大豆具放氧活性的光系统Ⅱ颗粒的光合特性

用去垢剂Triton X-100从大豆叶绿体制备出具放氧活性的光系统Ⅱ颗粒。放氧活性达208 μmol O_2 mg~(-1) Chl.hr~(-1)以吸氧表示的PSI活性以及低温荧光发射中代表光系统Ⅰ的F_(735)均比叶绿体明显下降。光诱导P_(700)吸收变化很难检测出来,用SDS-聚丙烯酰胺凝胶电泳几乎分离不出属光系统Ⅰ的叶绿素蛋白质复合物带来。代表光系统Ⅱ活性的DCIP光还原活性很高。颗粒的Chl a/b值为1.9。以上结果表明这颗粒十分富含光系统Ⅱ和放氧系统,其光系统Ⅰ含量是可以忽略的。 在文中也叙及从菠菜和蓖麻叶绿体得到的相似颗粒的一些光合特性。     

磷脂酰胆碱和Triton X—100对光系统Ⅱ蛋白二级结构及放氧活性？…

采用傅立叶变换红外光谱技术（ＦＴ－ＩＲ）和氧电极研究了磷脂酰胆碱和Ｔｒｉｔｏｎ Ｘ－１００对光系统Ⅱ膜复合物的蛋白二级结构及放氧活性的影响。结果表明,磷脂酰胆碱对光系统Ⅱ膜复合物的蛋白二级结构没有显著的影响,但能引起放氧活性的提高,而且脂酰侧链长度不同,对放氧活性的促进程度也不一样。相比较而言,ＴＸ－１００对膜脂的扰动却引起蛋白二级结构的明显改变,并能抑致放氧活性。结果说明,完整的膜结构对维持光合     

低浓度硫酸甲酯吩嗪（PMS）对叶片光合放氧的促进作用

外加低浓度循环光合磷酸化电子递体硫酸甲酯吩嗪(PMS)对菠菜、大豆、水稻和小麦叶片光合放氧有促进作用,与此同时叶片ATP含量也得到增加。PMS对经8 mmol L~(-1)NH_4Cl处理过的菠菜叶片的光合放氧也有促进,最适促进浓度比未经NH_4Gl处理的叶片高,促进的幅度也大。幼龄叶与成长叶相比,幼龄叶的光合磷酸化活性和P/O比值低于成长叶片,其光合放氧速率受PMS促进的幅度大于成长叶片。因此光合磷酸化也可以成为光合作用的一个重要限制因素。     

碳酸氢钾对大豆幼苗光合作用的影响

研究喷洒碳酸氢钾(KHCO3)对大豆幼苗叶片光合作用影响的结果表明,喷施KHCO3的大豆幼苗光合速率和核酮糖.1,5二磷酸羧化/氧化酶(Rubisco)羧化活性提高,加氧酶活性下降,PSI、PSII和光合电子传递速率均提高,光合色素含量也增加.     

磷脂酰胆碱和TritonX-100对光系统Ⅱ蛋白二级结构及放氧活性影响的比较(英文)

采用傅立叶变换红外光谱技术 (FT_IR)和氧电极研究了磷脂酰胆碱和TritonX_10 0对光系统Ⅱ膜复合物的蛋白二级结构及放氧活性的影响。结果表明 ,磷脂酰胆碱对光系统Ⅱ膜复合物的蛋白二级结构没有显著的影响 ,但能引起放氧活性的提高 ,而且脂酰侧链长度不同 ,对放氧活性的促进程度也不一样。相比较而言 ,TX_10 0对膜脂的扰动却引起蛋白二级结构的明显改变 ,并能抑致放氧活性。结果说明 ,完整的膜结构对维持光合膜蛋白的稳定是非常重要的。     

螺藻旋Spirulina platensis整体细胞放氢特性的研究

螺旋藻Spirulina platensis具有氢酶。由氢酶催化的放H_2活性受到培养基中硝酸盐的抑制。这是由于氢酶与硝酸还原酶之间存在还原能力的竞争。以脲素取代硝酸盐可以部分地解除其抑制作用。放H_2活性随着暗中时间的延长而成倍加强。在氮气或氩气中比在空气中的放氢活性分别高出244％和287％。氧气抑制放H_2活性,约5％O_2达到半抑制浓度。CO对,放H_2的半抑制浓度为2％。当光照强度大于2000lx时完全抑制放H_2活性。光合放氧与放氢的矛盾可以通过光、暗交替处理,由暗中的耗氧呼吸以加协调。     

