Photosystem Research Articles

In situ structural determination of cyanobacterial phycobilisome–PSII supercomplex by STAgSPA strategy

Photosynthesis converting solar energy to chemical energy is one of the most important chemical reactions on earth. In cyanobacteria, light energy is captured by antenna system phycobilisomes (PBSs) and transferred to photosynthetic reaction centers of photosystem II (PSII) and photosystem I (PSI). While most of the protein complexes involved in photosynthesis have been characterized by in vitro structural analyses, how these protein complexes function together in vivo is not well understood. Here we implemented STAgSPA, an in situ structural analysis strategy, to solve the native structure of PBS–PSII supercomplex from the cyanobacteria Arthrospira sp. FACHB439 at resolution of ~3.5 Å. The structure reveals coupling details among adjacent PBSs and PSII dimers, and the collaborative energy transfer mechanism mediated by multiple super-PBS in cyanobacteria. Our results provide insights into the diversity of photosynthesis-related systems between prokaryotic cyanobacteria and eukaryotic red algae but are also a methodological demonstration for high-resolution structural analysis in cellular or tissue samples.

Intermediate Formation via Proton Release during the Photoassembly of the Water-Oxidizing Mn4CaO5 Cluster in Photosystem II.

The early stages of the photoassembly of the water-oxidizing Mn4CaO5 cluster in spinach photosystem II (PSII) were monitored using rapid-scan time-resolved Fourier transform infrared (FTIR) spectroscopy. Carboxylate stretching and the amide I bands, which appeared upon the flash-induced oxidation of a Mn2+ ion, changed their features during the subsequent dark rearrangement process, indicating the relocation of the Mn3+ ion concomitant with protein conformational changes. Monitoring the isotope-edited FTIR signals of a Mes buffer estimated that nearly two protons are released upon the Mn2+ oxidation. Quantum chemical calculations for models of the Mn binding site suggested that the proton of a water ligand is transferred to D1-H332 through a hydrogen bond upon the Mn3+ formation and then released to the bulk as the Mn3+ shifts to bind to this histidine. Another Mn2+ ion may be inserted to form a binuclear Mn3+Mn2+ complex, whose structure was calculated to be stabilized by a μ-hydroxo bridge hydrogen-bonded with deprotonated D1-H337. Nearly one additional proton can thus be released from this histidine, assuming that it is mostly protonated before illumination. Alternatively, a proton could be released by further insertion of Ca2+, forming a Mn3+Mn2+Ca2+ complex with another hydroxo ligand connecting Ca2+ to the Mn3+Mn2+ complex.

Bidirectional Energy Flow in the Photosystem II Supercomplex.

The water-splitting capability of Photosystem II (PSII) of plants and green algae requires the system to balance efficient light harvesting along with effective photoprotection against excitation in excess of the photosynthetic capacity, particularly under the naturally fluctuating sunlight intensity. The comparatively flat energy landscape of the multicomponent structure, inferred from the spectra of the individual pigment-protein complexes and the rather narrow and featureless absorption spectrum, is well known. However, how the combination of the required functions emerges from the interactions among the multiple components of the PSII supercomplex (PSII-SC) cannot be inferred from the individual pigment-protein complexes. In this work, we investigate the energy transfer dynamics of the C2S2-type PSII-SC with a combined spectroscopic and modeling approach. Specifically, two-dimensional electronic-vibrational (2DEV) spectroscopy provides enhanced spectral resolution and the ability to map energy evolution in real space, while the quantum dynamical simulation allows complete kinetic modeling of the 210 chromophores. We demonstrate that additional pathways emerge within the supercomplex. In particular, we show that excitation energy can leave the vicinity of the charge separation components, the reaction center (RC), faster than it can transfer to it. This enables activatable quenching centers in the periphery of the PSII-SC to be effective in removing excessive energy in cases of overexcitation. Overall, we provide a quantitative description of how the seemingly contradictory functions of PSII-SC arise from the combination of its individual components. This provides a fundamental understanding that will allow further improvement of artificial solar energy devices and bioengineering processes for increasing crop yield.

