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1.
Nat Commun ; 12(1): 2333, 2021 04 20.
Artigo em Inglês | MEDLINE | ID: mdl-33879791

RESUMO

Acaryochloris marina is one of the cyanobacterial species that can use far-red light to drive photochemical reactions for oxygenic photosynthesis. Here, we report the structure of A. marina photosystem I (PSI) reaction center, determined by cryo-electron microscopy at 2.58 Å resolution. The structure reveals an arrangement of electron carriers and light-harvesting pigments distinct from other type I reaction centers. The paired chlorophyll, or special pair (also referred to as P740 in this case), is a dimer of chlorophyll d and its epimer chlorophyll d'. The primary electron acceptor is pheophytin a, a metal-less chlorin. We show the architecture of this PSI reaction center is composed of 11 subunits and we identify key components that help explain how the low energy yield from far-red light is efficiently utilized for driving oxygenic photosynthesis.


Assuntos
Proteínas de Bactérias/química , Cianobactérias/química , Complexo de Proteína do Fotossistema I/química , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Clorofila/química , Clorofila/metabolismo , Microscopia Crioeletrônica , Cianobactérias/genética , Cianobactérias/metabolismo , Transporte de Elétrons , Luz , Modelos Moleculares , Oxigênio/metabolismo , Fotossíntese , Complexo de Proteína do Fotossistema I/genética , Complexo de Proteína do Fotossistema I/metabolismo , Estrutura Quaternária de Proteína , Subunidades Proteicas , Eletricidade Estática
2.
Nat Commun ; 12(1): 1100, 2021 02 17.
Artigo em Inglês | MEDLINE | ID: mdl-33597543

RESUMO

Photosystem I (PSI) and II (PSII) balance their light energy distribution absorbed by their light-harvesting complexes (LHCs) through state transition to maintain the maximum photosynthetic performance and to avoid photodamage. In state 2, a part of LHCII moves to PSI, forming a PSI-LHCI-LHCII supercomplex. The green alga Chlamydomonas reinhardtii exhibits state transition to a far larger extent than higher plants. Here we report the cryo-electron microscopy structure of a PSI-LHCI-LHCII supercomplex in state 2 from C. reinhardtii at 3.42 Å resolution. The result reveals that the PSI-LHCI-LHCII of C. reinhardtii binds two LHCII trimers in addition to ten LHCI subunits. The PSI core subunits PsaO and PsaH, which were missed or not well-resolved in previous Cr-PSI-LHCI structures, are observed. The present results reveal the organization and assembly of PSI core subunits, LHCI and LHCII, pigment arrangement, and possible pathways of energy transfer from peripheral antennae to the PSI core.


Assuntos
Proteínas de Algas/metabolismo , Chlamydomonas reinhardtii/metabolismo , Complexos de Proteínas Captadores de Luz/metabolismo , Complexo de Proteína do Fotossistema I/metabolismo , Proteínas de Algas/química , Proteínas de Algas/ultraestrutura , Clorofila/metabolismo , Microscopia Crioeletrônica , Transferência de Energia , Complexos de Proteínas Captadores de Luz/química , Complexos de Proteínas Captadores de Luz/ultraestrutura , Modelos Moleculares , Fotossíntese , Complexo de Proteína do Fotossistema I/química , Complexo de Proteína do Fotossistema I/ultraestrutura , Complexo de Proteína do Fotossistema II/química , Complexo de Proteína do Fotossistema II/metabolismo , Complexo de Proteína do Fotossistema II/ultraestrutura , Ligação Proteica , Conformação Proteica , Multimerização Proteica , Tilacoides/metabolismo , Tilacoides/ultraestrutura
3.
Nat Plants ; 7(1): 87-98, 2021 01.
Artigo em Inglês | MEDLINE | ID: mdl-33432159

RESUMO

TAP38/STN7-dependent (de)phosphorylation of light-harvesting complex II (LHCII) regulates the relative excitation rates of photosystems I and II (PSI, PSII) (state transitions) and the size of the thylakoid grana stacks (dynamic thylakoid stacking). Yet, it remains unclear how changing grana size benefits photosynthesis and whether these two regulatory mechanisms function independently. Here, by comparing Arabidopsis wild-type, stn7 and tap38 plants with the psal mutant, which undergoes dynamic thylakoid stacking but lacks state transitions, we explain their distinct roles. Under low light, smaller grana increase the rate of PSI reduction and photosynthesis by reducing the diffusion distance for plastoquinol; however, this beneficial effect is only apparent when PSI/PSII excitation balance is maintained by state transitions or far-red light. Under high light, the larger grana slow plastoquinol diffusion and lower the equilibrium constant between plastocyanin and PSI, maximizing photosynthesis by avoiding PSI photoinhibition. Loss of state transitions in low light or maintenance of smaller grana in high light also both bring about a decrease in cyclic electron transfer and over-reduction of the PSI acceptor side. These results demonstrate that state transitions and dynamic thylakoid stacking work synergistically to regulate photosynthesis in variable light.


