radiação , Transporte de Elétrons/efeitos da radiação , Luz , Orchidaceae/efeitos da radiação , Complexo de Proteína do Fotossistema I/efeitos da radiação
9.
Biochim Biophys Acta Bioenerg ; 1860(11): 148073, 2019 11 01.
Artigo em Inglês | MEDLINE | ID: mdl-31473302

RESUMO

Photosystem I (PSI) is a potential target of photoinhibition under fluctuating light. However, photosynthetic regulation under fluctuating light in field-grown plants is little known. Furthermore, it is unclear how young leaves protect PSI against fluctuating light under natural field conditions. In the present study, we examined chlorophyll fluorescence, P700 redox state and the electrochromic shift signal in the young and mature leaves of field-grown Cerasus cerasoides (Rosaceae). Within the first seconds after any increase in light intensity, young leaves showed higher proton gradient (ΔpH) across the thylakoid membranes than the mature leaves, preventing over-reduction of PSI in the young leaves. As a result, PSI was more tolerant to fluctuating light in the young leaves than in the mature leaves. Interestingly, after transition from low to high light, the activity of cyclic electron flow (CEF) in young leaves increased first to a high level and then decreased to a stable value, while this rapid stimulation of CEF was not observed in the mature leaves. Furthermore, the over-reduction of PSI significantly stimulated CEF in the young leaves but not in the mature leaves. Taken together, within the first seconds after any increase in illumination, the stimulation of CEF favors the rapid lumen acidification and optimizes the PSI redox state in the young leaves, protecting PSI against photoinhibition under fluctuating light in field-grown plants.


Assuntos
Luz , Fotossíntese/fisiologia , Folhas de Planta/crescimento & desenvolvimento , Folhas de Planta/fisiologia , Prunus/crescimento & desenvolvimento , Prunus/fisiologia , Adaptação Fisiológica , Concentração de Íons de Hidrogênio , Oxirredução , Periodicidade , Fotossíntese/efeitos da radiação , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Folhas de Planta/efeitos da radiação , Prótons , Prunus/efeitos da radiação , Tilacoides/fisiologia , Tilacoides/efeitos da radiação
10.
Plant Cell Physiol ; 60(10): 2206-2219, 2019 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-31271439

RESUMO

Photosynthetic induction, a gradual increase in photosynthetic rate on a transition from darkness or low light to high light, has ecological significance, impact on biomass accumulation in fluctuating light and relevance to photoprotection in strong light. However, the experimental quantification of the component electron fluxes in and around both photosystems during induction has been rare. Combining optimized chlorophyll fluorescence, the redox kinetics of P700 [primary electron donor in Photosystem I (PSI)] and membrane inlet mass spectrometry in the absence/presence of inhibitors/mediator, we partially estimated the components of electron fluxes in spinach leaf disks on transition from darkness to 1,000 �mol photons�m-2�s-1 for up to 10 min, obtaining the following findings: (i) the partitioning of energy between both photosystems did not change noticeably; (ii) in Photosystem II (PSII), the combined cyclic electron flow (CEF2) and charge recombination (CR2) to the ground state decreased gradually toward 0 in steady state; (iii) oxygen reduction by electrons from PSII, partly bypassing PSI, was small but measurable; (iv) cyclic electron flow around PSI (CEF1) peaked before becoming somewhat steady; (v) peak magnitudes of some of the electron fluxes, all probably photoprotective, were in the descending order: CEF1 > CEF2 + CR2 > chloroplast O2 uptake; and (vi) the chloroplast NADH dehydrogenase-like complex appeared to aid the antimycin A-sensitive CEF1. The results are important for fine-tuning in silico simulation of in vivo photosynthetic electron transport processes; such simulation is, in turn, necessary to probe partial processes in a complex network of interactions in response to environmental changes.


Assuntos
Transporte de Elétrons , Oxigênio/metabolismo , Fotossíntese/fisiologia , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Spinacia oleracea/fisiologia , Antimicina A/farmacologia , Dióxido de Carbono/metabolismo , Clorofila/metabolismo , Cloroplastos/metabolismo , Escuridão , Fluorescência , Cinética , Luz , Oxirredução , Folhas de Planta/fisiologia , Folhas de Planta/efeitos da radiação , Spinacia oleracea/efeitos da radiação
11.
Biochim Biophys Acta Bioenerg ; 1860(12)2019 12 01.
Artigo em Inglês | MEDLINE | ID: mdl-31344362

