Dynamics affecting the primary charge transfer in photosynthesis

Analysis of a 60-picosecond molecular dynamics trajectory of the reaction center of Rhodopseudomonas viridis provides an understanding of observations concerning vibrational coherence and the nonexponential kinetics of the primary charge transfer in photosynthesis. Complex kinetics arises from energy gap correlations that persist beyond 1 picosecond.     

Quantum register based on individual electronic and nuclear spin qubits in diamond

The key challenge in experimental quantum information science is to identify isolated quantum mechanical systems with long coherence times that can be manipulated and coupled together in a scalable fashion. We describe the coherent manipulation of an individual electron spin and nearby individual nuclear spins to create a controllable quantum register. Using optical and microwave radiation to control an electron spin associated with the nitrogen vacancy (NV) color center in diamond, we demonstrated robust initialization of electron and nuclear spin quantum bits (qubits) and transfer of arbitrary quantum states between them at room temperature. Moreover, nuclear spin qubits could be well isolated from the electron spin, even during optical polarization and measurement of the electronic state. Finally, coherent interactions between individual nuclear spin qubits were observed and their excellent coherence properties were demonstrated. These registers can be used as a basis for scalable, optically coupled quantum information systems.     

Mimicking photosynthesis

Although the concept of an artificial photosynthetic reaction center that mimics natural electron-and energy-transfer processes is an old one, in recent years major advances have occurred. In this review, some relatively simple molecular dyads that mimic certain aspects of photosynthetic electron transfer and singlet or triplet energy transfer are described. Dyads of this type have proven to be extremely useful for elucidating basic photochemical principles. In addition, their limitations, particularly in the area of temporal stabilization of electronic charge separation, have inspired the development of much more complex multicomponent molecular devices. The use of the basic principles of photoinitiated electron transfer to engineer desirable properties into the more complex species is exemplified. The multiple electrontransfer pathways available with these molecules make it possible to fine-tune the systems in ways that are impossible with simpler molecules. The study of these devices not only contributes to our understanding of natural photosynthesis, but also aids in the design of artificial solar energy harvesting systems and provides an entry into the nascent field of molecular electronics.     

Quantum gas of deeply bound ground state molecules

Molecular cooling techniques face the hurdle of dissipating translational as well as internal energy in the presence of a rich electronic, vibrational, and rotational energy spectrum. In our experiment, we create a translationally ultracold, dense quantum gas of molecules bound by more than 1000 wave numbers in the electronic ground state. Specifically, we stimulate with 80% efficiency, a two-photon transfer of molecules associated on a Feshbach resonance from a Bose-Einstein condensate of cesium atoms. In the process, the initial loose, long-range electrostatic bond of the Feshbach molecule is coherently transformed into a tight chemical bond. We demonstrate coherence of the transfer in a Ramsey-type experiment and show that the molecular sample is not heated during the transfer. Our results show that the preparation of a quantum gas of molecules in specific rovibrational states is possible and that the creation of a Bose-Einstein condensate of molecules in their rovibronic ground state is within reach.     

越冬期间桂花光系统Ⅱ行为特征分析

为探究桂花在越冬期间遭受寒害时的光合机理,运用叶绿素荧光动力学手段,监测桂花叶片在北京地区越冬过程中光系统Ⅱ(PSⅡ)行为特征的变化。结果表明:随着越冬过程的推进,初始荧光(F_0)、PSⅡ最大光化学效率(F_v/F_m)、PSⅡ有效量子产额(yield)和PSⅡ电子传递速率(ETR)均随温度下降出现同步降低,并表明越冬过程中桂花叶片的捕光天线系统遭受破坏,从而抑制了光合作用的原初反应,桂花叶片通过减小天线系统捕获的光能来降低对PSⅡ反应中心的激发压。另外,桂花叶片的光化学猝灭系数(q P)始终较高,说明PSⅡ反应中心能够在越冬期间保持较高的开放程度,进而减少激发能在PSⅡ供体侧积累对PSⅡ反应中心的伤害;而非光化学猝灭系数(NPQ)伴随温度下降而明显降低,由此可以推断,桂花主要通过天线系统以外的热耗散途径来抵御冬季低温胁迫。     