褐藻裙带菜中PSII复合物及其亚复合物的分离和特性研究

用不连续梯度蔗糖密度超离心,从经TritonX-100增溶的褐藻裙带菜类囊体膜中分离到3种色素蛋白复合物条带,分别是捕光复合物、具有光氧化活性的PSII复合物颗粒(区带II)以及PSI(区带III)。PSII颗粒经毛地黄皂苷增溶后,再次超离心分离得到3条PSII的亚复合物条带。吸收和荧光激发谱显示其中的区带II-1为墨角藻黄素-Chla/c-蛋白复合物,区带II-2为Chla/c-蛋白复合物,两者都只含20kDa多肽;而鲜绿色的区带II-3为不含捕光复合物的活性PSII核心。     

磷脂酰胆碱和Triton X-100对光系统Ⅱ蛋白二级结构及放氧活性影响的比较

采用傅立叶变换红外光谱技术(FT-IR)和氧电极研究了磷脂酰胆碱和Triton X-100对光系统Ⅱ膜复合物的蛋白二级结构及放氧活性的影响.结果表明,磷脂酰胆碱对光系统Ⅱ膜复合物的蛋白二级结构没有显著的影响,但能引起放氧活性的提高,而且脂酰侧链长度不同,对放氧活性的促进程度也不一样.相比较而言,TX-100对膜脂的扰动却引起蛋白二级结构的明显改变,并能抑致放氧活性.结果说明,完整的膜结构对维持光合膜蛋白的稳定是非常重要的.     

光合放氧的电极电位测定法的研究

介绍了用电极电位法测定植物的光合放氧速率,由此可以测定其放氧活性,此法具有应用面广、设备简便、灵敏度高、反应快及可以连续记录的特点,是一种研究光合作用的新方法。     

从光合作用特性看铜绿微囊藻(Microcystis aeruginosa)的竞争优势

通过测定净光合放氧速率,研究了温度、光照和pH对铜绿微囊藻(M icrocystis aeruginosa)和玫瑰拟衣藻(Chlorom onas rosae)光合作用的影响。两种藻的光合放氧速率都随着温度的升高而加快,在10~35℃范围内,铜绿微囊藻净光合放氧速率随温度升高而直线上升,其最适温度高于35℃,而当温度高于30℃后玫瑰拟衣藻的净光合放氧速率迅速下降;两种微藻的光合放氧速率-光强变化曲线有所不同,铜绿微囊藻光饱和点在500μmol.m-2.s-1附近,光强达到900μmol.m-2.s-1时仍无光抑制现象发生,玫瑰拟衣藻光饱和点在630μmol.m-2.s-1附近,当光强进一步升高,光合放氧速率开始下降;铜绿微囊藻最适pH值是10.0,在pH值6.5~11.5范围内,光合放氧都很活跃,变化幅度不大,玫瑰拟衣藻最适pH值7.0,偏酸或偏碱光合放氧都迅速地下降,pH高于10.0出现了负值。比较两种藻的光合作用特性,铜绿微囊藻光合作用具有3个特点:(1)适应温度范围宽,对高温具有良好的适应性,并且光合作用随温度的升高显著提高;(2)光饱和点低,光合作用活性高,能在弱光环境中高效地进行光合作用,并且抗强光伤害;(3)对pH变化具有超强的适应能力,在中性和碱性环境中,都能进行活跃的光合作用。铜绿微囊藻在光能利用、温度和pH适应性方面的特点,可以使其快速生长繁殖,积累大量的生物量,在与其它藻类的竞争中占据显著的优势。     

Excitonic interactions in wild-type and mutant PSI reaction centers

Femtosecond excitation of the red edge of the chlorophyll a Q(Y) transition band in photosystem I (PSI), with light of wavelength > or = 700 nm, leads to wide transient (subpicosecond) absorbance changes: positive DeltaA between 635 and 665 nm, and four negative DeltaA bands at 667, 675, 683, and 695 nm. Here we compare the transient absorbance changes after excitation at 700, 705, and 710 nm at 20 K in several PSI preparations of Chlamydomonas reinhardtii where amino acid ligands of the primary donor, primary acceptor, or connecting chlorophylls have been mutated. Most of these mutations influence the spectrum of the absorbance changes. This supports the view that the chlorophylls of the electron transfer chain as well as the connecting chlorophylls are engaged in the observed absorbance changes. The wide absorption spectrum of the electron transfer chain revealed by the transient measurements may contribute to the high efficiency of energy trapping in photosystem 1. Exciton calculations, based on the recent PSI structure, allow an assignment of the DeltaA bands to particular chlorophylls: the bands at 675 and 695 nm to the dimers of primary acceptor and accessory chlorophyll and the band at 683 nm to the connecting chlorophylls. The subpicosecond transient absorption bands decay may reflect rapid charge separation in the PSI reaction center.     

