A synthetic model of the Mn₃Ca subsite of the oxygen-evolving complex in photosystem II

Within photosynthetic organisms, the oxygen-evolving complex (OEC) of photosystem II generates dioxygen from water using a catalytic Mn(4)CaO(n) cluster (n varies with the mechanism and nature of the intermediate). We report here the rational synthesis of a [Mn(3)CaO(4)](6+) cubane that structurally models the trimanganese-calcium-cubane subsite of the OEC. Structural and electrochemical comparison between Mn(3)CaO(4) and a related Mn(4)O(4) cubane alongside characterization of an intermediate calcium-manganese multinuclear complex reveals potential roles of calcium in facilitating high oxidation states at manganese and in the assembly of the biological cluster.     

Where water is oxidized to dioxygen: structure of the photosynthetic Mn4Ca cluster

The oxidation of water to dioxygen is catalyzed within photosystem II (PSII) by a Mn(4)Ca cluster, the structure of which remains elusive. Polarized extended x-ray absorption fine structure (EXAFS) measurements on PSII single crystals constrain the Mn(4)Ca cluster geometry to a set of three similar high-resolution structures. Combining polarized EXAFS and x-ray diffraction data, the cluster was placed within PSII, taking into account the overall trend of the electron density of the metal site and the putative ligands. The structure of the cluster from the present study is unlike either the 3.0 or 3.5 angstrom-resolution x-ray structures or other previously proposed models.     

B型烟粉虱危害对烟草叶片光系统II的影响

【目的】研究B型烟粉虱取食危害对烟草光系统II的影响,为明确烟粉虱对寄主植物光合作用的影响机制提供依据。【方法】通过测定烟草叶片叶绿素荧光快速诱导曲线,使用JIP-test分析技术进行参数分析,研究B型烟粉虱危害烟草后对烟草的局部虫体叶和系统叶光系统II（PSII）的影响。【结果】B型烟粉虱危害烟草后虫体叶和系统叶上的最大光化学效率（φpo）和光化学性能指数（PIABS）与对照相比均明显升高（P＜0.05）,表明处理烟草植株的局部叶和系统叶的原初光化学反应受到较大的伤害。B型烟粉虱危害烟草后虫体叶和系统叶PSII反应中心的电子传递均受阻,放氧复合体受到严重破坏。B型烟粉虱危害烟草后系统叶的单位反应中心吸收的能量（ABS/RC）和单位反应中心热耗散掉的能量（DIo/RC）增加,单位反应中心捕获的能量（TRo/RC）下降;B型烟粉虱危害的虫体叶中ABC/RC没有变化,DIo/RC增加,TRo/RC 下降。B型烟粉虱危害烟草后虫体叶和系统叶的单位面积反应中心数量（RC/CS）均明显降低（P＜0.05）,而光系统PSⅡ反应中心的关闭程度（1-qP）却明显升高,分别较各自对照升高了69.83%和142.58%（P＜0.05）。【结论】B型烟粉虱的危害严重影响了烟草叶片的光系统Ⅱ（PSII）,主要是由于PSII反应中心的失活和关闭以及对PSII电子传递的抑制,电子传递中受抑制的位点包括放氧复合体和QA到QB间的电子传递过程,同时B型烟粉虱危害影响了烟草叶片光系统的能量流动,且烟粉虱对烟草叶片PSII的影响具有系统传导性。     

外源CaCl2预处理对高温胁迫烟草叶片光合作用的影响

 【目的】研究喷施不同浓度CaCl2对高温胁迫下烟草叶片光合荧光特性及活性氧清除酶系统的影响,探讨外源Ca2+对高温胁迫下烟草叶片光合作用的保护机制。【方法】以烟草品种K326为材料,喷施0、10、20、30 mmol?L-1CaC12,43℃高温处理2 h,测定处理前后及恢复1 d 后烟草叶片光合速率、叶绿素荧光诱导动力学曲线、丙二醛(MDA)含量、过氧化氢(H2O2)含量和抗氧化酶活性等生理指标。【结果】高温胁迫下,CaCl2处理缓解了净光合速率(Pn)和PSII最大光化学效率(Fv/Fm)的降低程度。施钙显著缓解了PSII反应中心电子传递受阻程度和放氧复合体受破坏的程度,使PSII维持较高的活性。施钙明显激活了高温胁迫下烟草叶片超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)和抗坏血酸过氧化物酶(APX)的活性,减少了H2O2的积累;膜脂过氧化产物MDA含量显著降低。以喷施20 mmol?L-1 CaCl2时,烟草叶片的抗氧化酶活性较高,光合活性最高。【结论】施钙增强了烟草叶片抗氧化酶活性,H2O2的积累降低,从而减轻了高温胁迫对烟草叶片PSII反应中心和放氧复合体(OEC)的破坏,提高了烟草叶片的耐热性。     

