A vitamin-C-derived DNA modification catalysed by an algal TET homologue.

Methylation of cytosine to 5-methylcytosine (5mC) is a prevalent DNA modification found in many organisms. Sequential oxidation of 5mC by ten-eleven translocation (TET) dioxygenases results in a cascade of additional epigenetic marks and promotes demethylation of DNA in mammals1,2. However, the enzymatic activity and function of TET homologues in other eukaryotes remains largely unexplored. Here we show that the green alga Chlamydomonas reinhardtii contains a 5mC-modifying enzyme (CMD1) that is a TET homologue and catalyses the conjugation of a glyceryl moiety to the methyl group of 5mC through a carbon-carbon bond, resulting in two stereoisomeric nucleobase products. The catalytic activity of CMD1 requires Fe(II) and the integrity of its binding motif His-X-Asp, which is conserved in Fe-dependent dioxygenases3. However, unlike previously described TET enzymes, which use 2-oxoglutarate as a co-substrate4, CMD1 uses L-ascorbic acid (vitamin C) as an essential co-substrate. Vitamin C donates the glyceryl moiety to 5mC with concurrent formation of glyoxylic acid and CO2. The vitamin-C-derived DNA modification is present in the genome of wild-type C. reinhardtii but at a substantially lower level in a CMD1 mutant strain. The fitness of CMD1 mutant cells during exposure to high light levels is reduced. LHCSR3, a gene that is critical for the protection of C. reinhardtii from photo-oxidative damage under high light conditions, is hypermethylated and downregulated in CMD1 mutant cells compared to wild-type cells, causing a reduced capacity for photoprotective non-photochemical quenching. Our study thus identifies a eukaryotic DNA base modification that is catalysed by a divergent TET homologue and unexpectedly derived from vitamin C, and describes its role as a potential epigenetic mark that may counteract DNA methylation in the regulation of photosynthesis.

Near telomere-to-telomere genome assemblies of two Chlorella species unveil the composition and evolution of centromeres in green algae.

BACKGROUND: Centromeres play a crucial and conserved role in cell division, although their composition and evolutionary history in green algae, the evolutionary ancestors of land plants, remains largely unknown. RESULTS: We constructed near telomere-to-telomere (T2T) assemblies for two Trebouxiophyceae species, Chlorella sorokiniana NS4-2 and Chlorella pyrenoidosa DBH, with chromosome numbers of 12 and 13, and genome sizes of 58.11 Mb and 53.41 Mb, respectively. We identified and validated their centromere sequences using CENH3 ChIP-seq and found that, similar to humans and higher plants, the centromeric CENH3 signals of green algae display a pattern of hypomethylation. Interestingly, the centromeres of both species largely comprised transposable elements, although they differed significantly in their composition. Species within the Chlorella genus display a more diverse centromere composition, with major constituents including members of the LTR/Copia, LINE/L1, and LINE/RTEX families. This is in contrast to green algae including Chlamydomonas reinhardtii, Coccomyxa subellipsoidea, and Chromochloris zofingiensis, in which centromere composition instead has a pronounced single-element composition. Moreover, we observed significant differences in the composition and structure of centromeres among chromosomes with strong collinearity within the Chlorella genus, suggesting that centromeric sequence evolves more rapidly than sequence in non-centromeric regions. CONCLUSIONS: This study not only provides high-quality genome data for comparative genomics of green algae but gives insight into the composition and evolutionary history of centromeres in early plants, laying an important foundation for further research on their evolution.

How to adjust the expected waiting time to improve patient's satisfaction?

