Photosynthesis Research最新文献

This study examined the impacts of different LED spectra on the growth of in vitro cultures of Musa acuminata cv. red banana and their biochemical profile, including the antioxidant enzymes catalase and ascorbate peroxidase, photosynthetic pigment and accumulation of total carbohydrate content. The far-red LEDs significantly increase shoot elongation (10.04 cm). The greatest number of shoots (2.97) and the greatest multiplication rate (80%) were obtained under the treatment with blue + red LEDs. The formation of microshoots were also enhanced by blue and white LED exposure in a range of 2-2.57 shoots per explant. Root formation was also stimulated by dichromatic blue + red (6.00) LED using MS medium with 2 µM indole-3-butyric acid (IBA). The enzymes catalase and ascorbate peroxidase were significantly up-regulated by irradiation with far-red (0.11 ± 0.02 CAT, 0.18 ± 0.04 APX U/mg) and blue (0.08 ± 0.01CAT, 0.10 ± 0.01APX U/mg) LED light. Total chlorophyll (0.45 to 0.80 mg/g) was elevated significantly by blue, blue + red and mint-white LED. On the other hand, carotenoids (12.08-14.61 mg/g) were significantly boosted by blue + red, red and mint-white LED light. Meanwhile, porphyrin (294.10-350.57 mg/g) was highly synthesised after irradiation with mint-white light. Irradiation with LED light significantly increased the accumulation of carbohydrates with the highest carbohydrate content under blue + red LED light (102.22 ± 2.46 mg/g) and blue light (91.69 ± 2.10 mg/g). In conclusion, these results confirm that the vegetative properties and biochemical profile of red banana in vitro are eustress response to LED spectra.

In recent years, there has been a steady interest in unraveling the intricate mechanistic details of water oxidation mechanism in photosynthesis. Despite the substantial progress made over several decades, a comprehensive understanding of the precise kinetics underlying O-O bond formation and subsequent evolution remains elusive. However, it is well-established that the oxygen evolving complex (OEC), specifically the CaMn₄O₅ cluster, plays a crucial role in O-O bond formation, undergoing a series of four oxidative events as it progresses through the S-states of the Kok cycle. To gain further insights into the OEC, researchers have explored the substitution of the Ca²⁺ cofactor with strontium (Sr), the sole atomic replacement capable of retaining oxygen-evolving activity. Empirical investigations utilizing spectroscopic techniques such as XAS, XRD, EPR, FTIR, and XANES have been conducted to probe the structural consequences of Ca²⁺→Sr²⁺ substitution. In parallel, the development of DFT and QM/MM computational models has explored different oxidation and protonation states, as well as variations in ligand coordination at the catalytic center involving amino acid residues. In this review, we critically evaluate and integrate these computational and spectroscopic approaches, focusing on the structural and mechanistic implications of Ca²⁺→Sr²⁺ substitution in PS II. We contribute DFT modelling and simulate EXAFS Fourier transforms of Sr-substituted OEC, analyzing promising structures of the S₃ state. Through the combination of computational modeling and spectroscopic investigations, valuable insights have been gained, developing a deeper understanding of the photosynthetic process.

Light harvesting by antenna systems is the initial step in a series of electron-transfer reactions in all photosynthetic organisms, leading to energy trapping by reaction center proteins. Cyanobacteria are an ecologically diverse group and are the simplest organisms capable of oxygenic photosynthesis. The primary light-harvesting antenna in cyanobacteria is the large membrane extrinsic pigment-protein complex called the phycobilisome. In addition, cyanobacteria have also evolved specialized membrane-intrinsic chlorophyll-binding antenna proteins that transfer excitation energy to the reaction centers of photosystems I and II (PSI and PSII) and dissipate excess energy through nonphotochemical quenching. Primary among these are the CP43 and CP47 proteins of PSII, but in addition, some cyanobacteria also use IsiA and the prochlorophyte chlorophyll a/b binding (Pcb) family of proteins. Together, these proteins comprise the CP43 family of proteins owing to their sequence similarity with CP43. In this article, we have revisited the evolution of these chlorophyll-binding antenna proteins by examining their protein sequences in parallel with their spectral properties. Our phylogenetic and spectroscopic analyses support the idea of a common ancestor for CP43, IsiA, and Pcb proteins, and suggest that PcbC might be a distant ancestor of IsiA. The similar spectral properties of CP47 and IsiA suggest a closer evolutionary relationship between these proteins compared to CP43.

