大肠杆菌topA－菌株中质粒pBR322的超凝集结构

超凝集DNA是质粒DNA的一种特殊拓扑结构形式，最初在大肠杆菌SD108 (topA⁺ gyrB225)细胞中被发现. 现在大肠杆菌DM800(topA^－ gyrB225)细胞中也发现了这种结构，这说明超凝集DNA的形成与细胞内旋转酶活性降低有直接关系，而与拓扑异构酶Ⅰ的存在与否无关. 体外实验的结果显示，具有很强的正超螺旋松弛活性的拓扑异构酶Ⅳ可以将超凝集DNA完全松弛，这也证明质粒DNA的超凝集结构与超螺旋结构在细胞内是可以互变的. 使用原子力显微镜对分离到的pBR322 DNA超凝集结构进行分析，并与普通超螺旋进行比较，结果表明，超凝集DNA分子的结构发生了巨大的变化，其分子长度比正常超螺旋分子缩短了约30%，宽度和高度则增加了60%，结构更接近于A型DNA. 另外，原子力显微镜研究结果表明，氯喹的嵌入并非改变了超凝集DNA的超螺旋状态，而是使其打结并最终压缩成一团.     

核基质结合区对转爬山虎芪合酶基因烟草中产生白藜芦醇的作用

采用核基质结合区(MARs)来提高转芪合酶基因(STS)烟草(Nicotiana tabacum L.)中白藜芦醇产物的含量。MARs是细胞中能与核基质特异紧密结合的DNA片段,体外结合实验表明克隆自酵母的MARs序列能特异地与烟草核基质结合。芪合酶是白藜芦醇生物合成中的关键酶,用RT-PCR方法从川鄂爬山虎(Parthenocissus henryana(Hemsl.) Diels et Gilg)中克隆了与葡萄芪合酶基因有较高同源性的芪合酶编码区,将其置于CaMV35SW强启动子下,分别构建两侧带有MARs及不含MARs序列的表达载体,通过农杆菌介导转化烟草。Northern blot及HPLC等分析表明STS基因已整合至烟草染色体中并正常转录,且表达的外源芪合酶在烟草中可催化其底物合成白藜芦醇产物。与对照相比,MARs的存在使转芪合酶基因烟草中白藜芦醇的含量平均提高了约一倍。MARs在转芪合酶基因植物中的应用也为获得抗病性更强、白藜芦醇含量更高、更保健的转基因果蔬的研究奠定了基础。     

桂味荔枝花器官的发生和发育过程研究

利用SV11立体显微镜和JSM-6360LV型扫描电镜观察‘桂味’荔枝花器官的发生和发育过程。结果表明:花序原基最先发生,然后形成数个大小不等的单花原基;4个萼片原基的发生不同步,其中一侧对位先发生;6～10枚雄蕊原基以轮状方式几乎同时发生;心皮原基最后发生,2～3枚(稀4枚)心皮原基同时出现,随后进行侧向生长,逐渐合拢形成子房。雌花中,花柱、柱头分化明显,雄蕊退化。雄花中,花丝细长,花药饱满,雌蕊退化或发育不完全。两性花中,雌雄蕊发育完全。花粉粒近球形,具3孔沟,表面为条纹状纹饰。     

黄皮种子线粒体呼吸速率和活性氧清除酶活性对脱水的响应及其生态学意义

顽拗性种子脱落时具有较高的含水量和代谢活性, 对脱水高度敏感; 但顽拗性种子脱水敏感性的机理至今仍然不清楚。该文以顽拗性黄皮(Clausena lansium)种子为材料, 研究了种子和胚轴对水分丧失的响应, 在脱水过程中胚轴和子叶的呼吸速率, 胚轴和子叶线粒体的细胞色素c氧化酶(CCO)活性、外膜完整性、CCO和交替氧化酶(AOX)途径以及线粒体活性氧清除酶活性的变化。结果表明, 随着水分的丧失, 种子和胚轴的存活率逐渐下降, 种子的脱水敏感性大于胚轴; 胚轴和子叶的呼吸速率以及线粒体外膜的完整性降低。胚轴和子叶线粒体的CCO途径以及胚轴AOX途径的呼吸速率在脱水初期增加, 随着继续脱水下降, 胚轴线粒体AOX途径的呼吸速率则随着脱水显著下降。胚轴线粒体的超氧化物歧化酶(SOD)、抗坏血酸过氧化物酶(APX)和谷胱甘肽还原酶(GR)活性和子叶线粒体的APX活性随着脱水迅速下降; 胚轴线粒体的脱氢抗坏血酸还原酶(DHAR)活性和子叶线粒体的SOD、DHAR和GR活性在脱水初期增加, 然后下降。这些数据表明黄皮种子的脱水敏感性与线粒体的呼吸速率和活性氧清除酶的活性降低密切相关, 也与长期适应热带/亚热带的生境有关。     

Mechanical Wounding Caused by Inoculation Influences the Photosynthetic Response of Nicotiana benthamiana Plants to Plum Pox Potyvirus