BACKGROUND: Long waiting time in hospital leads to patient's low satisfaction. In addition to reducing the actual waiting time (AWT), we can also improve satisfaction by adjusting the expected waiting time (EWT). Then how much can the EWT be adjusted to attribute a higher satisfaction? METHODS: This study was conducted though experimental with hypothetical scenarios. A total of 303 patients who were treated by the same doctor from August 2021 to April 2022 voluntarily participated in this study. The patients were randomly divided into six groups: a control group (n = 52) and five experimental groups (n = 245). In the control group, the patients were asked their satisfaction degree regarding a communicated EWT (T0) and AWT (Ta) under a hypothetical situation. In the experimental groups, in addition to the same T0 and Ta as the control group, the patients were also asked about their satisfaction degree with the extended communicated EWT (T1). Patients in five experimental groups were given T1 values with 70, 80, 90, 100, and 110 min respectively. Patients in both control and experiment groups were asked to indicate their initial EWT, after given unfavorable information (UI) in a hypothetical situation, the experiment groups were asked to indicate their extended EWT. Each participant only participated in filling out one hypothetical scenario. 297 valid hypothetical scenarios were obtained from the 303 hypothetical scenarios given. RESULTS: The experimental groups had significant differences between the initial indicated EWT and extended indicated EWT under the effect of UI (20 [10, 30] vs. 30 [10, 50], Z = -4.086, P < 0.001). There was no significant difference in gender, age, education level and hospital visit history (χ2 = 3.198, P = 0.270; χ2 = 2.177, P = 0.903; χ2 = 3.988, P = 0.678; χ2 = 3.979, P = 0.264) in extended indicated EWT. As for patient's satisfaction, compared with the control group, significant differences were found when T1 = 80 min (χ2 = 13.511, P = 0.004), T1 = 90 min (χ2 = 12.207, P = 0.007) and T1 = 100 min (χ2 = 12.941, P = 0.005). When T1 = 90 min, which is equal to the Ta, 69.4% (34/49) of the patients felt "very satisfied", this proportion is not only significantly higher than that of the control group (34/ 49 vs. 19/52, χ2 = 10.916, P = 0.001), but also the highest among all groups. When T1 = 100 min (10 min longer than Ta), 62.5% (30/48) of the patients felt "very satisfied", it is significantly higher than that of the control group (30/ 48 vs. 19/52, χ2 = 6.732, P = 0.009). When T1 = 80 min (10 min shorter than Ta), 64.8% (35/54) of the patients felt "satisfied", it is significantly higher than that of the control group (35/ 54 vs. 17/52, χ2 = 10.938, P = 0.001). However, no significant difference was found when T1 = 70 min (χ2 = 7.747, P = 0.052) and T1 = 110 min (χ2 = 4.382, P = 0.223). CONCLUSIONS: Providing UI prompts can extend the EWT. When the extended EWT is closer to the AWT, the patient's satisfaction level can be improved higher. Therefore, medical institutions can adjust the EWT of patient's through UI release according to the AWT of hospitals to improve patient's satisfaction.

Novel Insights into the Contribution of Cyclic Electron Flow to Cotton Bracts in Response to High Light.

Cyclic electron flow around photosystem I (CEF-PSI) is shown to be an important protective mechanism to photosynthesis in cotton leaves. However, it is still unclear how CEF-PSI is regulated in non-foliar green photosynthetic tissues such as bracts. In order to learn more about the regulatory function of photoprotection in bracts, we investigated the CEF-PSI attributes in Yunnan 1 cotton genotypes (Gossypium bar-badense L.) between leaves and bracts. Our findings demonstrated that cotton bracts possessed PROTON GRADIENT REGULATION5 (PGR5)-mediated and the choroplastic NAD(P)H dehydrogenase (NDH)-mediated CEF-PSI by the same mechanism as leaves, albeit at a lower rate than in leaves. The ATP synthase activity of bracts was also lower, while the proton gradient across thylakoid membrane (ΔpH), rate of synthesis of zeaxanthin, and heat dissipation were higher than those of the leaves. These results imply that cotton leaves under high light conditions primarily depend on CEF to activate ATP synthase and optimize ATP/NADPH. In contrast, bracts mainly protect photosynthesis by establishing a ΔpH through CEF to stimulate the heat dissipation process.

Dark-Light Tandem Catalytic Oxidation of Formaldehyde over SrBi2Ta2O9 Nanosheets.

Formaldehyde (HCHO), as one of the main indoor toxic pollutions, presents a great threat to human health. Hence, it is imperative to efficiently remove HCHO and create a good indoor living environment for people. Herein, a layered perovskite material SrBi2Ta2O9 (SBT), was studied for the first time and exhibited superior photocatalytic efficiency and stability compared to commercial TiO2 (P25). Furthermore, a unique dark-light tandem catalytic mechanism was constructed. In the dark reaction stage, HCHO (Lewis base) site was adsorbed on the terminal (Bi2O2)2+ layer (Lewis acid) site of SBT in the form of Lewis acid-base complexation and was gradually oxidized to CO32- intermediate (HCHO → DOM (dioxymethylene) → HCOO- → CO32-). Then, in the light reaction stage, CO32- was completely converted into CO2 and H2O (CO32- → CO2). Our study contributes to a thorough comprehension of the photocatalytic oxidation of HCHO and points out its potential for day-night continuous work applications in a natural environment.