Cyanobacteria are prokaryotic photosynthetic microorganisms that can generate, in addition to biomass, useful chemicals and proteins/enzymes, essentially from sunlight, carbon dioxide, and water. Selected aspects of cyanobacterial production (isoprenoids and high-value proteins) and scale-up methods suitable for product generation and downstream processing are addressed in this review. The work focuses on the challenge and promise of specialty chemicals and proteins production, with isoprenoid products and biopharma proteins as study cases, and the challenges encountered in the expression of recombinant proteins/enzymes, which underline the essence of synthetic biology with these microorganisms. Progress and the current state-of-the-art in these targeted topics are emphasized.

Photoprotection mechanisms are ubiquitous among photosynthetic organisms. The photoprotection capacity of the green alga Chlamydomonas reinhardtii is correlated with protein levels of stress-related light-harvesting complex (LHCSR) proteins, which are strongly induced by high light (HL). However, the dynamic response of overall thylakoid structure during acclimation to growth in HL has not been fully understood. Here, we combined live-cell super-resolution microscopy and analytical membrane subfractionation to investigate macroscale structural changes of thylakoid membranes during HL acclimation in Chlamydomonas. Subdiffraction-resolution live-cell imaging revealed that the overall thylakoid structures became thinned and shrunken during HL acclimation. The stromal space around the pyrenoid also became enlarged. Analytical density-dependent membrane fractionation indicated that the structural changes were partly a consequence of membrane unstacking. The analysis of both an LHCSR loss-of-function mutant, npq4 lhcsr1, and a regulatory mutant that over-expresses LHCSR, spa1-1, showed that structural changes occurred independently of LHCSR protein levels, demonstrating that LHCSR was neither necessary nor sufficient to induce the thylakoid structural changes associated with HL acclimation. In contrast, stt7-9, a mutant lacking a kinase of major light-harvesting antenna proteins, had a slower thylakoid structural response to HL relative to all other lines tested but still showed membrane unstacking. These results indicate that neither LHCSR- nor antenna-phosphorylation-dependent HL acclimation are required for the observed macroscale structural changes of thylakoid membranes in HL conditions.

The green algal genus Picochlorum is of biotechnological interest because of its robust response to multiple environmental stresses. We compared the metabolic performance of P. SE3 and P. oklahomense to diverse microbial phototrophs and observed exceptional performance of photosystem II (PSII) in light energy conversion in both Picochlorum species. The quantum yield (QY) for O₂ evolution is the highest of any phototroph yet observed, 32% (20%) by P. SE3 (P. okl) when normalized to total PSII subunit PsbA (D1) protein, and 80% (75%) normalized per active PSII, respectively. Three factors contribute: (1) an efficient water oxidizing complex (WOC) with the fewest photochemical misses of any organism; (2) faster reoxidation of reduced (PQH₂)_B in P. SE3 than in P. okl. (period-2 Fourier amplitude); and (3) rapid reoxidation of the plastoquinol pool by downstream electron carriers (Cyt b₆f/PETC) that regenerates PQ faster in P. SE3. This performance gain is achieved without significant residue changes around the Q_B site and thus points to a pull mechanism involving faster PQH₂ reoxidation by Cyt b₆f/PETC that offsets charge recombination. This high flux in P. SE3 may be explained by genomically encoded plastoquinol terminal oxidases 1 and 2, whereas P. oklahomense has neither. Our results suggest two distinct types of PSII centers exist, one specializing in linear electron flow and the other in PSII-cyclic electron flow. Several amino acids within D1 differ from those in the low-light-descended D1 sequences conserved in Viridiplantae, and more closely match those in cyanobacterial high-light D1 isoforms, including changes near tyrosine Y_z and a water/proton channel near the WOC. These residue changes may contribute to the exceptional performance of Picochlorum at high-light intensities by increasing the water oxidation efficiency and the electron/proton flux through the PSII acceptors (Q_AQ_B).

This paper reviews our historical developments of broken-symmetry (BS) and beyond BS methods that are applicable for theoretical investigations of metalloenzymes such as OEC in PSII. The BS hybrid DFT (HDFT) calculations starting from high-resolution (HR) XRD structure in the most stable S₁ state have been performed to elucidate structure and bonding of whole possible intermediates of the CaMn₄O_x cluster (1) in the S_i (i = 0 ~ 4) states of the Kok cycle. The large-scale HDFT/MM computations starting from HR XRD have been performed to elucidate biomolecular system structures which are crucial for examination of possible water inlet and proton release pathways for water oxidation in OEC of PSII. DLPNO CCSD(T₀) computations have been performed for elucidation of scope and reliability of relative energies among the intermediates by HDFT. These computations combined with EXAFS, XRD, XFEL, and EPR experimental results have elucidated the structure, bonding, and reactivity of the key intermediates, which are indispensable for understanding and explanation of the mechanism of water oxidation in OEC of PSII. Interplay between theory and experiments have elucidated important roles of four degrees of freedom, spin, charge, orbital, and nuclear motion for understanding and explanation of the chemical reactivity of 1 embedded in protein matrix, indicating the participations of the Ca(H₂O)_n ion and tyrosine(Yz)-O radical as a one-electron acceptor for the O-O bond formation. The Ca-assisted Y_z-coupled O-O bond formation mechanisms for water oxidation are consistent with recent XES and very recent time-resolved SFX XFEL and FTIR results.