木霉对盐胁迫下枸杞根与叶内离子平衡和光系统II的影响

【目的】 研究木霉对枸杞（Lycium chinense）耐盐能力的影响,从离子平衡、氧化胁迫和光系统II（PSII）性能等方面揭示耐盐机理。【方法】 以枸杞为试验材料,施加木霉菌剂于根周围,浇灌NaCl溶液（300 mmol·L^-1）进行盐处理,比较盐胁迫下施加和未施加菌剂植株生物量、K⁺/Na⁺、根系钾钠离子吸收转运、叶片氧化损伤以及PSII性能的差异。【结果】 盐胁迫下,施加菌剂的植株生物量降幅较小,说明木霉能够提高枸杞耐盐能力,减少对生长的抑制。木霉缓解盐诱导的光合速率与PSII光化学效率的下降,抑制PSII激发压上升,有利于防御PSII光抑制。盐胁迫下施加菌剂的植株PSII最大光化学效率的降幅和PSII反应中心蛋白损失相对较少,证实了木霉缓解PSII光抑制,保护了PSII反应中心。与光抑制结果一致,盐胁迫下施加菌剂植株叶片膜脂过氧化程度和H₂O₂含量较低,氧化损伤较轻。盐胁迫下,施加菌剂植株光合电子传递到Q_A以下电子受体效率的降幅较小,叶绿素快速荧光诱导动力学（OJIP）曲线的J点也未明显上升,表明木霉保护了PSII受体侧电子传递体。木霉对PSII供体侧放氧复合体也起到保护作用,因为施加菌剂抑制了盐胁迫下K点相对可变荧光的显著上升以及避免了OJIP曲线中K点的出现。因此,木霉对PSII各组分都起到了保护作用,缓解了盐胁迫下PSII性能指数的下降,提高了PSII整体稳定性。盐胁迫下,施加菌剂的植株根和叶Na⁺含量较低,但K⁺含量较高,说明木霉通过减少根和叶中Na⁺积累及K⁺损失,缓解K⁺/Na⁺下降,维持离子平衡。木霉增强盐胁迫下根系Na⁺外排,保障根系K⁺吸收和向地上部转运,是维护枸杞离子平衡的关键机制。【结论】 木霉调控盐胁迫下根系钠钾离子吸收转运,维持离子平衡,减轻PSII氧化胁迫,增强枸杞耐盐能力,缓解对其生长的抑制。     

X-ray Detection of the Period-Four Cycling of the Manganese Cluster in Photosynthetic Water Oxidizing Enzyme

X-ray absorption near-edge structure spectra of the manganese (Mn) cluster in physiologically native intermediate states of photosynthetic water oxidation induced by short laser flash were measured with a compact heat-insulated chamber equipped with an x-ray detector near the sample surface. The half-height energy of the Mn Kedge showed a period-four oscillation dependent on cycling of the Joliot-Kok's oxygen clock. The flash number-dependent shift in the Mn K-edge suggests that the Mn cluster is oxidized by one electron upon the S(0)-to-S(1), S(1)-to-S(2), and S(2)-to-S(3) transitions and then reduced upon the S(3)-to-S(0) transition that releases molecular oxygen.     

Structural basis for allosteric regulation of GPCRs by sodium ions

Pharmacological responses of G protein-coupled receptors (GPCRs) can be fine-tuned by allosteric modulators. Structural studies of such effects have been limited due to the medium resolution of GPCR structures. We reengineered the human A(2A) adenosine receptor by replacing its third intracellular loop with apocytochrome b(562)RIL and solved the structure at 1.8 angstrom resolution. The high-resolution structure allowed us to identify 57 ordered water molecules inside the receptor comprising three major clusters. The central cluster harbors a putative sodium ion bound to the highly conserved aspartate residue Asp(2.50). Additionally, two cholesterols stabilize the conformation of helix VI, and one of 23 ordered lipids intercalates inside the ligand-binding pocket. These high-resolution details shed light on the potential role of structured water molecules, sodium ions, and lipids/cholesterol in GPCR stabilization and function.     

