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Frontiers in Plant Science 2021Photosynthesis needs to run efficiently under permanently changing illumination. To achieve this, highly dynamic acclimation processes optimize photosynthetic...
Photosynthesis needs to run efficiently under permanently changing illumination. To achieve this, highly dynamic acclimation processes optimize photosynthetic performance under a variety of rapidly changing light conditions. Such acclimation responses are acting by a complex interplay of reversible molecular changes in the photosynthetic antenna or photosystem assemblies which dissipate excess energy and balance uneven excitation between the two photosystems. This includes a number of non-photochemical quenching processes including state transitions and photosystem II remodeling. In the laboratory such processes are typically studied by selective illumination set-ups. Two set-ups known to be effective in a highly similar manner are (i) light quality shifts (inducing a preferential excitation of one photosystem over the other) or (ii) dark-light shifts (inducing a general off-on switch of the light harvesting machinery). Both set-ups result in similar effects on the plastoquinone redox state, but their equivalence in induction of photosynthetic acclimation responses remained still open. Here, we present a comparative study in which dark-light and light-quality shifts were applied to samples of the same growth batches of plants. Both illumination set-ups caused comparable effects on the phosphorylation of LHCII complexes and, hence, on the performance of state transitions, but generated different effects on the degree of state transitions and the formation of PSII super-complexes. The two light set-ups, thus, are not fully equivalent in their physiological effectiveness potentially leading to different conclusions in mechanistic models of photosynthetic acclimation. Studies on the regulation of photosynthetic light acclimation, therefore, requires to regard the respective illumination test set-up as a critical parameter that needs to be considered in the discussion of mechanistic and regulatory aspects in this subject.
PubMed: 35046964
DOI: 10.3389/fpls.2021.615253 -
Communications Biology May 2024Photosynthetic cryptophytes are eukaryotic algae that utilize membrane-embedded chlorophyll a/c binding proteins (CACs) and lumen-localized phycobiliproteins (PBPs) as...
Photosynthetic cryptophytes are eukaryotic algae that utilize membrane-embedded chlorophyll a/c binding proteins (CACs) and lumen-localized phycobiliproteins (PBPs) as their light-harvesting antennae. Cryptophytes go through logarithmic and stationary growth phases, and may adjust their light-harvesting capability according to their particular growth state. How cryptophytes change the type/arrangement of the photosynthetic antenna proteins to regulate their light-harvesting remains unknown. Here we solve four structures of cryptophyte photosystem I (PSI) bound with CACs that show the rearrangement of CACs at different growth phases. We identify a cryptophyte-unique protein, PsaQ, which harbors two chlorophyll molecules. PsaQ specifically binds to the lumenal region of PSI during logarithmic growth phase and may assist the association of PBPs with photosystems and energy transfer from PBPs to photosystems.
Topics: Photosystem I Protein Complex; Cryptophyta; Light-Harvesting Protein Complexes; Chlorophyll; Chlorophyll Binding Proteins; Photosynthesis; Phycobiliproteins
PubMed: 38734819
DOI: 10.1038/s42003-024-06268-5 -
Biochimica Et Biophysica Acta Sep 2005The widely held view that the maximum efficiency of a photosynthetic pigment system is given by the Carnot cycle expression (1-T/Tr) for energy transfer from a hot bath... (Comparative Study)
Comparative Study
The widely held view that the maximum efficiency of a photosynthetic pigment system is given by the Carnot cycle expression (1-T/Tr) for energy transfer from a hot bath (radiation at temperature Tr) to a cold bath (pigment system at temperature T) is critically examined and demonstrated to be inaccurate when the entropy changes associated with the microscopic process of photon absorption and photochemistry at the level of single photosystems are considered. This is because entropy losses due to excited state generation and relaxation are extremely small (DeltaS << T/Tr) and are essentially associated with the absorption-fluorescence Stokes shift. Total entropy changes associated with primary photochemistry for single photosystems are shown to depend critically on the thermodynamic efficiency of the process. This principle is applied to the case of primary photochemistry of the isolated core of higher plant photosystem I and photosystem II, which are demonstrated to have maximal thermodynamic efficiencies of xi > 0.98 and xi > 0.92 respectively, and which, in principle, function with negative entropy production. It is demonstrated that for the case of xi > (1-T/Tr) entropy production is always negative and only becomes positive when xi < (1-T/Tr).
Topics: Energy Transfer; Entropy; Fluorescence; Photosynthesis; Photosystem I Protein Complex; Photosystem II Protein Complex; Temperature; Thermodynamics; Zea mays
PubMed: 16139784
DOI: 10.1016/j.bbabio.2005.08.004 -
Biochimica Et Biophysica Acta.... Jan 2021The eukaryotic alga Chlamydomonas (C.) reinhardtii is used as a model organism to study photosynthetic efficiency. We studied the organization and protein profile of...
