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Energy status and nutrients regulate photosynthetic protein expression. The unicellular green alga Chromochloris zofingiensis switches off photosynthesis in the presence of exogenous glucose (+Glc) in a process that depends on hexokinase (HXK1). Here, we show that this response requires that cells lack sufficient iron (-Fe). Cells grown in -Fe+Glc accumulate triacylglycerol (TAG) while losing photosynthesis and thylakoid membranes. However, cells with an iron supplement (+Fe+Glc) maintain photosynthesis and thylakoids while still accumulating TAG. Proteomic analysis shows that known photosynthetic proteins are most depleted in heterotrophy, alongside hundreds of uncharacterized, conserved proteins. Photosynthesis repression is associated with enzyme and transporter regulation that redirects iron resources to (a) respiratory instead of photosynthetic complexes and (b) a ferredoxin-dependent desaturase pathway supporting TAG accumulation rather than thylakoid lipid synthesis. Combining insights from diverse organisms from green algae to vascular plants, we show how iron and trophic constraints on metabolism aid gene discovery for photosynthesis and biofuel production.

A central goal of photoprotective energy dissipation processes is the regulation of singlet oxygen (1O2*) and reactive oxygen species in the photosynthetic apparatus. Despite the involvement of 1O2* in photodamage and cell signaling, few studies directly correlate 1O2* formation to nonphotochemical quenching (NPQ) or lack thereof. Here, we combine spin-trapping electron paramagnetic resonance (EPR) and time-resolved fluorescence spectroscopies to track in real time the involvement of 1O2* during photoprotection in plant thylakoid membranes. The EPR spin-trapping method for detection of 1O2* was first optimized for photosensitization in dye-based chemical systems and then used to establish methods for monitoring the temporal dynamics of 1O2* in chlorophyll-containing photosynthetic membranes. We find that the apparent 1O2* concentration in membranes changes throughout a 1 h period of continuous illumination. During an initial response to high light intensity, the concentration of 1O2* decreased in parallel with a decrease in the chlorophyll fluorescence lifetime via NPQ. Treatment of membranes with nigericin, an uncoupler of the transmembrane proton gradient, delayed the activation of NPQ and the associated quenching of 1O2* during high light. Upon saturation of NPQ, the concentration of 1O2* increased in both untreated and nigericin-treated membranes, reflecting the utility of excess energy dissipation in mitigating photooxidative stress in the short term (i.e., the initial ∼10 min of high light).

Diclofenac, often detected in environmental samples, poses a potential hazard to the aquatic environment. The present study aimed to understand the effect of this drug on photosynthetic apparatus, which is a little-known aspect of its phytotoxicity. Chloroplasts and thylakoids isolated from spinach (Spinacia oleracea) were used for this study and treated with various concentrations of diclofenac (from 125 to 4000 μM). The parameters of chlorophyll a fluorescence (the OJIP test) as measurements for both the intact chloroplasts and the thylakoid membranes revealed that isolated thylakoids showed greater sensitivity to the drug than chloroplasts. The relatively high concentration of diclofenac that is required to inhibit chloroplast and thylakoid functions suggests a narcotic effect of that drug on photosynthetic membranes, rather than a specific interaction with a particular element of the electron transport chain. Using confocal microscopy, we confirmed the degradation of the chloroplast structure after DCF treatment, which has not been previously reported in the literature. In conclusion, it can be assumed that diclofenac's action originated from a non-specific interaction with photosynthetic membranes, leading to the disruption in the function of the electron transport chain. This, in turn, decreases the efficiency of photosynthesis, transforming part of the PSII reaction centers into heat sinks and enhancing non-photochemical energy dissipation. [ABSTRACT FROM AUTHOR]

Chlorophyll (Chl) plays a crucial role in photosynthesis, functioning as a photosensitizer. As an integral component of this process, energy absorbed by this pigment is partly emitted as red fluorescence. This signal can be readily imaged by fluorescence microscopy and provides a visualization of photosynthetic activity. However, due to limited resolution, signals cannot be assigned to specific subcellular/organellar membrane structures. By correlating fluorescence micrographs with transmission electron microscopy, researchers can identify sub‐cellular compartments and membranes, enabling the monitoring of Chl distribution within thylakoid membrane substructures in cyanobacteria, algae, and higher plant single cells. Here, we describe a simple and effective protocol for correlative light‐electron microscopy (CLEM) based on the autofluorescence of Chl and demonstrate its application to selected photosynthetic model organisms. Our findings illustrate the potential of this technique to identify areas of high Chl concentration and photochemical activity, such as grana regions in vascular plants, by mapping stacked thylakoids. [ABSTRACT FROM AUTHOR]

"Drawing inspiration from nature" offers a wealth of creative possibilities for designing cutting‐edge materials with improved properties and performance. Nature‐inspired thylakoid‐based nanoarchitectures, seamlessly integrate the inherent structures and functions of natural components with the diverse and controllable characteristics of nanotechnology. These innovative biomaterials have garnered significant attention for their potential in various biomedical applications. Thylakoids possess fundamental traits such as light harvesting, oxygen evolution, and photosynthesis. Through the integration of artificially fabricated nanostructures with distinct physical and chemical properties, novel photosynthetic nanoarchitectures can be catalytically generated, offering versatile functionalities for diverse biomedical applications. In this article, an overview of the properties and extraction methods of thylakoids are provided. Additionally, the recent advancements in the design, preparation, functions, and biomedical applications of a range of thylakoid‐based photosynthetic nanoarchitectures are reviewed. Finally, the foreseeable challenges and future prospects in this field is discussed. [ABSTRACT FROM AUTHOR]

SUMMARY: The determination of physiological tolerance ranges of photosynthetic species and of the biochemical mechanisms underneath are fundamental to identify target processes and metabolites that will inspire enhanced plant management and production for the future. In this context, the terrestrial green algae within the genus Prasiola represent ideal models due to their success in harsh environments (polar tundras) and their extraordinary ecological plasticity. Here we focus on the outstanding Prasiola antarctica and compare two natural populations living in very contrasting microenvironments in Antarctica: the dry sandy substrate of a beach and the rocky bed of an ephemeral freshwater stream. Specifically, we assessed their photosynthetic performance at different temperatures, reporting for the first time gnsd values in algae and changes in thylakoid metabolites in response to extreme desiccation. Stream population showed lower α‐tocopherol content and thicker cell walls and thus, lower gnsd and photosynthesis. Both populations had high temperatures for optimal photosynthesis (around +20°C) and strong constitutive tolerance to freezing and desiccation. This tolerance seems to be related to the high constitutive levels of xanthophylls and of the cylindrical lipids di‐ and tri‐galactosyldiacylglycerol in thylakoids, very likely related to the effective protection and stability of membranes. Overall, P. antarctica shows a complex battery of constitutive and plastic protective mechanisms that enable it to thrive under harsh conditions and to acclimate to very contrasting microenvironments, respectively. Some of these anatomical and biochemical adaptations may partially limit photosynthesis, but this has a great potential to rise in a context of increasing temperature. Significance Statement: By using Prasiola antarctica as a model system, this work highlights the relevance of constitutive protection mechanisms involved on chloroplast functioning in harsh environments, especially the high proportion of cylindrical galactolipids and xanthophylls, and also reports the first measured gnsd ('gm') values in algae. This species shows a remarkable plasticity to ensure its success in contrasting terrestrial and fresh‐water microenvironments due to anatomical and biochemical changes, such as engrossed cell walls and accumulation of tocopherol. [ABSTRACT FROM AUTHOR]