Triton X-100 as an effective surfactant for the isolation and purification of photosystem I from Arthrospira platensis

Surfactants play important roles in the preparation, structural, and functional research of membrane proteins, and solubilizing and isolating membrane protein, while keeping their structural integrity and activity intact is complicated. The commercial n-Dodecyl-β-D-maltoside (DDM) and Triton X-100 (TX) were used as solubilizers to extract and purify trimeric photosystem I (PSI) complex, an important photosynthetic membrane protein complex attracting broad interests. With an optimized procedure, TX can be used as an effective surfactant to isolate and purify PSI, as a replace of the much more expensive DDM. A mechanism was proposed to interpret the solubilization process at surfactant concentrations lower than the critical solubilization concentration. PSI-TX and PSI-DDM had identical polypeptide bands, pigment compositions, oxygen consumption, and photocurrent activities. This provides an alternative procedure and paves a way for economical and large-scale trimeric PSI preparation.     

Substrate specificity of glucose dehydrogenase (GDH) of Enterobacter asburiae PSI3 and rock phosphate solubilization with GDH substrates as C sources

Enterobacter asburiae PSI3 is a rhizospheric isolate that solubilizes mineral phosphates by the action of a phosphate starvation-inducible GDH (EC 1.1.5.2). We report here that GDH activity of this isolate shows broad substrate range, being able to act on mono and disaccharides. Enterobacter asburiae PSI3 was proficient at bringing about a drop in pH and solubilization of RP with the use of 75 mmol/L of each of the GDH substrate sugars tested as the sole C source. It liberated amounts of P ranging from 450 micromol/L (on arabinose) to 890 micromol/L (on glucose). When grown on a mixture of 7 GDH substrates at concentrations of 15 mmol/L each, the bacterium solubilized RP equivalent to 46% of the value when 75 mmol glucose/L was the C source. HPLC analysis of the culture supernatant under these conditions showed that the acidification of the media is primarily due to the production of organic acids. The significance of these results on the efficacy of E. asburiae PSI3 at solubilizing phosphates under rhizospheric conditions is discussed.     

Increase in the rate of photosynthetic linear electron transport in cyanobacteruim <Emphasis Type="Italic">Synechocystis</Emphasis> sp. PCC 6803 lacking phycobilisomes

Compensating changes in the pigment apparatus of photosynthesis that resulted from a complete loss of phycobilisomes (PBS) were investigated in the cells of a PAL mutant of cyanobacterium Synechocystis sp. PCC 6803. The ratio PBS/chlorophyll calculated on the basis of the intensity of bands in the action spectra of photosynthetic activity of two photosystems in the wild strain was 1: 70 for PSII and 1: 300 for PSI. Taking into consideration the number of chlorophyll molecules per reaction center in each photosystem, these ratios could be interpreted as association of PBS with dimers of PSII and trimers of PSI as well as greater dependence of PSII as compared with PSI on light absorption by PBS. The ratio PSI/PSII determined by photochemical cross-section of the reactions of two photosystems was 3.5: 1.0 for wild strain of Synechocystis sp. PCC 6803 and 0.7: 1.0 for the PAL mutant. A fivefold increase in the relative content of PSII in pigment apparatus corresponds to a 5-fold increase in the intensity of bands at 685 and 695 nm as related to the band of PSI at 726 nm recorded in low-temperature fluorescence spectrum of the PAL mutant. Inhibition of PSII with diuron resulted in a pronounced stimulation of chlorophyll fluorescence in the PAL mutant as compared to the wild strain of Synechocystis sp. PCC 6803; these data suggested an activation of electron transfer between PSII and PSI in the mutant cells. Thus, the lack of PBS in the mutant strain of Synechocystis sp. PCC 6803 was compensated for by the higher relative content of PSII in the pigment apparatus of photosynthesis and by a rise in the rate of linear electron transport.     

Red antenna states of photosystem I from Synechococcus sp. PCC 7002

Absorption, fluorescence and single-molecule spectroscopy at low temperatures were used to elucidate spectral properties, heterogeneities and dynamics of the red-shifted chlorophyll a (Chla) molecules responsible for the fluorescence in photosystem I (PSI) from the cyanobacterium Synechoccocus sp. PCC 7002. The 77 K absorption spectrum indicates the presence of 2–3 red-shifted Chla’s absorbing at about 708 nm. The fluorescence emission spectrum is dominated by a broad band at 714 nm. The emission spectra of single PSI complexes show zero-phonon lines (ZPLs) as well as a broad intensity distribution without ZPLs. The spectral region below 710 nm often shows ZPLs, they form a spectral band with a maximum at 698 nm (F698). The region above 710 nm is dominated by broad intensity distributions and the observation of ZPLs is less frequent. The broad distributions are due to the emission of the C708 Chla’s and the emission from F698 stems from a Chla species absorbing at the blue side of P700. The properties of these two emissions show a close relation to those of the C708 and C719 pools observed in T. elongatus. Therefore an assignment of F698 and C708 to Chla-species with similarities to C708 and C719 in T. elongatus is proposed.     