Assuntos
Complexo de Proteína do Fotossistema I/metabolismo , Tilacoides/metabolismo , Arabidopsis/metabolismo , Arabidopsis/fisiologia , Transporte de Elétrons , Fotossíntese , Complexo de Proteína do Fotossistema I/fisiologia , Tilacoides/fisiologia
4.
Plant Sci ; 303: 110795, 2021 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-33487367

RESUMO

Under natural field conditions, plants usually experience fluctuating light (FL) under moderate heat stress in summer. However, responses of photosystems I and II (PSI and PSII) to such combined stresses are not well known. Furthermore, the role of water-water cycle (WWC) in photoprotection in FL under moderate heat stress is poorly understood. In this study, we examined chlorophyll fluorescence and P700 redox state in FL at 42 °C in two orchids, Dendrobium officinale (with high WWC activity) and Bletilla striata (with low WWC activity). After FL treatment at 42 °C, PSI activity maintained stable while PSII activity decreased significantly in these two orchids. In D. officinale, the WWC could rapidly consume the excess excitation energy in PSI and thus avoided an over-reduction of PSI upon any increase in illumination. Therefore, in D. officinale, WWC likely protected PSI in FL at 42 °C. In B. striata, heat-induced PSII photoinhibition down-regulated electron flow from PSII and thus prevented an over-reduction of PSI after transition from low to high light. Consequently, in B. striata moderate PSII photoinhibition could protected PSI in FL at 42 °C. We conclude that, in addition to cyclic electron flow, WWC and PSII photoinhibition-repair cycle are two important strategies for preventing PSI photoinhibition in FL under moderate heat stress.


Assuntos
Dendrobium/metabolismo , Orchidaceae/metabolismo , Complexo de Proteína do Fotossistema I/fisiologia , Dendrobium/fisiologia , Resposta ao Choque Térmico , Luz , Oxirredução , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema I/efeitos da radiação , Complexo de Proteína do Fotossistema II/metabolismo , Complexo de Proteína do Fotossistema II/fisiologia , Complexo de Proteína do Fotossistema II/efeitos da radiação
5.
Nat Commun ; 12(1): 679, 2021 01 29.
Artigo em Inglês | MEDLINE | ID: mdl-33514722

RESUMO

Diverse algae of the red lineage possess chlorophyll a-binding proteins termed LHCR, comprising the PSI light-harvesting system, which represent an ancient antenna form that evolved in red algae and was acquired through secondary endosymbiosis. However, the function and regulation of LHCR complexes remain obscure. Here we describe isolation of a Nannochloropsis oceanica LHCR mutant, named hlr1, which exhibits a greater tolerance to high-light (HL) stress compared to the wild type. We show that increased tolerance to HL of the mutant can be attributed to alterations in PSI, making it less prone to ROS production, thereby limiting oxidative damage and favoring growth in HL. HLR1 deficiency attenuates PSI light-harvesting capacity and growth of the mutant under light-limiting conditions. We conclude that HLR1, a member of a conserved and broadly distributed clade of LHCR proteins, plays a pivotal role in a dynamic balancing act between photoprotection and efficient light harvesting for photosynthesis.


Assuntos
Adaptação Fisiológica/genética , Proteínas de Ligação à Clorofila/metabolismo , Luz/efeitos adversos , Complexo de Proteína do Fotossistema I/metabolismo , Estramenópilas/fisiologia , Adaptação Fisiológica/efeitos da radiação , Clorofila A/metabolismo , Proteínas de Ligação à Clorofila/genética , Proteínas de Ligação à Clorofila/isolamento & purificação , Mutação , Fotossíntese/genética , Fotossíntese/efeitos da radiação , Complexo de Proteína do Fotossistema I/genética , Estramenópilas/efeitos da radiação
6.
Ecotoxicol Environ Saf ; 209: 111851, 2021 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-33421673

