Photosynthesis Research最新文献

Modulation of the chlorophyll singlet state by protein environment is a key aspect of photosynthesis and light-harvesting in biological systems. This modulation affects excited-state dynamics, energy transfer efficiency, and photochemical reactivity. The PscB subunit of the reaction center (RC) of green sulfur bacterium Cba. tepidum contains an iron-sulfur cluster domain that is involved in light-driven electron transfer and a domain of intrinsically disordered region. The latter seemingly coil around one of the two trimeric FMO in the FMO-RC, acting as a molecular clamp. In this work, spectroscopic comparative studies of FMO-only and FMO-PscB complexes were performed. Our study reveals that reconstitution of the PscB with FMO protein alters the spectral line shape of the excitonic band of BChl a manifold and the properties of its singlet excited state as state lifetime. Though not substantial, the observable altered 815-nm excitonic band suggests that clamping of PscB around trimeric FMO shell slightly affects the overall pigment packing network. Further application of time-resolved fluorescence and absorption suggested that reconstitution of FMO trimers with PscB at the excess molecular ratio of the latter one likely leads to spontaneous oligomerization of the pigmented FMO with enhanced quenching capabilities which are essentially required during PscB's recruiting of FMO trimers and sandwiching them between chlorosome and the membrane-embedded RCs.

Oxidants attack lipids with carbon-carbon double bonds, causing the formation of lipid peroxyl radicals and hydroperoxides through a process called lipid peroxidation. Different aldehydes, including malondialdehyde, can also be formed as secondary products. The thiobarbituric acid reactive substances (TBARS) test is commonly used as an assay to measure lipid peroxidation, and its determination is based on spectrophotometric quantification of malondialdehyde. However, the TBARS test is not entirely specific for lipid peroxidation analysis because of the presence of other malondialdehyde sources and the possibility of reaction with other oxidation products. High temperature thermoluminescence technique is a useful method for studying lipid peroxidation in photosynthetic organisms. This technique measures the luminescence emission generated at high temperatures by some of the final products of lipid peroxidation. The breakdown of lipid peroxides is caused by high temperatures, which leads to the formation of carbonyl species in an excited triplet state. When chlorophyll molecules receive energy from excited carbonyls, they release this energy as luminescence once they settle into their ground state. Multiple studies have observed significant thermoluminescence emission bands at high temperatures caused by the energy transfer of lipid peroxidation by-products to chlorophyll. The band peaking at 115-130 °C correlates well with the concentration of different lipid peroxidation products. This band is an extremely sensitive in vivo indicator of the effects of stress conditions in photosynthetic materials. This technique has several benefits when used for lipid peroxidation assays. It is non-invasive, does not require the addition of external probes, and offers sensitive and continuous monitoring of peroxide levels.

Cyanidiophyceae represent basal, extremophilic taxa subdivided into several genetically distinct orders. While photosystem I supercomplexes containing light-harvesting complexes (PSI-LHCI) have been characterized in Cyanidioschyzonales and Galdieriales, their organization in Cyanidiales remains poorly understood. Here, we purified the PSI-LHCI supercomplex from Cyanidium caldarium NIES-551, and analyzed its biochemical and spectroscopic properties. SDS-PAGE and mass spectrometry identified canonical PSI and LHCI subunits. The chloroplast-encoded PSI proteins were identical to those of a previously sequenced Cd. caldarium strain. Comparative sequence analysis revealed substantial divergence in both PSI and LHCI proteins between the NIES-551 strain and Cyanidiococcus yangmingshanensis NIES-2137, a strain recently reclassified from Cd. caldarium. Pigment profiling of PSI-LHCI showed similar species across strains, yet carotenoid-to-chlorophyll a ratios were lower in NIES-551. 77-K fluorescence-emission spectra of PSI-LHCI highlighted a red-shifted emission peak in NIES-551 (734 nm) relative to NIES-2137 (727 nm), suggesting differences in pigment configuration and excitation-energy transfer. These findings indicate that PSI-LHCI in NIES-551 possesses lineage-specific pigment composition and LHCI organization. Together, these characteristics likely represent hallmarks of PSI-LHCI in Cyanidiales. Our results reinforce the evolutionary distinctiveness of Cyanidiales within Cyanidiophyceae and provide a foundation for future structural studies that will clarify the diversification of photosynthetic architecture in early-diverging red algae.