To increase the understanding of simple thin filamentous cyanobacteria in harsh environmental areas, we previously isolated and identified four strains (XN101, XN102, GS121, NX122) from desert soils and hot spring in China. As a result, two new Oculatellacean genera of these four strains, Gansulinema gen. nov. and Komarkovaeasiopsis gen. nov., are described based on a polyphasic approach. The ultrastructure of these strains showed a similar arrangement of peripheral thylakoids with three to four parallel layers, indicating that they belonged to the orders Nodosilineales, Oculatellales, or Leptolyngbyales. In the 16S rRNA gene phylogeny, two sequences of the Gansulinema strains and the two sequences of the Komarkovaeasiopsis strains formed two independent and robust clusters, within the order Oculatellales. The 16S rRNA gene sequences of strains of Komarkovaeasiopsis and Gansulinema showed low identity to each other (≤93.2%) and to other sequences of the Oculatellacean genera (≤94.5% and ≤93.3%, respectively). Furthermore, the 16S–23S internal transcribed spacer rRNA region secondary structures of strains of Komarkovaeasiopsis and Gansulinema were not consistent with all existing descriptions of Oculatellacean taxa. These data suggest that cyanobacterial communities are rich sources of new taxa in under‐exploited areas, such as desert soils and hot spring in China. [ABSTRACT FROM AUTHOR]

Plants and algae are faced with a conundrum: harvesting sufficient light to drive their metabolic needs while dissipating light in excess to prevent photodamage, a process known as nonphotochemical quenching. A slowly relaxing form of energy dissipation, termed qH, is critical for plants' survival under abiotic stress; however, qH location in the photosynthetic membrane is unresolved. Here, we tested whether we could isolate subcomplexes from plants in which qH was induced that would remain in an energy-dissipative state. Interestingly, we found that chlorophyll (Chl) fluorescence lifetimes were decreased by qH in isolated major trimeric antenna complexes, indicating that they serve as a site for qH-energy dissipation and providing a natively quenched complex with physiological relevance to natural conditions. Next, we monitored the changes in thylakoid pigment, protein, and lipid contents of antenna with active or inactive qH but did not detect any evident differences. Finally, we investigated whether specific subunits of the major antenna complexes were required for qH but found that qH was insensitive to trimer composition. Because we previously observed that qH can occur in the absence of specific xanthophylls, and no evident changes in pigments, proteins, or lipids were detected, we tentatively propose that the energy-dissipative state reported here may stem from Chl-Chl excitonic interaction.

Nanohybrid photosystems have advantages in converting solar energy into electricity, while natural photosystems based solar‐powered energy‐storage device is still under developed. Here, we fabricate a new kind of photo‐rechargeable zinc‐ion hybrid capacitor (ZHC) benefiting from light‐harvesting carbon dots (CDs) and natural thylakoids for realizing solar energy harvesting and storage simultaneously. Under solar light irradiation, the embedded CDs in thylakoids (CDs/Thy) can convert the less absorbed green light into highly absorbed red light for thylakoids, besides, Förster resonance energy transfer (FRET) between CDs and Thy also occurs, which facilitates the photoelectrons generation during thylakoids photosynthesis, thereby resulting in 6‐fold photocurrent output in CDs/Thy hybrid photosystem, compared to pristine thylakoids. Using CDs/Thy as the photocathode in ZHCs, the photonic hybrid capacitor shows photoelectric conversion and storage features. CDs can improve the photo‐charging voltage response of ZHCs to ≈1.2 V with a remarkable capacitance enhancement of 144 % under solar light. This study provides a promising strategy for designing plant‐based photonic and electric device for solar energy harvesting and storage. [ABSTRACT FROM AUTHOR]

The spatial separation of photosystems I and II (PSI and PSII) is thought to be essential for efficient photosynthesis by maintaining a balanced flow of excitation energy between them. Unlike the thylakoid membranes of plant chloroplasts, cyanobacterial thylakoids do not form tightly appressed grana stacks that enforce strict lateral separation. The coexistence of the two photosystems provides a ground for spillover—excitation energy transfer from PSII to PSI. Spillover has been considered as a pathway of energy transfer from the phycobilisomes to PSI and may also play a role in state transitions as means to avoid overexcitation of PSII. Here, we demonstrate a significant degree of energy spillover from PSII to PSI in reconstituted membranes and isolated thylakoid membranes of Thermosynechococcus (Thermostichus) vulcanus and Synechocystis sp. PCC 6803 by steady-state and time-resolved fluorescence spectroscopy. The quantum yield of spillover in these systems was determined to be up to 40%. Spillover was also found in intact cells but to a considerably lower degree (20%) than in isolated thylakoid membranes. The findings support a model of coexistence of laterally separated microdomains of PSI and PSII in the cyanobacterial cells as well as domains where the two photosystems are energetically connected. The methodology presented here can be applied to probe spillover in other photosynthetic organisms. [ABSTRACT FROM AUTHOR]

Abstract Background Women with polycystic ovary syndrome (PCOS) have higher intestinal mucosal permeability, leading to the lipopolysaccharide (LPS) leakage and endotoxemia. This, in turn, leads to oxidative stress (OS) and neuro-inflammation caused by the gut-brain axis, affecting the neurotrophic factors levels such as brain-derived neurotrophic factor (BDNF) and S100 calcium-binding protein B (S100 B) levels. In this study, it was hypothesized that the thylakoid membranes of spinach supplementation along with a hypocaloric diet may have improved the LPS levels, neurotrophic factors, and OS in PCOS patients. Methods In this double-blind, randomized, placebo-controlled, and clinical trial, 48 women with obesity and diagnosed with PCOS based on Rotterdam criteria were randomly assigned to thylakoid (N = 21) and placebo groups (N = 23). A personalized hypocaloric diet with 500 calories less than the total energy expenditure was prescribed to all patients. The participants were daily supplemented with either a 5 g/day thylakoid-rich spinach extract or a placebo (5 g cornstarch) for 12 weeks along with a prescribed low-calorie diet. Anthropometric measurements and biochemical parameters were assessed at baseline and after the 12-week intervention. Results A statistically significant decrease in the LPS levels (P 0.05). Conclusions In sum, the thylakoid membranes of spinach supplemented with a hypocaloric diet reduced the LPS levels, increased the BDNF levels, and improved the glycemic profile and sex-hormone levels; however, they had no effects on the OS markers levels after 12 weeks of intervention.

Diclofenac, often detected in environmental samples, poses a potential hazard to the aquatic environment. The present study aimed to understand the effect of this drug on photosynthetic apparatus, which is a little-known aspect of its phytotoxicity. Chloroplasts and thylakoids isolated from spinach (Spinacia oleracea) were used for this study and treated with various concentrations of diclofenac (from 125 to 4000 μM). The parameters of chlorophyll a fluorescence (the OJIP test) as measurements for both the intact chloroplasts and the thylakoid membranes revealed that isolated thylakoids showed greater sensitivity to the drug than chloroplasts. The relatively high concentration of diclofenac that is required to inhibit chloroplast and thylakoid functions suggests a narcotic effect of that drug on photosynthetic membranes, rather than a specific interaction with a particular element of the electron transport chain. Using confocal microscopy, we confirmed the degradation of the chloroplast structure after DCF treatment, which has not been previously reported in the literature. In conclusion, it can be assumed that diclofenac’s action originated from a non-specific interaction with photosynthetic membranes, leading to the disruption in the function of the electron transport chain. This, in turn, decreases the efficiency of photosynthesis, transforming part of the PSII reaction centers into heat sinks and enhancing non-photochemical energy dissipation.