RESUMO

The herbal plant Salvia sclarea L. (clary sage) is classified to cadmium (Cd) accumulators and considered as a potential plant for phytoremediation of heavy metal polluted soil. However, the effect of Cd only treatment on the function of the photosynthetic apparatus of S. sclarea, as well as the mechanisms involved in Cd tolerance have not yet been studied in detail. This study was conducted to examine the integrative responses of S. sclarea plants exposed to a high Cd supply (100 µM) for 3 and 8 days by investigating element nutrient uptake, oxidative stress markers, pigment composition, photosynthetic performance and leaf structure. Measurements of the functional activities of photosystem I (PSI, by P700 photooxidation), photosystem II (PSII, by chlorophyll fluorescence parameters), the oxygen-evolving complex (oxygen evolution by Joliot- and Clark-type electrodes), as well as the leaf pigment and phenolic contents, were used to evaluate the protective mechanisms of the photosynthetic apparatus under Cd stress. Data suggested that the molecular mechanisms included in the photosynthetic tolerance to Cd toxicity involve strongly increased phenolic and anthocyanin contents, as well as an increased non-photochemical quenching and accelerated cyclic electron transport around PSI up to 61%, which protect the function of the photosynthetic apparatus under stress. Furthermore, the tolerance of S. sclarea to Cd stress is also associated with increased accumulation of Fe in leaves by 25%. All the above, clearly suggest that S. sclarea plants employ several different mechanisms to protect the function of the photosynthetic apparatus against Cd stress, which are discussed here.


Assuntos
Cádmio/toxicidade , Salvia/fisiologia , Poluentes do Solo/toxicidade , Biodegradação Ambiental , Clorofila/metabolismo , Transporte de Elétrons , Estresse Oxidativo/fisiologia , Fotossíntese/efeitos dos fármacos , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Folhas de Planta/metabolismo , Salvia/metabolismo , Solo
7.
Chemistry ; 27(16): 5277-5282, 2021 Mar 17.
Artigo em Inglês | MEDLINE | ID: mdl-33438792

RESUMO

The Z-scheme process is a photoinduced electron-transfer pathway in natural oxygenic photosynthesis involving electron transport from photosystem II (PSII) to photosystem I (PSI). Inspired by the interesting Z-scheme process, herein a photocatalytic hydrogen evolution reaction (HER) employing chlorophyll (Chl) derivatives, Chl-1 and Chl-2, on the surface of Ti3 C2 Tx MXene with two-dimensional accordion-like morphology, forming Chl-1@Chl-2@Ti3 C2 Tx composite, is demonstrated. Due to the frontier molecular orbital energy alignments of Chl-1 and Chl-2, sublayer Chl-1 is a simulation of PSI, whereas upper layer Chl-2 is equivalent to PSII, and the resultant electron transport can take place from Chl-2 to Chl-1. Under the illumination of visible light (>420 nm), the HER performance of Chl-1@Chl-2@Ti3 C2 Tx photocatalyst was found to be as high as 143 µmol h-1 gcat -1 , which was substantially higher than that of photocatalysts of either Chl-1@Ti3 C2 Tx (20 µmol h-1 g-1 ) or Chl-2@Ti3 C2 Tx (15 µmol h-1 g-1 ).


Assuntos
Clorofila , Titânio , Hidrogênio , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo
8.
Biochim Biophys Acta Bioenerg ; 1862(1): 148318, 2021 01 01.
Artigo em Inglês | MEDLINE | ID: mdl-32979345

RESUMO

Photosynthetic organisms adjust their activity to changes in irradiance by different ways, including the operation of cyclic electron flow around photosystem I (PSI) and state transitions that redistribute amounts of light energy absorbed by PSI and PSII. In dark-acclimated wild type cells of Synechocystis PCC 6803, linear electron transport was activated after the first 500 ms of illumination, while cyclic electron flow around PSI was long predominant in the mutant deficient in flavodiiron protein Flv3. Chlorophyll P700 oxidation associated with activation of linear electron flow extended in the Flv3- mutant to several tens of seconds and included a P700+ re-reduction phase. Parallel monitoring of chlorophyll fluorescence and the redox state of P700 indicated that, at low light intensity both in wild type and in the Flv3- mutant, the transient re-reduction step coincided in time with S-M fluorescence rise, which reflected state 2-state 1 transition (Kana et al., 2012). Despite variations in the initial redox state of plastoquinone pool, the oxidases-deficient mutant, succinate dehydrogenase-deficient mutant, and wild type cells did not show the S-M rise under high-intensity light until additional Flv3- mutation was introduced in these strains. Thus, the lack of available electron acceptor for PSI was the main cause for the appearance of S-M fluorescence rise under high light. It is concluded that the lack of Flv3 protein promotes cyclic electron flow around PSI and facilitates the subsequent state 2-state 1 transition in the absence of strict relation to the dark-operated pathways of plastoquinone reduction or oxidation.


