团藻目分子系统学研究进展

包含许多重要类群的团藻目在绿色植物系统演化中占有十分重要的地位。普遍认 为现在的绿色植物起源于团藻目的绿色鞭毛类,有人认为鞭毛细胞表面覆盖有鳞片的塔胞藻类是绿色植物的祖先。团藻目是分子系统学研究比较多和比较深入的一个类群,通过研究证实其有单一共同祖先,而莱茵衣藻在所有已经经过DNA测序分析系统发育的绿色单细胞类群中是最可能的种类。本文结合自己的工作,对国内外这一研究领域概况进行综述。     

团藻的结构和生殖

团藻(Volvox)属于绿藻门、团藻目植物,约有20种,是淡水池塘中常见的一类浮游藻类。常于夏季的一些临时积水坑中大量出现,有时形成纯群。团藻目的种类均具鞭毛能游动。衣藻属是此目中原始类型的代表,团藻则是该目中进化水平最高的类型。     

多细胞团藻分化年代超预期

团藻属植物是研究从单细胞到多细胞生命形式转变的一种模型，一项新研究指出，它从祖先那里分化的年代远远早于此前认为（约500077年到7500万年前）。团藻属及其亲缘物种组成的“团藻”显示出一种合作性质的结合——从嵌入一个粘性基质上的4个细胞到由5万个细胞组成的球形的、由鞭毛推动的团藻。     

团藻目群体鞭毛类的中国新记录

于2015年3月到7月在湖北省内多处水体采集浮游藻类样品,通过光学显微镜观察样品形态,共鉴定出团藻目群体鞭毛类3科5属8种。其中四豆藻科Tetrabaenaceae Nozaki et Itoh为中国新记录科,四豆藻属Tetra-baena（Dujardin）Fromentel和似团藻属Volvulina Playfair为中国新记录属,发现了5个新记录种分别为简单四豆藻Tetrabaena socialis（Dujardin）Nozaki et Itoh、科尔曼实球藻Pandorina colemaniae Nozaki、致密似团藻Vol-vulina compacta Nozaki、柱状空球藻Eudorina cylindrical Korshikov和单果空球藻Eudorina unicocca Smith。基于3种分子标记进行的系统发育分析验证了各样品的形态学鉴定;同时四豆藻科、盘藻科和团藻科均为单系类群,进一步支持了Nozaki的分类系统。     

绿色鞭毛藻类的新种及中国新记录种

作者在四川、广东、湖北等地发现了一些中国罕见和新的绿色鞭毛类,文中报道了其中团藻目6个属的5个新种,10个中国新记录,其中喙藻Myochloris和肾爿藻属Nephroselmis为中国新记录属,具孔衣藻、四川衣藻、纵纹衣藻、椭圆红球藻、中华拟四鞭为新种。     

团藻的培养与观察

团藻为绿藻门(Chlorophyta)团藻目(Volvocalea)中多细胞群体,国外藻类学者对团藻目各属培养研究已有多篇报导,而这些研究工作都是在室内培养的.随着植物学教学不断提高,需要随时提供新鲜的实验材料,为此,我们将团藻的分离培养方法作一报导.     

中国根鞭毛目—新纪录种

中国根鞭毛目—新纪录种宋碧玉,刘勇,刘顺淑１．武汉水利电力大学热动系４３００７２２．渝州大学恨鞭毛目种类为有鞭毛的变形虫类（ｆｌａｇｅｌｌａｔｅｄａｍｏｅｂａｅ）,是介于肉足虫（Ｓａｒｃｏｄ－ｉｎａ）和鞭毛虫（Ｍａｓｔｉｇｏｐｈｏｒａ）之间的一个类群...     

