Ultrastructure of P-protein inHevea brasiliensis during sieve-tube development and after wounding

Summary P-protein and the changes it undergoes after wounding of sieve tubes of secondary phloem in one- to two-year old shoots ofHevea brasiliensis has been studied using electron microscopy. The P-protein in the form of tubules with a diameter of 8–9 nm and a lumen of 2–2.5 nm occurred in differentiating sieve elements and appeared as compact bodies which consisted of small aggregates of the tubules. As the sieve elements matured, these P-protein bodies dispersed with a disaggregation of the tubules before they turned into striated fibrils, 10–11 nm in diameter. In wounding experiments, as the mature sieve elements collapsed after cutting, their striated P-protein converted into tubules. These tubules were the same in ultrastructure as the tubules in differentiating sieve elements and they often were arranged in crystalline aggregates.     

以“环境微生物学”为载体的环境生态工程专业本科生科创能力培养

环境生态工程是一个设立较晚的新专业,其基本的教学体系和专业课程设计还有待摸索和完善。"环境微生物学"作为环境生态工程专业普遍设置的专业必修课,其授课内容和形式如何适应专业整体的培养需求是一个值得探讨的问题。我们结合所在学校、学院的特点和优势,提出将融入海洋特色和生态学思想的"环境微生物学"作为载体,结合课上理论教学、学生课堂报告、课下专题培训和实验技能培养等形式,培养环境生态工程专业本科生的科创能力。这可为同专业开设"环境微生物学"课程的教师提供教学参考,也可以为其他院校环境生态工程专业本科生科创能力的培养提供借鉴。     

金沙江河谷特有单种属植物丁茜的染色体数目报道

报道茜草科植物丁茜（Trailliaedoxa gracilis）的染色体数目,2n=22,基数x=11。     

In vivo evidence for the iron-binding activity of an iron-sulfur cluster assembly protein IscA in Escherichia coli

IscA is a key member of the iron-sulfur cluster assembly machinery in prokaryotic and eukaryotic organisms; however, the physiological function of IscA still remains elusive. In the present paper we report the in vivo evidence demonstrating the iron-binding activity of IscA in Escherichia coli cells. Supplement of exogenous iron (1 μM) in M9 minimal medium is sufficient to maximize the iron binding in IscA expressed in E. coli cells under aerobic growth conditions. In contrast, IscU, an iron-sulfur cluster assembly scaffold protein, or CyaY, a bacterial frataxin homologue, fails to bind any iron in E. coli cells under the same experimental conditions. Interestingly, the strong iron-binding activity of IscA is greatly diminished in E. coli cells under anaerobic growth conditions. Additional studies reveal that oxygen in medium promotes the iron binding in IscA, and that the iron binding in IscA in turn prevents formation of biologically inaccessible ferric hydroxide under aerobic conditions. Consistent with the differential iron-binding activity of IscA under aerobic and anaerobic conditions, we find that IscA and its paralogue SufA are essential for the iron-sulfur cluster assembly in E. coli cells under aerobic growth conditions, but not under anaerobic growth conditions. The results provide in vivo evidence that IscA may act as an iron chaperone for the biogenesis of iron-sulfur clusters in E. coli cells under aerobic conditions.     

垦殖对沼泽湿地土壤呼吸速率的影响

三江平原是我国最大的沼泽化低平原,同时也是受人类活动影响最剧烈的区域之一。选取三江平原两类典型湿地-常年积水的毛果苔草(Carex lasiocapa)沼泽和季节性积水的小叶章(Deyeuxia angustifolia)草甸及由其垦殖的水田和旱田为研究对象,利用静态暗箱-气相色谱法对土壤呼吸速率进行了观测。研究结果表明,小叶章草甸与毛果苔草沼泽土壤呼吸速率的季节变化形式相同,为单峰型,在夏季出现排放峰值,而冬季呼吸速率最低。沼泽湿地垦殖为旱田后,土壤呼吸速率的季节变化形式未发生变化,但垦殖为水田后,土壤呼吸速率排放峰值的时间延后在秋季出现。毛果苔草沼泽、小叶章草甸、旱田及水田通过土壤呼吸释放的碳量分别为(3.1±0.4)、(4.8±0.7)、(2.8±0.4)、(2.2±0.3)tC.hm-2.a-1。毛果苔草沼泽土壤呼吸速率低于小叶章草甸是由沼泽湿地的积水环境差异造成的,而沼泽湿地垦殖为农田后土壤呼吸作用减弱,主要是由于垦殖后土壤有机碳含量大幅降低所致。相关分析表明,温度和土壤湿度(或积水深度)是影响土壤呼吸速率的重要因素,温度与小叶章草甸、毛果苔草沼泽以及旱田土壤呼吸速率呈显著指数关系,Q10值分别为2.1、2.5和1.8,沼泽湿地垦殖为旱田后温度敏感性指数降低,主要是由于土壤微生物营养源减少从而对微生物营养供应受限造成的。小叶章草甸、毛果苔草沼泽、旱田以及水田土壤呼吸速率与土壤湿度/积水深度之间的关系可用线性或二次曲线方程来描述。     