北疆棉花叶绿素荧光猝灭特性对渗透胁迫的响应

为了解水分抑制条件下棉花光合生理和叶绿素荧光特性响应机理,为抗旱棉花品种的筛选和培育提供理论依据,试验以3个北疆主栽棉花品种为材料,利用叶绿素荧光分析技术,研究了渗透胁迫下棉花品种的叶绿素荧光猝灭特性的响应变化.结果表明,长时间(16 h)和高浓度(30;)渗透胁迫会降低棉花PSⅡ的原初光能转化效率(Fv/Fm),使PSⅡ反应中心开放部分的比例(qP)缩小,用于光合作用电子传递的份额(qP)减少,从而使光合器官受到损伤,非辐射能量耗散增加,抑制了棉花叶片的光合功能.响应的结果同时与品种自身的恢复能力差异性有密切的关系.各个品种对长时间、高浓度胁迫后恢复的Fv/Fm、qP和qN及其与对照之间差异分别达到了极显著水平,建议用长时间、高浓度渗透胁迫的荧光猝灭特性的恢复能力差异来作为辅助鉴定和筛选棉花品种抗旱性的依据.     

Effect of Nitrogen Fertilization on Leaf Chlorophyll Fluorescence in Field-Grown Winter Wheat Under Rainfed Conditions

The effect of nitrogen fertilization on leaf chlorophyll fluorescence was studied in field-grown winter wheat during grain filling under rainfed conditions in Loess Plateau. Results showed that the actual photochemical efficiency of PS Ⅱ reaction center (Ф PS Ⅱ) decreased significantly as leaf water stress progressed, however, the Ф PS was increased by nitrogen fertilization. The Ф PS Ⅱ of 0, 90 and 180 kg ha-1 nitrogen treatments at noon were 0.197, 0.279 and 0.283, respectively, which decreased by 57.7, 56.4 and 40.2% as compared was even higher than that in the moming. Application of nitrogen fertilizer significantly increased maximum photochemical efficiency (Fv/Fm), photochemical quenching coefficient (qP) and non-photochemical quenching coefficient (qNP). These results indicated that application of nitrogen fertilizer could increase the light energy conversion efficiency, the potential activity of photosynthetic reaction center, and the non-photochemical dissipation of excess light energy, which can prevent leaf photosynthetic apparatus from damage of treatments, indicating that the excess nitrogen was unfavorable to photosynthesis.     

不同连作年限土壤对甜瓜幼苗叶绿素含量和光合特性的影响

[目的]探讨不同连作年限的土壤对甜瓜幼苗叶绿素含量和光合特性的影响。[方法]选取连作1、3、5和7年的土壤盆栽甜瓜,以露地非连作菜园土壤为对照。定植后30d,测定甜瓜幼苗叶绿素含量、光合及荧光动力学参数的变化情况。[结果]随着连作年限的增加,甜瓜叶片叶绿素含量、净光合速率、气孔导度、蒸腾速率、PSⅡ最大光化学效率、PSⅡ实际光化学效率、光化学淬灭逐渐降低,但胞间CO2浓度和初始荧光升高。[结论]连作易造成甜瓜叶绿素合成受阻,PSⅡ反应中心受到光化学损害,光合电子传递受抑制,表明甜瓜不耐连作,尤其不适宜长期连作。     

Chemistry of excited electronic States

Atomic and molecular orbitals are among the tools used by chemists to view the world. The validity of this view for reaction systems can be experimentally probed by examination of the chemistry of electronically excited states and, in particular, by comparison of the reactivities of states having different orbital occupations (electron configurations). Reactivity changes associated with electron configuration are instructive with regard to chemists' views of molecular orbital interactions, but electronic excitation can also influence the course of a chemical reaction by increasing the energy content of the system or by affecting access to different potential energy surfaces by changing spin, orbital symmetry, or spin-orbit level. These various effects are illustrated by studies of gasphase transition metal-mediated H-H and C-H bond-activation processes.     