从团藻目植物来看植物界的一些进化趋势

在高中生物学“組织和器官”这一章的“細胞的集合和組織的出現”这一节中,采用了四种常见的团藻目植物——衣藻、盤藻、实球藻和团藻——来說明由單细胞生物到多細胞生物的发展过程,闡明由于有了細胞的集合,引起了生理上的分工,从而为組织的出現开辟了途徑。为什么要采用团藻目植物而不用别的材料呢?团藻目植物除了說明植物体由單細胞到多細胞的发展过程以外,还可以說明什么进化趋势呢?团藻目植物在植物界中的系統地位如何?怎样采集和观察它們呢?現在准备就这些問题来談一談。     

白蚁的社会组织和社会行为

白蚁属于等翅目昆虫,共有7科2 750种,这是昆虫纲中唯一的一个目,其所有的种类都靠消化道内共生的鞭毛类、原生动物利用和消化纤维素。介绍了白蚁社会组织和社会存为的特点,比较了白蚁与蚂蚁的异同,并指出两者相似是由于趋同进化,而两者不同是由于亲缘关系相距甚远,各来自不同祖先。     

盐藻的生物学特性与开发利用

盐藻即杜氏藻（Ｄｕｎａｌｉｅｌａ）,是绿藻门团藻目多睫毛藻科的一个属,包含约３０个种,其中最有代表性和应用最广的是盐生杜氏藻（Ｄ．Ｓａｌｉｎａ）。盐藻为单细胞藻类,外包一层薄胶鞘,无细胞壁。个体呈梨形、卵形或椭圆形,具２条等长鞭毛,可自由游动。藻体内...     

Ribosomal DNA and ITS-2 sequence comparisons as a tool for predicting genetic relatedness

The determination of the secondary structure of the internal transcribed spacer (ITS) regions separating nuclear ribosomal RNA genes of Chlorophytes has improved the fidelity of alignment of nuclear ribosomal ITS sequences from related organisms. Application of this information to sequences from green algae and plants suggested that a subset of the ITS-2 positions is relatively conserved. Organisms that can mate are identical at all of these 116 positions, or differ by at most, one nucleotide change. Here we sequenced and compared the ITS-1 and ITS-2 of 40 green flagellates in search of the nearest relative to Chlamydomonas reinhardtii. The analysis clearly revealed one unique candidate, C. incerta. Several ancillary benefits of the analysis included the identification of mislabelled cultures, the resolution of confusion concerning C. smithii, the discovery of misidentified sequences in GenBank derived from a green algal contaminant, and an overview of evolutionary relationships among the Volvocales, which is congruent with that derived from rDNA gene sequence comparisons but improves upon its resolution. The study further delineates the taxonomic level at which ITS sequences, in comparison to ribosomal gene sequences, are most useful in systematic and other studies. Received: 14 February 1997 / Accepted: 28 March 1997     

Phylogenetic position of endosymbiotic green algae in Paramecium bursaria Ehrenberg from Japan

Endosymbiotic green algae of Japanese Paramecium bursaria were phylogenetically analyzed based on DNA sequences from the ribosomal DNA operon (18S rDNA, ITS1, 5.8S rDNA, and ITS2). Phylogenetic trees constructed using 18S rDNA sequences showed that the symbionts belong to the Chlorella sensu stricto (Trebouxiophyceae) group. They are genetically closer to the C. vulgaris Beijerinck group than to C. kessleri Fott et Nováková as proposed previously. Branching order in C. vulgaris group was unresolved in 18S rDNA trees. Compared heterogeneities of 18S rDNA, ITS1, 5.8S r, and ITS2 among symbionts and two Chlorella species, indicated that the ITS2 region (and probably also ITS1) is better able to resolve phylogenetic problems in such closely related taxa. All six symbiotic sequences obtained here (approximately 4000-bp sequences of 18S rDNA, ITS1, 5.8S rDNA, and ITS2) were completely identical in each, strongly suggesting a common origin.     

