被子植物系统学中花发育研究的进展及对今后研究的思考

从花发育研究的方法、花发育与被子植物花部结构的多样性、花发育与被子植物的系统发育以及 花发育的分子遗传学等四个方面对近年来被子植物系统学中花发育研究的主要进展作一综述,例举了 一些重要结果。同时,对该领域今后研究的方向和应注意的一些问题作了简要评论。作者认为植物的 形态结构可以看作是一个时空过程,在系统学研究中对花部性状的分析和认识应该树立动态的观点。 今后应该从动态的角度开展被子植物花的发生和发育以及性状在不同类群间的比较等方面的广泛研究,并加强对在被子植物花的起源和演化中起重要作用的花部同源异型现象的发育过程的观察。     

DNA水平上的植物系统学研究进展

分子钟假说为在分子水平上研究生物进化提供了理论基础,分子系统学已成为当前生物学领域中的热门课题,并取得了许多引人注目的进展。本方要以高等植物为对象,从核ＤＮＡ,叶绿体ＤＮＡ和线粒体ＤＮＡ三方面对植物分子系统学进行了综述。     

核基因在两栖爬行动物分子系统学中的研究进展

从DNA水平探索生物进化的理论、生物类群的演化历史具有重要的意义,应用DNA序列研究生物的系统发育和进化规律成为当前分子系统学研究的热点,与线粒体DNA相比,核基因由于包含有更加丰富的生物学信息,运用核基因序列或将核基因序列与线粒体基因序列相结合研究两栖爬行动物的系统发育,正成为分子系统学领域的新的发展趋势.Rag-1、Rag-2、tyrosinase、rhodopsin、C-mos等核基因已在两栖爬行动物分子系统学中得到了广泛的应用.由于目前的技术手段等诸多因素,限制了更多的核基因用于两栖爬行动物分子系统学研究.为此简要介绍了目前核基因在两栖爬行动物分子系统学方面的研究进展,并分析了核基因序列在分子系统学应用上面临的问题和应用前景.     

直翅目昆虫分子系统学研究新进展

对1994年以来国内外在直翅目昆虫种群遗传变异及进化、种及种下阶元的分类鉴定、种上阶元的系统发育分析及分子进化等分子系统学方面的研究进展进行了综述。近年来,蝗亚目昆虫分子系统学方面的研究成果较为丰富,而有关螽亚目的分子系统学研究较少。线粒体基因和核基因序列联合分析、整个基因组全序列分析以及分子数据与形态学的密切结合将是分子系统学未来发展的主要研究手段。     

核基因序列在昆虫分子系统学上的应用

核基因中含有更加丰富的生物学信息,运用核基因序列或将核基因序列与线粒体基因序列相结合研究昆虫的系统发育正成为分子系统学领域的一种发展趋势.核糖体基因中18S rDNA、28S rDNA、ITS已在昆虫分子系统学中得到了广泛的应用.与核糖体基因相比,虽然编码蛋白的核基因应用于昆虫分子系统学的种类不少,但大部分都是应用于双翅目和鳞翅目昆虫的分子系统学研究中,能够成功地普遍用于多个目昆虫的系统学研究的核基因并不多.本文简要介绍了应用于昆虫分子系统学的核中核糖体基因和编码蛋白的核基因,并分析了核基因序列在分子系统学应用上的局限性和应用前景.     

块菌属分子系统学及菌根共生机制研究进展

块菌属Tuber是一类珍贵的地下生外生菌根食药用真菌,具有重要的经济和生态价值。分子生物学技术的快速发展尤其是高通量测序技术在块菌属研究领域的应用,极大地推动了块菌属分类、系统学、生态、生化、菌根共生机制及人工种植等研究。本文重点从块菌的分子系统学、群体遗传学及菌根共生机制3个方面对近5年的研究成果进行综述,并对其研究和应用前景进行了展望。     

被子植物花的起源:假说和证据

达尔文的 令人讨厌之谜 ,即被子植物的起源和早期演化 ,一直是植物系统学研究领域的热点 .被子植物区别于其它植物类群的一个显著特征就是花 ,因此 ,解决被子植物的起源之谜很大程度上取决于对被子植物花器官起源的研究 .对被子植物花器官的详尽研究已经在形态、解剖、古植物、形态发生、分子等方面积累了大量的证据 ,植物学家基于这些证据为被子植物花器官的起源提出了各种各样的解释 .综述了迄今为止被子植物花器官起源的主要学说流派 ,如 :真花学说、假花学说、生殖叶学说、生殖茎节学说、生花植物学说、新假花学说、古草本学说和 ANITA学说等 .根据研究手段和获得证据的方式 ,作者将被子植物花器官起源研究划分为 5个阶段 ,并简要阐述了各个阶段的代表学说和主要研究特点     