高温胁迫对樟树光合性能的影响

光合作用是植物对环境变化最为敏感的生理过程。通过研究高温胁迫对樟树Cinnamomum camphora叶绿素荧光诱导动力学、气体交换速率和水分利用效率的影响,以期从光合作用的角度揭示高温对樟树的危害机制。结果表明:35和45℃高温胁迫后,樟树叶绿素荧光诱导动力学曲线O到P点的荧光强度均随胁迫增强而明显降低,同时诱导动力学参数单位反应中心吸收的光能总量、单位反应中心捕获的光能总量、单位反应中心内电子传递的量子产额、光合性能指数和单位吸收面积上天线色素能量吸收的驱动力均明显降低,其中在45℃时降至最低,与对照（25℃）相比分别降低了21.7%（P < 0.01）,17.6%（P < 0.01）,38.8%（P < 0.01）,60.2%（P < 0.01）和26.9%（P < 0.01）。35和45℃高温胁迫后,单位反应中心热耗散的能量明显升高,与对照相比分别增加了13.5%（P < 0.05）和78.4%（P < 0.01）;此外,樟树光合速率、气孔导度、蒸腾速率和水分利用效率亦均明显降低,其中最大光合速率分别降低了16.0%（P < 0.05）和44.6%（P < 0.01）。由此可见,高温胁迫可通过降低樟树的光能吸收、量子产量和电子传递,并促进吸收光能进行热耗散,降低光系统Ⅱ效率,进而减少同化力以降低光合速率。     

Breakdown of the Born-Oppenheimer approximation in the F+ o-D2 -> DF + D reaction

The reaction of F with H2 and its isotopomers is the paradigm for an exothermic triatomic abstraction reaction. In a crossed-beam scattering experiment, we determined relative integral and differential cross sections for reaction of the ground F(2P(3/2)) and excited F*(2P(1/2)) spin-orbit states with D2 for collision energies of 0.25 to 1.2 kilocalorie/mole. At the lowest collision energy, F* is approximately 1.6 times more reactive than F, although reaction of F* is forbidden within the Born-Oppenheimer (BO) approximation. As the collision energy increases, the BO-allowed reaction rapidly dominates. We found excellent agreement between multistate, quantum reactive scattering calculations and both the measured energy dependence of the F*/F reactivity ratio and the differential cross sections. This agreement confirms the fundamental understanding of the factors controlling electronic nonadiabaticity in abstraction reactions.     

淹水条件下紫丁香幼苗叶片的PSⅡ能量分配特点

[目的]为探究淹水条件下紫丁香幼苗叶片PSⅡ能量分配特点.[方法]在盆栽条件下,利用叶绿素快相荧光动力学曲线研究胁迫对紫丁香叶片PSⅡ能量分配的影响.[结果]淹水胁迫下紫丁香幼苗叶片单位反应中心吸收光能ABS/RC增加,其原因可能是由于在淹水胁迫导致紫丁香幼苗有活性PSⅡ反应中心数量降低的情况下,通过以剩余有活性反应中心的功能增强的方式来维持淹水胁迫下PSⅡ的光能供应.在剩余有活性PSⅡ反应中心吸收光能增强造成PSⅡ反应中心压力增大的情况下,紫丁香幼苗叶片PSⅡ反应中心的光能分配参数发生了明显的改变,淹水6d后紫丁香幼苗叶片PSⅡ反应中心吸收光能用于光化学反应的量子产额（ΦNSⅡ）明显降低,而失活PSⅡ反应中心的热耗散量子产额（ΦNF）明显增加,说明淹水胁迫导致紫丁香幼苗叶片PSⅡ反应中心光化学效率降低,失活反应中心的比例也随着淹水时间的延长而增加.但在淹水过程中紫丁香幼苗叶片Φf,D呈增加趋势,而ΦNPQ呈先增加后降低趋势.[结论]紫丁香幼苗不但可以通过热能和荧光的形式耗散过剩光能,而且可以通过启动依赖于叶黄素循环的非辐射能量耗散过程来调整过量能量的耗散,以降低PSⅡ反应中心过剩光能的压力,但是在淹水第10天开始ΦNPQ却呈降低趋势,说明在长期淹水胁迫下这种光保护机制的作用逐渐降低,从而导致光能分配到失活反应中心的比例剧增.     