Optimized nitrogen application ameliorates the photosynthetic performance and yield potential in peanuts as revealed by OJIP chlorophyll fluorescence kinetics

BackgroundNitrogen (N) is a crucial element for increasing photosynthesis and crop yields. The study aims to evaluate the photosynthetic regulation and yield formation mechanisms of different nodulating peanut varieties with N fertilizer application.MethodThe present work explored the effect of N fertilizer application rates (N0, N45, N105, and N165) on the photosynthetic characteristics, chlorophyll fluorescence characteristics, dry matter, N accumulation, and yield of four peanut varieties.ResultsThe results showed that N application increased the photosynthetic capacity, dry matter, N accumulation, and yield of peanuts. The measurement of chlorophyll a fluorescence revealed that the K-phase, J-phase, and I-phase from the OJIP curve decreased under N105 treatment compared with N0, and WOI, ET0/CSM, RE0/CSM, ET0/RC, RE0/RC, φPo, φEo, φRo, and Ψ0 increased, whereas VJ, VI, WK, ABS/RC, TR0/RC, DI0/RC, and φDo decreased. Meanwhile, the photosystem activity and electron transfer efficiency of nodulating peanut varieties decreased with an increase in N (N165). However, the photosynthetic capacity and yield of the non-nodulating peanut variety, which highly depended on N fertilizer, increased with an increase in N.ConclusionOptimized N application (N105) increased the activity of the photosystem II (PSII) reaction center, improved the electron and energy transfer performance in the photosynthetic electron transport chain, and reduced the energy dissipation of leaves in nodulating peanut varieties, which is conducive to improving the yield. Nevertheless, high N (N165) had a positive effect on the photosystem and yield of non-nodulating peanut. The results provide highly valuable guidance for optimizing peanut N management and cultivation measures.

Photosystem I: A Paradigm for Understanding Biological Environmental Adaptation Mechanisms in Cyanobacteria and Algae.

The process of oxygenic photosynthesis is primarily driven by two multiprotein complexes known as photosystem II (PSII) and photosystem I (PSI). PSII facilitates the light-induced reactions of water-splitting and plastoquinone reduction, while PSI functions as the light-driven plastocyanin-ferredoxin oxidoreductase. In contrast to the highly conserved structure of PSII among all oxygen-evolving photosynthetic organisms, the structures of PSI exhibit remarkable variations, especially for photosynthetic organisms that grow in special environments. In this review, we make a concise overview of the recent investigations of PSI from photosynthetic microorganisms including prokaryotic cyanobacteria and eukaryotic algae from the perspective of structural biology. All known PSI complexes contain a highly conserved heterodimeric core; however, their pigment compositions and peripheral light-harvesting proteins are substantially flexible. This structural plasticity of PSI reveals the dynamic adaptation to environmental changes for photosynthetic organisms.

The mechanisms of photoinhibition and repair in plants under high light conditions and interplay with abiotic stressors

This review comprehensively examines the phenomenon of photoinhibition in plants, focusing mainly on the intricate relationship between photodamage and photosystem II (PSII) repair and the role of PSII extrinsic proteins and protein phosphorylation in these processes. In natural environments, photoinhibition occurs together with a suite of concurrent stress factors, including extreme temperatures, drought and salinization. Photoinhibition, primarily caused by high irradiance, results in a critical imbalance between the rate of PSII photodamage and its repair. Central to this process is the generation of reactive oxygen species (ROS), which not only impair the photosynthetic apparatus first PSII but also play a signalling role in chloroplasts and other cellulular structures. ROS generated under stress conditions inhibit the repair of photodamaged PSII by suppressing D1 protein synthesis and affecting PSII protein phosphorylation. Furthermore, this review considers how environmental stressors exacerbate PSII damage by interfering with PSII repair primarily by reducing de novo protein synthesis. In addition to causing direct damage, these stressors also contribute to ROS production by restricting CO2 fixation, which also reduces the intensity of protein synthesis. This knowledge has significant implications for agricultural practices and crop improvement under stressful conditions.