Plants of Nicotiana benthamiana (Gray) (60 d old) were mechanically inoculated by a spreading of the fourth and fifth leaves with inoculum with or without plum pox potyvirus (PPV). Changes in growth parameters and selected photosynthetic characteristics were followed in control and inoculated plants in the locally affected leaves (LA) during 11 d after inoculation (DAI), in systemically affected leaves immature at time of inoculation (SAI) during 14–25 DAI, and in systemically affected leaves developed after the inoculation (SAD) during 28–39 DAI. The pure mechanical damage caused by inoculation induced a decrease in the net photosynthetic rate (P _N) in LA and SAD leaves, and an increase in the steady-state value of the non-photochemical chlorophyll (Chl) fluorescence quenching q_N. The q_N increase appeared in certain time intervals in all measured leaves on plants, so it could be regarded as indication of a systemic reaction of plant to the local mechanical injury. The viral infection developed in LA leaves and spread to SAI and SAD leaves was documented by the ELISA-DASI method. The plant height and area of SAI and SAD leaves were lower in infected plants. The combined effect of mechanical damage and viral infection caused a decrease in P _N only in LA and SAD leaves. In SAD leaves, an increased relative height of the J step (V_J) in the O-J-I-P Chl fluorescence transient together with a lower B/A band ratio of thermoluminescence glow curves reflected a damage to the acceptor side of photosystem 2 (PS2) caused by the viral infection, and a faster kinetics of the induction of the photochemical quenching coefficient q_P of Chl fluorescence indicated a faster Q_A ^– re-oxidation in the remaining undamaged centres of PS2.     

Glutathione‐stabilized Cu nanocluster‐based fluorescent probe for sensitive and selective detection of Hg2+ in water

In this paper, an innovative and facile one‐pot method for synthesizing water‐soluble and stable fluorescent Cu nanoclusters (CuNCs), in which glutathione (GSH) served as protecting ligand and ascorbic acid (AA) as reducing agent was reported. The resultant CuNCs emitted blue‐green fluorescence at 440 nm, with a quantum yield (QD) of about 3.08%. In addition, the prepared CuNCs exhibited excellent properties such as good water solubility, photostability and high stability toward high ionic strength. On the basis of the selective quenching of Hg²⁺ on CuNCs fluorescence, which may be the result of Hg²⁺ ion‐induced aggregation of the CuNCs, the CuNCs was used for the selective and sensitive determination of Hg²⁺ in aqueous solution. The proposed analytical strategy permitted detection of Hg²⁺ in a linear range of 4 × 10^?8 to 6 × 10^?5 M, with a detection limit of 2.2 × 10^?8 M. Eventually, the practicability of this sensing approach was confirmed by its successful application to assay Hg²⁺ in tap water, Lotus lake water and river water samples with the quantitative spike recoveries ranging from 96.9% to 105.4%.     

Photosystem I of Chlamydomonas reinhardtii contains nine light-harvesting complexes (Lhca) located on one side of the core

In this work we have purified the Photosystem I (PSI) complex of Chlamydomonas reinhardtii to homogeneity. Biochemical, proteomic, spectroscopic, and structural analyses reveal the main properties of this PSI-LHCI supercomplex. The data show that the largest purified complex is composed of one core complex and nine Lhca antennas and that it contains all Lhca gene products. A projection map at 15 ? resolution obtained by electron microscopy reveals that the Lhcas are organized on one side of the core in a double half-ring arrangement, in contrast with previous suggestions. A series of stable disassembled PSI-LHCI intermediates was purified. The analysis of these complexes suggests the sequence of the assembly/disassembly process. It is shown that PSI-LHCI of C. reinhardtii is larger but far less stable than the complex from higher plants. Lhca2 and Lhca9 (the red-most antenna complexes), although present in the largest complex in 1:1 ratio with the core, are only loosely associated with it. This can explain the large variation in antenna composition of PSI-LHCI from C. reinhardtii found in the literature. The analysis of several subcomplexes with reduced antenna size allows determination of the position of Lhca2 and Lhca9 and leads to a proposal for a model of the organization of the Lhcas within the PSI-LHCI supercomplex.     

青藏高原东部高寒草甸54种禾本科植物种子的萌发特性

在实验室条件下观测了青藏高原东部高寒草甸54种禾本科植物的种子萌发特点。结果发现:在54种植物中,有43种植物种子萌发率都达到了50%,其中萌发率80%以上的物种有26种,60%~80%的有11种,40%~60%的有8种,20%~40%的有5种,小于20%的有4种; 萌发开始时间为3~5 d的植物有14种,6~8 d的植物有29种,9~10 d的植物有10种,大于10 d的有1种;萌发持续时间为1~7 d的植物有16种,8~14 d的植物有28种,15~21 d的有10种;达50%萌发率的时间为1~7 d的植物有11种,8~14 d的植物有27种,大于14 d的植物有5种,萌发率一直没达到50%的植物有11种。这些植物显示了4种萌发类型:爆发型、过渡型、缓萌型(萌发率大于50%的物种)和低萌型(萌发率小于50%的物种)。     

综述与专论: 认知行为疗法和虚拟现实疗法干预神经性疼痛的作用及机制

神经性疼痛（neuropathic pain，NP）是由外周或中枢躯体感觉系统的损伤或疾病导致的疼痛。药物治疗在镇痛中占据重要地位，但是过量药物治疗往往会引起严重的副作用，或在可耐受剂量下仅提供了部分的疼痛缓解。认知行为疗法（cognitive-behavioral therapy，CBT）和虚拟现实（virtual reality，VR）干预作为新的、非侵入性的，以及更为安全的疼痛替代治疗方法引起了广泛的关注。CBT和VR疗法可通过转移注意力、改变神经可塑性和神经环路，以及调节促炎和抗炎因子水平缓解神经性疼痛。本文旨在对神经性疼痛的发病机制以及CBT和VR疗法的镇痛效果和机制做出解析，从而为神经性疼痛的治疗干预提供重要的理论指导。