IDENTIFICATION OF A PSYCHROPHILIC GREEN ALGA FROM LAKE BONNEY ANTARCTICA: CHLAMYDOMONAS RAUDENSIS ETTL. (UWO 241) CHLOROPHYCEAE1

An unusual psychrophilic green alga was isolated from the deepest portion of the photic zone (<0.1% of incident PAR) at a depth of 17 m in the permanently ice‐covered lake, Lake Bonney, Antarctica. Here we identify and report the first detailed morphological and molecular examination of this Antarctic green alga, which we refer to as strain UWO 241. To determine the taxonomic identity, UWO 241 was examined using LM and TEM and partial sequences of the small subunit (SSU), internal transcribed spacer (ITS) 1 and ITS2 regions (including the 5.8S) of the ribosomal operon. These data were compared with those of previously described taxa. We identified UWO 241 as a strain of Chlamydomonas raudensis Ettl (SAG 49.72). Chlamydomonas raudensis is closely related to C. noctigama Korshikov (UTEX 2289) as well as foraminifer symbionts such as C. hedleyi Lee, Crockett, Hagen et Stone (ATCC 50216). In addition, its morphology, pigment complement, and phototactic response to temperature are reported. Chlamydomonas raudensis (UWO 241) contains relatively high levels of lutein and low chl a/b ratios (1.6±0.15), and the phototactic response was temperature dependent. The Antarctic isolate (UWO 241) included the typical photosynthetic pigments found in all chl a/b containing green algae. It possesses a small eyespot and, interestingly, was positively phototactic only at higher nonpermissive growth temperatures. Comparison of SSU and ITS rDNA sequences confirms the identification of the strain UWO 241 as C. raudensis Ettl and contradicts the previous designation as C. subcaudata Wille.     

Phylogeny of the quadriflagellate Volvocales (Chlorophyceae) based on chloroplast multigene sequences

Since the phylogenetic relationships of the green plants (green algae and land plants) have been extensively studied using 18S ribosomal RNA sequences, change in the arrangement of basal bodies in flagellate cells is considered to be one of the major evolutionary events in the green plants. However, the phylogenetic relationships between biflagellate and quadriflagellate species within the Volvocales remain uncertain. This study examined the phylogeny of three genera of quadriflagellate Volvocales (Carteria, Pseudocarteria, and Hafniomonas) using concatenated sequences from three chloroplast genes. Using these multigene sequences, all three quadriflagellate genera were basal to other members (biflagellates) of the CW (clockwise) group (the Volvocales and their relatives, the Chlorophyceae) and formed three robust clades. Since the flagellar apparatuses of these three quadriflagellate lineages are diverse, including counter clockwise (CCW) and CW orientation of the basal bodies, the CW orientation of the basal bodies might have evolved from the CCW orientation in the ancestral quadriflagellate volvocalean algae, giving rise to the biflagellates, major members of the CW group.     

Plectin-like proteins are present in cells of Chlamydomonas eugametos (Volvocales)

Using both monoclonal and polyclonal antibodies against mammalian plectin (multifunctional protein cross-linking cytoskeletal structures, mainly intermediate filaments, in mammalian cells), several putative isoforms of plectin-like proteins were found in protein extracts from the green algaChlamydomonas eugametos (Volvocales). Immunofluorescence and immunoblotting revealed that some of the plectin-like proteins were present in perinuclear region or localized near the cell wall, probably being attached to the cytoplasmic membrane.     

Phylogenetic relationships of the green algeVolvox carteri deduced from small-subunit ribosomal RNA comparisons

Summary The 1788-nucleotide sequence of the small-subunit ribosomal RNA (srRNA) coding region from the chlorophyteVolvox carteri was determined. The secondary structure bears features typical of the universal model of srRNA, including about 40 helices and a division into four domains. Phylogenetic relationships to 17 other eukaryotes, including two other chlorophytes, were explored by comparing srRNA sequences. Similarity values and the inspection of phylogenetic trees derived by distance matrix methods revealed a close relationship betweenV. carteri andChlamydomonas reinhardtii. The results are consistent with the view that these Volvocales, and the third green alga,Nanochlorum eucaryotum, are more closely related to higher plants than to any other major eukaryotic group, but constitute a distinct lineage that has long been separated from the line leading to the higher plants.     