A practical approach for extracting the photosystem II (PSII) contribution to near-infrared solar-induced chlorophyll fluorescence

Recent studies have indicated a good potential for using solar-induced chlorophyll fluorescence (SIF) to estimate photosynthetic CO2 assimilation. SIF can be emitted by both Photosystem I (PSI) and Photosystem II (PSII), but it is the SIF signals from PSII which are related to photosynthetic carbon fixation. However, since top-of-canopy SIF observations (SIFTOC) always contain contributions from both photosystems, to mechanistically estimate gross primary productivity (GPP) from SIF, it is essential to extract PSII SIF from SIFTOC. Based on the differences in the relative contribution of PSII across different wavelengths, we propose a practical approach for extracting PSII contribution to SIFTOC at the near-infrared (NIR) band (fPSII_760) using measurements of SIFTOC in the red and NIR spectral regions. A leaf-scale concurrent instrument was developed to assess the response of fPSII_760 under varying environments. For winter-wheat leaves, as light intensity increased from 0 to 400 μmol m−2 s−1, fPSII_760 rose from 0.6 to 0.8; with further increase in light intensity to 1800 μmol m−2 s−1, fPSII_760 consistently decreased to 0.65. There was a slight decreasing trend in fPSII_760 with rising temperatures, with values dropping from 0.65 at 15 °C to 0.61 at 40 °C. We found that variations in fPSII_760 are due to changes in the fluorescence yield of PSII, with the two having a positively proportional relationship. We also estimated canopy-scale fPSII_760 for a winter-wheat study site: fPSII_760 varied from 0.61 to 0.83, with a mean value of 0.78 during the peak growing season. A comparison with eddy covariance-derived GPP reveals that GPP estimated with dynamic fPSII_760 was more accurate than that calculated using fixed fPSII_760, with R2 increasing from 0.6 to 0.84. This study contributes to a deeper understanding of the link between SIF and photosynthetic CO2 assimilation, paving the way for more effective use of SIF to estimate GPP.

Structural basis for the distinct core-antenna assembly of cryptophyte photosystem II

Photosystem II (PSII) catalyzes the light-driven charge separation and water oxidation reactions of photosynthesis. Eukaryotic PSII core is usually associated with membrane-embedded light-harvesting antennae, which greatly increase the absorbance cross-section of the core. The peripheral antennae in different phototrophs vary considerably in protein composition and arrangement. Photosynthetic cryptophytes possess chlorophyll a/c binding proteins (CACs) that serve as their antennae. How these CACs assemble with the PSII core remains unclear. Here, we report the 2.57-Å resolution structure of cryptophyte PSII-CAC purified from cells at nitrogen-limited stationary growth phase. We show that each monomer of the PSII homodimer contains a core complex, six chlorophyll a/c binding proteins (CACs) and a previously unseen chlorophyll-binding protein (termed CAL-II). Six CACs are arranged as a double-layered arc-shaped non-parallel belt, and two such belts attach to the dimeric core from opposite sides. The CAL-II simultaneously interacts with a number of core subunits and five CACs. The distinct organization of CACs and the presence of CAL-II may play a critical role in stabilizing the dimeric PSII-CAC complex under stress conditions. Our study provides mechanistic insights into the assembly and function of the PSII-CAC complex as well as the possible adaptation of cryptophytes in response to environmental stresses.