Partial symmetrization of the photosynthetic reaction center

The bacterial photosynthetic reaction center (RC) is a pigmented intrinsic membrane protein that performs the primary charge separation event of photosynthesis, thereby converting light to chemical energy. The RC pigments are bound primarily by two homologous peptides, the L and M subunits, each containing five transmembrane helices. These alpha helices and pigments are arranged in an approximate C2 symmetry and form two possible electron transfer pathways. Only one of these pathways is actually used. In an attempt to identify nonhomologous residues that are responsible for functional differences between the two branches, homologous helical regions that interact extensively with the pigments were genetically symmetrized (that is, exchanged). For example, replacement of the fourth transmembrane helix (D helix) in the M subunit with the homologous helix from the L subunit yields photosynthetically inactive RCs lacking a critical photoactive pigment. Photosynthetic revertants have been isolated in which single amino acid substitutions (intragenic suppressors) compensate for this partial symmetrization.     

氨基酸叶面肥对砂梨叶片光合作用的促进效应

以8个砂梨品种叶片为材料,研究了含有0.05、0.5和5 mg.L-15-氨基乙酰丙酸(ALA)的"爱乐壮"氨基酸叶面肥处理对砂梨叶片叶绿素相对含量(SPAD)、净光合速率(Pn)和叶绿素快速诱导荧光参数的影响。结果表明:3个处理均能不同程度地提高砂梨叶片SPAD值,增加Pn,提高PSⅡ反应中心供体侧与受体侧光合能量转换活性,减少热能量耗散。相关性分析表明,砂梨叶片Pn与光合性能指数(PIABS)、放氧复合体活性(Wk)、PSⅡ反应中心最大关闭速率(Mo)、捕获激子将电子传递到Q-A下游其他电子受体的概率(Ψo)、PSⅡ反应中心用于电子传递的量子产额(φEo)以及能量热耗散比率(φDo)等荧光参数密切相关,说明"爱乐壮"氨基酸叶面肥可以通过提高砂梨叶片光化学能量转换效率促进光合作用。从农业生产成本上看,添加0.05～0.5 mg.L-1ALA性价比更高。     

唐菖蒲光合特性的研究

采用光合作用测定仪和植物效率分析仪对生长在冀西北坝上高原唐菖蒲的光合特性和荧光参数生理生态特点进行了研究,结果表明:①夏季在晴天、土壤水肥充足条件下,唐菖蒲叶片的光合速率呈双峰曲线,其光饱和点为2145μmol/(m2.s),光补偿点为174.8μmol/(m2.s),净光合速率的最大值为36.4μmol/(m2.s),唐菖蒲为典型的阳性植物。②晴天唐菖蒲叶片的AQY由10:00时的0.0878下降到了13时的0.0640,PSⅡ最大光化学效率Fv/Fm由10时的0.79下降到14时的0.69,比最大值下降约13%,唐菖蒲在中午发生了一定的光抑制。③由叶片能量流动模型分析,高辐射使PSⅡ部分反应中心失活或降解,叶片遭受高辐射胁迫后启动了相应的防御机制,使过剩激发能得以及时耗散。由类囊体膜能量流动模型分析,高辐射导致叶片单位面积部分反应中心失活或裂解后,启动了剩余的有活性反应中心的补偿机制,使其能量传递效率提高。     

Coherent control of retinal isomerization in bacteriorhodopsin

Optical control of the primary step of photoisomerization of the retinal molecule in bacteriorhodopsin from the all-trans to the 13-cis state was demonstrated under weak field conditions (where only 1 of 300 retinal molecules absorbs a photon during the excitation cycle) that are relevant to understanding biological processes. By modulating the phases and amplitudes of the spectral components in the photoexcitation pulse, we showed that the absolute quantity of 13-cis retinal formed upon excitation can be enhanced or suppressed by +/-20% of the yield observed using a short transform-limited pulse having the same actinic energy. The shaped pulses were shown to be phase-sensitive at intensities too low to access different higher electronic states, and so these pulses apparently steer the isomerization through constructive and destructive interference effects, a mechanism supported by observed signatures of vibrational coherence. These results show that the wave properties of matter can be observed and even manipulated in a system as large and complex as a protein.     