Assuntos
Luz , Mutação , Complexo de Proteína do Fotossistema I , Complexo de Proteína do Fotossistema II , Synechocystis , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Transporte de Elétrons/genética , Transporte de Elétrons/efeitos da radiação , 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 , Synechocystis/genética , Synechocystis/metabolismo
9.
Biochim Biophys Acta Bioenerg ; 1862(1): 148324, 2021 01 01.
Artigo em Inglês | MEDLINE | ID: mdl-33039349

RESUMO

All known Type I photochemical reaction center protein complexes contain a form of the pigment chlorophyll a in their primary electron acceptor site (termed ec3). In the reaction center from the primitive heliobacteria (HbRC), all of the pigment cofactors are bacteriochlorophyll g except in the ec3 sites, which contain 81-hydroxychlorophyll a. To explore the energetic flexibility of this site, we performed site-directed mutagenesis on two of the amino acids of the PshA core polypeptide responsible for coordinating the 81-hydroxychlorophyll a. These two amino acids are serine-545, which coordinates the central Mg(II) through an intermediary water molecule, and serine-553, which participates in a hydrogen bond with the 131-keto O atom. Mutagenesis of serine-545 to histidine (S545H) changes how the chlorophyll's central Mg(II) is coordinated, with the result of decreasing the chlorophyll's site energy. Mutagenesis of serine-545 to methionine (S545M), which was made to mimic the ec3 site of Photosystem I, abolishes chlorophyll binding and charge separation altogether. Mutagenesis of serine-553 to alanine (S553A) removes the aforementioned hydrogen bond, increasing the site energy of the chlorophyll. In the S545H and S553A mutants, the forward and reverse electron transfer rates from ec3 are both faster. This coincides with a decrease in both the quantum yield of initial charge separation and the overall photochemical quantum yield. Taken together, these data indicate that wild-type HbRC is optimized for overall photochemical efficiency, rather than just for maximizing the forward electron transfer rate. The necessity for a chlorophyll a derivative at the ec3 site is also discussed.


Assuntos
Substituição de Aminoácidos , Proteínas de Bactérias/química , Clorofila/química , Clostridiales/química , Mutação de Sentido Incorreto , Complexo de Proteína do Fotossistema I/química , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Sítios de Ligação , Clorofila/genética , Clorofila/metabolismo , Clostridiales/genética , Clostridiales/metabolismo , Complexo de Proteína do Fotossistema I/genética , Complexo de Proteína do Fotossistema I/metabolismo
10.
Biochim Biophys Acta Bioenerg ; 1862(1): 148331, 2021 01 01.
Artigo em Inglês | MEDLINE | ID: mdl-33127356

RESUMO

The eukaryotic alga Chlamydomonas (C.) reinhardtii is used as a model organism to study photosynthetic efficiency. We studied the organization and protein profile of thylakoid membranes under severe iron (Fe2+) deficiency condition and iron supplement for their restoration. Chlorophyll (Chl) a fluorescence fast OJIP transients were decreased in the severe Fe2+ deficient cells resulting in the reduction of the photochemical efficiency. The circular dichroism (CD) results from Fe2+ deficient thylakoid membranes show a significant change in pigment-pigment and pigment-protein excitonic interactions. The organization of super-complexes was also affected significantly. Furthermore, super-complexes of photosystem (PS) II and PSI, along with its dimers, were severely reduced. The complexes separated using sucrose gradient centrifugation shows that loss of super-complexes and excitonic pigment-pigment interactions were restored in the severely Fe2+ deficient cells upon Fe supplementation for three generations. Additionally, the immunoblots demonstrated that both PSII, PSI core, and their light-harvesting complex antenna proteins were differentially decreased. However, reduced core proteins were aggregated, which in turn proteins were unfold and destabilized the supercomplexes and its function. Interestingly, the aggregated proteins were insoluble after n-Dodecyl ß-D-maltoside solubilization. Further, they were identified in the pellet form. When Fe2+ was added to the severely deficient cells, the photosynthetic activity, pigment-proteins complexes, and proteins were restored to the level of control after 3rd generation.


Assuntos
Chlamydomonas reinhardtii/metabolismo , Clorofila A/metabolismo , Ferro/metabolismo , Fotossíntese , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Tilacoides/metabolismo
11.
Physiol Plant ; 171(2): 291-300, 2021 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-33314124

RESUMO

The so-called afterglow, AG, thermoluminescence (TL) band is a useful indicator of the presence of cyclic electron flow (CEF), which is mediated by the NADH dehydrogenase-like (NDH) complex in higher plants. Although NDH-dependent CEF occurs also in cyanobacteria, the AG band has previously not been found in these organisms. In the present study, we tested various experimental conditions and could identify a TL component with ca. +40°C peak temperature in Synechocystis PCC 6803 cells, which were illuminated by far-red (FR) light at around -10°C. The +40°C band could be observed when WT cells were grown under ambient air level CO2 , but was absent in the M55 mutant, which is deficient in the NDH-1 complex. These experimental observations match the characteristics of the AG band of higher plants. Therefore, we conclude that the newly identified +40°C TL component in Synechocystis PCC 6803 is the cyanobacterial counterpart of the plant AG band and originates from NDH-1-mediated CEF. The cyanobacterial AG band was most efficiently induced when FR illumination was applied at -10°C and its contribution to the total TL intensity declined when cells were illuminated above and below this temperature. Based on this phenomenon we also conclude that CEF is blocked by low temperatures at two different sites in Synechocystis PCC 6803: (1) Below -10°C at the level of NDH-1 and (2) below -30°C at the donor or acceptor side of Photosystem I.


