Precious things come in little packages

The 110-amino acid multidrug transporter from E. coli, EmrE, is a member of the family of MiniTexan or Smr drug transporters. EmrE can transport acriflavine, ethidium bromide, tetraphenylphosphonium (TPP+), benzalkonium and several other drugs with relatively high affinities. EmrE is an H+/drug antiporter, utilizing the proton electrochemical gradient generated across the bacterial cytoplasmic membrane by exchanging two protons with one substrate molecule. The EmrE multidrug transporter is unique in its small size and hydrophobic nature. Hydropathic analysis of the EmrE sequence predicts four alpha-helical transmembrane segments. This model is experimentally supported by FTIR studies that confirm the high alpha-helicity of the protein and by high-resolution heteronuclear NMR analysis of the protein structure. The TMS of EmrE are tightly packed in the membrane without any continuous aqueous domain, as was shown by Cysteine scanning experiments. These results suggest the existence of a hydrophobic pathway through which the substrates are translocated. EmrE is functional as a homo-oligomer as suggested by several lines of evidence, including co-reconstitution experiments of wild-type protein with inactive mutants in which negative dominance has been observed. EmrE has only one membrane embedded charged residue, Glu-14, that is conserved in more than fifty homologous proteins and it is a simple model system to study the role of carboxylic residues in ion-coupled transporters. We have used mutagenesis and chemical modification to show that Glu-14 is part of the substrate-binding site. Its role in proton binding and translocation was shown by a study of the effect of pH on ligand binding, uptake, efflux and exchange reactions. We conclude that Glu-14 is an essential part of a binding site, common to substrates and protons. The occupancy of this site is mutually exclusive and provides the basis of the simplest coupling of two fluxes. Because of some of its properties and its size, EmrE provides a unique system to understand mechanisms of substrate recognition and translocation.     

The trace metal economy of the coral holobiont: supplies,demands and exchanges

The juxtaposition of highly productive coral reef ecosystems in oligotrophic waters has spurred substantial interest and progress in our understanding of macronutrient uptake, exchange, and recycling among coral holobiont partners (host coral, dinoflagellate endosymbiont, endolithic algae, fungi, viruses, bacterial communities). By contrast, the contribution of trace metals to the physiological performance of the coral holobiont and, in turn, the functional ecology of reef-building corals remains unclear. The coral holobiont's trace metal economy is a network of supply, demand, and exchanges upheld by cross-kingdom symbiotic partnerships. Each partner has unique trace metal requirements that are central to their biochemical functions and the metabolic stability of the holobiont. Organismal homeostasis and the exchanges among partners determine the ability of the coral holobiont to adjust to fluctuating trace metal supplies in heterogeneous reef environments. This review details the requirements for trace metals in core biological processes and describes how metal exchanges among holobiont partners are key to sustaining complex nutritional symbioses in oligotrophic environments. Specifically, we discuss how trace metals contribute to partner compatibility, ability to cope with stress, and thereby to organismal fitness and distribution. Beyond holobiont trace metal cycling, we outline how the dynamic nature of the availability of environmental trace metal supplies can be influenced by a variability of abiotic factors (e.g. temperature, light, pH, etc.). Climate change will have profound consequences on the availability of trace metals and further intensify the myriad stressors that influence coral survival. Lastly, we suggest future research directions necessary for understanding the impacts of trace metals on the coral holobiont symbioses spanning subcellular to organismal levels, which will inform nutrient cycling in coral ecosystems more broadly. Collectively, this cross-scale elucidation of the role of trace metals for the coral holobiont will allow us to improve forecasts of future coral reef function.     

名贵茶花种质资源的RAPD分析

采用RAPD方法构建了国内外23个茶花品种的指纹图谱。从100个随机引物中筛选出的20个有效引物共产生136条DNA片段,遗传多态性带120条占总数88．2％。遗传相似性分析表明,各基因型间的Nei＇s相似系数分布在0．4386～0．8936之间,平均相似性系数为0．7668。通过非加权算术平均数聚类（UPGMA）法,绘制了它们的遗传关系树状图,23个品种可划分为3个类群。研究结果表明,RAPD技术可用于茶花品种的鉴别以及种质资源遗传多态性的研究。     

北京的珍贵自然遗产——植物多样性

植物多样性是一个地区最重要的自然遗产之一,是人类生存和发展不可缺少的依靠,认识并理解这一自然遗产,并在经济发展中特别加以保护,是不可推卸的责任.北京是举世公认的文化名都,它的众多的文化古迹有大量文献加以记述和评论,但其独特的自然遗产,一直未受到应有的注意.从物种和群落两个层次论述了北京地区植物多样性的组成和特点,并指出过渡性的气候及复杂的地质地貌条件,也就是它的地多样性（geodiversity）是形成其复杂的植物多样性的基础,最后对北京地区植物多样性当前面临的威胁及其缓解办法,提出建议.     