Synergistic Interplay of Dual-Active-Sites on Metallic Ni-MOFs Loaded with Pt for Thermal-Photocatalytic Conversion of Atmospheric CO2 under Infrared Light Irradiation.

Infrared light driven photocatalytic reduction of atmospheric CO2 is challenging due to the ultralow concentration of CO2 (0.04 %) and the low energy of infrared light. Herein, we develop a metallic nickel-based metal-organic framework loaded with Pt (Pt/Ni-MOF), which shows excellent activity for thermal-photocatalytic conversion of atmospheric CO2 with H2 even under infrared light irradiation. The open Ni sites are beneficial to capture and activate atmospheric CO2 , while the photogenerated electrons dominate H2 dissociation on the Pt sites. Simultaneously, thermal energy results in spilling of the dissociated H2 to Ni sites, where the adsorbed CO2 is thermally reduced to CO and CH4 . The synergistic interplay of dual-active-sites renders Pt/Ni-MOF a record efficiency of 9.57 % at 940 nm for converting atmospheric CO2 , enables the procurement of CO2 to be independent of the emission sources, and improves the energy efficiency for trace CO2 conversion by eliminating the capture media regeneration and molecular CO2 release.

Alkali-Induced In Situ Formation of Amorphous NixFe1-x(OH)2 from a Linear [M3(COO)6]-Based MOF Template for Overall Electrochemical Water Splitting.

Amorphous and bifunctional electrocatalysts based on 3d transition metals tend to exhibit better performance than their crystalline counterparts and are a promising choice for efficient overall water splitting yet far from being well explored. A 3,6-net metal-organic framework (MOF) of [Ni3(bpt)2(DMF)2(H2O)2]·1.5DMF (Ni-MOF), based on linear [Ni3(COO)6] as a node and [1,1'-biphenyl]-3,4',5-tricarboxylic acid (H3bpt) as a linker, was conveniently prepared via a hydrothermal reaction. Benefitting from the wide compatibility of the octahedral coordination geometry in Ni-MOF for different 3d metal ions, the molecular level and controllable metal doping facilitates the production of the desired Ni/Fe bimetallic MOF. A high-concentration alkali solution of 1 M KOH induced the in situ transformation of the MOF as a precursor to new amorphous electrocatalysts of [Ni(OH)2(H2O)0.6]·H2O [a-Ni(OH)2] and its metal-doped derivatives of a-Ni0.77Fe0.23(OH)2 and a-Ni0.65Fe0.35(OH)2. In particular, the costly organic ligand H3bpt was fully dissolved in the alkaline solution and can be recovered for cyclic utilization by subsequent acidification. The obtained amorphous hydroxide was deduced to be loose and defective layers containing both coordinated and lattice water based on combined characterizations of TG, IR, Raman, XPS, and sorption analysis. As opposed to the crystalline counterpart of Ni(OH)2 with stacked packing layers and an absent lattice water, the abundant catalytic active sites of the amorphous electrocatalyst endow good performance in both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The bifunctional a-Ni0.65Fe0.35(OH)2 coated on nickel foam realizes small overpotentials of 247 and 99 mV for OER and HER, respectively, under a current density of 10 mA cm-2, which can work with a cell voltage of merely 1.60 V for overall water splitting. This study provides an efficient strategy for widely screening and preparing new functional amorphous materials for electrocatalytic application.

Ssl3451 is Important for Accumulation of NDH-1 Assembly Intermediates in the Cytoplasm of Synechocystis sp. Strain PCC 6803.