Phycobilisomes (PBS) are antenna megacomplexes that transfer energy to photosystems II and I in thylakoids. PBS likely evolved from a basic, inefficient form into the predominant hemidiscoidal shape with radiating peripheral rods. However, it has been challenging to test this hypothesis because ancestral species are generally inaccessible. Here we use spectroscopy and cryo-electron microscopy to reveal a structure of a "paddle-shaped" PBS from a thylakoid-free cyanobacterium that likely retains ancestral traits. This PBS lacks rods and specialized ApcD and ApcF subunits, indicating relict characteristics. Other features include linkers connecting two chains of five phycocyanin hexamers (CpcN) and two core subdomains (ApcH), resulting in a paddle-shaped configuration. Energy transfer calculations demonstrate that chains are less efficient than rods. These features may nevertheless have increased light absorption by elongating PBS before multilayered thylakoids with hemidiscoidal PBS evolved. Our results provide insights into the evolution and diversification of light-harvesting strategies before the origin of thylakoids. Phycobilisomes are megacomplexes in cyanobacteria that capture light. Here, authors characterize a relict paddle-shaped phycobilisome structure, revealing phycobilisome diversity prior to the development of thylakoids. [ABSTRACT FROM AUTHOR]

In this study, 18 strains of cyanobacteria were isolated from seven sites, including the Han River and Anseong Stream in Republic of Korea, and we propose these isolated strains as Limnonema gen. nov., belonging to the Aerosakkonemataceae family of the Oscillatoriales order, and also, as L. hangangris sp. nov. and L. anseonga sp. nov. These strains were identified based on morphological data using a light microscope and a transmission electron microscope, and molecular data using 16S rRNA and 16S–23S ITS gene sequences. The genus Limnonema was mainly collected as planktons, and some L. hangangris (ACKU-695–697) appeared as epilithic cyanobacteria. The genus Limnonema showed filamentous trichomes, intracellular gas vacuoles, and irregular thylakoids arrangement, which was distinct from genera Cephalothrix, Microseira, and Potamosiphon belonging to the family Aerosakkonemataceae. Moreover, the cell widths of genus Limnonema were narrower than those of genus Aerosakkonema, which is the type genus of the family Aerosakkonemataceae, and L. anseonga contained more cells with wider widths than those of L. hangangris. In the 16S rRNA gene sequence phylogeny, genus Limnonema belonged to the family Aerosakkonemataceae and was distinguished from its close relatives, genera Aerosakkonema and Cephalothrix, and L. hangangris and L. anseonga formed different branches. In 16S rRNA gene sequence similarity, genus Limnonema showed 95.4–95.9% and 93.6–94.4% similarity with genera Aerosakkonema and Cephalothrix, respectively, and L. hangangris and L. anseonga showed 97.6–97.7% similarity between each other. In the 16S–23S ITS secondary structure, the D1–D1′, Box-B, and V3 helices of genus Limnonema were distinguished from genera belonging to the family Aerosakkonemataceae, and the V3 helices of L. hangangris and L. anseonga were also different from each other. [ABSTRACT FROM AUTHOR]

In this work, a new approach to construct self‐assembled hybrid systems based on natural PSII‐enriched thylakoid membranes (PSII BBY) is demonstrated. Superfine m‐WO3 NPs (≈1–2 nm) are introduced into PSII BBY. Transmission electron microscopy (TEM) measurements showed that even the highest concentrations of NPs used did not degrade the PSII BBY membranes. Using atomic force microscopy (AFM), it is shown that the organization of PSII BBY depends strongly on the concentration of NPs applied. This proved that the superfine NPs can easily penetrate the thylakoid membrane and interact with its components. These changes are also related to the modified energy transfer between the external light‐harvesting antennas and the PSII reaction center, shown by absorption and fluorescence experiments. The biohybrid system shows stability at pH 6.5, the native operating environment of PSII, so a high rate of O2 evolution is expected. In addition, the light‐induced water‐splitting process can be further stimulated by the direct interaction of superfine WO3 NPs with the donor and acceptor sides of PSII. The water‐splitting activity and stability of this colloidal system are under investigation. Research Highlights: The phenomenon of the self‐organization of a biohybrid system composed of thylakoid membranes enriched in photosystem II and superfine WO3 nanoparticles is studied using AFM and TEM.A strong dependence of the organization of PSII complexes within PSII BBY membranes on the concentration of NPs applied is observed.This observation turns out to be crucial to understand the complexity of the mechanism of the action of WO3 NPs on modifications of energy transfer from external antenna complexes to the PSII reaction center. [ABSTRACT FROM AUTHOR]

Background: Women with polycystic ovary syndrome (PCOS) have higher intestinal mucosal permeability, leading to the lipopolysaccharide (LPS) leakage and endotoxemia. This, in turn, leads to oxidative stress (OS) and neuro-inflammation caused by the gut-brain axis, affecting the neurotrophic factors levels such as brain-derived neurotrophic factor (BDNF) and S100 calcium-binding protein B (S100 B) levels. In this study, it was hypothesized that the thylakoid membranes of spinach supplementation along with a hypocaloric diet may have improved the LPS levels, neurotrophic factors, and OS in PCOS patients. Methods: In this double-blind, randomized, placebo-controlled, and clinical trial, 48 women with obesity and diagnosed with PCOS based on Rotterdam criteria were randomly assigned to thylakoid (N = 21) and placebo groups (N = 23). A personalized hypocaloric diet with 500 calories less than the total energy expenditure was prescribed to all patients. The participants were daily supplemented with either a 5 g/day thylakoid-rich spinach extract or a placebo (5 g cornstarch) for 12 weeks along with a prescribed low-calorie diet. Anthropometric measurements and biochemical parameters were assessed at baseline and after the 12-week intervention. Results: A statistically significant decrease in the LPS levels (P < 0.001) and an increase in the BDNF levels (P < 0.001) were recorded for the participants receiving the oral thylakoid supplements and a low-calorie diet. Furthermore, significant decreases were observed in fasting blood glucose, insulin, homeostatic model of assessment for insulin resistance, free testosterone index, and follicle-stimulating hormone / luteinizing hormone ratio in both groups (P < 0.05). No significant differences were detected between the two groups regarding the changes in malondialdehyde, catalase, total antioxidant capacity, and S100B levels (P > 0.05). Conclusions: In sum, the thylakoid membranes of spinach supplemented with a hypocaloric diet reduced the LPS levels, increased the BDNF levels, and improved the glycemic profile and sex-hormone levels; however, they had no effects on the OS markers levels after 12 weeks of intervention. [ABSTRACT FROM AUTHOR]