Assuntos
Synechocystis , Transporte de Elétrons , Luz , Complexo de Proteína do Fotossistema I/metabolismo , Prata , Synechocystis/metabolismo
12.
Ecotoxicol Environ Saf ; 209: 111844, 2021 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-33383337

RESUMO

Nitrogen dioxide (NO2) is a major air pollutant that affects plant growth, development and yields. Previous studies have found that atmospheric NO2 changes plant photosynthesis in a concentration-dependent manner. Low concentrations of NO2 (4.0 µL L-1) can increase photosynthetic rates, while high concentrations of NO2 (16.0 µL L-1) can have an inhibitory effect. However, the specific effects of a critical intermediate concentration of NO2 on the photosynthetic apparatus of plants has remained unknown. Therefore, in this study, tobacco seedlings at three-leaf ages were fumigated with a intermediate concentration of 8.0 µL L-1 NO2 for 15 days to determine the effects on leaf weight, leaf number per plant, chlorophyll content, net photosynthetic rate, the reaction center activity of photosystems I and II (PSI and PSII, respectively) and core protein gene expression (PsbA and PsaA). Fumigation with 8.0 µL L-1 NO2 increased the number of leaves per plant and the weight of leaves, and the leaves became dark green and curly after 10 days of fumigation. During NO2 fumigation for 15 days, the chlorophyll content, PSII maximum photochemical efficiency (Fv/Fm), electron transfer rate (ETR) and non-photochemical quenching (NPQ) increased most in the oldest leaves (Lmax leaves), but decreased PSI activity (∆I/Io). The Fv/Fm, ETR and NPQ in the youngest leaves (Lmin leaves) were lower than those of Lmax leaves, but the actual photochemical efficiency (ΦPSII) of PSII increased most and ∆I/Io was the highest in these samples. The Fv/Fm, ETR, NPQ and ΦPSII in the leaves at the middle leaf age (Lmid leaves) were lower than those of Lmin and Lmax leaves, but the relative fluorescence intensity of point L (VL) and the relative fluorescence intensity of point K (VK) decreased the most in these samples. Thus, this critical concentration of atmospheric NO2 increased the activity of PSII and inhibited PSI activity in expanded leaves of tobacco seedlings.


Assuntos
Poluentes Atmosféricos/análise , Dióxido de Nitrogênio/análise , Tabaco/efeitos dos fármacos , Poluentes Atmosféricos/toxicidade , Atmosfera/química , Clorofila/metabolismo , Transporte de Elétrons/efeitos dos fármacos , Dióxido de Nitrogênio/toxicidade , Fotossíntese/efeitos dos fármacos , Complexo de Proteína do Fotossistema I/efeitos dos fármacos , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Folhas de Planta/metabolismo , Plântula/metabolismo , Tabaco/fisiologia
13.
Nat Commun ; 11(1): 6388, 2020 12 15.
Artigo em Inglês | MEDLINE | ID: mdl-33319777

RESUMO

Evergreen conifers in boreal forests can survive extremely cold (freezing) temperatures during long dark winter and fully recover during summer. A phenomenon called "sustained quenching" putatively provides photoprotection and enables their survival, but its precise molecular and physiological mechanisms are not understood. To unveil them, here we have analyzed seasonal adjustment of the photosynthetic machinery of Scots pine (Pinus sylvestris) trees by monitoring multi-year changes in weather, chlorophyll fluorescence, chloroplast ultrastructure, and changes in pigment-protein composition. Analysis of Photosystem II and Photosystem I performance parameters indicate that highly dynamic structural and functional seasonal rearrangements of the photosynthetic apparatus occur. Although several mechanisms might contribute to 'sustained quenching' of winter/early spring pine needles, time-resolved fluorescence analysis shows that extreme down-regulation of photosystem II activity along with direct energy transfer from photosystem II to photosystem I play a major role. This mechanism is enabled by extensive thylakoid destacking allowing for the mixing of PSII with PSI complexes. These two linked phenomena play crucial roles in winter acclimation and protection.