A Strategy to Enhance Photo-Algal Hydrogen Production Using External H+ Ions in a Dual Photobioreactor

The use of microalgae for direct biohydrogen energy generation exhibits significant promise as an alternative to traditional bio-energy production due to zero-emission of CO2. It is known that during photolysis, algae are capable of producing hydrogen (H2) gas instead of oxygen (O2) under enriched acetate conditions by algal fermentative metabolisms [1]. The utilization of acetate as a practical oxygen regulator in photosystem II (PSII), but the algal hydrogen production was relatively low due to the insufficient H+ ions available in the photobioreactor (PBR) [2]. Therefore, given that hydrogen ions from acetate contribute to H2 production, it is still unclear whether supplying additional external H+ ions can enhance H2 production.Here, we demonstrate a feasibility study on improving algal H2 production using a dual PBR system. This system enables the continuous transfer of H+ ions generated from photolysis to an algal H2 PBR through a proton exchange membrane (PEM), thereby enhancing photo-algal hydrogen production. The maximum H2 production of 108 µmol L-1 was obtained for Chlamydomonas reinhardtii in a single PBR for 15 days at a light intensity of 100 µmol m-2 s-1 [3]. However, by leveraging the external H+ ions supply, the dual PBR system increased photo-algal hydrogen production from 108 up to 760 µmol L-1 for the same period, which is 7 times greater compared to single chamber operation. This indicates that supplying external H+ ions in the operation of the dual PBR is one of the important parameters for improving biohydrogen production. Our findings contribute to the ongoing development of high-performance algal H2 production, offering valuable insights into optimizing the amount of H+ ions for enhanced hydrogen production.[1] Clemens KL, Force DA, Britt RD. Acetate binding at the photosystem II oxygen evolving complex: an S2-state multiline signal ESEEM study. J Am Chem Soc. 2002;124(36):10921-33.[2] Hwang J-H, Church J, Lim J, Lee WH. Photosynthetic biohydrogen production in a wastewater environment and its potential as renewable energy. Energy. 2018;149:222-9.[3] Hwang J-H, Lee WH. Continuous photosynthetic biohydrogen production from acetate-rich wastewater: Influence of light intensity. Int J Hydrogen Energy. 2021;46(42):21812-21.

Screening New Mungbean Varieties for Terminal Drought Tolerance

Rainfed mungbean crops in Queensland Australia frequently experience terminal drought (drought stress in the final stages of reproductive development), highlighting the importance of drought-tolerant varieties for sustainable mungbean production. Given there is limited information on the relative drought tolerance of current mungbean varieties in Australia, the study of genetic variations and mechanisms of drought tolerance in summer mungbean can provide a basis for developing drought-tolerant mungbean varieties. This study evaluated the physiological, biochemical, and phenological traits underpinning yield attributes associated with drought tolerance in selected mungbean varieties. Four new mungbean varieties (AVTMB#1 to 4) and the Australian commercial line (Jade-AU) were grown in tall (75 cm) polyvinyl chloride (PVC) lysimeters where drought stress was imposed at the early flowering stage (R1) and maintained until maturity. Drought stress significantly impacted all the varieties. Averaged across all the varieties, drought stress was associated with a reduction in stomatal conductance (gs) and photosynthetic rate (Asat) by 78% and 86%, respectively, compared to well-watered plants. Internal carbon dioxide concentration (Ci), the effective quantum yield of photosystem II (ΦPSII) and maximum light-use efficiency of light-acclimated photosystem II (PSII) centres (Fv’/Fm’) were also decreased, while excitation pressure (1-qP) increased with drought treatment. A positive correlation (r = 0.60) existed between seed yield and ΦPSII assessed at R1, while a weak correlation with Fv’/Fm’ (r = 0.24) was observed. Excitation pressure (1-qP) at the R1 stage was negatively correlated with seed yield (r = −0.66). Therefore, leaf fluorescence measures, viz., 1-qP and ΦPSII, were recommended for use in screening mungbean varieties for drought tolerance. The varieties, AVTMB#1 and AVTMB#4, respectively achieved 39 and 38% greater seed yields relative to the commercial variety, Jade-AU, under terminal drought conditions.