RESUMO

Thylakoids are the place of the light-photosynthetic reactions. To gain maximal efficiency, these reactions are conditional to proper pigment-pigment and protein-protein interactions. In higher plants thylakoids, the interactions lead to a lateral asymmetry in localization of protein complexes (i.e. granal/stromal thylakoids) that have been defined as a domain-like structures characteristic by different biochemical composition and function (Albertsson P-Å. 2001,Trends Plant Science 6: 349-354). We explored this complex organization of thylakoid pigment-proteins at single cell level in the cyanobacterium Synechocystis sp. PCC 6803. Our 3D confocal images captured heterogeneous distribution of all main photosynthetic pigment-protein complexes (PPCs), Photosystem I (fluorescently tagged by YFP), Photosystem II and Phycobilisomes. The acquired images depicted cyanobacterial thylakoid membrane as a stable, mosaic-like structure formed by microdomains (MDs). These microcompartments are of sub-micrometer in sizes (~0.5-1.5 µm), typical by particular PPCs ratios and importantly without full segregation of observed complexes. The most prevailing MD is represented by MD with high Photosystem I content which allows also partial separation of Photosystems like in higher plants thylakoids. We assume that MDs stability (in minutes) provides optimal conditions for efficient excitation/electron transfer. The cyanobacterial MDs thus define thylakoid membrane organization as a system controlled by co-localization of three main PPCs leading to formation of thylakoid membrane mosaic. This organization might represent evolutional and functional precursor for the granal/stromal spatial heterogeneity in photosystems that is typical for higher plant thylakoids.


Assuntos
Proteínas de Bactérias/metabolismo , Microdomínios da Membrana/metabolismo , Tilacoides/metabolismo , Imagem Tridimensional , Microscopia Confocal , Fotossíntese/fisiologia , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Ficobilissomas/metabolismo , Synechocystis
12.
Biochim Biophys Acta Bioenerg ; 1860(9): 689-698, 2019 09 01.
Artigo em Inglês | MEDLINE | ID: mdl-31336103

RESUMO

The binding of FNR to PSI has been postulated long ago, however, a clear evidence is still missing. In this work, using isothermal titration calorimetry (ITC), we found that FNR binds to photosystem I with its light harvesting complex I (PSI-LHCI) from C. reinhardtii with a 1:1 stoichiometry, a Kd of ~0.8 µM and ∆H of -20.7 kcal/mol. Titrations at different temperatures were used to determine the heat capacity change, ∆CP, of the binding, through which the size of the interface area between the proteins was assessed as ~3000 Å2. In a different set of ITC experiments, introduction of various sucrose concentrations was used to estimate that ~95 water molecules are released to the solvent. These observations support the notion of a binding site shared by few of the photosystem I - light harvesting complex I (PSI-LHCI) subunits in addition to PsaE. Based on these results, a hypothetical model was built for the binding site of FNR at PSI, using known crystallographic structures of: cyanobacterial PSI in complex with ferredoxin (Fd), plant PSI-LHCI and Fd:FNR complex from cyanobacteria. FNR binding site location is proposed to be at the foot of the stromal ridge and above the inner LHCI belt. It is expected to form contacts with PsaE, PsaB, PsaF and at least one of the LHCI. In addition, a ~4.5-fold increased affinity between FNR and PSI-LHCI under crowded 1 M sucrose environment led us to conclude that in C. reinhardtii FNR also functions as a subunit of PSI-LHCI.


Assuntos
Arabidopsis/metabolismo , Chlamydomonas reinhardtii/enzimologia , Ferredoxina-NADP Redutase/metabolismo , Ferredoxinas/metabolismo , NADP/metabolismo , Fotossíntese , Complexo de Proteína do Fotossistema I/metabolismo , Cristalografia por Raios X , Cianobactérias/metabolismo , Transporte de Elétrons , Ferredoxina-NADP Redutase/química , Ferredoxinas/química , Luz , Complexos de Proteínas Captadores de Luz , NADP/química , Complexo de Proteína do Fotossistema I/química , Conformação Proteica
13.
Biochim Biophys Acta Bioenerg ; 1860(9): 699-707, 2019 09 01.
Artigo em Inglês | MEDLINE | ID: mdl-31306624