Assuntos
Transferência de Energia , Fotossíntese/fisiologia , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Pinus sylvestris/metabolismo , Aclimatação , Clorofila , Cloroplastos/metabolismo , Cloroplastos/ultraestrutura , Fluorescência , Cinética , Luz , Processos Fotoquímicos , Complexo de Proteína do Fotossistema I/química , Complexo de Proteína do Fotossistema II/química , Estações do Ano , Temperatura , Tilacoides/metabolismo , Fatores de Tempo , Árvores/metabolismo
14.
Ecotoxicol Environ Saf ; 203: 111019, 2020 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-32888606

RESUMO

Sulfur dioxide (SO2) is one of the most common and harmful air pollutants. High concentrations of SO2 can induce a series of defensive responses in Arabidopsis plants. However, the role of photosynthesis in the plant response to SO2 stress is not clear. Here, we report the photosynthetic responses of Arabidopsis plants to SO2 stress. Exposure to 30 mg/m3 SO2 decreased stomatal conductance (Gs) and transpiration rate (Tr) but increased photosynthetic pigments and net photosynthetic rate (Pn). The contents of carbohydrates and sucrose were not altered. The transcript levels of most genes related to photosystem II (PSII), cytochrome b6/f (Cytb6f), photosystem I (PSI) and carbon fixation were upregulated, revealing one important regulatory circuit for the maintenance of chloroplast homeostasis under SO2 stress. Exposure to SO2 triggered reactive oxygen species (ROS) generation, accompanied by increases in superoxide dismutase (SOD) activity and the contents of cysteine (Cys), glutathione (GSH) and non-protein thiol (NPT), which maintained cellular redox homeostasis. Together, our results indicated that chloroplast photosynthesis was involved in the plant response to SO2 stress. The photosynthetic responses were related to photosynthetic pigments, photosynthesis gene expression and redox regulation.


Assuntos
Poluentes Atmosféricos/toxicidade , Arabidopsis/efeitos dos fármacos , Expressão Gênica/efeitos dos fármacos , Estresse Oxidativo/efeitos dos fármacos , Fotossíntese/efeitos dos fármacos , Pigmentos Biológicos/metabolismo , Dióxido de Enxofre/toxicidade , Arabidopsis/genética , Arabidopsis/metabolismo , Cloroplastos/metabolismo , Regulação para Baixo , Fotossíntese/genética , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Folhas de Planta/efeitos dos fármacos , Folhas de Planta/metabolismo , Regulação para Cima
15.
Ecotoxicol Environ Saf ; 204: 111136, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32798755

RESUMO

High temperature can lead to increased production of excess light energy, thus reducing photosynthetic capacity in plants. Photosynthetic cyclic electron flow (CEF) in photosystem I (PSI) can effectively protect photosystems, but its physiological mechanism under high temperature is poorly understood. In this study, antimycin A (AA) and thenoyltrifluoroacetone (TTFA) were used to inhibit PGR5-and NDH-dependent CEF pathways, respectively, to reveal the photoprotective functions of CEF for PSII in tobacco leaves under high temperature stress (37 °C, HT). High temperatures caused decreases in maximal photochemistry efficiency (Fv/Fm) and damaged photosystem II (PSII) in tobacco leaves. Under AA inhibition of PGR5-dependent CEF, high temperature increased the fluorescence intensity of point O (Fo) in OJIP curves, i.e., the energy absorption per active reaction center (ABS/RC), the trapping rate of the reaction center (TRo/RC), and the electron transport efficiency per reaction center (ETo/RC) in tobacco leaves. High temperature induced an increase in the hydrogen peroxide content and a decrease in pigment content in tobacco leaves. Under the high temperature treatment, inhibition of PGR5-dependent CEF reduced the activities of the PSII reaction center significantly, destroyed the oxygen-evolving complex (OEC), and impeded photosynthetic electron transfer from PSII to the plastoquinone (PQ) pool in tobacco leaves. The TTFA treatment inhibited the NDH-dependent pathway under high temperature conditions, with the relative fluorescence intensity of point I (VI) decreased significantly, and the content of hydrogen peroxide and superoxide anion increased significantly. Additionally, Fo and the redox degree of the PSII donor side (Wk) increased, and pigment content decreased compared to the control, but with little change compared to high temperature treatment, indicating that the inhibition of the NDH-dependent pathway directly weakened the capacity of the PQ pool to lead to the accumulation of reactive oxygen species (ROS) in tobacco leaves. In conclusion, CEF alleviated damage to the photosynthetic apparatus in tobacco leaves by increasing PSII heat dissipation, reducing ROS production, and maintaining the stability of the PQ pool to accommodate photosynthetic electron flow.


Assuntos
Temperatura Alta , Fotossíntese/fisiologia , Complexo de Proteína do Fotossistema I/metabolismo , Tabaco/metabolismo , Clorofila/metabolismo , Transporte de Elétrons , Elétrons , Fluorescência , Oxirredução , Complexo de Proteína do Fotossistema II/metabolismo , Folhas de Planta/metabolismo , Temperatura , Tabaco/fisiologia
16.
PLoS One ; 15(8): e0237173, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32845897

