State transitions and light adaptation require chloroplast thylakoid protein kinase STN7

Photosynthetic organisms are able to adjust to changing light conditions through state transitions, a process that involves the redistribution of light excitation energy between photosystem II (PSII) and photosystem I (PSI). Balancing of the light absorption capacity of these two photosystems is achieved through the reversible association of the major antenna complex (LHCII) between PSII and PSI (ref. 3). Excess stimulation of PSII relative to PSI leads to the reduction of the plastoquinone pool and the activation of a kinase; the phosphorylation of LHCII; and the displacement of LHCII from PSII to PSI (state 2). Oxidation of the plastoquinone pool by excess stimulation of PSI reverses this process (state 1). The Chlamydomonas thylakoid-associated Ser-Thr kinase Stt7, which is required for state transitions, has an orthologue named STN7 in Arabidopsis. Here we show that loss of STN7 blocks state transitions and LHCII phosphorylation. In stn7 mutant plants the plastoquinone pool is more reduced and growth is impaired under changing light conditions, indicating that STN7, and probably state transitions, have an important role in response to environmental changes.     

The PSI-H subunit of photosystem I is essential for state transitions in plant photosynthesis

Photosynthesis in plants involves two photosystems responsible for converting light energy into redox processes. The photosystems, PSI and PSII, operate largely in series, and therefore their excitation must be balanced in order to optimize photosynthetic performance. When plants are exposed to illumination favouring either PSII or PSI they can redistribute excitation towards the light-limited photosystem. Long-term changes in illumination lead to changes in photosystem stoichiometry. In contrast, state transition is a dynamic mechanism that enables plants to respond rapidly to changes in illumination. When PSII is favoured (state 2), the redox conditions in the thylakoids change and result in activation of a protein kinase. The kinase phosphorylates the main light-harvesting complex (LHCII) and the mobile antenna complex is detached from PSII. It has not been clear if attachment of LHCII to PSI in state 2 is important in state transitions. Here we show that in the absence of a specific PSI subunit, PSI-H, LHCII cannot transfer energy to PSI, and state transitions are impaired.     

Changes in the transthylakoid proton gradient are caused by the movement of phycobilisomes in the cyanobacterium <Emphasis Type="Italic">Synechocystis</Emphasis> sp. strain PCC 6803

Phycobilisomes (PBSs) are the main accessory light-harvesting complexes in cyanobacteria and their movement between photosystems (PSs) affects cyclic and respiratory electron transport. However, it remains unclear whether the movement of PBSs between PSs also affects the transthylakoid proton gradient (ΔpH). We investigated the effect of PBS movement on ΔpH levels in a unicellular cyanobacterium Synechocystis sp. strain PCC 6803, using glycinebetaine to immobilize and couple PBSs to photosystem II (PSII) or photosystem I (PSI) by applying under far-red or green light, respectively. The immobilization of PBSs at PSII inhibited decreases in ΔpH, as reflected by the slow phase of millisecond-delayed light emission (ms-DLE) that occurs during the movement of PBSs from PSII to PSI. By contrast, the immobilization of PBSs at PSI inhibited the increase in ΔpH that occurs when PBSs move from PSI to PSII. Comparison of the changes in ΔpH and electron transport caused by the movement of PBSs between PSs indicated that the changes in ΔpH were most likely caused by respiratory electron transport. This will further improve our understanding of the physiological role of PBS movement in cyanobacteria.     

Effects of temperature on the expression of STN7 and phosphorylation of LHCII proteins in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

In Arabidopsis thaliana, STN7 kinase is required for phosphorylation of LHCII and for state transitions. In this paper, a hydrophilic polypeptide, derived from the amino acid sequence of STN7, was conjugated to a carrier protein, bovine serum albumin （BSA）, to obtain the polyclonal antibody. Immunogenicity and specificity of the polyclonal antibody were evaluated by agar gel immunodiffusion （AGID） test and Western blot analysis. The results show that besides the phosphorylation of LHCII proteins, also the expression of STN7 was regulated by temperature conditions. In addition, the change tendency of LHCII proteins phosphorylation was not only coherent with expression of STN7 with respect to increasing temperature, but also closely related to state transitions. These results would provide useful information for studying regulatory mechanism of LHCII proteins phosphorylation and expression of STN7.     