Styrene‐maleic acid copolymers (SMAs), and related amphiphilic copolymers, are promising tools for isolating and studying integral membrane proteins in a native‐like state. However, they do not exhibit this ability universally, as several reports have found that SMAs and related amphiphilic copolymers show little to no efficiency when extracting specific membrane proteins. Recently, it was discovered that esterified SMAs could enhance the selective extraction of trimeric Photosystem I from the thylakoid membranes of thermophilic cyanobacteria; however, these polymers are susceptible to saponification that can result from harsh preparation or storage conditions. To address this concern, we herein describe the development of α‐olefin‐maleic acid copolymers (αMAs) that can extract trimeric PSI from cyanobacterial membranes with the highest extraction efficiencies observed when using any amphiphilic copolymers, including diisobutylene‐co‐maleic acid (DIBMA) and functionalized SMA samples. Furthermore, we will show that αMAs facilitate the formation of photosystem I‐containing nanodiscs that retain an annulus of native lipids and a native‐like activity. We also highlight how αMAs provide an agile, tailorable synthetic platform that enables fine‐tuning hydrophobicity, controllable molar mass, and consistent monomer incorporation while overcoming shortcomings of prior amphiphilic copolymers. [ABSTRACT FROM AUTHOR]

Following an application from Greenleaf Medical AB, submitted for authorisation of a health claim pursuant to Article 13(5) of Regulation (EC) No 1924/2006 via the Competent Authority of Sweden, the EFSA Panel on Nutrition, Novel Foods and Food allergens (NDA) was asked to deliver an opinion on the scientific substantiation of a health claim related to Appethyl® and reduction of body weight. Appethyl® is an aqueous extract from spinach leaves standardised by the manufacturing process and its lipase/colipase inhibition capacity in vitro. The Panel considers that the food is sufficiently characterised. A reduction in body weight is a beneficial physiological effect for overweight/obese individuals. The applicant identified a total of three human intervention studies that investigated the effects of Appethyl® on body weight as being pertinent to the claim. In weighing the evidence, the Panel took into account that Appethyl® (5 g/day for 12 weeks) had no effect on body weight as compared to placebo under minimal dietary counselling and moderate physical activity, and that no beneficial physiological effects are to be expected for the target population of overweight/obese individuals from the weight loss that could be attributed to the intervention with Appethyl® under predefined energy restriction and moderate physical activity. The Panel also considered that the effect of Appethyl® (5 g/day for 24 weeks) on body weight maintenance after initial weight loss shown in one study has not been replicated in different settings, which questions the external validity of the results, and that no evidence was provided for a plausible mechanism by which daily consumption of Appethyl® could exert a sustained effect on body weight in humans. The Panel concludes that a cause‐and‐effect relationship has not been established between the consumption of Appethyl® and a reduction of body weight under the conditions of use proposed by the applicant. [ABSTRACT FROM AUTHOR]

As the most suitable potential clean energy power generation technology, biophotovoltaics (BPV) not only inherits the advantages of traditional photovoltaics, such as safety, reliability and no noise, but also solves the disadvantages of high pollution and high energy consumption in the manufacturing process, providing new functions of self-repair and natural degradation. The basic idea of BPV is to collect light energy and generate electric energy by using photosynthetic autotrophs or their parts, and the core is how these biological materials can quickly and low-loss transfer electrons to the anode through mediators after absorbing light energy and generating electrons. In this mini-review, we summarized the biological materials widely used in BPV at present, mainly cyanobacteria, green algae, biological combinations (using multiple microorganisms in the same BPV system) and isolated products (purified thylakoids, chloroplasts, photosystem I, photosystem II), introduced how researchers overcome the shortcomings of low photocurrent output of BPV, pointed out the limitations that affected the development of BPV’ biological materials, and put forward reasonable assumptions accordingly. [ABSTRACT FROM AUTHOR]

Soil cyanobacterium, FBCC-A195 were isolated from the soil underneath the Jangnak Bridge, Republic of Korea. The FBCC-A195 was studied using light microscopy (LM), transmission electron microscopy (TEM), 16S rRNA, 16S–23S ITS, and ecological data. FBCC-A195 showed the circular cross-section of the trichome, broad mucilaginous envelopes, a swirl-like pattern of thylakoids inside the cell, and the lowest length/width ratio within the genus. In the 16S rRNA phylogeny, FBCC-A195 showed a sister relationship of Hormoscilla and belonged to the family Gomontiellaceae. The p-distance of FBCC-A195 ranged from 1.7% with H. pringsheimii to 12% with Komvophoron kgarii in the family. In the secondary structure of 16S–23S ITS, D1–D1', Box-B, and V3 helix of FBCC-A195 were distinguished from those of other taxa in the Gomontiellaceae. Based upon morphological, ecological, and molecular traits, Katagnymene terrestris proved to be a unique and novel species of the Katagnymene. [ABSTRACT FROM AUTHOR]

Abstract Following an application from Greenleaf Medical AB, submitted for authorisation of a health claim pursuant to Article 13(5) of Regulation (EC) No 1924/2006 via the Competent Authority of Sweden, the EFSA Panel on Nutrition, Novel Foods and Food allergens (NDA) was asked to deliver an opinion on the scientific substantiation of a health claim related to Appethyl® and reduction of body weight. Appethyl® is an aqueous extract from spinach leaves standardised by the manufacturing process and its lipase/colipase inhibition capacity in vitro. The Panel considers that the food is sufficiently characterised. A reduction in body weight is a beneficial physiological effect for overweight/obese individuals. The applicant identified a total of three human intervention studies that investigated the effects of Appethyl® on body weight as being pertinent to the claim. In weighing the evidence, the Panel took into account that Appethyl® (5 g/day for 12 weeks) had no effect on body weight as compared to placebo under minimal dietary counselling and moderate physical activity, and that no beneficial physiological effects are to be expected for the target population of overweight/obese individuals from the weight loss that could be attributed to the intervention with Appethyl® under predefined energy restriction and moderate physical activity. The Panel also considered that the effect of Appethyl® (5 g/day for 24 weeks) on body weight maintenance after initial weight loss shown in one study has not been replicated in different settings, which questions the external validity of the results, and that no evidence was provided for a plausible mechanism by which daily consumption of Appethyl® could exert a sustained effect on body weight in humans. The Panel concludes that a cause‐and‐effect relationship has not been established between the consumption of Appethyl® and a reduction of body weight under the conditions of use proposed by the applicant.

SUMMARY: Five strains of Drouetiella (ACKU666, 667, 668, 669 and 670) were isolated from gravels in water, stone monument and coastal mudflat in Korea, and were studied using morphological and molecular traits. All five strains had thin and simple trichomes and exhibited false branching. From these strains, four strains (ACKU666, 667, 668 and 669) exhibited similar cell lengths with reddish–brown colored cells such as Drouetiella lurida. The 16S rRNA gene phylogeny showed the four strains formed a clade with Drouetiella lurida, and their DNA similarity was calculated to be 99.1–100%. The color of strain ACKU670 appeared to be in bright blue–green color like Drouetiella fasciculata, and their thylakoids showed a parietal arrangement, which is a characteristic feature of the family Oculatellaceae. Strain ACKU670 turned out to be a sister clade to the D. lurida according to the phylogenetic analysis of the 16S rRNA gene. The 16–23S rRNA internal transcribed spacer secondary folding structure (D1–D1′, Box‐B and V3 helices) confirmed the uniqueness of strain ACKU670, therefore indicating differences from the related species. Considering all the results, we described our strain ACKU670 as Drouetiella epilithica sp. nov. in accordance with the International Code of Nomenclature for Algae, Fungi and Plants. [ABSTRACT FROM AUTHOR]