RESUMO

Gentian is an important ornamental flower in Japan. The corolla of the majority of cultivated Japanese gentians have green spots, which are rarely encountered in flowers of other angiosperms. Little information is available on the functional traits of the green spots. In this study, we characterized the green spots in the Japanese gentian corolla using a number of microscopic techniques. Opto-digital microscopy revealed that a single visible green spot is composed of approximately 100 epidermal cells. The epidermal cells of a green spot formed a dome-like structure and the cell lumen contained many green structures that were granular and approximately 5 µm in diameter. The green structures emitted red autofluorescence when irradiated with 488 nm excitation light. Transmission electron microscopy revealed that the green structures contained typical thylakoids and grana, thus indicating they are chloroplasts. No grana were observed and the thylakoids had collapsed in the plastids of epidermal cells surrounding green spots. To estimate the rate of photosynthetic electron transfer of the green spots, we measured chlorophyll fluorescence using the MICROSCOPY version of an Imaging-PAM (pulse-amplitude-modulated) fluorometer. Under actinic light of 449 µmol m-2 s-1, substantial electron flow through photosystem II was observed. Observation of green spot formation during corolla development revealed that immature green spots formed at an early bud stage and developed to maturity associated with chloroplast degradation in the surrounding epidermal cells. These results confirmed that the Japanese gentian corolla contains functional chloroplasts in restricted areas of epidermal cells and indicated that a sophisticated program for differential regulation of chloroplast formation and degradation is operative in the epidermis.


Assuntos
Flores/citologia , Flores/metabolismo , Gentiana/anatomia & histologia , Tilacoides/metabolismo , Clorofila/metabolismo , Transporte de Elétrons , Japão , Microscopia Eletrônica de Transmissão , Microscopia de Fluorescência , Fotossíntese , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Epiderme Vegetal/citologia , Epiderme Vegetal/metabolismo , Folhas de Planta/metabolismo
17.
PLoS One ; 15(8): e0237569, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32817667

RESUMO

Several 'super-complexes' of individual hetero-oligomeric membrane protein complexes, whose function is to facilitate intra-membrane electron and proton transfer and harvesting of light energy, have been previously characterized in the mitochondrial cristae and chloroplast thylakoid membranes. We report the presence of an intra-membrane super-complex dominated by the ATP-synthase, photosystem I (PSI) reaction-center complex and the ferredoxin-NADP+ Reductase (FNR) in the thylakoid membrane. The presence of the super-complex has been documented by mass spectrometry, clear-native PAGE and Western Blot analyses. This is the first documented presence of ATP synthase in a super-complex with the PSI reaction-center located in the non-appressed stromal domain of the thylakoid membrane.


Assuntos
Cloroplastos/metabolismo , Ferredoxina-NADP Redutase/metabolismo , Óxido Nítrico Sintase/metabolismo , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , ATPases Translocadoras de Prótons/metabolismo , Tilacoides/metabolismo , Trifosfato de Adenosina/metabolismo , Transporte de Elétrons , Fotossíntese , Folhas de Planta/metabolismo , Proteínas de Plantas/metabolismo , Spinacia oleracea/crescimento & desenvolvimento , Spinacia oleracea/metabolismo
18.
Ecotoxicol Environ Saf ; 202: 110856, 2020 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-32629202