Functional analysis of cold-inducible cDNA clones in the legume Ammopiptanthus mongolicus

Functional analysis of cold-inducible cDNA clones in the legume Ammopiptanthus mongolicus     

在干旱胁迫下有性四倍体木薯叶片的蛋白质组学研究

为了研究木薯(Manihot esculenta Crantz)有性四倍体的抗旱性,笔者以木薯有性四倍体为供试材料,其母本华南5号(SC5)为对照材料,通过比较在干旱胁迫下木薯的叶片形态和叶片中丙二醛含量、游离脯氨酸含量、超氧化物歧化酶活性等生理生化指标,发现有性四倍体较SC5具有更强的抗旱性.对供试木薯材料进行干旱处...     

Photosynthetic Characteristics of a Super High Yield Cultivar of Winter Wheat During Late Growth Period

The mechanism of high yield of winter wheat in the field at late growth period was investigated by measuring the photosynthetic characteristics of photosystem Ⅱ （PSⅡ） and xanthophylls cycle, which could provide physiological reference for breeding. Weimai 8 （W8）, a super high yield cultivar, and Lumai 14 （L14）, a control cultivar were object. The photosynthetic rate （Pn）, parameters of chlorophyll fluorescence and chlorophyll content were measured. The Pn, maximum photochemical efficiency of PSII （Fv/Fm）, quantum yield of PSII electron transport （ΦPSⅡ）, efficiency of excitation energy capture by open PSII reaction centers （Fv＇/Fm＇）, and photochemical quenching coefficient （qP） were higher in Weimai 8 compared to that in Lumai 14, a commercial high yield cultivar. Furthermore, Weirnai 8 showed a lower non- photochemical quenching coefficient and a lower de-epoxidized ratio of the xanthophyll cycle pigments than of Lumai 14 at late growth period. At mature stage, chlorophyll content of different leaves decreased both in Weimai 8 and Lumai 14. Chlorophyll content in flag, second and third leaf from the top of plant decreased more in Lumai 14 than in Weimai 8. These results suggested that Weimai 8 had more antenna pigments to absorb light energy, and had higher photosynthetic capability and photochemical efficiency of PSⅡ. The yield of Weimai 8 was also higher than that of Lumai 14.     

Increased grain yield with improved photosynthetic characters in modern maize parental lines

The grain yield of maize has increased continuously in past decades, largely through hybrid innovation, cultivation technology, and in particular, recent genetic improvements in photosynthesis. Elite inbred lines are crucial for innovating new germplasm. Here, we analyzed variations in grain yield and a series of eco-physiological photosynthetic traits after anthesis in sixteen parental lines of maize(Zea mays L.) released during three different eras(1960s, 1980 s, 2000s). We found that grain yield and biomass significantly increased in the 2000 s than those in the 1980 s and 1960 s. Leaf area, chlorophyll, and soluble protein content slowly decreased, and maintained a higher net photosynthesis rate(Pn) and improved stomatal conductance(Gs) after anthesis in the 2000 s. In addition, the parental lines in the 2000 s obtained higher actual photochemistry efficiency(ФPSII) and the maximum PSII photochemistry efficiency(Fv/Fm), which largely improved light partitioning and chlorophyll fluorescence characteristic, including higher photochemical and photosystem II(PSII) reaction center activity, lower thermal energy dissipation in antenna proteins. Meanwhile, more lamellae per granum within chloroplasts were observed in the parental lines of the 2000 s, with a clear and complete chloroplast membrane, which will greatly help to improve photosynthetic capacity and energy efficiency of ear leaf in maize parental lines. It is concluded that grain yield increase in modern maize parental lines is mainly attributed to the improved chloroplast structure and more light energy catched for the photochemical reaction, thus having a better stay-green characteristic and stronger photosynthetic capacity after anthesis. Our direct physiological evaluation of these inbred lines provides important information for the further development of promising maize cultivars.     