Far-red absorbing allophycocyanins (APC), identified in cyanobacteria capable of FRL photoacclimation (FaRLiP) and low-light photoacclimation (LoLiP), absorb far-red light, functioning in energy transfer as light-harvesting proteins. We report an optimized method to obtain high purity far-red absorbing allophycocyanin B, AP-B2, of Chroococcidiopsis thermalis sp. PCC7203 by synthesis in Escherichia coli and an improved purification protocol. The crystal structure of the trimer, (PCB-ApcD5/PCB-ApcB2)₃, has been resolved to 2.8 Å. The main difference to conventional APCs absorbing in the 650-670 nm range is a largely flat chromophore with the co-planarity extending, in particular, from rings BCD to ring A. This effectively extends the conjugation system of PCB and contributes to the super-red-shifted absorption of the α-subunit (λ_max = 697 nm). On complexation with the β-subunit, it is even further red-shifted (λ_{max, absorption} = 707 nm, λ_{max, emission} = 721 nm). The relevance of ring A for this shift is supported by mutagenesis data. A variant of the α-subunit, I123M, has been generated that shows an intense FR-band already in the absence of the β-subunit, a possible model is discussed. Two additional mechanisms are known to red-shift the chromophore spectrum: lactam-lactim tautomerism and deprotonation of the chromophore that both mechanisms appear inconsistent with our data, leaving this question unresolved.

The influence of poly(ethylene glycol) (PEG) polymers H-(O-CH₂-CH₂)_p-OH with different average molecular sizes $p$ on the micelle formation of n-alkyl-β-D-maltoside detergents with the number of carbon atoms in the alkyl chain ranging from $10$ to $12$ is investigated with the aim to learn more about the detergent behavior under conditions suitable for the crystallization of the photosynthetic pigment-protein complex photosystem II. PEG is shown to increase the critical micelle concentration (CMC) of all three detergents in the crystallization buffer in a way that the free energy of micelle formation increases linearly with the concentration of oxyethylene units (O-CH₂-CH₂) irrespective of the actual molecular weight of the polymer. The CMC shift is modeled by assuming for simplicity that it is dominated by the interaction between PEG and detergent monomers and is interpreted in terms of an increase of the transfer free energy of a methylene group of the alkyl chain by 0.2 kJ mol^-1 per 1 mol L^-1 increase of the concentration of oxyethylene units at 298 K. Implications of this effect for the solubilization and crystallization of protein-detergent complexes as well as detergent extraction from crystals are discussed.

Chlorophylls and bacteriochlorophylls are the primary pigments used by photosynthetic organisms for light harvesting, energy transfer, and electron transfer. Many molecular structures of (bacterio)chlorophyll-containing protein complexes are available, some of which contain mixtures of different (bacterio)chlorophyll types. Differentiating these, which sometimes are structurally similar, is challenging but is required for leveraging structural data to gain functional insight. The reaction center complex from Chloroacidobacterium thermophilum has a hybrid (bacterio)chlorophyll antenna system containing both chlorophyll a and bacteriochlorophyll a molecules. The recent availability of its cryogenic electron microscopy (cryo-EM) structure provides an opportunity for a quantitative analysis of their identities and chemical environments. Here, we describe a theoretical basis for differentiating chlorophyll a and bacteriochlorophyll a in a cryo-EM map, and apply the approach to the experimental cryo-EM maps of the (bacterio)chlorophyll sites of the chloroacidobacterial reaction center. The comparison reveals that at ~ 2.2-Å resolution, chlorophyll a and bacteriochlorophyll a are easily distinguishable, but the orientation of the bacteriochlorophyll a acetyl moiety is not; however, the latter can confidently be assigned by identifying a hydrogen bond donor from the protein environment. This study reveals the opportunities and challenges in assigning (bacterio)chlorophyll types in structural biology, the accuracy of which is vital for downstream investigations.