New mechanism revealed for light-state transition in cyanobacterium Arthrospira platensis according to 77-K fluorescence kinetics

The mechanisms of oxygen evolution and carbon fixation in oxygenic organisms depend on the equal distribution of excitation energy to photosystems Ⅰ and Ⅱ, which is regulated by a mechanism referred to as light-state transition. In this work, a novel mechanism, energy spillover from PS Ⅰ to PS Ⅱ referred to as "inverse spillover", was revealed besides "mobile phycobilisome (PBS)" and the "spillover" of energy from PS Ⅱ to PS Ⅰ in cyanobacteria. Under continuous illumination with blue light, time-dependent 77-K fluorescence spectra demonstrated heterogeneous kinetics for the PBS and photosystem components, indicating that inverse spillover and mobile PBS work successively to regulate the excitation to a balanced distribution in cyanobacterial cells under blue light. Inverse spillover and mobile PBS occur under both 100 and 300 μmol m-2 s-1 blue-light conditions but they are accelerated under the latter.     

Mutagenesis of Ser24 of Cytochrome b559 α Subunit Affects PSII Acitivies in Chlamydomonas reinhardtii

In order to study the functions of cytochrome b559 (Cyt b559) in photosystem two (PSII) activity, mutant S24F of Chlamydomonas reinhardtii was constructed using site directed mutagenesis, in which Serine24 (Ser24) locating downstream of Histidine23 (His23) in α subunit of Cyt b559 was replaced by Phenylalanine (Phe). Physiological and biochemical analysis showed that mutant S24F could be grown photoautotrophically or photoheterotrophically. However, their growth rate was slower either on HSM or TAP medium than that of the control; Analysis of PSII activity revealed that its oxygen evolution was about 71% of wild type (WT); The Photochemical efficiency of PSII (Fv/Fm) of S24F was reduced 0.23 compared with WT; S24F was more sensitive to strong light irradiance than the wild type; Furthermore, SDS-PAGE and Western-blotting analysis indicated that the expression levels of α subunit of Cyt b559, LHCII and PsbO of S24F were a little less than those of the wild type. Overall, these data suggests that Ser24 plays a significant role in making Cyt b559 structure maintain PSII complex activity of oxygen evolution although it is not directly bound to heme group.     

Excitation energy distribution between two photosystems inPorphyra yezoensis and its significance in photosynthesis evolution

Comparative investigation on energy distribution between two photosystems were carried out in the sporo- phytes and gametophytes of Porphyra yezoensis. By perfor- ming 77 K fluorescence spectra, we suggested that there probably existed a pathway for energy transfer from PSⅡ to PSⅠ to redistribute the absorbed energy in gametophytes, while no such a way or at minor level in sporophytes. Electron transfer inhibitor DCMU blocked the energy transfer from PSⅡ to PSⅠ in gametophytes, but no obvious effects on sporophytes. These indicated that excitation energy distribution between two photosystems in gametophytes was more cooperative than that in sporophytes. These data in ontogenesis reflected the evolution process of photosynthetic organisms and supported the hypothesis of independent evolution of each photosystem.     

A pigment-binding protein essential for regulation of photosynthetic light harvesting

Photosynthetic light harvesting in plants is regulated in response to changes in incident light intensity. Absorption of light that exceeds a plant's capacity for fixation of CO2 results in thermal dissipation of excitation energy in the pigment antenna of photosystem II by a poorly understood mechanism. This regulatory process, termed nonphotochemical quenching, maintains the balance between dissipation and utilization of light energy to minimize generation of oxidizing molecules, thereby protecting the plant against photo-oxidative damage. To identify specific proteins that are involved in nonphotochemical quenching, we have isolated mutants of Arabidopsis thaliana that cannot dissipate excess absorbed light energy. Here we show that the gene encoding PsbS, an intrinsic chlorophyll-binding protein of photosystem II, is necessary for nonphotochemical quenching but not for efficient light harvesting and photosynthesis. These results indicate that PsbS may be the site for nonphotochemical quenching, a finding that has implications for the functional evolution of pigment-binding proteins.     