Physcomitrium patens flavodiiron proteins form heterotetrametric complexes

Flavodiiron proteins (FLVs) catalyze the reduction of oxygen to water by using electrons from Photosystem I (PSI). In several photosynthetic organisms such as cyanobacteria, green algae, mosses and gymnosperms, FLV-dependent electron flow protects PSI from over-reduction and consequent damage especially under fluctuating light conditions. In this work we investigated biochemical and structural properties of FLVA and FLVB from the model moss Physcomitrium patens. The two proteins, expressed and purified from Escherichia coli, bind both iron and flavin cofactors and show NAD(P)H oxidase activity as well as oxygen reductase capacities. Moreover, the co-expression of both FLVA and FLVB, coupled to a tandem affinity purification procedure with two different affinity tags, enabled the isolation of the stable and catalytically active FLVA/B hetero tetrameric protein complex with cooperative nature. The multimeric organization was shown to be stabilized by inter-subunit disulfide bonds. This investigation provides valuable new information on the biochemical properties of FLVs, with new insights into their in vivo activity.

Environment-dependent chlorophyll-chlorophyll charge transfer states in Lhca4 pigment-protein complex.

Photosystem I (PSI) light-harvesting antenna complexes LHCI contain spectral forms that absorb and emit photons of lower energy than that of its primary electron donor, P700. The most red-shifted fluorescence is associated with the Lhca4 complex. It has been suggested that this red emission is related to the inter-chlorophyll charge transfer (CT) states. In this work we present a systematic quantum-chemical study of the CT states in Lhca4, accounting for the influence of the protein environment by estimating the electrostatic interactions. We show that significant energy shifts result from these interactions and propose that the emission of the Lhca4 complex is related not only to the previously proposed a603+-a608- state, but also to the a602+-a603- state. We also investigate how different protonation patterns of protein amino acids affect the energetics of the CT states.

NDT-C11 as a Viable Novel Detergent for Single Particle Cryo-EM.

Single particle cryo electron microscopy (cryo-EM) is now the major method for the determination of integral membrane protein structure. For the success of a given project the type of membrane mimetic used for extraction from the native cell membrane, purification to homogeneity and finally cryo-grid vitrification is crucial. Although small molecule amphiphiles - detergents - are the most widely used membrane mimetic, specific tailoring of detergent structure for single particle cryo-EM is rare and the demand for effective detergents not satisfied. Here, we compare the popular detergent lauryl maltose-neopentyl glycol (LMNG) with the novel detergent neopentyl glycol-derived triglucoside-C11 (NDT-C11) in its behavior as free detergent and when bound to two types of multisubunit membrane protein complexes - cyanobacterial photosystem I (PSI) and mammalian F-ATP synthase. We conclude that NDT-C11 has high potential to become a very useful detergent for single particle cryo-EM of integral membrane proteins.

Hormetic Response of Photosystem II Function Induced by Nontoxic Calcium Hydroxide Nanoparticles.