Two mutants sensitive to high light for growth and impaired in NDH-1 activity were isolated from a transposon-tagged library of Synechocystis sp. strain PCC 6803. Both mutants were tagged in the ssl3451 gene encoding a hypothetical protein, which shares a significant homology with the Arabidopsis (Arabidopsis thaliana) CHLORORESPIRATORY REDUCTION 42 (CRR42). In Arabidopsis, CRR42 associates only with an NDH-1 hydrophilic arm assembly intermediate (NAI) of about 400 kDa (NAI400), one of total three NAIs (NAI800, NAI500 and NAI400), and its deletion has little, if any, effect on accumulation of any NAIs in the stroma. In comparison, the ssl3451 product was localized mainly in the cytoplasm and associates with two NAIs of about 300 kDa (NAI300) and 130 kDa (NAI130). Deletion of Ssl3451 reduced the abundance of the NAI300 complex to levels no longer visible on gels and of the NAI130 complex to a low level, thereby impeding the assembly process of NDH-1 hydrophilic arm. Further, Ssl3451 interacts with another assembly factor Ssl3829 and they have a similar effect on accumulation of NAIs and NdhI maturation factor Slr1097 in the cytoplasm. We thus propose that Ssl3451 plays an important role in accumulation of the NAI300 and NAI130 complexes in the cytoplasm via its interacting protein Ssl3829.

Color-Tuning and Near-Sunlight White Emission in Highly Stable Rod-Spacer MOFs with Defective Dicubane Based Lead(II)-Carboxyl Chains.

The active lone pair electron effect and highly flexible coordination geometry of Pb2+ prevented the rational construction of metal-organic frameworks (MOFs) but promoted excellent fluorescence tuning. The regulation on organic and alkali templates facilitated the assemblies of three new Pb-MOFs: [Pb2(pia)2(DMA)]·DMA (1), [Pb2(pia)2(DMF)]·1.5DMF (2), and [Pb2(pia)2(DMF)]·NEt3 (3). They were rigid rod-spacer and double-walls frameworks, which possess defective dicubane [Pb4O6] based metal-carboxyl chains constructed from both semidirected and holodirected Pb2+ ions. These MOFs exhibited thermal stability up to 370 °C and unprecedented chemical stability in H2O and acidic (pH 2) and alkaline (pH 12) aqueous solutions, found for the first time in Pb-MOFs. A single-phase and rare-earth-free white-emitting phosphor, 1, was screen out, which showed a near-sunlight and human-vision-friendly broadband spectrum covering the full visible region, possessing the close-to-pure-white chromaticity coordinates of (0.332, 0.347), a near-daylight color temperature of 5696 K, and a high color rendering index of 95. The replacement of DMF as apical ligand and guest in 2 resulted in an intrinsic single and narrow emission at 562 nm with yellow color. The convenient yellow-and-blue color-tuning until white for 2 was realized by either solution or solid blending with blue-emissive H2pia, benefited from their highly matched excitation spectra. Using large NEt3 as template guest induced great framework distortion for 3 and led to white emission with chromaticity coordinates of (0.302, 0.294), stemming from nonequivalent dual emission at 450 and 545 nm. In-depth structure analysis revealed intra-/interchain Pb···Pb interactions in the lead(II)-carboxyl chains greatly affected the photochemical output.

Improving outpatient satisfaction by extending expected waiting time.

BACKGROUND: Long waiting times result in low satisfaction. Although several methods are used to shorten the actual waiting time (AWT) in large hospitals of China, the outpatients still have a long actual waiting time. This study aimed to explore whether satisfaction could be improved by extending the expected waiting time (EWT) instead of shortening the AWT. METHODS: In October 2016, 257 students in grade one voluntarily participated in this study. They came from 6 classes, which were randomly divided into two groups: 3 classes comprised the control group (n = 125) and 3 classes comprised the experimental group (n = 132). Unfavorable information (UI) was given to the experimental group alone. Six distinct questionnaires were designed to explore the effects of UI on EWT and the effects of an extended EWT on satisfaction. Satisfaction scores ranged from 0 to 100: 0-25, very dissatisfied; 26-50, dissatisfied; 51-75, satisfied; 76-100, very satisfied. Each participant finished one of the 6 questionnaires online. Of the 257 questionnaires, 233 were valid. RESULTS: Before UI was given, the initial EWT (T0) was similar between the control and experimental groups (Z = -1.924, P = 0.054). Under the effects of UI, individuals in the experimental group extended their EWT (T1) from 121.0 to 180.0 min (Z = -6.367, P < 0.001). Females prolonged their EWT longer than males did (Z = -2.239, P = 0.025). Then, this study defined T0 = 1.5 h and T1 = 2.5 h, and compared the satisfaction scores between the control and experimental groups: a significant difference was found when AWT =2.0 h (t = - 3.568, P = 0.001), but not when AWT =3.0 h (t = - 0.718, P = 0.475) or when AWT =1.0 h (t = - 1.088, P = 0.280). When AWT =3.0 h, fewer individuals felt "very dissatisfied" in the experimental group (21.2%) than in the control group (44.7%) (χ2 = 4.368, P = 0.037). CONCLUSIONS: EWT was found to be extended greatly by UI. An extended EWT could improve satisfaction scores.