RESUMO

To explore the mechanisms underlying the action of the heavy metals Cd and Zn on the photosynthetic function of plant leaves, the effects of 100 µmol L-1 Cd and 200 µmol L-1 Zn stress (the exposure concentrations of Cd and Zn in the culture medium were 2.24 mg kg-1 and 5.36 mg kg-1) on the chlorophyll and carotenoid contents as well as the photosynthetic function of tobacco leaves (Long Jiang 911) were studied. The key proteins in these physiological processes were quantitatively analyzed using a TMT-based proteomics approach. Cd stress was found to inhibit the expression of key enzymes during chlorophyll synthesis in leaves, resulting in a decrease of the Chl content. However, Zn stress did not significantly influence the chlorophyll content. Leaves adapted to Zn stress by upregulating CAO expression and increase the Chl b content. Although the Car content in leaves did not significantly change under either Cd or Zn stress, the expressions of ZE and VDE during Car metabolism decreased significantly under Cd stress. This was accompanied by damages to the xanthophyll cycle and the NPQ-dependent energy dissipation mechanism. In contrast, under Zn stress, leaves adapted to Zn stress by increasing the expression of VDE, thus improving NPQ. Under Cd stress, the expressions of three sets of proteins were significantly down-regulated, including PSII donor-side proteins (PPD3, PPD6, OEE1, OEE2-1, OEE2-2, OEE2-3, and OEE3-2), receptor-side proteins (D1, D2, CP43, CP47, Cyt b559α, Cyt b559ß, PsbL, PsbQ, PsbR, Psb27-H1, and Psb28), and core proteins of the PSI reaction center (psaA, psaB, psaC, psaD, psaE-A, PsaE-B, psaF, psaG, psaH-1, psaK, psaL, psaN, and psaOL). In comparison, only eight of the above proteins (PPD6, OEE3-2, PsbL, PsbQ, Psb27-H1, psaL, and psaOL) were significantly down-regulated by Zn stress. Under Cd stress, both the donor side and the receptor side of PSII were damaged, and PSII and PSI experienced severe photoinhibition. However, Zn stress did not decrease either PSII or PSI activities in tobacco leaves. In addition, the expression of electron transport-related proteins (cytb6/f complex, PC, Fd, and FNR), ATPase subunits, Rubisco subunits, and RCA decreased significantly in leaves under Cd stress. However, no significant changes were observed in any of these proteins under Zn stress. Although Cd stress was found to up-regulate the expressions of PGRL1A and PGRL1B and induce an increase of PGR5/PGRL1-CEF in tobacco leaves, NDH-CEF was significantly inhibited. Under Zn stress, the expressions of ndhH and PGRL1A in leaves were significantly up-regulated, but there were no significant changes in either NDH-CEF or PGR5/PGRL-CEF. Under Cd stress, the expressions of proteins related to Fd-dependent nitrogen metabolism and reactive oxygen species (ROS) scavenging processes (e.g., FTR, Fd-NiR, and Fd-GOGAT) were significantly down-regulated in leaves. However, no significant changes of any of the above proteins were identified under Zn stress. In summary, Cd stress could inhibit the synthesis of chlorophyll in tobacco leaves, significantly down-regulate the expressions of photosynthesis-related proteins or subunits, and suppress both the xanthophyll cycle and NDH-CEF process. The expressions of proteins related to the Fd-dependent nitrogen metabolism and ROS scavenging were also significantly down-regulated, which blocked the photosynthetic electron transport, thus resulting in severe photoinhibition of both PSII and PSI. However, Zn stress had little effect on the photosynthetic function of tobacco leaves.


Assuntos
Cádmio/toxicidade , Carotenoides/metabolismo , Clorofila/metabolismo , Fotossíntese/efeitos dos fármacos , Tabaco/efeitos dos fármacos , Zinco/toxicidade , Cádmio/metabolismo , Transporte de Elétrons/efeitos dos fármacos , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Folhas de Planta/metabolismo , Proteômica , Tabaco/metabolismo , Tabaco/fisiologia , Zinco/metabolismo
19.
Biochim Biophys Acta Bioenerg ; 1861(10): 148255, 2020 10 01.
Artigo em Inglês | MEDLINE | ID: mdl-32619427

RESUMO

Cyanobacteria can rapidly regulate the relative activity of their photosynthetic complexes photosystem I and II (PSI and PSII) in response to changes in the illumination conditions. This process is known as state transitions. If PSI is preferentially excited, they go to state I whereas state II is induced either after preferential excitation of PSII or after dark adaptation. Different underlying mechanisms have been proposed in literature, in particular i) reversible shuttling of the external antenna complexes, the phycobilisomes, between PSI and PSII, ii) reversible spillover of excitation energy from PSII to PSI, iii) a combination of both and, iv) increased excited-state quenching of the PSII core in state II. Here we investigated wild-type and mutant strains of Synechococcus sp. PCC 7942 and Synechocystis sp. PCC 6803 using time-resolved fluorescence spectroscopy at room temperature. Our observations support model iv, meaning that increased excited-state quenching of the PSII core occurs in state II thereby balancing the photochemistry of photosystems I and II.


Assuntos
Synechococcus/metabolismo , Synechocystis/metabolismo , Temperatura , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Ficobilissomas/metabolismo , Ficocianina/metabolismo , Espectrometria de Fluorescência , Fatores de Tempo
20.
Biochim Biophys Acta Bioenerg ; 1861(10): 148253, 2020 10 01.
Artigo em Inglês | MEDLINE | ID: mdl-32569661

RESUMO

Oxygenic photosynthesis evolved more than 3 billion years ago in cyanobacteria. The increased complexity of photosystem I (PSI) became apparent from the high-resolution structures that were obtained for the complexes that were isolated from various organisms, ranging from cyanobacteria to plants. These complexes are all evolutionarily linked. In this paper, the researchers have uncovered the increased complexity of PSI in a single organism demonstrated by the coexistance of two distinct PSI compositions. The Large Dunaliella PSI contains eight additional subunits, six in PSI core and two light harvesting complexes. Two additional chlorophyll a molecules pertinent for efficient excitation energy transfer in state II transition were identified in PsaL and PsaO. Short distances between these newly identified chlorophylls correspond with fast excitation transfer rates previously reported during state II transition. The apparent PSI conformations could be a coping mechanism for the high salinity.


Assuntos
Clorófitas/enzimologia , Transferência de Energia , Complexo de Proteína do Fotossistema I/química , Complexo de Proteína do Fotossistema I/metabolismo , Modelos Moleculares , Conformação Proteica
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