Diatom thylakoids contain much higher amounts of sulfoquinovosyl diacylglycerol (SQDG) than vascular plants and the hypothesis was brought forward that this relates to their special thylakoid structure. To test this hypothesis we created knock-down mutants in Thalassiosira pseudonana that exhibited a decreased SQDG content per cell. Surprisingly, the ratio between the different lipid classes did not change, pointing to strict regulation of thylakoid lipid composition. The antenna proteins, fucoxanthin-chlorophyll proteins (FCP), were reduced and photosystem (PS) I compared to PSII was increased as judged from absorbance spectra. CD spectroscopy indicated a tighter packing of chromophores. The reduction in FCP might help to avoid diametral changes in excitation energy transfer. In contrast, the increase in PSI in the mutants might counteract the diminishment of the usually huge PSI antenna. No changes in thylakoid structure were observed since the stoichiometry between different lipid classes seems to be carefully balanced. [ABSTRACT FROM AUTHOR]

The importance of green light for driving natural photosynthesis has long been underappreciated, however, under the presence of strong illumination, green light actually drives photosynthesis more efficiently than red light. This green light is absorbed by mixed vibronic Qy-Qx states, arising from chlorophyll (Chl)-Chl interactions, although almost nothing is known about these states. Here, we employ polarization-dependent two-dimensional electronic-vibrational spectroscopy to study the origin and dynamics of the mixed vibronic Qy-Qx states of light-harvesting complex II. We show the states in this region dominantly arise from Chl b and demonstrate how it is possible to distinguish between the degree of vibronic Qy versus Qx character. We find that the dynamics for states of predominately Chl b Qy versus Chl b Qx character are markedly different, as excitation persists for significantly longer in the Qx states and there is an oscillatory component to the Qx dynamics, which is discussed. Our findings demonstrate the central role of electronic-nuclear mixing in efficient light-harvesting and the different functionalities of Chl a and Chl b.

Leaf color mutants are important materials for studying chloroplast and photomorphogenesis, and can function as basic germplasms for genetic breeding. In an ethylmethanesulfonate mutagenesis population of watermelon cultivar "703", a chlorophyll-deficient mutant with yellow leaf (Yl2) color was identified. The contents of chlorophyll a, chlorophyll b, and carotenoids in Yl2 leaves were lower than those in wild-type (WT) leaves. The chloroplast ultrastructure in the leaves revealed that the chloroplasts in Yl2 were degraded. The numbers of chloroplasts and thylakoids in the Yl2 mutant were lower, resulting in lower photosynthetic parameters. Transcriptomic analysis identified 1292 differentially expressed genes, including1002 upregulated and 290 downregulated genes. The genes involved in chlorophyll biosynthesis (HEMA, HEMD, CHL1, CHLM, and CAO) were significantly downregulated in the Yl2 mutant, which may explain why chlorophyll pigment content was lower than that in the WT. Chlorophyll metabolism genes such as PDS, ZDS and VDE, were upregulated, which form the xanthophyll cycle and may protect the yellow‒leaves plants from photodamage. Taken together, our findings provide insight into the molecular mechanisms of leading to leaf color formation and chloroplast development in watermelon. [ABSTRACT FROM AUTHOR]

The barley cultivar Sarab 1 (SRB1) can continue photosynthesis despite its low Fe acquisition potential via roots and dramatically reduced amounts of photosystem I (PSI) reaction-center proteins under Fe-deficient conditions. We compared the characteristics of photosynthetic electron transfer (ET), thylakoid ultrastructure, and Fe and protein distribution on thylakoid membranes among barley cultivars. The Fe-deficient SRB1 had a large proportion of functional PSI proteins by avoiding P700 over-reduction. An analysis of the thylakoid ultrastructure clarified that SRB1 had a larger proportion of non-appressed thylakoid membranes than those in another Fe-tolerant cultivar, Ehimehadaka-1 (EHM1). Separating thylakoids by differential centrifugation further revealed that the Fe-deficient SRB1 had increased amounts of low/light-density thylakoids with increased Fe and light-harvesting complex II (LHCII) than did EHM1. LHCII with uncommon localization probably prevents excessive ET from PSII leading to elevated NPQ and lower PSI photodamage in SRB1 than in EHM1, as supported by increased Y(NPQ) and Y(ND) in the Fe-deficient SRB1. Unlike this strategy, EHM1 may preferentially supply Fe cofactors to PSI, thereby exploiting more surplus reaction center proteins than SRB1 under Fe-deficient conditions. In summary, SRB1 and EHM1 support PSI through different mechanisms during Fe deficiency, suggesting that barley species have multiple strategies for acclimating photosynthetic apparatus to Fe deficiency. [ABSTRACT FROM AUTHOR]

Green organisms evolve oxygen (O2) via photosynthesis and consume it by respiration. Generally, net O2 consumption only becomes dominant when photosynthesis is suppressed at night. Here, we show that green thylakoid membranes of Scots pine (Pinus sylvestris L) and Norway spruce (Picea abies) needles display strong O2 consumption even in the presence of light when extremely low temperatures coincide with high solar irradiation during early spring (ES). By employing different electron transport chain inhibitors, we show that this unusual light-induced O2 consumption occurs around photosystem (PS) I and correlates with higher abundance of flavodiiron (Flv) A protein in ES thylakoids. With P700 absorption changes, we demonstrate that electron scavenging from the acceptor-side of PSI via O2 photoreduction is a major alternative pathway in ES. This photoprotection mechanism in vascular plants indicates that conifers have developed an adaptative evolution trajectory for growing in harsh environments. Generally, net O2 consumption becomes dominant when photosynthesis is suppressed at night in green organisms. Here, Bag et al. show that Scots pine and Norway spruce needles display strong O2 consumption when extremely low temperatures coincide with high solar irradiation during early spring. [ABSTRACT FROM AUTHOR]

The knockout of the At2g28210 gene encoding α-carbonic anhydrase 2 (α-CA2) in Arabidopsis thaliana (Columbia) led to alterations in photosynthetic processes. The effective quantum yields of both photosystem II (PSII) and photosystem I (PSI) were higher in α-carbonic anhydrase 2 knockout plants (α-CA2-KO), and the reduction state of plastoquinone pool was lower than in wild type (WT). The electron transport rate in the isolated thylakoids measured with methyl viologen was higher in α-CA2-KO plants. The amounts of reaction centers of PSII and PSI were similar in WT and α-CA2-KO plants. The non-photochemical quenching of chlorophyll a fluorescence in α-CA2-KO leaves was lower at the beginning of illumination, but became slightly higher than in WT leaves when the steady state was achieved. The degree of state transitions in the leaves was lower in α-CA2-KO than in WT plants. Measurements of the electrochromic carotenoid absorbance shift (ECS) revealed that the light-dependent pH gradient (ΔpH) across the thylakoid membrane was lower in the leaves of α-CA2-KO plants than in WT plants. The starch content in α-CA2-KO leaves was lower than in WT plants. The expression levels of the genes encoding chloroplast CAs in α-CA2-KO changed noticeably, whereas the expression levels of genes of cytoplasmic CAs remained almost the same. It is proposed that α-CA2 may be situated in the chloroplasts. [ABSTRACT FROM AUTHOR]