Improvement in the Photobiological Hydrogen Production of Aggregated Chlorella by Dimethyl Sulfoxide.

Photobiological hydrogen production plays a vital role in generating clean renewable energy owing to its low energy consumption and environmental friendliness. Although materials-induced Chlorella aggregates have been developed to achieve sustained photobiological hydrogen production under normal aerobic conditions, the yield is relatively low and equals only 0.42 % of the light-to-H2 energy-conversion efficiency. Herein, we report that only 0.5 vol % dimethyl sulfoxide in an aqueous environment significantly enhances the H2 yield produced by aggregated Chlorella, reaching 0.69 % of the light-to-H2 energy-conversion efficiency. This improvement can be attributed to an increase in the cellular respiration rate by dimethyl sulfoxide, which results in a decrease in the oxygen content inside the aggregates and, ultimately, to the activation of more hydrogenases. More generally, this strategy consists of a functional enhancement in organism-material hybrids by using small molecules.

Light Intensity is Important for Hydrogen Production in NaHSO3-Treated Chlamydomonas reinhardtii.

Chlamydomonas reinhardtii is a unicellular green alga that can use light energy to produce H2 from H2O in the background of NaHSO3 treatment. However, the role of light intensity in such H2 production remains elusive. Here, light intensity significantly affected the yield of H2 production in NaHSO3-treated C. reinhardtii, which was consistent with its effects on the content of O2 and the expression and activity of hydrogenase. Further, NaHSO3 was found to be able to remove O2 via a reaction of bisulfite with superoxide anion produced at the acceptor side of PSI, and light intensity affected the reaction rate significantly. Accordingly, high light and strong light but not low light can create an anaerobic environment, which is important to activate hydrogenase and produce H2. Based on the above results, we conclude that light intensity plays an important role in removing O2 and consequently activating hydrogenase and producing H2 in NaHSO3-treated C. reinhardtii.

NdhV Is a Subunit of NADPH Dehydrogenase Essential for Cyclic Electron Transport in Synechocystis sp. Strain PCC 6803.

Two mutants sensitive to heat stress for growth and impaired in NADPH dehydrogenase (NDH-1)-dependent cyclic electron transport around photosystem I (NDH-CET) were isolated from the cyanobacterium Synechocystis sp. strain PCC 6803 transformed with a transposon-bearing library. Both mutants had a tag in the same sll0272 gene, encoding a protein highly homologous to NdhV identified in Arabidopsis (Arabidopsis thaliana). Deletion of the sll0272 gene (ndhV) did not influence the assembly of NDH-1 complexes and the activities of CO2 uptake and respiration but reduced the activity of NDH-CET. NdhV interacted with NdhS, a ferredoxin-binding subunit of cyanobacterial NDH-1 complex. Deletion of NdhS completely abolished NdhV, but deletion of NdhV had no effect on the amount of NdhS. Reduction of NDH-CET activity was more significant in ΔndhS than in ΔndhV. We therefore propose that NdhV cooperates with NdhS to accept electrons from reduced ferredoxin.

A Cytoplasmic Protein Ssl3829 Is Important for NDH-1 Hydrophilic Arm Assembly in Synechocystis sp. Strain PCC 6803.

Despite significant progress in clarifying the subunit compositions and functions of the multiple NDH-1 complexes in cyanobacteria, the assembly factors and their roles in assembling these NDH-1 complexes remain elusive. Two mutants sensitive to high light for growth and impaired in NDH-1-dependent cyclic electron transport around photosystem I were isolated from Synechocystis sp. strain PCC 6803 transformed with a transposon-tagged library. Both mutants were tagged in the ssl3829 gene encoding an unknown protein, which shares significant similarity with Arabidopsis (Arabidopsis thaliana) CHLORORESPIRATORY REDUCTION7. The ssl3829 product was localized in the cytoplasm and associates with an NDH-1 hydrophilic arm assembly intermediate (NAI) of about 300 kD (NAI300) and an NdhI maturation factor, Slr1097. Upon deletion of Ssl3829, the NAI300 complex was no longer visible on gels, thereby impeding the assembly of the NDH-1 hydrophilic arm. The deletion also abolished Slr1097 and consequently reduced the amount of mature NdhI in the cytoplasm, which repressed the dynamic assembly process of the NDH-1 hydrophilic arm because mature NdhI was essential to stabilize all functional NAIs. Therefore, Ssl3829 plays an important role in the assembly of the NDH-1 hydrophilic arm by accumulating the NAI300 complex and Slr1097 protein in the cytoplasm.