RESUMO

Time-resolved (P700+A1- - P700A1) FTIR difference spectra have been obtained using photosystem I (PSI) particles with several different quinones incorporated into the A1 protein binding site. Difference spectra were obtained for PSI with unlabeled and 18O labeled phylloquinone (2-methyl-3-phytyl-1,4-naphthoquinone) and 2-methyl-1,4-naphthaquinone (2MNQ) incorporated, and for PSI with unlabeled 2,3-dimethyl-1,4-naphthoquinone (DMNQ) incorporated. (18O - 16O), (2MNQ - PhQ) and (DMNQ - PhQ) FTIR double difference spectra were constructed from the difference spectra. These double difference spectra allow one to more easily distinguish protein and pigment bands in convoluted difference spectra. To further aid in the interpretation of the difference spectra, particularly the spectra associated with the semiquinones, we have used two-layer ONIOM methods to calculate corresponding difference and double difference spectra. In all cases, the experimental and calculated double difference spectra are in excellent agreement. In previous two and three-layer ONIOM calculations it was not possible to adequately simulate multiple difference and double difference spectra. So, the computational approach outlined here is an improvement over previous calculations. It is shown that the calculated spectra can vary depending on the details of the molecular model that is used. Specifically, a molecular model that includes several water molecules that are near the incorporated semiquinones is required.


Assuntos
Complexo de Proteína do Fotossistema I/metabolismo , Quinonas/química , Synechococcus/metabolismo , Sítios de Ligação , Transporte de Elétrons , Modelos Moleculares , Complexo de Proteína do Fotossistema I/química , Ligação Proteica , Conformação Proteica , Domínios Proteicos , Vibração
14.
Biochim Biophys Acta Bioenerg ; 1860(8): 601-610, 2019 08 01.
Artigo em Inglês | MEDLINE | ID: mdl-31247172

RESUMO

The kinetics of charge recombination in Photosystem I P700-FA/FB complexes and P700-FX cores lacking the terminal iron­sulfur clusters were studied over a temperatures range of 310 K to 4.2 K. Analysis of the charge recombination kinetics in this temperature range allowed the assignment of backward electron transfer from the different electron acceptors to P700+. The kinetic and thermodynamic parameters of these recombination reactions were determined. The kinetics of all electron transfer reactions were activation-less below 170 K, the glass transition temperature of the water-glycerol solution. Above this temperature, recombination from [FA/FB]- in P700-FA/FB complexes was found to proceed along two pathways with different activation energies (Ea). The charge recombination via A1A has an Ea of ~290 meV and is dominant at temperatures above ~280 K, whereas the direct recombination from FX- has an Ea of 22 meV and is prevalent in the 200 K to 270 K temperature range. Charge recombination from the FX cluster becomes highly heterogeneous at temperatures below 200 K. The conformational mobility of Photosystem I was studied by molecular dynamics simulations. The FX cluster was found to 'swing' by ~30° along the axis between the two sulfur atoms proximal to FA/FB. The partial rotation of FX is accompanied by significant changes of electric potential within the iron­sulfur cluster, which may induce preferential electron localization at different atoms of the FX cluster. These effects may account for the partial arrest of forward electron transfer and for the heterogeneity of charge recombination observed at the glass transition temperature.


Assuntos
Cianobactérias/metabolismo , Complexo de Proteína do Fotossistema I/química , Transporte de Elétrons , Cinética , Simulação de Dinâmica Molecular , Complexo de Proteína do Fotossistema I/metabolismo , Conformação Proteica , Temperatura Ambiente , Termodinâmica , Vitrificação
15.
Int J Mol Sci ; 20(9)2019 Apr 26.
Artigo em Inglês | MEDLINE | ID: mdl-31027369

RESUMO

It is of interest how photosynthetic electron transport (PET) reactions respond to excess light energy caused by the combination of drought stress and high temperatures. Since such information is scarcely available for photosystem I (PSI), this question was explored in rice (Oryza sativa L.) plants subjected to drought stress, using culture solutions that contain poly(ethylene glycol) at different concentrations under two day/night temperature regimes. At 27/22 °C (day/night), drought stress led to the oxidation of the reaction center of the chlorophyll of PSI (P700), and also led to decreases in the quantum efficiencies of photosystem II (PSII) and PSI, and a reduction of the primary quinone electron acceptor of PSI. Such drought stress responses were wholly stimulated at 35/30 °C. These parameters were strongly correlated with each other and were minimally affected by temperature. These results indicate that the drought stress responses of the respective PET reactions are closely associated with each other in the oxidization of P700 and that such responses are stimulated at high temperatures. The underlying mechanisms of these phenomena were discussed. While P700 oxidation is thought to suppress reactive oxygen species (ROS) production, PSI photoinhibition was observed under severe stress conditions, implying that P700 oxidation is not sufficient for the protection of PSI under drought stress.