Ultrafast transient absorption studies on Photosystem I reaction centers from Chlamydomonas reinhardtii. 1. A new interpretation of the energy trapping and early electron transfer steps in Photosystem I

The energy transfer and charge separation kinetics in core Photosystem I (PSI) particles of Chlamydomonas reinhardtii has been studied using ultrafast transient absorption in the femtosecond-to-nanosecond time range. Although the energy transfer processes in the antenna are found to be generally in good agreement with previous interpretations, we present evidence that the interpretation of the energy trapping and electron transfer processes in terms of both kinetics and mechanisms has to be revised substantially as compared to current interpretations in the literature. We resolved for the first time i), the transient difference spectrum for the excited reaction center state, and ii), the formation and decay of the primary radical pair and its intermediate spectrum directly from measurements on open PSI reaction centers. It is shown that the dominant energy trapping lifetime due to charge separation is only 6-9 ps, i.e., by a factor of 3 shorter than assumed so far. The spectrum of the first radical pair shows the expected strong bleaching band at 680 nm which decays again in the next electron transfer step. We show furthermore that the early electron transfer processes up to approximately 100 ps are more complex than assumed so far. Several possibilities are discussed for the intermediate redox states and their sequence which involve oxidation of P700 in the first electron transfer step, as assumed so far, or only in the second electron transfer step, which would represent a fundamental change from the presently assumed mechanism. To explain the data we favor the inclusion of an additional redox state in the electron transfer scheme. Thus we distinguish three different redox intermediates on the timescale up to 100 ps. At this level no final conclusion as to the exact mechanism and the nature of the intermediates can be drawn, however. From comparison of our data with fluorescence kinetics in the literature we also propose a reversible first charge separation step which has been excluded so far for open PSI reaction centers. For the first time an ultrafast 150-fs equilibration process, occurring among exciton states in the reaction center proper, upon direct excitation of the reaction center at 700 nm, has been resolved. Taken together the data call for a fundamental revision of the present understanding of the energy trapping and early electron transfer kinetics in the PSI reaction center. Due to the fact that it shows the fastest trapping time observed so far of any intact PSI particle, the PSI core of C. reinhardtii seems to be best suited to further characterize the electron transfer steps and mechanisms in the reaction center of PSI.     

FdC1, a novel ferredoxin protein capable of alternative electron partitioning, increases in conditions of acceptor limitation at photosystem I

In higher plants, [2Fe-2S] ferredoxin (Fd) proteins are the unique electron acceptors from photosystem I (PSI). Fds are soluble, and distribute electrons to many enzymes, including Fd:NADP(H) reductase (FNR), for the photoreduction of NADP(+). In addition to well studied [2Fe-2S] Fd proteins, higher plants also possess genes for significantly different, as yet uncharacterized Fd proteins, with extended C termini (FdCs). Whether these FdC proteins function as photosynthetic electron transfer proteins is not known. We examined whether these proteins play a role as alternative electron acceptors at PSI, using quantitative RT-PCR to follow how their expression changes in response to acceptor limitation at PSI, in mutant Arabidopsis plants lacking 90-95% of photosynthetic [2Fe-2S] Fd. Expression of the gene encoding one FdC protein, FdC1, was identified as being strongly up-regulated. We confirmed that this protein was chloroplast localized and increased in abundance on PSI acceptor limitation. We purified the recombinant FdC1 protein, which exhibited a UV-visible spectrum consistent with a [2Fe-2S] cluster, confirmed by EPR analysis. Measurements of electron transfer show that FdC1 is capable of accepting electrons from PSI, but cannot support photoreduction of NADP(+). Whereas FdC1 was capable of electron transfer with FNR, redox potentiometry showed that it had a more positive redox potential than photosynthetic Fds by around 220 mV. These results indicate that FdC1 electron donation to FNR is prevented because it is thermodynamically unfavorable. Based on our data, we speculate that FdC1 has a specific function in conditions of acceptor limitation at PSI, and channels electrons away from NADP(+) photoreduction.     