Limnospira fusiformis (also known as Spirulina) is a cyanobacterium that is widely cultivated due to its economic importance. It has specific pigments such as phycocyanin that allow it to grow at different light wavelengths compared to other cultivated algae. Our study investigated the effect of yellow (590 nm) and blue (460 nm) light fields on various biochemical features, including the pigment concentration, protein content, dry weight, and cell ultrastructure of L. fusiformis. Our findings revealed that biomass growth was faster in yellow light compared to blue light, with a higher relative amount of proteins even after one day of exposure. However, after eight days, the relative protein content in yellow versus blue light was not statistically different. Furthermore, in yellow light, we observed a decrease in chlorophyll a, an increase in cyanophycin granules, and an increase in the amount of dilated thylakoids. On the other hand, in blue light, there was an increase in phycocyanin after one day, along with an increase in electron-dense bodies, which are attributable to carboxysomes. However, after eight days, the differences in pigment content compared to the control were not statistically significant. Our study showed that using specific wavelengths during the harvesting phase of spirulina growth can enhance phycocyanin content with blue light (after one day) and biomass, growth rates, and protein content with yellow light after six days. This highlights the biotechnological potential of this approach. [ABSTRACT FROM AUTHOR]

In eukaryotic photosynthetic organisms, the conversion of solar into chemical energy occurs in thylakoid membranes in the chloroplast. How thylakoid membranes are formed and maintained is poorly understood. However, previous observations of vesicles adjacent to the stromal side of the inner envelope membrane of the chloroplast suggest a possible role of membrane transport via vesicle trafficking from the inner envelope to the thylakoids. Here we show that the model plant Arabidopsis thaliana has a chloroplast-localized Sec14-like protein (CPSFL1) that is necessary for photoautotrophic growth and vesicle formation at the inner envelope membrane of the chloroplast. The cpsfl1 mutants are seedling lethal, show a defect in thylakoid structure, and lack chloroplast vesicles. Sec14 domain proteins are found only in eukaryotes and have been well characterized in yeast, where they regulate vesicle budding at the trans-Golgi network. Like the yeast Sec14p, CPSFL1 binds phosphatidylinositol phosphates (PIPs) and phosphatidic acid (PA) and acts as a phosphatidylinositol transfer protein in vitro, and expression of Arabidopsis CPSFL1 can complement the yeast sec14 mutation. CPSFL1 can transfer PIP into PA-rich membrane bilayers in vitro, suggesting that CPSFL1 potentially facilitates vesicle formation by trafficking PA and/or PIP, known regulators of membrane trafficking between organellar subcompartments. These results underscore the role of vesicles in thylakoid biogenesis and/or maintenance. CPSFL1 appears to be an example of a eukaryotic cytosolic protein that has been coopted for a function in the chloroplast, an organelle derived from endosymbiosis of a cyanobacterium.

Thylakoid membranes in chloroplasts contain photosynthetic protein complexes that convert light energy into chemical energy. Photosynthetic protein complexes are considered to undergo structural reorganization to maintain the efficiency of photochemical reactions. A detailed description of the mobility of photosynthetic complexes in real time is necessary to understand how macromolecular organization of the membrane is altered by environmental fluctuations. Here, we used high-speed atomic force microscopy to visualize and characterize the in situ mobility of individual protein complexes in grana thylakoid membranes isolated from Spinacia oleracea. Our observations reveal that these membranes can harbor complexes with at least two distinctive classes of mobility. A large fraction of grana membranes contained proteins with quasistatic mobility exhibiting molecular displacements smaller than 10 nm2. In the remaining fraction, the protein mobility is variable with molecular displacements of up to 100 nm2. This visualization at high spatiotemporal resolution enabled us to estimate an average diffusion coefficient of ∼1 nm2 s-1. Interestingly, both confined and Brownian diffusion models could describe the protein mobility of the second group of membranes. We also provide the first direct evidence, to our knowledge, of rotational diffusion of photosynthetic complexes. The rotational diffusion of photosynthetic complexes could be an adaptive response to the high protein density in the membrane to guarantee the efficiency of electron transfer reactions. This characterization of the mobility of individual photosynthetic complexes in grana membranes establishes a foundation that could be adapted to study the dynamics of the complexes inside intact and photosynthetically functional thylakoid membranes to be able to understand its structural responses to diverse environmental fluctuations.

Integral membrane proteins are exposed to a complex and dynamic lipid environment modulated by nonbilayer lipids that can influence protein functions by lipid-protein interactions. The nonbilayer lipid monogalactosyldiacylglycerol (MGDG) is the most abundant lipid in plant photosynthetic thylakoid membranes, but its impact on the functionality of energy-converting membrane protein complexes is unknown. Here, we optimized a detergent-based reconstitution protocol to develop a proteoliposome technique that incorporates the major light-harvesting complex II (LHCII) into compositionally well-defined large unilamellar lipid bilayer vesicles to study the impact of MGDG on light harvesting by LHCII. Using steady-state fluorescence spectroscopy, CD spectroscopy, and time-correlated single-photon counting, we found that both chlorophyll fluorescence quantum yields and fluorescence lifetimes clearly indicate that the presence of MGDG in lipid bilayers switches LHCII from a light-harvesting to a more energy-quenching mode that dissipates harvested light into heat. It is hypothesized that in the in vitro system developed here, MGDG controls light harvesting of LHCII by modulating the hydrostatic lateral membrane pressure profile in the lipid bilayer sensed by LHCII-bound peripheral pigments.

Since the discovery of quantum beats in the two-dimensional electronic spectra of photosynthetic pigment-protein complexes over a decade ago, the origin and mechanistic function of these beats in photosynthetic light-harvesting has been extensively debated. The current consensus is that these long-lived oscillatory features likely result from electronic-vibrational mixing, however, it remains uncertain if such mixing significantly influences energy transport. Here, we examine the interplay between the electronic and nuclear degrees of freedom (DoF) during the excitation energy transfer (EET) dynamics of light-harvesting complex II (LHCII) with two-dimensional electronic-vibrational spectroscopy. Particularly, we show the involvement of the nuclear DoF during EET through the participation of higher-lying vibronic chlorophyll states and assign observed oscillatory features to specific EET pathways, demonstrating a significant step in mapping evolution from energy to physical space. These frequencies correspond to known vibrational modes of chlorophyll, suggesting that electronic-vibrational mixing facilitates rapid EET over moderately size energy gaps.

Several 'super-complexes' of individual hetero-oligomeric membrane protein complexes, whose function is to facilitate intra-membrane electron and proton transfer and harvesting of light energy, have been previously characterized in the mitochondrial cristae and chloroplast thylakoid membranes. We report the presence of an intra-membrane super-complex dominated by the ATP-synthase, photosystem I (PSI) reaction-center complex and the ferredoxin-NADP+ Reductase (FNR) in the thylakoid membrane. The presence of the super-complex has been documented by mass spectrometry, clear-native PAGE and Western Blot analyses. This is the first documented presence of ATP synthase in a super-complex with the PSI reaction-center located in the non-appressed stromal domain of the thylakoid membrane.