预测性编码在视听觉神经活动中的典型表征

现代神经科学研究指出,大脑是外部世界的“预测器”,它能根据先验知识和当前信息对即将到来的感觉信息进行主动估计,从而完成与外部世界的高效交互。预测性编码是描述预期作用机制的主要理论模型,梳理其在解释视、听觉神经现象方面的研究进展,可为深入理解大脑工作模式提供新的理论基础。本文简述了预测性编码的内容;从常用范式、典型现象、面临争议等方面梳理预期与感觉输入相互作用的典型研究;从有预期无刺激的神经表征、预期相关神经振荡模式两方面简述预期独立于刺激的内源性神经表征;进而回顾了支持预测性编码中分级结构的神经生理证据及重要神经结构。最后,本文从深化理论研究、助力疾病诊疗、启发脑-机接口技术等方面对预测性编码相关研究的发展进行了展望。深入理解预测性编码在视、听觉神经活动中的计算模型及神经表征,有望为揭示大脑感知觉神经活动工作模式开辟新途径。     

哈维氏弧菌胞外蛋白酶基因的表型克隆与序列分析

哈维氏弧菌是引起大黄鱼疾病的主要致病菌之一,胞外蛋白酶是哈维氏弧菌GYC1108-1的主要致病因子。利用表型克隆技术,用Sau3AⅠ将提取的哈维氏弧菌基因组DNA酶切成短片段,纯化回收1-5 kb的片段与BamH I酶切的pUC118在T4连接酶的作用下进行连接,并转化感受态细胞TG1,在含0.5%脱脂奶和100μg/mL氨苄青霉素的LB平板上筛选胞外蛋白酶阳性株,命名为YZ。测定阳性株YZ的胞外蛋白酶活性,并对阳性株的重组质粒的插入片段进行序列测定,分析开放阅读框,确定胞外蛋白酶基因编码区。发现蛋白酶基因的ORF编码531个氨基酸,在起始密码子ATG上游存在一个核糖体结合位点(SD),其上游的启动区与大肠杆菌的σ70启动区和枯草芽孢杆菌的启动区高度同源。在终止子(TAG)下游,存在两个反向重复序列,为推导的2个转录终止子。哈维氏弧菌胞外蛋白酶基因的克隆与诠释为哈维氏弧菌致病机理和疫苗的开发奠定了基础。     

A new neutralizing antibody against botulinum neurotoxin B recognizes the protein receptor binding sites for synaptotagmins II

Botulinum neurotoxins (BoNts) pose a biological hazard to humans and a serious potential bioweapon threat. Given the safety concern regarding the currently used equine antitoxin therapy for botulism, it is imperative to develop agents that are effective binding inhibitors. The aim of this study was to identify a novel neutralizing antibody against botulinum neurotoxin B (BoNtb) that recognizes the protein receptor binding sites for synaptotagmins II. This antibody showed significant dose-dependent protection against lethal toxin challenge in vivo at an intraperitoneal (i.p.) dose 10 times the half lethal dose (LD50). We proved that the efficacy of SC12 was based on its counteraction on the recognition and binding of BoNtb to target cells, resulting from the combination of antibody with the high affinity (KD: 1.34 nM) to protein receptor binding sites of BoNt by targeting a 25-mer dominant antigenic site on Hcc region (residues 1253–1277). The structure of the site targeted by this antibody overlaps the pocket-like protein receptor binding sites located at the distal tip of toxin molecule. Information gained from this study will facilitate the development of potent inhibitors that prevent the binding of BoNts with its receptors.     

The Exo70 Subunit of the Exocyst Is an Effector for Both Cdc42 and Rho3 Function in Polarized Exocytosis

The Rho3 and Cdc42 members of the Rho GTPase family are important regulators of exocytosis in yeast. However, the precise mechanism by which they regulate this process is controversial. Here, we present evidence that the Exo70 component of the exocyst complex is a direct effector of both Rho3 and Cdc42. We identify gain-of-function mutants in EXO70 that potently suppress mutants in RHO3 and CDC42 defective for exocytic function. We show that Exo70 has the biochemical properties expected of a direct effector for both Rho3 and Cdc42. Surprisingly, we find that C-terminal prenylation of these GTPases both promotes the interaction and influences the sites of binding within Exo70. Finally, we demonstrate that the phenotypes associated with novel loss-of-function mutants in EXO70, are entirely consistent with Exo70 as an effector for both Rho3 and Cdc42 function in secretion. These data suggest that interaction with the Exo70 component of the exocyst is a key event in spatial regulation of exocytosis by Rho GTPases.