In recent years, inorganic nanoparticles, including calcium hydroxide nanoparticles [Ca Ca(OH)2 NPs], have attracted significant interest for their ability to impact plant photosynthesis and boost agricultural productivity. In this study, the effects of 15 and 30 mg L-1 oleylamine-coated calcium hydroxide nanoparticles [Ca(OH)2@OAm NPs] on photosystem II (PSII) photochemistry were investigated on tomato plants at their growth irradiance (GI) (580 μmol photons m-2 s-1) and at high irradiance (HI) (1000 μmol photons m-2 s-1). Ca(OH)2@OAm NPs synthesized via a microwave-assisted method revealed a crystallite size of 25 nm with 34% w/w of oleylamine coater, a hydrodynamic size of 145 nm, and a ζ-potential of 4 mV. Compared with the control plants (sprayed with distilled water), PSII efficiency in tomato plants sprayed with Ca(OH)2@OAm NPs declined as soon as 90 min after the spray, accompanied by a higher excess excitation energy at PSII. Nevertheless, after 72 h, the effective quantum yield of PSII electron transport (ΦPSII) in tomato plants sprayed with Ca(OH)2@OAm NPs enhanced due to both an increase in the fraction of open PSII reaction centers (qp) and to the enhancement in the excitation capture efficiency (Fv'/Fm') of these centers. However, the decrease at the same time in non-photochemical quenching (NPQ) resulted in an increased generation of reactive oxygen species (ROS). It can be concluded that Ca(OH)2@OAm NPs, by effectively regulating the non-photochemical quenching (NPQ) mechanism, enhanced the electron transport rate (ETR) and decreased the excess excitation energy in tomato leaves. The delay in the enhancement of PSII photochemistry by the calcium hydroxide NPs was less at the GI than at the HI. The enhancement of PSII function by calcium hydroxide NPs is suggested to be triggered by the NPQ mechanism that intensifies ROS generation, which is considered to be beneficial. Calcium hydroxide nanoparticles, in less than 72 h, activated a ROS regulatory network of light energy partitioning signaling that enhanced PSII function. Therefore, synthesized Ca(OH)2@OAm NPs could potentially be used as photosynthetic biostimulants to enhance crop yields, pending further testing on other plant species.

Application of Trichoderma asperellum spore powder helps maintain ionic balance and photosystem II activity in wolfberry in saline soil

The mechanisms how Trichoderma enhances plant salt tolerance remain to be further dissected. Trichoderma asperellum spore powder (TS) was supplemented to saline soil around the stem base of potted wolfberry (Lycium chinense), and the role of Trichoderma asperellum in ameliorating salt tolerance of wolfberry was investigated with emphasis on ionic balance and photosystems II (PSII) activity. Plant dry weight was significantly increased by TS supplement, suggesting that Trichoderma asperellum promoted wolfberry growth in saline soil. As TS supplement elevated leaf and root K+/Na+ by increasing K+ content and decreasing Na+ content, Trichoderma asperellum improved ionic balance in wolfberry under saline soil stress, and the mechanism depended on that Trichoderma asperellum raised root Na+ exclusion and blocked root K+ loss. Consequentially, oxidative stress was ameliorated by Trichoderma asperellum according to lower leaf lipid peroxidation and H2O2 content in plants with TS supplement. Moreover, PSII was protected against oxidative injury and could maintain higher photochemical efficacy with TS supplement. K and J steps in prompt chlorophyll fluorescence transients were lowered by TS supplement, suggesting that Trichoderma asperellum alleviated salt-induced inhibition on electron transport at both PSII donor and acceptor sides, and consistently, more PSII centers became reactive. In addition, higher delayed chlorophyll fluorescence transients under TS supplement corroborated that Trichoderma asperellum enhanced whole PSII performance. Overall, Trichoderma asperellum helped maintain ionic balance by preventing K+ loss and elevating Na+ exclusion in roots and protect PSII by alleviating oxidative stress in wolfberry cultivated in saline soil.

Light-Driven H2 Production in Chlamydomonas reinhardtii: Lessons from Engineering of Photosynthesis.

In the green alga Chlamydomonas reinhardtii, hydrogen production is catalyzed via the [FeFe]-hydrogenases HydA1 and HydA2. The electrons required for the catalysis are transferred from ferredoxin (FDX) towards the hydrogenases. In the light, ferredoxin receives its electrons from photosystem I (PSI) so that H2 production becomes a fully light-driven process. HydA1 and HydA2 are highly O2 sensitive; consequently, the formation of H2 occurs mainly under anoxic conditions. Yet, photo-H2 production is tightly coupled to the efficiency of photosynthetic electron transport and linked to the photosynthetic control via the Cyt b6f complex, the control of electron transfer at the level of photosystem II (PSII) and the structural remodeling of photosystem I (PSI). These processes also determine the efficiency of linear (LEF) and cyclic electron flow (CEF). The latter is competitive with H2 photoproduction. Additionally, the CBB cycle competes with H2 photoproduction. Consequently, an in-depth understanding of light-driven H2 production via photosynthetic electron transfer and its competition with CO2 fixation is essential for improving photo-H2 production. At the same time, the smart design of photo-H2 production schemes and photo-H2 bioreactors are challenges for efficient up-scaling of light-driven photo-H2 production.