The Chroococcales is one of the least studied cyanobacterial orders comprising the non-baeocyte-producing coccoids cyanobacteria with stacked and fasciculated thylakoids. During a survey of aquatic biodiversity in Caohai Lake in Guizhou Province, China, a coccoid-like cyanobacterium was isolated. It was characterized using a polyphasic approach, based on morphology, electron microscopy, and molecular phylogenetic analyses. This species' colonies exhibited morphological similarity to those of Microcystis species but differed in their larger colony sizes and widely oval cells. The 16S rRNA gene sequence of this species had the maximum homology, corresponding to 93.10%, to that of the genus Microcystis. The results of 16S rRNA gene threshold value and 16S rRNA phylogenetic analyses confirmed that the studied species belongs to the family Microcystaceae but is phylogenetically distinct from the other species of Microcystaceae. Furthermore, The D1–D1′, Box–B helix, and V3 helix of the 16S–23S ITS region were also different from those previously described in Microcystaceae taxa. Combining the morphological, ecological, and molecular features of the coccoid-like cyanobacterium, we here propose the establishment of the Cyanodorina gen. nov. and the Cyanodorina ovale sp. nov. [ABSTRACT FROM AUTHOR]

Nitrogen (N) is an important contributor to photosynthetic rate (Pn). However, during grain-filling stage in maize, some leaf N is remobilized to meet demands for grain protein accumulation rather than photosynthetic demands. Therefore, plants that can maintain a relatively high Pn during the N remobilization process would have the key to achieving both high grain yields (HGY) and high grain protein concentrations (HGPC). In this study, we investigated two high-yielding maize hybrids in photosynthetic apparatus and N allocation in a two-year field experiment. During grain filling, XY335 had a higher Pn and photosynthetic N-use efficiency than ZD958 had in the upper leaf, but not in the middle or lower leaves. In the upper leaf, the diameter and area of the bundle sheath (BS) were larger and the distance between bundle sheaths was greater in XY335 than in ZD958. XY335 had more bundle sheath cells (BSCs) and a larger BSC area, as well as a larger chloroplast area in the BSC, resulting in a higher total number and total area of chloroplasts in the BS. XY335 also had higher stomatal conductance (g s), intercellular CO 2 concentration, and N allocation to the thylakoids. No genotypic differences were found in mesophyll cell ultrastructure, N content and starch content in the three types of leaves. Therefore, a trifecta of higher g s , greater N allocation to thylakoids for photo-phosphorylation and electron transport, and more and larger chloroplasts promoting CO 2 assimilation in the BS confers a high Pn to simultaneously achieve HGY and high HGPC in maize. • How to stabilize Pn during N remobilization process is the key to synchronize HGY and HGPC. • The combination of high g s , NTH, more and larger chloroplasts of BSC confer high Pn. • Genotypic difference in Pn was not related to MS ultrastructure or starch conte. [ABSTRACT FROM AUTHOR]

Leaf-color mutations have been studied extensively in plants. However, to better understand the complex mechanisms underlying the formation of leaf color, it is essential to continue discover novel genes involved in the process of leaf color development. In this study, we identified a variegated-leaf (vg) mutant in tomato that exhibited defective phenotypes in thylakoids and photosynthesis. To clone the vg locus, an F 2 population was constructed from the cross between the vg mutant (Solanum lycopersicum) and the wild tomato LA1589 (S. pimpinellifolium). Using the map-based cloning approach, the vg locus was mapped on chromosome 7 and narrowed down to a 128 kb region that contained 21 open reading frames (ORFs). The expression levels of ORF9, ORF10, and ORF13 were significantly lower in vg than in the wild-type plants, while the ORF11 transcript level was elevated in vg. We then mutagenized ORF9, ORF10, and ORF13 by the CRISPR/Cas9 system in the wild-type tomato background and found that only the ORF10 mutation reproduced the phenotype of variegated leaves, indicating that ORF10 represents VG and its down-regulated expression was responsible for the variegated leaf phenotype. ORF10 encodes a thylakoid formation protein and its mutant lines showed reduced levels of chlorophyll synthesis and photosynthesis. Taken together, these results suggest that VG is necessary for chloroplast development, chlorophyll synthesis, and photosynthesis in tomato. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: The bottom‐up construction of self‐powered artificial cells is significant to understand the energy supply and metabolism of nature cells. Here, we demonstrate an efficient manner to build thylakoid‐containing artificial cells, which continuously convert light energy into chemical energy to supply adenosine 5'‐triphosphate (ATP) under light illumination. The production of ATP supplies energy to promote the biological enzyme cascade reactions, where glucose is transformed into glucose 6‐phosphate (G6P) under the catalysis of hexokinase (HK). G6P was further converted to gluconolactone 6‐phosphate (PG) in the presence of 6‐phosphate dehydrogenase (G6PDH), meanwhile NADP+ was converted to nicotinamide adenine dinucleotide phosphate (NADPH). The self‐powered artificial cells were demonstrated to generate ATP and NADPH successively, which provided a way for building more complicated artificial cells. [ABSTRACT FROM AUTHOR]

Summary: Singlet oxygen (1O2) is a harmful species that functions also as a signaling molecule. In chloroplasts, 1O2 is produced via charge recombination reactions in photosystem II, but which recombination pathway(s) produce triplet Chl and 1O2 remains open. Furthermore, the role of 1O2 in photoinhibition is not clear.We compared temperature dependences of 1O2 production, photoinhibition, and recombination pathways.1O2 production by pumpkin thylakoids increased from −2 to +35°C, ruling out recombination of the primary charge pair as a main contributor. S2QA− or S2QB− recombination pathways, in turn, had too steep temperature dependences. Instead, the temperature dependence of 1O2 production matched that of misses (failures of the oxygen (O2) evolving complex to advance an S‐state). Photoinhibition in vitro and in vivo (also in Synechocystis), and in the presence or absence of O2, had the same temperature dependence, but ultraviolet (UV)‐radiation‐caused photoinhibition showed a weaker temperature response.We suggest that the miss‐associated recombination of P680+QA− is the main producer of 1O2. Our results indicate three parallel photoinhibition mechanisms. The manganese mechanism dominates in UV radiation but also functions in white light. Mechanisms that depend on light absorption by Chls, having 1O2 or long‐lived P680+ as damaging agents, dominate in red light. [ABSTRACT FROM AUTHOR]

SUMMARY: The effects of drought on photosynthesis have been extensively studied, whereas those on thylakoid organization are limited. We observed a significant decline in gas exchange parameters of pea (Pisum sativum) leaves under progressive drought stress. Chl a fluorescence kinetics revealed the reduction of photochemical efficiency of photosystem (PS)II and PSI. The non‐photochemical quenching (NPQ) and the levels of PSII subunit PSBS increased. Furthermore, the light‐harvesting complexes (LHCs) and some of the PSI and PSII core proteins were disassembled in drought conditions, whereas these complexes were reassociated during recovery. By contrast, the abundance of supercomplexes of PSII‐LHCII and PSII dimer were reduced, whereas LHCII monomers increased following the change in the macro‐organization of thylakoids. The stacks of thylakoids were loosely arranged in drought‐affected plants, which could be attributed to changes in the supercomplexes of thylakoids. Severe drought stress caused a reduction of both LHCI and LHCII and a few reaction center proteins of PSI and PSII, indicating significant disorganization of the photosynthetic machinery. After 7 days of rewatering, plants recovered well, with restored chloroplast thylakoid structure and photosynthetic efficiency. The correlation of structural changes with leaf reactive oxygen species levels indicated that these changes were associated with the production of reactive oxygen species. Significance Statement: Drought affects the photosynthetic apparatus and organization of thylakoid proteins, which are relatively reversible by rewatering. The present study shows that the drought conditions equally damaged both photosystems. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: The bottom‐up construction of self‐powered artificial cells is significant to understand the energy supply and metabolism of nature cells. Here, we demonstrate an efficient manner to build thylakoid‐containing artificial cells, which continuously convert light energy into chemical energy to supply adenosine 5'‐triphosphate (ATP) under light illumination. The production of ATP supplies energy to promote the biological enzyme cascade reactions, where glucose is transformed into glucose 6‐phosphate (G6P) under the catalysis of hexokinase (HK). G6P was further converted to gluconolactone 6‐phosphate (PG) in the presence of 6‐phosphate dehydrogenase (G6PDH), meanwhile NADP+ was converted to nicotinamide adenine dinucleotide phosphate (NADPH). The self‐powered artificial cells were demonstrated to generate ATP and NADPH successively, which provided a way for building more complicated artificial cells. [ABSTRACT FROM AUTHOR]