Assuntos
Clorofila/metabolismo , Oryza/metabolismo , Complexo de Proteína do Fotossistema I/metabolismo , Clorofila/genética , Transporte de Elétrons/genética , Transporte de Elétrons/fisiologia , Temperatura Alta , Oryza/genética , Fotossíntese/genética , Fotossíntese/fisiologia , Complexo de Proteína do Fotossistema I/genética
16.
Biochim Biophys Acta Bioenerg ; 1860(6): 488-498, 2019 06 01.
Artigo em Inglês | MEDLINE | ID: mdl-31029593

RESUMO

The phycobilisome, the cyanobacterial light harvesting complex, is a huge phycobiliprotein containing extramembrane complex, formed by a core from which rods radiate. The phycobilisome has evolved to efficiently absorb sun energy and transfer it to the photosystems via the last energy acceptors of the phycobilisome, ApcD and ApcE. ApcF also affects energy transfer by interacting with ApcE. In this work we studied the role of ApcD and ApcF in energy transfer and state transitions in Synechococcus elongatus and Synechocystis PCC6803. Our results demonstrate that these proteins have different roles in both processes in the two strains. The lack of ApcD and ApcF inhibits state transitions in Synechocystis but not in S. elongatus. In addition, lack of ApcF decreases energy transfer to both photosystems only in Synechocystis, while the lack of ApcD alters energy transfer to photosystem I only in S. elongatus. Thus, conclusions based on results obtained in one cyanobacterial strain cannot be systematically transferred to other strains and the putative role(s) of phycobilisomes in state transitions need to be reconsidered.


Assuntos
Proteínas de Bactérias/metabolismo , Ficobilissomas/metabolismo , Ficocianina/metabolismo , Synechococcus/metabolismo , Proteínas de Bactérias/genética , Transferência de Energia/fisiologia , Mutação , Complexo de Proteína do Fotossistema I/metabolismo , Espectrometria de Fluorescência , Espectrometria de Massas em Tandem
17.
Photosynth Res ; 141(3): 343-353, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-30929163

RESUMO

The acclimation of cyanobacterial photosynthetic apparatus to iron deficiency is crucial for their performance under limiting conditions. In many cyanobacterial species, one of the major responses to iron deficiency is the induction of isiA. The function of the IsiA pigment-protein complex has been the subject of intensive research. In this study of the model Synechocystis sp. PCC 6803 strain, we probe the accumulation of the pigment-protein complex and its effects on in vivo photosynthetic performance. We provide evidence that in this organism the dominant factor controlling IsiA accumulation is the intracellular iron concentration and not photo-oxidative stress or redox poise. These findings support the use of IsiA as a tool for assessing iron bioavailability in environmental studies. We also present evidence demonstrating that the IsiA pigment-protein complex exerts only small effects on the performance of the reaction centers. We propose that its major function is as a storage depot able to hold up to 50% of the cellular chlorophyll content during transition into iron limitation. During recovery from iron limitation, chlorophyll is released from the complex and used for the reconstruction of photosystems. Therefore, the IsiA pigment-protein complex can play a critical role not only when cells transition into iron limitation, but also in supporting efficient recovery of the photosynthetic apparatus in the transition back out of the iron-limited state.


Assuntos
Proteínas de Bactérias/metabolismo , Pigmentos Biológicos/metabolismo , Synechocystis/metabolismo , Clorofila/metabolismo , Fluorescência , Ferro/deficiência , Oxirredução , Fotossíntese , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo
18.
Aquat Toxicol ; 211: 163-172, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-30991162

RESUMO

The mechanisms of cadmium toxicity to cyanobacterial photosynthesis have been extensively studied, but the response mechanisms to combinations of different cadmium concentrations and different light intensities are not yet well understood. The two principal objectives of the present work were to: 1) study the short term (5 h) toxic effects of cadmium on Synechocystis PCC6803 under three different culturing light intensity conditions; and, 2) investigate the effects of light history on Cd toxicity to Synechocystis. The maximal (ФM) and operational (Ф'M) photosystem II quantum yields, photosystem I quantum yield [Y (I)], cyclic electron flow, relative photochemical quenching (qPrel), relative non-photochemical quenching (qNrel), relative unquenched fluorescence (UQFrel), pigment contents, and cadmium uptake were evaluated when Synechocystis cells were treated with cadmium for 5 h under three different light conditions. We demonstrated that cadmium toxicity was enhanced with increasing growth light intensities due to increased cadmium uptake under higher light exposures, and the photoprotective mechanisms could not cope with cadmium and light stress under high light conditions. We also investigated Cd toxicity to Synechocystis adapted to three growth light intensities and subsequently shifted to different light intensity conditions to compare the effects of light regime shift on cadmium toxicity. We observed increased cadmium toxicity when the cells were transferred from low light to high light conditions. Interestingly, Synechocystis cells grown at high light intensities were more tolerant to cadmium than cells grown at low light intensities after the same light regime shift, due to the development of photoprotective mechanisms.