The NDH-1L-PSI Supercomplex Is Important for Efficient Cyclic Electron Transport in Cyanobacteria.

Two mutants isolated from a tagging library of Synechocystis sp. strain PCC 6803 were sensitive to high light and had a tag in sll1471 encoding CpcG2, a linker protein for photosystem I (PSI)-specific antenna. Both mutants demonstrated strongly impaired NDH-1-dependent cyclic electron transport. Blue native-polyacrylamide gel electrophoresis followed by immunoblotting and mass spectrometry analyses of the wild type and a mutant containing CpcG2 fused with yellow fluorescent protein-histidine6 indicated the presence of a novel NDH-1L-CpcG2-PSI supercomplex, which was absent in the cpcG2 deletion mutant, the PSI-less mutant, and several other strains deficient in NDH-1L and/or NDH-1M. Coimmunoprecipitation and pull-down analyses on CpcG2-yellow fluorescent protein-histidine6, using antibody against green fluorescent protein and nickel column chromatography, confirmed the association of CpcG2 with the supercomplex. Conversely, the use of antibodies against NdhH or NdhK after blue native-polyacrylamide gel electrophoresis and in coimmunoprecipitation experiments verified the necessity of CpcG2 in stabilizing the supercomplex. Furthermore, deletion of CpcG2 destabilized NDH-1L as well as its degradation product NDH-1M and significantly decreased the number of functional PSI centers, consistent with the involvement of CpcG2 in NDH-1-dependent cyclic electron transport. The CpcG2 deletion, however, had no effect on respiration. Thus, we propose that the formation of an NDH-1L-CpcG2-PSI supercomplex in cyanobacteria facilitates PSI cyclic electron transport via NDH-1L.

Protection of Photosynthetic Algae against Ultraviolet Radiation by One-Step CeO2 Shellization.

Photosynthetic microalgae play an important role in solar-to-chemical energy conversion on Earth, but the increasing solar ultraviolet (UV) radiation seriously reduces the biological photosynthesis. Here, we developed a one-step approach to construct cell-in-shell hybrid structure by using direct adsorption of CeO2 nanoparticles onto cells. The engineered CeO2 nanoshell can efficiently protect the enclosed Chlorella cell due to its excellent UV filter property, which can also eliminate UV-induced oxidative stress. The experiments demonstrate that the resulted algae-CeO2 composites can guarantee their biological photosynthetic process and efficiency even under UV. This study follows a feasible strategy to protect living organisms by using functional nanomaterials to improve their biological functions.

Prevention of Cyanobacterial Blooms Using Nanosilica: A Biomineralization-Inspired Strategy.

Cyanobacterial blooms represent a significant threat to global water resources because blooming cyanobacteria deplete oxygen and release cyanotoxins, which cause the mass death of aquatic organisms. In nature, a large biomass volume of cyanobacteria is a precondition for a bloom, and the cyanobacteria buoyancy is a key parameter for inducing the dense accumulation of cells on the water surface. Therefore, blooms will likely be curtailed if buoyancy is inhibited. Inspired by diatoms with naturally generated silica shells, we found that silica nanoparticles can be spontaneously incorporated onto cyanobacteria in the presence of poly(diallyldimethylammonium chloride), a cationic polyelectrolyte that can simulate biosilicification proteins. The resulting cyanobacteria-SiO2 complexes can remain sedimentary in water. This strategy significantly inhibited the photoautotrophic growth of the cyanobacteria and decreased their biomass accumulation, which could effectively suppress harmful bloom events. Consequently, several of the adverse consequences of cyanobacteria blooms in water bodies, including oxygen consumption and microcystin release, were significantly alleviated. Based on the above results, we propose that the silica nanoparticle treatment has the potential for use as an efficient strategy for preventing cyanobacteria blooms.

Subunit Q Is Required to Stabilize the Large Complex of NADPH Dehydrogenase in Synechocystis sp. Strain PCC 6803.