溶磷真菌的筛选及耐盐特性分析

【背景】土壤盐渍化已成为影响土壤质量和作物产量的重要因素之一,利用微生物改良盐渍化土壤是既经济又环保的方法。【目的】从不同土壤样品和生物肥料中筛选溶磷能力较强的真菌并讨论其耐盐能力,为盐渍化土壤改良提供菌种资源。【方法】采用平板培养法筛选有一定溶磷能力的真菌,经ITS序列分析初步确定菌株的分类地位。以溶磷能力为考察指标,以NaCl梯度和磷酸钙梯度为考察因素,分析不同菌株利用无机磷源的能力,以及溶磷能力与pH的关系。【结果】共筛选得到16株具有较强溶磷能力的真菌,其中4株真菌对水稻发芽有显著的促进作用,它们是1株长枝木霉(MF-1)和3株踝节菌属菌株(SD-2、XJ-7和HLJ-3)。菌株SD-2和XJ-7生长的耐盐能力显著好于菌株MF-1和HLJ-3。当NaCl浓度为5%时,菌株XJ-7的溶磷能力最好,溶磷率可达9.50%;当NaCl浓度为1%时,菌株HLJ-3的溶磷能力较好,溶磷率为6.93%;当NaCl浓度为0时,菌株SD-2和MF-1的溶磷能力较强,溶磷率分别为9.07%和3.73%。进一步研究发现踝节菌属真菌的溶磷能力与菌液pH呈显著负相关关系。【结论】筛选获得的4株真菌其溶磷能力在不同盐环境中有显著差异,为今后土壤改良和生物肥料中菌种的选择提供理论依据和试验基础。     

On the nature of uncoupled chlorophylls in the extremophilic photosystem I-light harvesting I supercomplex

Photosystem I core-light-harvesting antenna supercomplexes (PSI-LHCI) were isolated from the extremophilic red alga Cyanidioschyzon merolae and studied by three fluorescence techniques in order to characterize chlorophylls (Chls) energetically uncoupled from the PSI reaction center (RC). Such Chls are observed in virtually all optical experiments of any PSI core and PSI-LHCI supercomplex preparations across various species and may influence the operation of PSI-based solar cells and other biohybrid systems. However, the nature of the uncoupled Chls (uChls) has never been explored deeply before. In this work, the amount of uChls was controlled by stirring the solution of C. merolae PSI-LHCI supercomplex samples at elevated temperature (~303 K) and was found to increase from <2% in control samples up to 47% in solutions stirred for 3.5 h. The fluorescence spectrum of uChls was found to be blue-shifted by ~20 nm (to ~680 nm) relative to the fluorescence band from Chls that are well coupled to PSI RC. This effect indicates that mechanical stirring leads to disappearance of some red Chls (emitting at above ~700 nm) that are present in the intact LHCI antenna associated with the PSI core. Comparative diffusion studies of control and stirred samples by fluorescence correlation spectroscopy together with biochemical analysis by SDS-PAGE and BN-PAGE indicate that energetically uncoupled Lhcr subunits are likely to be still physically attached to the PSI core, albeit with altered three-dimensional organization due to the mechanical stress.     

A retrieval algorithm to evaluate the Photosystem I and Photosystem II spectral contributions to leaf chlorophyll fluorescence at physiological temperatures

A new computational procedure to resolve the contribution of Photosystem I (PSI) and Photosystem II (PSII) to the leaf chlorophyll fluorescence emission spectra at room temperature has been developed. It is based on the Principal Component Analysis (PCA) of the leaf fluorescence emission spectra measured during the OI photochemical phase of fluorescence induction kinetics. During this phase, we can assume that only two spectral components are present, one of which is constant (PSI) and the other variable in intensity (PSII). Application of the PCA method to the measured fluorescence emission spectra of Ficus benjamina L. evidences that the temporal variation in the spectra can be ascribed to a single spectral component (the first principal component extracted by PCA), which can be considered to be a good approximation of the PSII fluorescence emission spectrum. The PSI fluorescence emission spectrum was deduced by difference between measured spectra and the first principal component. A single-band spectrum for the PSI fluorescence emission, peaked at about 735?nm, and a 2-band spectrum with maxima at 685 and 740?nm for the PSII were obtained. A linear combination of only these two spectral shapes produced a good fit for any measured emission spectrum of the leaf under investigation and can be used to obtain the fluorescence emission contributions of photosystems under different conditions. With the use of our approach, the dynamics of energy distribution between the two photosystems, such as state transition, can be monitored in vivo, directly at physiological temperatures. Separation of the PSI and PSII emission components can improve the understanding of the fluorescence signal changes induced by environmental factors or stress conditions on plants.