Assuntos
Cádmio/toxicidade , Luz , Synechocystis/efeitos dos fármacos , Poluentes Químicos da Água/toxicidade , Cádmio/metabolismo , Fotossíntese/efeitos dos fármacos , Fotossíntese/efeitos da radiação , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Synechocystis/metabolismo , Synechocystis/efeitos da radiação , Poluentes Químicos da Água/metabolismo
19.
Biochim Biophys Acta Bioenerg ; 1860(6): 452-460, 2019 06 01.
Artigo em Inglês | MEDLINE | ID: mdl-30986391

RESUMO

(P700+ - P700) Fourier transform visible and infrared difference spectra (DS) have been obtained using photosystem I (PSI) complexes isolated from cells of Fischerella thermalis PCC 7521 grown under white light (WL) or far-red light (FRL). PSI from cells grown under FRL (FRL-PSI) contain ~8 chlorophyll f (Chl f) molecules (Shen et al., Photosynth. Res. Jan. 2019). Both the visible and infrared DS indicate that neither the PA or PB pigments of P700 are Chl f molecules, but do support the conclusion that at least one of the A-1 cofactors is a Chl f molecule. The FTIR DS indicate that the hydrogen bond to the 131-keto CO group of the PA pigment of P700 is weakened in FRL-PSI, as might be expected given that the proteins that bind the P700 pigments are substantially different in FRL-PSI (Gan et al., Science 345, 1312-1317, 2014). The FTIR DS obtained using FRL-PSI display a band at 1664 cm-1 that is assigned (based on density functional theory calculations) to the 21-formyl CO group of Chl f, that upshifts 5 cm-1 upon P700+ formation. This is much less than expected for a cation-induced upshift, indicating that the Chl f molecule is not one of the pigments of P700. In WL-PSI the A-1 cofactor is a Chl a molecule with 131-keto and 133-methylester CO mode vibrations at 1696 and 1750 cm-1, respectively. In FRL-PSI the A-1 cofactor is a Chl f molecule with 131-keto and 133-methylester CO mode vibrations at 1702 and 1754 cm-1, respectively.


Assuntos
Proteínas de Bactérias/química , Proteínas de Bactérias/efeitos da radiação , Clorofila/análogos & derivados , Cianobactérias/química , Luz , Complexo de Proteína do Fotossistema I/química , Proteínas de Bactérias/metabolismo , Clorofila/química , Clorofila/metabolismo , Cianobactérias/metabolismo , Ligações de Hidrogênio , Modelos Moleculares , Estrutura Molecular , Fotossíntese , Complexo de Proteína do Fotossistema I/metabolismo , Espectrofotometria
20.
Nat Plants ; 5(3): 273-281, 2019 03.
Artigo em Inglês | MEDLINE | ID: mdl-30850819

RESUMO

During oxygenic photosynthesis, photosystems I and II (PSI and PSII) are essential for light-driven electron transport. Excitation energy transfer in PSI occurs extremely quickly, making it an efficient energy converter. In the alga Chlamydomonas reinhardtii (Cr), multiple units of light-harvesting complex I (LHCI) bind to the PSI core and function as peripheral antennae, forming a PSI-LHCI supercomplex. CrPSI-LHCI shows significantly larger antennae compared with plant PSI-LHCI while maintaining highly efficient energy transfer from LHCI to PSI. Here, we report structures of CrPSI-LHCI, solved by cryo-electron microscopy, revealing that up to ten LHCIs are associated with the PSI core. The structures provide detailed information about antenna organization and pigment arrangement within the supercomplexes. Highly populated and closely associated chlorophylls in the antennae explain the high efficiency of light harvesting and excitation energy transfer in CrPSI-LHCI.


Assuntos
Chlamydomonas reinhardtii/metabolismo , Complexos de Proteínas Captadores de Luz/química , Complexos de Proteínas Captadores de Luz/metabolismo , Complexo de Proteína do Fotossistema I/química , Complexo de Proteína do Fotossistema I/metabolismo , Chlamydomonas reinhardtii/química , Microscopia Crioeletrônica , Transferência de Energia , Modelos Moleculares , Conformação Proteica , Subunidades Proteicas
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