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 (Fe) deficiency condition and iron supplement for their restoration. Chlorophyll (Chl) a fluorescence fast OJIP transients were decreased in the severe Fe deficient cells resulting in the reduction of the photochemical efficiency. The circular dichroism (CD) results from Fe 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 Fe 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 β-D-maltoside solubilization. Further, they were identified in the pellet form. When Fe was added to the severely deficient cells, the photosynthetic activity, pigment-proteins complexes, and proteins were restored to the level of control after 3 generation.
Topics: Chlamydomonas reinhardtii; Chlorophyll A; Iron; Photosynthesis; Photosystem I Protein Complex; Photosystem II Protein Complex; Thylakoids
PubMed: 33127356
DOI: 10.1016/j.bbabio.2020.148331 -
Journal of Experimental Botany Jul 2017On Earth, solar irradiance varies as the sun rises and sets over the horizon, and sunlight is thus in constant fluctuation, following a slow dark-low-high-low-dark...
On Earth, solar irradiance varies as the sun rises and sets over the horizon, and sunlight is thus in constant fluctuation, following a slow dark-low-high-low-dark curve. Optimal plant growth and development are dependent on the capacity of plants to acclimate and regulate photosynthesis in response to these changes of light. Little is known of regulative processes for photosynthesis during nocturnal events. The nucleus-encoded plant lineage-specific protein PSB33 has been described as stabilizing the photosystem II complex, especially under light stress conditions, and plants lacking PSB33 have a dysfunctional state transition. To clarify the localization and function of this protein, we used phenomic, biochemical and proteomics approaches in the model plant Arabidopsis. We report that PSB33 is predominantly located in non-appressed thylakoid regions and dynamically associates with a thylakoid protein complex in a light-dependent manner. Moreover, plants lacking PSB33 show an accelerated D1 protein degradation in nocturnal periods, and show severely stunted growth when challenged with fluctuating light. We further show that the function of PSB33 precedes the STN7 kinase to regulate or balance the excitation energy of photosystems I and II in fluctuating light conditions.
Topics: Acclimatization; Arabidopsis; Arabidopsis Proteins; Light; Photosynthesis; Photosystem II Protein Complex
PubMed: 28922769
DOI: 10.1093/jxb/erx218 -
Photosynthesis Research May 2022The photoexcited triplet state of the "primary donors" in the two photosystems of oxygenic photosynthesis has been investigated by means of electron-nuclear double...
The photoexcited triplet state of the "primary donors" in the two photosystems of oxygenic photosynthesis has been investigated by means of electron-nuclear double resonance (ENDOR) at Q-band (34 GHz). The data obtained represent the first set of H hyperfine coupling tensors of the P700 triplet state in PSI and expand the existing data set for P680. We achieved an extensive assignment of the observed electron-nuclear hyperfine coupling constants (hfcs) corresponding to the methine α-protons and the methyl group β-protons of the chlorophyll (Chl) macrocycle. The data clearly confirm that in both photosystems the primary donor triplet is located on one specific monomeric Chl at cryogenic temperature. In comparison to previous transient ENDOR and pulse ENDOR experiments at standard X-band (9-10 GHz), the pulse Q-band ENDOR spectra demonstrate both improved signal-to-noise ratio and increased resolution. The observed ENDOR spectra for P700 and P680 differ in terms of the intensity loss of lines from specific methyl group protons, which is explained by hindered methyl group rotation produced by binding site effects. Contact analysis of the methyl groups in the PSI crystal structure in combination with the ENDOR analysis of P700 suggests that the triplet is located on the Chl a' (P) in PSI. The results also provide additional evidence for the localization of P680 on the accessory Chl in PSII.
Topics: Chlorophyll A; Electron Spin Resonance Spectroscopy; Photosynthesis; Photosystem I Protein Complex; Protons
PubMed: 35290567
DOI: 10.1007/s11120-022-00905-y -
Nature Communications Jan 2020Chlorophylls (Chl) play pivotal roles in energy capture, transfer and charge separation in photosynthesis. Among Chls functioning in oxygenic photosynthesis, Chl f is...
Chlorophylls (Chl) play pivotal roles in energy capture, transfer and charge separation in photosynthesis. Among Chls functioning in oxygenic photosynthesis, Chl f is the most red-shifted type first found in a cyanobacterium Halomicronema hongdechloris. The location and function of Chl f in photosystems are not clear. Here we analyzed the high-resolution structures of photosystem I (PSI) core from H. hongdechloris grown under white or far-red light by cryo-electron microscopy. The structure showed that, far-red PSI binds 83 Chl a and 7 Chl f, and Chl f are associated at the periphery of PSI but not in the electron transfer chain. The appearance of Chl f is well correlated with the expression of PSI genes induced under far-red light. These results indicate that Chl f functions to harvest the far-red light and enhance uphill energy transfer, and changes in the gene sequences are essential for the binding of Chl f.