The heliobacteria are a family of phototrophic bacteria known for their unique production of bacteriochlorophyll g and for their use of the simplest known Type I reaction center. In this work, we characterize P800 oxidation kinetics in whole cells of Heliomicrobium modesticaldum under the continuous illumination that is more consistent with in vivo conditions, an area of research that remains largely unexplored. When assayed at 800 nm, whole cells display a large bleaching immediately upon illumination by actinic light, corresponding to the production of P800⁺. The initial bleaching typically reaches a maximum intensity at 10-30 ms, at which point a slower, partial recovery leads to a steady-state that is smaller than the initial bleaching. The effects of charged redox reagents, in particular ferric ammonium citrate, and the cytochrome bc complex inhibitor azoxystrobin, demonstrate that this recovery phase is due to forward donation to P800⁺ from cytochrome c. A steady-state kinetics analysis comparing the effects of actinic intensity on the rate of P800 oxidation to that of P700 oxidation in spinach chloroplasts and whole cells of Synechococcus sp. PCC 7002, suggest that the heliobacterial reaction center is inherently light-limited. In support of a light-limited model, light saturation profiles of untreated cells compared to those treated with ferric ammonium citrate indicated that only 32% of the P800 pool is oxidized during continuous illumination. Taken together, these results indicate that, in stark contrast to all other known phototrophs, phototrophy in the heliobacteria is light-limited.

Euglena sanguinea (Ehrenberg 1831) is one of the earliest reported species within the genus Euglena. Its prolific proliferation leading to red algal bloom has garnered significant scientific attention due to its ecological and environmental impacts. Despite this, research on E. sanguinea remains relatively sparse. In this study, we isolated and purified algal strains collected from the water of the Shanghai Botanical Garden, identifying them as E. sanguinea based on 16S and 23S rDNA sequence alignment. The cellular density and carotenoids content of E. sanguinea were observed to vary under different abiotic culture conditions, including varying temperatures, light intensities, potassium iodide and sucrose concentration. Notably, significant rapid accumulation of carotenoids in E. sanguinea was observed under continuous culture at a light intensity of 130 µmol m^- 2 s ^- 1. Furthermore, exposure to a strong light intensity resulted in changes in the activity of the antioxidant enzymes and malondialdehyde (MDA) content. Moreover, through de novo transcriptome sequencing and Gene Ontology (GO) analysis of E. sanguinea cultured under different light intensities, we identified a total of 111 differentially expressed genes (DEGs), comprising 44 upregulated and 67 downregulated genes. Among these, eight genes are associated with photosynthesis and chloroplast function, including upregulated genes encoding Photosystem II protein D1, Photosystem II protein K, and Cytochrome b6/f complex subunit V, as well as translation elongation factor EF-Tu; conversely, downregulated genes include those encoding cell wall-associated hydrolases and enzymes involved in carbon fixation in photosynthetic organisms. These findings provide foundational data for investigating the photoprotective mechanisms in E. sanguinea and serve as a reference for the regulatory factors involved in carotenoids biosynthesis within Euglena.

Pulse-amplitude modulated (PAM) chlorophyll fluorescence (ChlF) measurements provide a non-invasive method to study the regulation of the light reactions of photosynthesis in situ. PAM ChlF contributes also to the advancement of the interpretation of long-term observations of remotely sensed solar induced fluorescence by revealing the mechanistic connection between ChlF and photosynthetic function. However, long-term field PAM ChlF measurements remain uncommon due to challenges associated with the outdoor environment, instrument installation and maintenance, or data processing and interpretation. We here provide guidelines and recommendations to support long-term field installation of PAM ChlF systems, including the design of specialized field installation supports. We also introduce a dedicated R-package (LongTermPAM) to help users filter and analyse long-term data. Methods are demonstrated using two long-term datasets obtained with a MONI-PAM system (Monitoring PAM, Walz GmbH, Germany) on Scots pine and Norway spruce in a boreal forest. The LongTermPAM R-package helped filter spurious observations caused by dew, ice or snow, permitting calculation of photochemical (PQ) and non-photochemical quenching (NPQ) parameters and their associated yields. Finally, we illustrate how PQ and NPQ regulate the relationship between ChlF and photochemical yields, and discuss how variations in leaf PAR absorption, energy partitioning between photosystems II and I, and the contribution of photosystem I to the total ChlF signal can influence the interpretation of PAM ChlF, emphasizing the value of complementary measurements to capture variability in these factors. Although based on our experience with the MONI-PAM system in a boreal environment, most issues hereby addressed can be broadly applied to other long-term PAM monitoring systems and environments.