Two major complexes of NADPH dehydrogenase (NDH-1) have been identified in cyanobacteria. A large complex (NDH-1L) contains NdhD1, NdhF1, and NdhP, which are absent in a medium size complex (NDH-1M). They play important roles in respiration, NDH-1-dependent cyclic electron transport around photosystem I, and CO2 uptake. Two mutants sensitive to high light for growth and impaired in cyclic electron transport around photosystem I were isolated from the cyanobacterium Synechocystis sp. strain PCC 6803 transformed with a transposon-bearing library. Both mutants had a tag in an open reading frame encoding a product highly homologous to NdhQ, a single-transmembrane small subunit of the NDH-1L complex, identified in Thermosynechococcus elongatus by proteomics strategy. Deletion of ndhQ disassembled about one-half of the NDH-1L to NDH-1M and consequently impaired respiration, but not CO2 uptake. During prolonged incubation of the thylakoid membrane with n-dodecyl-ß-D-maltoside at room temperature, the rest of the NDH-1L in ΔndhQ was disassembled completely to NDH-1M and was much faster than in the wild type. In the ndhP-deletion mutant (ΔndhP) background, absence of NdhQ almost completely disassembled the NDH-1L to NDH-1M, similar to the results observed in the ΔndhD1/ΔndhD2 mutant. We therefore conclude that both NdhQ and NdhP are essential to stabilize the NDH-1L complex.

Obstacles in the quantification of the cyclic electron flux around Photosystem I in leaves of C3 plants.

Sixty years ago Arnon and co-workers discovered photophosphorylation driven by a cyclic electron flux (CEF) around Photosystem I. Since then understanding the physiological roles and the regulation of CEF has progressed, mainly via genetic approaches. One basic problem remains, however: quantifying CEF in the absence of a net product. Quantification of CEF under physiological conditions is a crucial prerequisite for investigating the physiological roles of CEF. Here we summarize current progress in methods of CEF quantification in leaves and, in some cases, in isolated thylakoids, of C3 plants. Evidently, all present methods have their own shortcomings. We conclude that to quantify CEF in vivo, the best way currently is to measure the electron flux through PS I (ETR1) and that through PS II and PS I in series (ETR2) for the whole leaf tissue under identical conditions. The difference between ETR1 and ETR2 is an upper estimate of CEF, mainly consisting, in C3 plants, of a major PGR5-PGRL1-dependent CEF component and a minor chloroplast NDH-dependent component, where PGR5 stands for Proton Gradient Regulation 5 protein, PGRL1 for PGR5-like photosynthesis phenotype 1, and NDH for Chloroplast NADH dehydrogenase-like complex. These two CEF components can be separated by the use of antimycin A to inhibit the former (major) component. Membrane inlet mass spectrometry utilizing stable oxygen isotopes provides a reliable estimation of ETR2, whilst ETR1 can be estimated from a method based on the photochemical yield of PS I, Y(I). However, some issues for the recommended method remain unresolved.

NdhO, a subunit of NADPH dehydrogenase, destabilizes medium size complex of the enzyme in Synechocystis sp. strain PCC 6803.

Two mutants that grew faster than the wild-type (WT) strain under high light conditions were isolated from Synechocystis sp. strain PCC 6803 transformed with a transposon-bearing library. Both mutants had a tag in ssl1690 encoding NdhO. Deletion of ndhO increased the activity of NADPH dehydrogenase (NDH-1)-dependent cyclic electron transport around photosystem I (NDH-CET), while overexpression decreased the activity. Although deletion and overexpression of ndhO did not have significant effects on the amount of other subunits such as NdhH, NdhI, NdhK, and NdhM in the cells, the amount of these subunits in the medium size NDH-1 (NDH-1M) complex was higher in the ndhO-deletion mutant and much lower in the overexpression strain than in the WT. NdhO strongly interacts with NdhI and NdhK but not with other subunits. NdhI interacts with NdhK and the interaction was blocked by NdhO. The blocking may destabilize the NDH-1M complex and repress the NDH-CET activity. When cells were transferred from growth light to high light, the amounts of NdhI and NdhK increased without significant change in the amount of NdhO, thus decreasing the relative amount of NdhO. This might have decreased the blocking, thereby stabilizing the NDH-1M complex and increasing the NDH-CET activity under high light conditions.