秦川牛抽样遗传检测报告

在陕西省关中平原,用系统随机整群抽样方法以3个系统9个地域群(共224头)的6个血液蛋白、6个毛色位点的基因频率、7种外形特征的表型频率,检测了产区1988年秦川牛群体(共642913头)的遗传结构。肯定了秦川牛具有中国黄牛的典型特征。列表详示了各频率值及其估计可靠性、精确度的参数。     

干旱和盐胁迫对白榆叶片光系统Ⅱ活力的影响

通过PEG-6000和NaCl模拟试验研究了干旱和盐胁迫对白榆幼苗叶片光系统Ⅱ (PSII)活力的影响,结果显示:盐分和干旱胁迫诱导白榆叶片PSII快速荧光上升曲线在300 μs处K点的出现,造成放氧复合体OEC的损伤,同时也引起PSII有活力反应中心密度(Rc/Cso)、最大量子产量(Fv/Fm)、分配进入电子传递链...     

Improvement in winter wheat productivity through regulating PSⅡ photochemistry,photosynthesis and chlorophyll fluorescence under deficit irrigation conditions

Deficit irrigation is critical to global food production, particularly in arid and semi-arid regions with low precipitation. Given water shortage has threatened agricultural sustainability under the dry-land farming system in China, there is an urgent need to develop effective water-saving technologies. We carried out a field study under two cultivation techniques:(1) the ridge and furrow cultivation model(R); and(2) the conventional flat farming model(F), and three simulated precipitation level...     

土壤干旱对真桦和白桦叶片光化学效率的影响

应用叶绿素荧光技术,研究了土壤水分受限对真桦和白桦叶片光反应系统II的光化学效率影响。结果表明:土壤水分受限条件下,桦树叶片光化学效率存在域值反应,重度土壤干旱(土壤含水量13.1%～15.0%)时,两种桦树叶片实际光化学效率(ΦPSII)和表观电子传递速率(ETR)均显著降低,而轻度和中度土壤干旱时,ΦPSII和ETR与对照值差异不显著;重度土壤干旱条件下,两种桦树叶片最大光化学效率(Fv/Fm)和初始荧光(Fo)较对照没有显著差异,说明3周的土壤水分胁迫未对叶片光合机构造成实质性的损伤。土壤干旱影响叶片光化学诱导过程,且两树种间差异显著:重度干旱第3周时,真桦ΦPSII快相诱导速率由0.118 0降低到0.071 5,诱导平衡值(0.46)较对照(0.60)低;而白桦叶片ΦPSII快相诱导速率则由0.093升高到0.117,胁迫叶片和对照叶片光诱导稳定值也较接近。两种桦树叶片ΦPSII光诱导差异主要与非光化学淬灭(qN)诱导过程密切相关。     

西南乌江流域石灰岩风化过程中锰和磷的迁移富集

如何提高石灰土中锰和磷矿质养分的植物利用效率,已成为喀斯特地区面临的重要问题。选取乌江流域9条石灰岩风化剖面,运用R型聚类分析和质量平衡法,研究了石灰岩风化过程中锰和磷迁移富集行为。结果表明,区内石灰土中锰和磷的富集程度远高于上陆壳、桂林石灰土和世界土壤。土壤中锰的富集是钙等易溶元素迁出以及锰从剖面上部淋滤到下部并沉淀的结果。磷在石灰土中的富集主要是钙等更易溶组分迁出的结果。研究区石灰土相对于桂林石灰土具有低pH值特征,相对于桂林石灰土、世界土壤和上陆壳具有低盐基度特征,其富集的锰和磷具有一定的迁移活性。图4表1参23     

Architecture of a charge-transfer state regulating light harvesting in a plant antenna protein

Energy-dependent quenching of excess absorbed light energy (qE) is a vital mechanism for regulating photosynthetic light harvesting in higher plants. All of the physiological characteristics of qE have been positively correlated with charge transfer between coupled chlorophyll and zeaxanthin molecules in the light-harvesting antenna of photosystem II (PSII). We found evidence for charge-transfer quenching in all three of the individual minor antenna complexes of PSII (CP29, CP26, and CP24), and we conclude that charge-transfer quenching in CP29 involves a delocalized state of an excitonically coupled chlorophyll dimer. We propose that reversible conformational changes in CP29 can "tune" the electronic coupling between the chlorophylls in this dimer, thereby modulating the energy of the chlorophyll-zeaxanthin charge-transfer state and switching on and off the charge-transfer quenching during qE.     