Although the importance of nonphotochemical quenching (NPQ) on photosynthetic biomass production and crop yields is well established, the in vivo operation of the individual mechanisms contributing to overall NPQ is still a matter of controversy. In order to investigate the timescale and activation dynamics of specific quenching mechanisms, we have developed a technique called snapshot transient absorption (TA) spectroscopy, which can monitor molecular species involved in the quenching response with a time resolution of 30 s. Using intact thylakoid membrane samples, we show how conventional TA kinetic and spectral analyses enable the determination of the appropriate wavelength and time delay for snapshot TA experiments. As an example, we show how the chlorophyll-carotenoid charge transfer and excitation energy transfer mechanisms can be monitored based on signals corresponding to the carotenoid (Car) radical cation and Car S1 excited state absorption, respectively. The use of snapshot TA spectroscopy together with the previously reported fluorescence lifetime snapshot technique (Sylak-Glassman et al. in Photosynth Res 127:69-76, 2016) provides valuable information such as the concurrent appearance of specific quenching species and overall quenching of excited Chl. Furthermore, we show that the snapshot TA technique can be successfully applied to completely intact photosynthetic organisms such as live cells of Nannochloropsis. This demonstrates that the snapshot TA technique is a valuable method for tracking the dynamics of intact samples that evolve over time, such as the photosynthetic system in response to high-light exposure.

Photosystem II (PSII) undergoes frequent photooxidative damage that, if not repaired, impairs photosynthetic activity and growth. How photosynthetic organisms protect vulnerable PSII intermediate complexes during de novo assembly and repair remains poorly understood. Here, we report the genetic and biochemical characterization of chloroplast-located rubredoxin 1 (RBD1), a PSII assembly factor containing a redox-active rubredoxin domain and a single C-terminal transmembrane α-helix (TMH) domain. RBD1 is an integral thylakoid membrane protein that is enriched in stroma lamellae fractions with the rubredoxin domain exposed on the stromal side. RBD1 also interacts with PSII intermediate complexes containing cytochrome b559 Complementation of the Chlamydomonas reinhardtii (hereafter Chlamydomonas) RBD1-deficient 2pac mutant with constructs encoding RBD1 protein truncations and site-directed mutations demonstrated that the TMH domain is essential for de novo PSII assembly, whereas the rubredoxin domain is involved in PSII repair. The rubredoxin domain exhibits a redox midpoint potential of +114 mV and is proficient in 1-electron transfers to a surrogate cytochrome c in vitro. Reduction of oxidized RBD1 is NADPH dependent and can be mediated by ferredoxin-NADP+ reductase (FNR) in vitro. We propose that RBD1 participates, together with the cytochrome b559, in the protection of PSII intermediate complexes from photooxidative damage during de novo assembly and repair. This role of RBD1 is consistent with its evolutionary conservation among photosynthetic organisms and the fact that it is essential in photosynthetic eukaryotes.

Light and nutrients are critical regulators of photosynthesis and metabolism in plants and algae. Many algae have the metabolic flexibility to grow photoautotrophically, heterotrophically, or mixotrophically. Here, we describe reversible Glc-dependent repression/activation of oxygenic photosynthesis in the unicellular green alga Chromochloris zofingiensis. We observed rapid and reversible changes in photosynthesis, in the photosynthetic apparatus, in thylakoid ultrastructure, and in energy stores including lipids and starch. Following Glc addition in the light, C. zofingiensis shuts off photosynthesis within days and accumulates large amounts of commercially relevant bioproducts, including triacylglycerols and the high-value nutraceutical ketocarotenoid astaxanthin, while increasing culture biomass. RNA sequencing reveals reversible changes in the transcriptome that form the basis of this metabolic regulation. Functional enrichment analyses show that Glc represses photosynthetic pathways while ketocarotenoid biosynthesis and heterotrophic carbon metabolism are upregulated. Because sugars play fundamental regulatory roles in gene expression, physiology, metabolism, and growth in both plants and animals, we have developed a simple algal model system to investigate conserved eukaryotic sugar responses as well as mechanisms of thylakoid breakdown and biogenesis in chloroplasts. Understanding regulation of photosynthesis and metabolism in algae could enable bioengineering to reroute metabolism toward beneficial bioproducts for energy, food, pharmaceuticals, and human health.

A recent study by Catherine Demoulin, Yannick Lara, Alexandre Lambion, and Emmanuelle Javaux has provided evidence for the presence of thylakoids, membrane-bound compartments where photosynthesis takes place, in microfossils that may be cyanobacteria. The researchers used transmission electron microscopy to examine fossils from Australia, Canada, and the Democratic Republic of the Congo. The discovery of preserved thylakoids within these microfossils establishes a minimum age of about 1.75 billion years ago for the divergence of cyanobacteria with and without thylakoids. This finding contributes to our understanding of the history of photosynthesis and the organisms that played a role in the oxygenation of the atmosphere and oceans. [Extracted from the article]

The chloroplast is the chlorophyll-containing organelle that produces energy through photosynthesis. Within the chloroplast is an intricate network of thylakoid membranes containing photosynthetic membrane proteins that mediate electron transport and generate chemical energy. Historically, electron microscopy (EM) has been a powerful tool for visualizing the macromolecular structure and organization of thylakoid membranes. However, an understanding of thylakoid membrane dynamics remains elusive because EM requires fixation and sectioning. To improve our knowledge of thylakoid membrane dynamics we need to consider at least two issues: (i) the live-cell imaging conditions needed to visualize active processes in vivo; and (ii) the spatial resolution required to differentiate the characteristics of thylakoid membranes. Here, we utilize three-dimensional structured illumination microscopy (3D-SIM) to explore the optimal imaging conditions for investigating the dynamics of thylakoid membranes in living plant and algal cells. We show that 3D-SIM is capable of examining broad characteristics of thylakoid structures in chloroplasts of the vascular plant Arabidopsis thaliana and distinguishing the structural differences between wild-type and mutant strains. Using 3D-SIM, we also visualize thylakoid organization in whole cells of the green alga Chlamydomonas reinhardtii. These data reveal that high light intensity changes thylakoid membrane structure in C. reinhardtii. Moreover, we observed the green alga Chromochloris zofingiensis and the moss Physcomitrella patens to show the applicability of 3D-SIM. This study demonstrates that 3D-SIM is a promising approach for studying the dynamics of thylakoid membranes in photoautotrophic organisms during photoacclimation processes.