光声光谱技术在光合作用研究中的应用

当光照射密闭容器里的样品时,容器内能产生声波,这一现象称为光声效应,光声光谱是基于光声效应的一种光谱技术。由于光声光谱技术本身的特点,光合作用研究领域越来越多地应用该技术研究光合作用的机理,比如：光谱扫描、光声能量储存的性质、环式电子传递、状态转变与爱默生效应、光反应中心的原初光化学过程、光声瞬态研究、环境胁迫等。光声光谱技术在光合作用研究中的应用,开拓了视野,丰富了对光合作用机理的认识。     

Hydrogen ions directly regulating the oligomerization state of Photosystem I in intact <Emphasis Type="Italic">Spirulina platensis</Emphasis> cells

H^＋ concentration induced-monomerization or trimerization of photosystem Ⅰ （PSI） in cyanobacteria has never been directly observed. In this work, taking characteristic spectra for the trimers and monomers as the indicators, it was experimentally demonstrated that H^＋ could induce the oligomeric changes of PSI reaction centers in the intact Spirulina platensis cells and also in the isolated thylakoid membrane complexes. Especially, the higher concentration of H^＋ would induce the monomerization while the lower the trimerization, suggesting the electrostatic interaction should be mainly responsible for changes in the oligomeric state of PSI in Spirulina platensis.     

Photosystem II core phosphorylation and photosynthetic acclimation require two different protein kinases

Illumination changes elicit modifications of thylakoid proteins and reorganization of the photosynthetic machinery. This involves, in the short term, phosphorylation of photosystem II (PSII) and light-harvesting (LHCII) proteins. PSII phosphorylation is thought to be relevant for PSII turnover, whereas LHCII phosphorylation is associated with the relocation of LHCII and the redistribution of excitation energy (state transitions) between photosystems. In the long term, imbalances in energy distribution between photosystems are counteracted by adjusting photosystem stoichiometry. In the green alga Chlamydomonas and the plant Arabidopsis, state transitions require the orthologous protein kinases STT7 and STN7, respectively. Here we show that in Arabidopsis a second protein kinase, STN8, is required for the quantitative phosphorylation of PSII core proteins. However, PSII activity under high-intensity light is affected only slightly in stn8 mutants, and D1 turnover is indistinguishable from the wild type, implying that reversible protein phosphorylation is not essential for PSII repair. Acclimation to changes in light quality is defective in stn7 but not in stn8 mutants, indicating that short-term and long-term photosynthetic adaptations are coupled. Therefore the phosphorylation of LHCII, or of an unknown substrate of STN7, is also crucial for the control of photosynthetic gene expression.     

Compression behavior and equation of state of Ni77P23 amorphous alloy

The compression behavior of Ni77P23 amorphous alloy is investigated at room temperature in a diamond-anvil cell instrument using insitu high pressure energy dispersive X-ray diffraction with a syn- chrotron radiation source. The equation of state is determined by fitting the experimental data accord- ing to Birch-Murnaghan equation: -ΔV/V0=0.08606P-3.2×10-4P2 5.7×10-6P3. It is found that the structure of Ni77P23 amorphous alloy is stable under pressures up to 30.5 GPa.     

A giant chlorophyll-protein complex induced by iron deficiency in cyanobacteria

Cyanobacteria are abundant throughout most of the world's water bodies and contribute significantly to global primary productivity through oxygenic photosynthesis. This reaction is catalysed by two membrane-bound protein complexes, photosystem I (PSI) and photosystem II (PSII), which both contain chlorophyll-binding subunits functioning as an internal antenna. In addition, phycobilisomes act as peripheral antenna systems, but no additional light-harvesting systems have been found under normal growth conditions. Iron deficiency, which is often the limiting factor for cyanobacterial growth in aquatic ecosystems, leads to the induction of additional proteins such as IsiA (ref. 3). Although IsiA has been implicated in chlorophyll storage, energy absorption and protection against excessive light, its precise molecular function and association to other proteins is unknown. Here we report the purification of a specific PSI-IsiA supercomplex, which is abundant under conditions of iron limitation. Electron microscopy shows that this supercomplex consists of trimeric PSI surrounded by a closed ring of 18 IsiA proteins binding around 180 chlorophyll molecules. We provide a structural characterization of an additional chlorophyll-containing, membrane-integral antenna in a cyanobacterial photosystem.     

Direct electrochemistry and electrocatalysis of horseradish peroxidase in MnO2 nanosheet film

A novel material MnO2 nanosheet has been used as the support matrix for the immobilization of horseradish peroxidase （HRP）. HRP entrapped in MnO2 nanosheet film exhibits facile direct electron transfer with the electron transfer rate constant of 6.86 s^-1. The HRP/MnO2 nanosheet film gives a reversible redox couple with the apparent formal peak potential （E^0＇） of -0.315 V （vs. Ag/AgCl） in pH 6.5 phosphate buffer solution （PBS）. The formal potential E^0＇ of HRP shifts linearly with pH with a slope of -53.75 mV.pH^-1, denoting that an electron transfer accompanies single-proton transportation. The immobilized HRP shows an electrocatslytic activity to the reduction of H2O2. The response time of the biosensor for H2O2 is less than 3 s, and the detection limit is 0.21 μmol · L^-1 based on signal/noise = 3.     