Leaf photosynthesis and yield components of mung bean under fully open-air elevated[CO_2]

Mung bean(Vigna radiata L.) has the potential to establish symbiosis with rhizobia,and symbiotic association of soil micro flora may facilitate the photosynthesis and plant growth response to elevated[CO_2].Mung bean was grown at either ambient CO_2 400 μmol mol~(-1) or[CO_2]((550+17) μmol mol~(-1)) under free air carbon dioxide enrichment(FACE) experimental facility in North China.Elevated[CO_2]increased net photosynthetic rate(P_n),water use efficiency(WUE) and the non-photochemical quenching(NPQ) of upper most fully-expanded leaves,but decreased stomatal conductance(G_s),intrinsic efficiency of PSII(F_v '/F_m'),quantum yield of PSII(φ_(PSll)) and proportion of open PSII reaction centers(q_p).At elevated[CO_2],the decrease of F_v'/F_m',φ_(PSII),q_p at the bloom stage were smaller than that at the pod stage.On the other hand,P_n was increased at elevated[CO_2]by 18.7 and 7.4%at full bloom(R2) and pod maturity stages(R4),respectively.From these findings,we concluded that as a legume despite greater nutrient supply to the carbon assimilation at elevated[CO_2],photosynthetic capacity of mung bean was still suppressed under elevated[CO_2]particularly at pod maturity stage but plant biomass and yield was increased by 11.6 and 14.2%,respectively.Further,these findings suggest that even under higher nutrient acquisition systems such as legumes,nutrient assimilation does not match carbon assimilation under elevated[CO_2]and leads photosynthesis down-regulation to elevated[CO_2].     

低温弱光胁迫对棉花幼苗叶绿素荧光特性及能量分配的影响

[目的]探讨低温弱光胁迫下不同基因型棉花幼苗叶绿素荧光特性及能量分配的响应机制,为棉花耐低温品种选育及筛选耐低温鉴定指标和方法提供理论依据.[方法]以6种不同基因型棉花幼苗为试材,通过5℃、100 μmol/( m2·s)低温弱光处理,测定12 h内叶绿素荧光相关参数.[结果]低温弱光胁迫提高了初始荧光Fo、光合功能相对限制值L(PFD),显著降低了PSⅡ最大光化学效率Fv/Fm、PSⅡ实际光化学效率φPSⅡ、光合电子传递速率ETR、光化学猝灭系数qP等指标,非光化学猝灭系数NPQ则呈现先升后降的趋势;同时,PSⅠ激发能分配系数σ、天线热耗散速率Drate增大,PSⅡ激发能分配系数β、光化学速率Prate降低.[结论]低温弱光胁迫导致棉花幼苗叶片PSⅡ光化学活性降低,光合电子传递过程受抑,更多的光能用于天线热耗散,且干扰了PSⅠ和PSⅡ间的激发能分配和传递.综合各指标分析,新陆中28号与中棉所50号在低温弱光胁迫下表现出良好的光能分配、利用能力,耐低温能力较强,新陆早42号与中棉所43号次之,新陆早33号和新陆早19号较差.     

不同光强下含笑叶绿素荧光特性研究

测定研究了不同光照强度下,含笑的最大量子效率(PSII)和实际量子效率(ΦPSII)等叶绿素荧光参数的变化规律,及其对光照强度的适应特征.结果表明,随着日间光强的增大 ,叶片PQ还原程度和非光化学猝灭(NPQ)增加,ΦPSII则下降,但后者午后随着光强的下降可得到完全恢复;叶片吸收光能分配于光化学反应的比例随着光强的增大而迅速减少;而天线色素耗散部分及反应中心过剩的光能则显著增加,在午后光强减弱后两者均可恢复到早晨的初始水平.在弱光条件下,其叶片PQ还原程度、NPQ以及ΦPSII均无明显变化,叶片吸收光能也主要用于光化学反应,热耗散及过剩光能比例均较低.