中药乌头及其近缘种的rDNA—ITS序列分析

运用PCR扩增产物直接测序的方法对云南、安徽的乌头及其近缘种植物的ITS区碱基序列测定。表明核糖体DNA中ITS区的完整序列（包括ITS1,ITS2和5．8s）,4种乌头属植物的ITS1序列长度为249bp,云南鸟头和安徽乌头及黄山鸟头ITS2序列长度为189bp,赣皖乌头ITS2序列长度为217bp。运用Mega2软件进行系统分析得到系统进化树。ITS序列特征是乌头鉴别的有效分子标记。     

Molecular Identification of Algal Endosymbionts in Large Miliolid Foraminifera: 1. Chlorophytes

Large miliolid foraminifers bear various types of algal endosymbionts including chlorophytes, dinoflagellates, rhodophytes, and diatoms. Symbiosis plays a key role in the adaptation of large foraminifera to survival and growth in oligotrophic seas. The identity and diversity of foraminiferal symbionts, however, remain largely unknown. In the present work we use ribosomal DNA (rDNA) sequences to identify chlorophyte endosymbionts in large miliolid foraminifera of the superfamily Soritacea. Partial 18S and complete Internal Transcribed Spacer (ITS) rDNA sequences were obtained from symbionts of eight species representing all genera of extant chlorophyte-bearing Soritacea. Phylogenetic analysis of the sequences confirms the previous fine structure-based identification of these endosymbionts as belonging to the genus Chlamydomonas. All foraminiferal symbionts form a monophyletic group closely related to Chlamydomonas noctigama. The group is composed of seven types identified in this study, including one previously morphologically described species, Chlamydomonas hedleyi. Each of these types can be considered as a separate species, based on the comparison of genetic differences observed between other established Chlamydomonas species. Several foraminiferal species share the same symbiont type, but only one species, Archaias angulatus, was found to bear more than one type.     

The pherophorins: common, versatile building blocks in the evolution of extracellular matrix architecture in Volvocales

Green algae of the order Volvocales provide an unrivalled opportunity for exploring the transition from unicellularity to multicellularity. They range from unicells, like Chlamydomonas, through homocytic colonial forms with increasing cooperation of individual cells, like Gonium or Pandorina, to heterocytic multicellular forms with different cell types and a complete division of labour, like Volvox. A fundamental requirement for the evolution of multicellularity is the development of a complex, multifunctional extracellular matrix (ECM). The ECM has many functions, which can change under developmental control or as a result of environmental factors. Here molecular data from 15 novel proteins are presented. These proteins have been identified in Chlamydomonas reinhardtii, Gonium pectorale, Pandorina morum and Volvox carteri, and all belong to a single protein family, the pherophorins. Pherophorin-V1 is shown to be a glycoprotein localized to the 'cellular zone' of the V. carteri ECM. Pherophorin-V1 and -V2 mRNAs are strongly induced not only by the sex inducer, which triggers sexual development at extremely low concentrations, but also by mechanical wounding. Like the extensins of higher plants, which are also developmentally controlled or sometimes inducible by wounding, the pherophorins contain a (hydroxy-)proline-rich (HR) rod-like domain and are abundant within the extracellular compartment. In contrast to most extensins, pherophorins have additional globular A and B domains on both ends of the HR domains. Therefore pherophorins most closely resemble a particular class of higher plant extensin, the solanaceous lectins (e.g. potato lectin), suggesting multivalent carbohydrate-binding functions are present within the A and B domains and are responsible for cross-linking. Our results suggest that pherophorins are used as the building blocks for the extracellular scaffold throughout the Volvocales, with the characteristic mesh sizes in different ECM structures being a result of the highly diverse extensions of the HR domains. Pherophorins have therefore been a versatile element during the evolution of ECM architecture in these green algae.