An <Emphasis Type="Italic">Arabidopsis ctpA</Emphasis> homologue is involved in the repair of photosystem II under high light

A T-DNA insertion mutant AtctpA1 was identified to study the physiological roles of a carboxyl-terminal processing protease （CtpA） homologue in Arabidopsis. Under normal growth conditions, disruption of AtctpA1 did not result in any apparent alterations in growth rate and thylakoid membrane protein components. However the mutant plants exhibited increased sensitivity to high irradiance. Degradation of PSII reaction center protein D1 was accelerated in the mutant during photoinhibition. These results demostrated that AtctpA1 was required for efficient repair of PSII in Arabidopsis under high irradiance.     

Inductive transfer learning for unlabeled target-domain via hybrid regularization

Recent years have witnessed an increasing interest in transfer learning. This paper deals with the classification problem that the target-domain with a different distribution from the source-domain is totally unlabeled, and aims to build an inductive model for unseen data. Firstly, we analyze the problem of class ratio drift in the previous work of transductive transfer learning, and propose to use a normalization method to move towards the desired class ratio. Furthermore, we develop a hybrid regularization framework for inductive transfer learning. It considers three factors, including the distribution geometry of the target-domain by manifold regularization, the entropy value of prediction probability by entropy regularization, and the class prior by expectation regularization. This framework is used to adapt the inductive model learnt from the source-domain to the target-domain. Finally, the experiments on the real-world text data show the effectiveness of our inductive method of transfer learning. Meanwhile, it can handle unseen test points.     

Comparison between P25 and anatase-based TiO<Subscript>2</Subscript> quasi-solid state dye sensitized solar cells

Pure anatase TiO2 films have been made via hydration of titanium isopropoxide using a sol-gel tech-nique, while mixed TiO2 films which contained both anatase and rutile TiO2 were made from commercial P25 powder. Quasi-solid state dye-sensitized solar cells were fabricated with these two kinds of mesoporous films and a comparison study was carried out. The result showed that the open-circuit photovoltages （Voc） for both kinds of cells were essentially the same, whereas the short-circuit photo-currents （1sc） of the anatase-based cells were about 33% higher than that of the P25-based cells. The highest photocurrent intensity of the anatase-based cell was 6.12 mA/cm^2 and that of the P25-based cell was 4.60 mA/cm^2. Under an illumination with the light intensity of 30 mW/cm^2, the corresponding energy conversion efficiency was measured to be 7.07% and 6.89% for anatase-based cells and P25-based cells, respectively.     

The role of β18-β19 loop structure in insecticidal activity of Cry1Ac toxin from Bacillus thuringiensis

The β18-β19 loop in domain Ⅲ of Cry1Ac toxin is unique among Bacillus thuringlensis Cry proteins. In this study, the role of the loop structure in insecticidal activity of Cry1Ac toxin was investigated. Alanine scanning mutations within the loop were initially generated and most mutants were over-expressed and reduced toxicity at different degrees, except mutant N546A that showed almost 2 times enhanced toxicity against Helicoverpa armigera larvae. Further mutagenic analysis of N546 revealed that a charged amino acid in this position would cause very unfavorable influence on insecticidal activity. In addition, the deletion of N546 led to protein instability because of destruction of the loop integrity. Besides, mutant W544F was much more toxic than W544Y, indicating that hydrophobic nature of the position was important for maintaining the stability and activity of Cry1Ac protein. These findings are the first biological evidence for a structural function of β18-β19 loop in insecticidal activity of the Cry1Ac toxin.     

Crystal structures of catalytic and regulatory subunits of rat protein kinase CK2

Protein kinase CK2 consists of two catalytic subunits (CK2α) and two regulatory subunits (CK2β). Here, we report the crystal structures of rat CK2α mutant (rCK2α-△C, 1—335) and CK2β (rCK2β). The overall topology of rCK2α-△C and rCK2β are very similar to the human enzyme, although large structural differences could be observed in the N-terminal domain of rCK2α-△C. Our reported structure of rCK2α-△C is in the close conformation state while the counterpart hCK2α is in the open conformation state, indi- cating ...