Structure of the red-shifted Fittonia albivenis photosystem I

Photosystem I (PSI) from Fittonia albivenis, an Acanthaceae ornamental plant, is notable among green plants for its red-shifted emission spectrum. Here, we solved the structure of a PSI–light harvesting complex I (LHCI) supercomplex from F. albivenis at 2.46-Å resolution using cryo-electron microscopy. The supercomplex contains a core complex of 14 subunits and an LHCI belt with four antenna subunits (Lhca1–4) similar to previously reported angiosperm PSI–LHCI structures; however, Lhca3 differs in three regions surrounding a dimer of low-energy chlorophylls (Chls) termed red Chls, which absorb far-red beyond visible light. The unique amino acid sequences within these regions are exclusively shared by plants with strongly red-shifted fluorescence emission, suggesting candidate structural elements for regulating the energy state of red Chls. These results provide a structural basis for unraveling the mechanisms of light harvest and transfer in PSI–LHCI of under canopy plants and for designing Lhc to harness longer-wavelength light in the far-red spectral range.

Light-Induced Charge Separation in Photosystem I from Different Biological Species Characterized by Multifrequency Electron Paramagnetic Resonance Spectroscopy.

Photosystem I (PSI) serves as a model system for studying fundamental processes such as electron transfer (ET) and energy conversion, which are not only central to photosynthesis but also have broader implications for bioenergy production and biomimetic device design. In this study, we employed electron paramagnetic resonance (EPR) spectroscopy to investigate key light-induced charge separation steps in PSI isolated from several green algal and cyanobacterial species. Following photoexcitation, rapid sequential ET occurs through either of two quasi-symmetric branches of donor/acceptor cofactors embedded within the protein core, termed the A and B branches. Using high-frequency (130 GHz) time-resolved EPR (TR-EPR) and deuteration techniques to enhance spectral resolution, we observed that at low temperatures prokaryotic PSI exhibits reversible ET in the A branch and irreversible ET in the B branch, while PSI from eukaryotic counterparts displays either reversible ET in both branches or exclusively in the B branch. Furthermore, we observed a notable correlation between low-temperature charge separation to the terminal [4Fe-4S] clusters of PSI, termed FA and FB, as reflected in the measured FA/FB ratio. These findings enhance our understanding of the mechanistic diversity of PSI's ET across different species and underscore the importance of experimental design in resolving these differences. Though further research is necessary to elucidate the underlying mechanisms and the evolutionary significance of these variations in PSI charge separation, this study sets the stage for future investigations into the complex interplay between protein structure, ET pathways, and the environmental adaptations of photosynthetic organisms.

Adequate water supply enhances seedling growth and metabolism in Festuca kryloviana: insights from physiological and transcriptomic analys

