Photosynthesis Research最新文献

Leaf anatomical structure and stomata play pivotal roles in optimizing and regulating photosynthesis and transpiration. Exploring the plastic variability and allometric relationships of leaf anatomical and stomatal traits across an elevational gradient is of great significance for revealing plants' adaptation strategies to varying environments. This study focused on Quercus variabilis distributed at elevations of 800-1500 m on Mt. Li, a warm-temperate forest zone in China. We assessed the elevational variation in leaf anatomical and stomatal traits, and determined the allometric relationships among these traits using standardized major axis regression. With increasing elevation, the five anatomical traits overall exhibited a synergistic increasing trend, including leaf thickness (LT), palisade tissue thickness (PTT), spongy tissue thickness (STT), upper epidermis thickness (UET), and lower epidermis thickness (LET). Stomatal length (SL), width (SW), and area (SA) presented trend first increasing then decreasing, while stomatal density (SD) and stomatal area fraction (SAF) demonstrated the opposite pattern. SAF was primarily determined by SD rather than SA, despite a stable negative correlation between SD and SA. Additionally, five anatomical traits were significantly positively correlated with SD and negatively correlated with SA. Importantly, PTT, STT, LT, and SD, exhibiting higher plastic variability, had allometric relationships with other traits and demonstrated a faster rate of change. Our findings suggest that Q. variabilis leaves tend to be thicker, with smaller and denser stomata at higher elevations. The plastic adjustments of palisade tissue, spongy tissue, and stomatal density are crucial for Q. variabilis to adapt to heterogeneous habitats caused by elevational gradients.

Allophycocyanin (APC) protein subunits responsible for red-shifted phycobilisomes are induced under far-red light conditions. The ApcB2 (encoded by gene XM38_020890) and ApcD4 (encoded by gene XM38_020900) in H. hongdechloris are paralogous APC subunits encoded in the termed low-light photoacclimation (LoLiP) gene cluster, which are only detected from cells grown under far-red light (FRL) conditions. We examined the function of these allophycocyanin subunits using heterogeneous recombinant E. coli systems. The recombinant chromophorylated ApcB2 showed absorptionpeaking at 618 nm and fluorescence peaking at 642 nm and the chromophorylated ApcD4 demonstrated two absorption peaks of 618 and 676 nm and fluorescence peaks of 625 and 698 nm, respectively. Interestingly, the heterodimer of ApcB2/ApcD4 demonstrated even further FRL absorption of 728 nm and fluorescence emission peaking at 742 nm. Using ΔApcB2-W75T to replace ApcB2 for APC ab heterodimeric formation, the red-shifted absorption at 728 nm disappeared, suggesting that Trp75 of ApcB2 is essential for the heterodimer maintaining the red-shifted 728 nm spectroscopic feature. The extremely red-shifted spectroscopic properties of ApcD4/ApcB2 complexes reveal the strain-specific diversity of FRL-phycobilisomes and advance our understanding of remodelled light-harvesting complexes that capture FRL. In H. hongdechloris, besides the well-known Far-red light Photoacclimation (FaRLiP) gene cluster, the APC αβ heterodimer of ApcB2/ApcD4 from LoLiP gene cluster likely functions as the terminal emitter of red-shifted phycobilisomes for chlorophyll f-binding protein complexes. The recombinant, red-shifted APC αβ heterodimer offers a potential new class of fluorescence labels in the near-infrared spectral region.

Under high-light conditions, the dissipation of excess energy as heat in the light-harvesting antenna is essential for photosynthetic organisms to protect the photosynthetic machinery. In the case of cyanobacteria, however, the induction of the thermal dissipation in the antennae is insufficient to dissipate all excess energy, which is manifested as the increase in the steady-state level of chlorophyll fluorescence (Fs) under high light. To elucidate the underlying cause of the incomplete dissipation of excess light in the antenna, we investigated the impact of depletion and overexpression of orange carotenoid protein (OCP), which is essential to induce thermal dissipation in the antenna, on photosynthesis in Synechocystis sp. PCC 6803. The suppression of the OCP-dependent thermal dissipation resulted in elevated Fs with a constant yield of photosynthesis, suggesting that the light-induced increase in Fs might function as an acclimation mechanism to high light, which compensated for the lower OCP-dependent thermal dissipation. By contrast, over-induction of the OCP-dependent thermal dissipation decreased not only Fs but also the yield of photosynthesis under high light, due to the reduced energy transfer from the antenna to photosystem II. These results indicate that the complete removal of excess energy via the OCP-dependent mechanism has a drawback in photosynthetic efficiency under high-light conditions, and the strategy independent of OCP is employed to cope with excess light without lowering the yield of photosynthesis in cyanobacteria.