兰花,茂兰的另一张名片

茂兰的岛屿状喀斯特峰丛洼地地貌,特殊的碳酸盐岩着生基质,使这里的很多植物被打上了“茂兰”的标记。每一种茂兰特有植物的发现和命名,都记载着植物学家艰苦的工作和他们付出的汗水、心血,以及发现后的喜悦欣慰。白花兜兰的发现．也经历了这样一个曲折而漫长的过程。     

福建珍稀南药植物资源及其开发利用

基于多年南药植物引种、种植和驯化的实践经验,概述福建35种珍稀南药植物,编录了各植物的药用部位、性味及生境等,并提出南药资源合理开发和持续利用的建议。     

珍贵用材树种红椿的组培育苗技术初探

以红椿种子为外植体材料,对其组织培养技术进行初步研究。结果表明,适宜红椿种子无菌苗芽诱导的培养基为MS＋6-BA 0.5 mg·L^-1＋NAA 0.2 mg·L^-1,适宜的芽继代增殖培养基为2/3MS＋6-BA 0.5 mg·L^-1＋NAA 0.2 mg·L^-1＋GA3 1.0 mg·L^-1,适宜生根培养基为1/2MS＋IBA 0.5 mg·L^-1,以泥炭土、黄心土、河沙按1∶1∶1混合作为基质,移栽成活率达85%以上。     

Precious essences: female secretions promote sperm storage in Drosophila

Sperm that females receive during mating are stored in special places in the females' reproductive tracts. These storage sites serve to support and retain the sperm, maintaining the sperms' motility and, in mammals, permitting final sperm-maturation. The molecules that attract sperm to these sites and mediate what happens to them there have remained elusive. New research, using elegant genetic tools in Drosophila, shows that secretory cells associated with a sperm storage organ are important in sperm-supportive functions. When females lack function of these cells, they do not store sperm, or the sperm that they do store lose motility. Intriguingly, these effects influence gametes beyond the secretory cells' immediate vicinity. Loss of these cells eliminates the motility of sperm stored elsewhere in the reproductive tract and prevents the movement of eggs through the tract to exit the female. As a result of the latter problem, fertilized eggs hatch inside female flies that lack these secretory cells: instead of laying eggs, these females can "give birth" to live offspring. Because the cellular source of these gamete-regulating substances is now known, future studies can identify the specific molecules and mechanisms by which a female attracts sperm into storage and regulates the movement of sperm and eggs within her reproductive tract. It will be fascinating to determine how these molecules and mechanisms maintain gametes in active and viable forms and how evolution can modulate this to result in diverse reproductive strategies. Identification of these molecules also has potential practical implications for strategies to regulate the reproduction of insects of medical or agricultural importance.     

珍稀食用菌绣球菌研究进展

绣球菌为新近开发的一种珍稀食用菌,因其味道鲜美,富含β-葡聚糖而受到人们的关注。文中对绣球菌属的种类、我国人工栽培绣球菌的名称、人工栽培和液体发酵、营养和化学成分、药理学功能等方面的研究现状进行综述,对目前研究中存在的问题进行了分析,在此基础上,对其未来的研究方向进行了展望,旨在为其生物学研究和开发利用提供依据和借鉴。     

珍贵药材黄花倒水莲的群落结构及物种多样性研究

黄花倒水莲系华南民间常用且珍贵中药材。采用样方调查法对福建省三明地区黄花倒水莲群落的植物组成、群落结构和物种多样性进行了分析。结果表明,在26个样方、共计2600m2的样地内,群落有维管植物89科167属205种。种子植物属的区系成分划分为12个分布型和8个变型,热带性分布属稍占优势,占总属数的57.85%;温带性成分占总属数的40.7%。生活型谱分析显示群落包括藤本在内的高位芽植物占总种数的58.53%,其中以小高位芽和矮高位芽植物占优势;地面芽和地上芽占较大比例,以蕨类植物和多年生草本植物为主,地下芽和1年生植物很少。群落垂直结构分为乔木层、灌木层和草本层。物种丰富度指数、Simpson指数、Shannon-Wiener指数和Pielou均匀度指数分析表明:群落垂直结构多样性特点为草本层>灌木层>乔木层>层外层,草本层的各项多样性指数均显著大于其他层次。为黄花倒水莲人工栽培选择适生环境提供参考,提出了开发利用和资源保护的建议。     

Notes on paradigm economy

It is shown that assuming instances of syncretism to be systematic in the unmarked case may significantly reduce the number of possible inflection classes that can be generated on the basis of a given inventory of markers, without recourse to specific constraints like Carstairs’ (Allomorphy in Inflection, Croom Helm 1987) Paradigm Economy Principle or Carstairs-McCarthy’s (Language 70:737–787, 1994) No Blur Principle. If there is always one radically underspecified (i.e., elsewhere) marker per morphological domain, and if there is always one unique marker that is chosen in cases of marker competition, it turns out that there can be at most 2 ⁿ  − 1 inflection classes for n markers, independently of the number of instantiations of the grammatical category that the markers have to distribute over. The argument relies on the notion of marker deactivation combinations.