BackgroundFestuca kryloviana is a significant native grass species in the Qinghai Lake region, and its low emergence rate is a primary factor limiting the successful establishment of cultivated grasslands. The region’s arid and low-rainfall climate characteristics result in reduced soil moisture content at the surface. Despite the recognized impact of water availability on plant growth, the specific role of moisture in seedling development remains not fully elucidated. This study aims to investigate the germination rate and seedling growth velocity of F. kryloviana seeds under varying moisture conditions, and to integrate physiological and transcriptomic analyses of seedlings under these conditions to reveal the mechanisms by which water influences seedling development.ResultsThe emergence rate of F. kryloviana seedlings exhibited an initial increase followed by a decrease with increasing moisture content. The highest emergence rate, reaching 75%, was observed under 20% soil moisture conditions. By the eighth day of the experiment, the lengths of the plumules and radicles under the optimal emergence rate (full water, FW) were 21.82% and 10.87% longer, respectively, than those under closely matching the soil moisture content during the background survey (stress water, SW). The differential development of seedlings under varying moisture regimes is attributed to sugar metabolism within the seeds and the accumulation of abscisic acid (ABA). At FW conditions, enhanced sugar metabolism, which generates more energy for seedling development, is facilitated by higher activities of α-amylase, sucrose synthase, and trehalose-6-phosphate synthase compared to SW conditions. This is reflected at the transcriptomic level with upregulated expression of the α-amylase (AMY2) gene and trehalose-6-phosphate synthase (TPS6), while genes associated with ABA signaling and transduction are downregulated. Additionally, under FW conditions, the expression of genes related to the chloroplast thylakoid photosystems, such as photosystem II (PSII) and photosystem I (PSI), is upregulated, enhancing the seedlings’ light-capturing ability and photosynthetic efficiency, thereby improving their autotrophic capacity. Furthermore, FW treatment enhances the expression of the non-enzymatic antioxidant system, promoting metabolism within the seeds. In contrast, SW treatment increases the activity of the enzymatic antioxidant system, including peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT), to cope with water stress.ConclusionsOur experiment systematically evaluated the impact of moisture conditions on the growth and development of F. kryloviana seedlings. Physiological and transcriptomic data collectively indicate that adequate water (20%) supply enhances seedling growth and development by reducing ABA levels and increasing α-amylase activity within seeds, thereby boosting sugar metabolism and promoting the growth of seedling, which in turn leads to an improved emergence rate. Considering water management in future cultivation practices may be a crucial strategy for enhancing the successful establishment of F. kryloviana in grassland ecosystems.

Deciphering desiccation tolerance in wild eggplant species: insights from chlorophyll fluorescence dynamics

BackgroundClimate change exacerbates abiotic stresses, which are expected to intensify their impact on crop plants. Drought, the most prevalent abiotic stress, significantly affects agricultural production worldwide. Improving eggplant varieties to withstand abiotic stress is vital due to rising drought from climate change. Despite the diversity of wild eggplant species that thrive under harsh conditions, the understanding of their drought tolerance mechanisms remains limited. In the present study, we used chlorophyll fluorescence (ChlaF) imaging, which reveals a plant’s photosynthetic health, to investigate desiccation tolerance in eggplant and its wild relatives. Conventional fluorescence measurements lack spatial heterogeneity, whereas ChlaF imaging offers comprehensive insights into plant responses to environmental stresses. Hence, employing noninvasive imaging techniques is essential for understanding this heterogeneity.ResultsDesiccation significantly reduced the leaf tissue moisture content (TMC) across species. ChlaF and TMC displayed greater photosystem II (PSII) efficiency after 54 h of desiccation in S. macrocarpum, S. torvum, and S. indicum, with S. macrocarpum demonstrating superior efficiency due to sustained fluorescence. PSII functions declined gradually in S. macrocarpum and S. torvum, unlike those in other species, which exhibited abrupt declines after 54 h of desiccation. However, after 54 h, PSII efficiency remained above 50% of its initial quantum yield in S. macrocarpum at 35% leaf RWC (relative water content), while S. torvum and S. indicum displayed 50% decreases at 31% and 33% RWC, respectively. Conversely, the susceptible species S. gilo and S. sisymbriifolium exhibited a 50% reduction in PSII function at an early stage of 50% RWC, whereas in S. melongena, this reduction occurred at 40% RWC.ConclusionOverall, our study revealed notably greater leaf desiccation tolerance, especially in S. macrocarpum, S. torvum, and S. indicum, attributed to sustained PSII efficiency at low TMC levels, indicating that these species are promising sources of drought tolerance.