In oxygenic photosynthetic organisms, the light reactions are performed by protein complexes embedded in the lipid bilayer of thylakoid membranes (TMs). The organization of the bulk lipid molecules into bilayer structures provide optimal conditions for the build-up of the proton motive force (pmf) and its utilization for ATP synthesis. However, the lipid composition of TMs is dominated by the non-bilayer lipid species monogalactosyl diacylglycerol (MGDG), and functional plant TMs, besides the bilayer, contain large amounts of non-bilayer lipid phases. Bulk lipids have been shown to be associated with lumenal, stromal-side and marginal-region proteins and proposed to play roles in the self-assembly and photoprotection of the photosynthetic machinery. Furthermore, it has recently been pointed out that the generation and utilization of pmf for ATP synthesis according to the 'protet' or protonic charge transfer model Kell (Biochim Biophys Acta Bioenerg 1865(4):149504, 2024), requires high MGDG content Garab (Physiol Plant 177(2):e70230, 2025). In this study, to gain better insight into the structural and functional roles of MGDG, we employed all atom and coarse-grained molecular dynamics simulations to explore how temperature, hydration levels and varying MGDG concentrations affect the structural and dynamic properties of bilayer membranes constituted of plant thylakoid lipids. Our findings reveal that MGDG promotes increased membrane fluidity and dynamic fluctuations in membrane thickness. MGDG-rich stacked bilayers spontaneously formed inverted hexagonal phases; these transitions were enhanced at low hydration levels and at elevated but physiologically relevant temperatures. It can thus be inferred that MGDG plays important roles in heat and drought stress mechanisms.

The literature showed contradictory results regarding the acclimation of C3 and C4 photosynthesis to low light intensities. Atriplex halimus, A. nummularia (C4, NAD-ME), A. portulacoides and A. prostrata (C3) were exposed to three natural light intensities: full light (FL), medium light (ML) and low light (LL) under control or drought condition. Under control condition, in A. halimus and A. nummularia, photosynthetic rate (A) was proportionally linked to stomatal conductance (g_s). In A. halimus, A and gs peaked at 9:00 and 12:00 at FL only. However, A and gs peaked at 9:00 and 12:00 under FL and ML, respectively, in A. nummularia. The leakage of CO₂ could limit A in the C4 species under lower light intensities. A. halimus reduced g_s and A (a typical NAD-ME strategy) to cope with lower light intensities. However, A. nummularia optimized leaf anatomical features and PEPC/ Rubisco ratio to reduce CO₂ leakage, leading to improved g_s, A and biomass. In contrast, the increase in g_s reflected no increase in A, which could be attributed to the negative effect of low light on the electron transport system in the C3 species. Under drought condition, the performance of the C3 and C4 species was better at ML and LL than that at FL because of enhanced g_s and A. The present study concluded that the C4 species acclimated better to low light intensities than the C3 species. The acclimation of the C4 species was dependent on the species and the soil water content rather than the biochemical subtype.

Cytochrome b₅₅₉ (Cyt b₅₅₉) is an essential component of the photosystem II (PSII) reaction center core. It consists of two subunits, PsbE and PsbF, which together coordinate a redox-active heme. While extensive studies have revealed the importance of Cyt b₅₅₉, its structural and functional roles are not fully understood. Previous studies have implied that the lumenal region of Cyt b₅₅₉, interacting with the PSII extrinsic subunit PsbP in green plant PSII, may have important roles. However, few studies have investigated its lumenal region. Here, we have focused on a well-conserved lumenal region of PsbE, which was found to interact with the N-terminal region of PsbP in green-lineage PSII (from green algae and land plants). In red-lineage PSII (from red algae and algae possessing red algal-derived plastids), very similar interactions were observed between the same lumenal region of PsbE and the N-terminal region of PsbQ'. We generated Arabidopsis thaliana mutants harboring mutations in the well-conserved lumenal region of PsbE through targeted base editing of the plastid genome by ptpTALECD. The mutations led to strong growth defects and extremely low F_v/F_m. This study suggests the importance of the lumenal regions of Cyt b₅₅₉, and gives insight into possible structural and functional compensation between the N-terminal regions of PsbP in green-lineage PSII and PsbQ' in red-lineage PSII.