Subtropical forests are vital to global carbon pools, and their responses to increasing warming may significantly influence carbon sequestration. However, how subtropical tree species adjust the photosynthesis and respiration process in response to climatic warming through phenotypic plasticity is still unclear which is critical for predicting future forest carbon dynamics. A two-year warming experiment was conducted using open-top chambers (OTCs) in a subtropical forest in South China, increasing ambient temperature by approximately 1.5 ± 0.5 °C. Measurements included photosynthetic rate, stomatal conductance, chlorophyll fluorescence (Fv/Fm), night respiration, predawn and midday water potential, and key leaf structural traits across ten individuals of Schima superba, Ormosia pinnata, Pinus massoniana, and Castanopsis hystrix. Schima superba, Ormosia pinnata, and Pinus massoniana exhibited increased photosynthesis, stomatal conductance, leaf area, and biomass under warming, indicating strong physiological plasticity. In contrast, Castanopsis hystrix showed reduced gas exchange, growth, and stomatal traits because it may lack adaptive traits critical for warming resilience, indicating a divergent response to the same environmental condition. All species exhibited reduced PSII efficiency (Fv/Fm) and more negative water potentials under warming. Several structural traits, including stomatal density and specific leaf area, were positively correlated with improved physiological performance. Subtropical tree species exhibit distinct thermal response strategies, with some benefiting from modest warming and others displaying signs of stress. Species with high physiological plasticity may better maintain function and productivity under warming. These findings highlight the importance of accounting for species-specific traits in predicting forest responses to climate change and inform forest management under future warming scenarios.

To enhance land use efficiency and meet rising cassava demand, cultivation is expected to expand into unsuitable lowland areas. This trend highlights the need for waterlogging-tolerant cassava genotypes. However, research on cassava survival mechanisms under waterlogged conditions through photosynthetic functions remains limited. This study investigated the physiological responses of cassava to waterlogging stress. It focused on photosynthesis, stomatal conductance, soil plant analysis development (SPAD), and chlorophyll fluorescence (Fv/Fm) to determine chlorophyll degradation and its effect on photoreceptors. Cassava was subjected to waterlogging by maintaining water-filled buckets throughout the treatment. Variables were measured periodically at intervals of 0, 3, 6, 9, 12, and 15 days after treatment (DAT). Results showed a reduction of net photosynthetic rate (A) by 82.6%, resulting from a 96.7% reduction in stomatal conductance (gs) and 21% in transpiration rate (E). A, gs, and E in three-month-old cassava varied and declined with increasing waterlogging duration, while SPAD value showed no significant differences compared to the control across all measurement dates. Fv/Fm showed a significant decrease at 3DAT followed by recovery, likely due to light de-excitation rather than chlorophyll degradation, as SPAD value remained unchanged, indicating no chlorophyll breakdown or photoreceptor damage in three-month-old cassava under waterlogging conditions. The study concluded that cassava exhibits a functional stay-green type of SPAD, and photosynthetic nitrogen use efficiency, along with stomatal and nonstomatal limitations that regulate photosynthesis under waterlogged conditions. Study provides insights into how cassava cope with waterlogging and guide breeding or agronomic strategies to improve their resilience in waterlogged environments.

The net photosynthetic rate (A) decreases with leaf aging and senescence, primarily due to reductions in stomatal conductance (g_s), mesophyll conductance (g_m), and the maximum carboxylation rate (V_cmax). However, the relative contributions of these factors to age-related declines in photosynthesis remain insufficiently understood. In this study, we investigated gas exchange parameters, chlorophyll fluorescence, and biochemical traits in mature and senescing rice leaves. The net photosynthetic rate (A) decreased with leaf age, from 22.2 µmol m⁻² s⁻¹ in mature leaves to 15.9 µmol m⁻² s⁻¹ in older leaves. The absolute limitations imposed by g_s (LS), g_m (LM), and V_cmax (LB) were 8.54%, 9.33%, and 11.2%, respectively. The observed reduction in V_cmax in senescing leaves was primarily attributed to a decline in Rubisco content, while the in vivo specific activity of Rubisco (V_cmax/Rubisco) remained comparable between mature and older leaves. Similarly, the apparent decrease in Rubisco activity was driven by reduced Rubisco content rather than limited CO₂ availability, as the ratio of chloroplast CO₂ concentration to Rubisco content (C_c/Rubisco) was even higher in older leaves, indicating that substrate supply was not a limiting factor for catalysis. Taken together, stomatal conductance, mesophyll conductance, and V_cmax imposed comparable limitations on photosynthesis during leaf aging, with the decline in V_cmax and Rubisco activity largely attributed to a reduction in Rubisco content.