A photoinduced persistent structural transformation of the special pair of a bacterial reaction center

Structural modification of photosynthetic reaction centers is an important approach for understanding their charge-separation processes. An unprecedented persistent structural transformation of the special pair (dimer) of bacteriochlorophyll molecules can be produced by light absorption alone. The nonphotochemical hole-burned spectra for the reaction center of Rhodopseudomonas viridis show that the phototransformation leads to a red shift of 150 wave numbers for the special pair's lowest energy absorption band, P960, and a comparable blue shift for a state at 850 nanometers, which can now be definitively assigned as being most closely associated with the upper dimer component. Additional insights on excited-state electronic structure include the identification of a new state.     

Unconventional sequence of fractional quantum Hall states in suspended graphene

Graphene provides a rich platform to study many-body effects, owing to its massless chiral charge carriers and the fourfold degeneracy arising from their spin and valley degrees of freedom. We use a scanning single-electron transistor to measure the local electronic compressibility of suspended graphene, and we observed an unusual pattern of incompressible fractional quantum Hall states that follows the standard composite fermion sequence between filling factors ν = 0 and 1 but involves only even-numerator fractions between ν = 1 and 2. We further investigated this surprising hierarchy by extracting the corresponding energy gaps as a function of the magnetic field. The sequence and relative strengths of the fractional quantum Hall states provide insight into the interplay between electronic correlations and the inherent symmetries of graphene.     

Nonadiabatic interactions in the Cl + H2 reaction probed by ClH2- and ClD2- photoelectron imaging

The degree of electronic and nuclear coupling in the Cl + H2 reaction has become a vexing problem in chemical dynamics. We report slow electron velocity-map imaging (SEVI) spectra of ClH2- and ClD2-. These spectra probe the reactant valley of the neutral reaction potential energy surface, where nonadiabatic transitions responsible for reactivity of the Cl excited spin-orbit state with H2 would occur. The SEVI spectra reveal progressions in low-frequency Cl.H2 bending and stretching modes, and are compared to simulations with and without nonadiabatic couplings between the Cl spin-orbit states. Although nonadiabatic effects are small, their inclusion improves agreement with experiment. This comparison validates the theoretical treatment, especially of the nonadiabatic effects, in this critical region of the Cl + H2 reaction, and suggests strongly that these effects are minor.     

华南8号木薯及其四倍体诱导株系叶片蛋白质组及叶绿素荧光差异分析

【目的】通过对华南8号木薯及其四倍体诱导株系叶片差异蛋白质及叶绿素荧光参数的分析,在蛋白质水平上揭示两者叶片存在的差异以及其与光合效率间的关系。【方法】通过木薯嫩叶、根尖染色体压片及流式细胞观察对华南8号四倍体诱导株系进行鉴定,采用双向电泳技术分离叶片蛋白质,Delta 2D软件分析差异蛋白质并通过质谱技术鉴定,利用Western blot技术对部分差异蛋白质进行验证;采用95%乙醇直接提取法测定叶绿素含量,并用Imaging-Pam测定叶绿素荧光动力学参数。【结果】染色体压片及流式细胞结果均显示,诱导得到SC8多倍体株系为四倍体株系;得到的13个差异蛋白质点中上调表达12个,下调表达1个;经质谱技术成功鉴定到12个,其功能涉及碳代谢及能量代谢、光合作用、抗氧化、蛋白质代谢调控等;1个下调表达的蛋白质未得到成功匹配,其中参与光合作用的蛋白质占46.2%;四倍体株系叶片叶绿素a、叶绿素b和总叶绿素均显著升高;叶绿素荧光参数,包括Fo、ΦPSII、qP、NPQ和ETR均显著升高;【结论】参与碳代谢及能量代谢、光合作用等途径相关蛋白质表达水平的上调;叶绿素含量及叶绿素荧光参数的升高;表明四倍体株系叶片PSII反应中心捕光能力强、光化学转化效率高,从而提高了叶片的光合速率。