The effect of the cationic antiseptics octenidine and miramistin on electron transfer reactions in photosynthetic bacterial chromatophores of Cereibacter sphaeroides has been studied using direct electrometric and flash photolysis techniques. When the ubiquinone pool and cytochrome bc₁ complex were oxidized, the addition of octеnidine at a concentration of 100 µM completely inhibited the generation of transmembrane electric potential difference (Δψ) caused by protonation of the doubly reduced secondary quinone acceptor Q_B in the reaction center and, accordingly, vectorial charge transfer within the bc₁ complex in response to a second laser flash. The lack of an effect of octenidine and miramistin on the rapid rise of Δψ (τ < 0.1 µs) due to charge separation between the primary electron donor P₈₇₀ and the primary quinone acceptor Q_A was accompanied by an acceleration of Δψ decay kinetics over a period of ~ 10 ms in the presence of the former. The effect of miramistin was less pronounced. Overall, the data obtained by the two methods are qualitatively similar. The different effects of octanidine and miramistin are undoubtedly due to their structural features and may be related to their disordering influences on both the Q_B-binding site of the reaction center and the structure of the bilayer phospholipid membrane of chromatophores. These results are also important for understanding the molecular mechanisms of action of cationic antiseptics on both charge transfer reactions and thylakoid membrane integrity in oxygenic photosynthetic organisms.

Oxygenic photosynthetic organisms employ light-harvesting complexes (LHCs) to capture solar energy and regulate excess excitation. Tetraselmis species belong to Chlorodendrophyceae, one of the earliest-diverging lineages within core Chlorophyta. While these organisms exhibit distinctive pigment compositions, their LHC organization and function remain largely uncharacterized. Here, we examined the biochemical and spectral properties of LHC, PSI-LHCI, and PSII-LHCII complexes from Tetraselmis striata NIES-1019. Pigment analysis identified loroxanthin derivatives, loroxanthin decenoate and loroxanthin dodecenoate, in all three complexes. Notably, these carotenoids are absent in Chlamydomonas reinhardtii and Ostreococcus tauri, implying a lineage-specific adaptation. Fluorescence spectra of PSII-LHCII and PSI-LHCI from T. striata exhibited distinct characteristics compared with their counterparts in C. reinhardtii and land plants, indicating differences in pigment organization. In contrast, LHC fluorescence properties closely resembled those of green-lineage organisms, suggesting conservation of chlorophyll-binding arrangements. Phylogenetic analyses revealed that T. striata possesses LHCBM-based LHCII trimers, consistent with other core Chlorophyta, but its PSI antenna composition diverges from that of these algae. Among LHCIs in the PSI outer belt, only LHCA5a was identified, whereas LHCA4a and LHCA6a were absent, implying structural divergence from C. reinhardtii. These findings provide insights into the evolution of LHCs in Chlorophyta and the distinct pigment-protein interactions underlying Tetraselmis light-harvesting strategies.

PsbR is a nonpigmented 10 kDa protein in Photosystem II (PSII) in algae and plants. A recent structural study clarified its enigmatic structural location in a Photosystem II megacomplex that has baffled the community for more than four decades. Our current study interrogates whether absence of PsbR affects the overall dynamics of excitation energy migration within light harvesting complexes (LHC) and PSII super assemblies using highly-active PSII membrane particles, so-called BBY particles, isolated from a PsbR deletion mutant (ΔPsbR) of Arabidopsis thaliana. A femto-second (fs)-time-resolved transient absorption experimentation recorded at 77 K with selective excitation of Chl b which is exclusively present in LHCs enabled us to resolve the temporal differences in LHC→LHC and LHC→PSII excitation energy transfer steps. By applying specific target spectro-kinetic models to the transient absorption datasets, we demonstrated that the time constants of Chl a_LHC → Chl a_LHC excitation transfer significantly elongates in the ΔPsbR LHC-PSII particles, suggestive of the decreased aggregation level of photosynthetic proteins in the mutant. These findings highlight excitation energy transfer integrity in LHC-PSII assembly is not only determined by the pigmented light-harvesting complexes, but also synergistically by the nonpigmented PSII components. The disturbed integrity in dynamics of excitation energy transfer pathway within LHC-PSII supercomplex is discussed in the context of the altered LHC-PSII megacomplexes type I and II architectures which result from the absence of the PsbR protein in higher plant PSII.