Topics: Binding Sites; Chlorophyll; Chlorophyll A; Cryoelectron Microscopy; Cyanobacteria; Energy Transfer; Light; Models, Molecular; Photosystem I Protein Complex; Protein Conformation
PubMed: 31932639
DOI: 10.1038/s41467-019-13898-5 -
Philosophical Transactions of the Royal... Dec 2012The concept that the two photosystems of photosynthesis cooperate in series, immortalized in Hill and Bendall's Z scheme, was still a black box that defined neither the... (Review)
Review
The concept that the two photosystems of photosynthesis cooperate in series, immortalized in Hill and Bendall's Z scheme, was still a black box that defined neither the structural nor the molecular organization of the thylakoid membrane network into grana and stroma thylakoids. The differentiation of the continuous thylakoid membrane into stacked grana thylakoids interconnected by single stroma thylakoids is a morphological reflection of the non-random distribution of photosystem II/light-harvesting complex of photosystem II, photosystem I and ATP synthase, which became known as lateral heterogeneity.
Topics: Chloroplast Proteins; Chloroplast Proton-Translocating ATPases; Electron Transport; Light-Harvesting Protein Complexes; Phospholipids; Photosynthesis; Photosystem I Protein Complex; Photosystem II Protein Complex; Plants; Thylakoids
PubMed: 23148264
DOI: 10.1098/rstb.2012.0060 -
Nature Oct 2005Illumination changes elicit modifications of thylakoid proteins and reorganization of the photosynthetic machinery. This involves, in the short term, phosphorylation of...
Illumination changes elicit modifications of thylakoid proteins and reorganization of the photosynthetic machinery. This involves, in the short term, phosphorylation of photosystem II (PSII) and light-harvesting (LHCII) proteins. PSII phosphorylation is thought to be relevant for PSII turnover, whereas LHCII phosphorylation is associated with the relocation of LHCII and the redistribution of excitation energy (state transitions) between photosystems. In the long term, imbalances in energy distribution between photosystems are counteracted by adjusting photosystem stoichiometry. In the green alga Chlamydomonas and the plant Arabidopsis, state transitions require the orthologous protein kinases STT7 and STN7, respectively. Here we show that in Arabidopsis a second protein kinase, STN8, is required for the quantitative phosphorylation of PSII core proteins. However, PSII activity under high-intensity light is affected only slightly in stn8 mutants, and D1 turnover is indistinguishable from the wild type, implying that reversible protein phosphorylation is not essential for PSII repair. Acclimation to changes in light quality is defective in stn7 but not in stn8 mutants, indicating that short-term and long-term photosynthetic adaptations are coupled. Therefore the phosphorylation of LHCII, or of an unknown substrate of STN7, is also crucial for the control of photosynthetic gene expression.
Topics: Acclimatization; Arabidopsis; Arabidopsis Proteins; Light-Harvesting Protein Complexes; Mutation; Phosphorylation; Photosynthesis; Photosystem II Protein Complex; Protein Kinases; Protein Serine-Threonine Kinases
PubMed: 16237446
DOI: 10.1038/nature04016 -
Frontiers in Plant Science 2020Photosynthetic light reactions proceed in thylakoid membranes (TMs) due to the activity of pigment-protein complexes. These complexes are heterogeneously organized into...
Photosynthetic light reactions proceed in thylakoid membranes (TMs) due to the activity of pigment-protein complexes. These complexes are heterogeneously organized into granal/stromal thylakoids (in plants) or into recently identified cyanobacterial microdomains (MDs). MDs are characterized by specific ratios of photosystem I (PSI), photosystem II (PSII), and phycobilisomes (PBS) and they are visible as sub-micrometer sized areas with different fluorescence ratios. In this report, the process of long-term plasticity in cyanobacterial thylakoid MDs has been explored under variable growth light conditions using sp. expressing YFP tagged PSI. TM organization into MDs has been observed for all categorized shapes of cells independently of their stage in cell cycle. The heterogeneous PSI, PSII, and PBS thylakoid areas were also identified under two types of growth conditions: at continuous light (CL) and at light-dark (L-D) cycle. The acclimation from CL to L-D cycle changed spatial distribution of photosystems, in particular PSI became more evenly distributed in thylakoids under L-D cycle. The process of the spatial PSI (and partially also PSII) redistribution required 1 week and was accompanied by temporal appearance of PBS decoupling probably caused by the re-organization of photosystems. The overall acclimation we observed was defined as TM plasticity as it resembles higher plants grana/stroma reorganization at variable growth light conditions. In addition, we observed large cell to cell variability in the actual MDs organization. It leads us to suggest that the plasticity, and cell to cell variability in MDs could be a manifestation of phenotypic heterogeneity, a recently broadly discussed phenomenon for prokaryotes.
PubMed: 33304364
DOI: 10.3389/fpls.2020.586543