被子植物花的起源：假说和证据

达尔文的“令人讨厌之谜”,即被子植物的起源和早期演化,一直是植物系统学研究领域的热点。被子植物区别于其它植物类群的一个显著特征就是花,因此,解决被子植物的起源之谜很大程度上取决于对被子植物花器官起源的研究,对被子植物花器官的详尽研究已经在形态、解剖、古植物、形态发生、分子等方面积累了大量的证据,植物学家基于这些证据为被子植物花器官的起源提出了各种各样的解释。综述了迄今为止被子植物花器官起源的主要学说流派,如：真花学说、假花学说、生殖叶学说、生殖茎节学说、生花植物学说、新假花学说、古草本学说和ANITA学说等。根据研究手段和获得证据的方式。作者将被子植物花器官起源研究划分为5个阶段,并简要阐述了各个阶段的代表学说和主要研究特点。     

蓝藻的分子系统学研究

藻类分子系统学是一门新兴的学科。介绍了蓝藻分子系统学的发展、定义和蓝藻分子系统学的研究方法,并举例说明了各种方法的应用。同时,对蓝藻分子系统学发展前景作出了展望。     

分子生物学技术在昆虫系统学研究中的应用

分子生物学技术应用于昆虫系统学研究,是８０年代末新兴起来的,近几年来发展相当迅速。为了把握这个研究方向,并促进这个研究领域的发展,作者从研究方法、研究内容、研究对象等方面着手,对近１０年来分子生物学技术应用于昆虫系统学中的研究进展进行了概括和总结。介绍了ＤＮＡ序列测定、ＲＦＬＰ,分子杂交技术、ＲＦＰＬ、分子杂交技术、ＲＡＰＤ、ＳＳＣＰ及ＤＳＣＰ等几种主要方法及其应用情况,并从种及种下阶元的分类鉴定     

Floral structure and evolution of primitive angiosperms: Recent advances

Concepts of primitive angiosperm flowers have changed in recent years due to new studies on relic archaic groups, new paleobotanical finds and the addition of molecular biological techniques to the study of angiosperm systematics and evolution.Magnoliidae are still the hot group, but emphasis is now on small primitive flowers with few organs and also on the great lability of organ number. Of the extant groups, a potential basal position of the paleoherbs has been discussed by some authors. Although some paleoherbs have a simple gynoecium with a single orthotropous ovule, anatropous ovules may still be seen as plesiomorphic in angiosperms. Anatropy is not necessarily a consequence of the advent of closed carpels. It may also exhibit biological advantages under other circumstances as is the case in podocarps among gymnosperms. Valvate anthers have now been found in most larger subgroups of theMagnoliidae (recently also in paleoherbs) and in some Cretaceous fossils. Nevertheless, as seen from its systematic distribution, valvate dehiscence is not necessarily plesiomorphic for the angiosperms, but may be a facultative by-product of the thick connectives and comparatively undifferentiated anther shape inMagnoliidae and lowerHamamelididae. A perianth is relatively simple in extantMagnoliidae or even wanting in some families. In groups with naked flowers the perianth may have been easily lost because integration in the floral architecture was less pronounced than in more advanced angiosperm groups. Problems with the comparison of paleoherb flowers with those ofGnetales are discussed. The rapid growth of information from paleobotany and molecular systematics requires an especially open attitude towards the evaluation of various hypotheses on early flower evolution in the coming years.     

POLLINATOR-MEDIATED SELECTION ON FLORAL DISPLAY AND FLOWERING TIME IN THE PERENNIAL HERB ARABIDOPSIS LYRATA

The evolution of floral display and flowering time in animal-pollinated plants is commonly attributed to pollinator-mediated selection. Yet, the causes of selection on flowering phenology and traits contributing to floral display have rarely been tested experimentally in natural populations. We quantified phenotypic selection on morphological and phenological characters in the perennial, outcrossing herb Arabidopsis lyrata in two years using female reproductive success as a proxy of fitness. To determine whether selection on floral display and flowering phenology can be attributed to interactions with pollinators, selection was quantified both for open-pollinated controls and for plants receiving supplemental hand-pollination. We documented directional selection for many flowers, large petals, late start of flowering, and early end of flowering. Seed output was pollen-limited in both years and supplemental hand-pollination reduced the magnitude of selection on number of flowers, and reversed the direction of selection on end of flowering. The results demonstrate that interactions with pollinators may affect the strength of selection on floral display and the direction of selection on phenology of flowering in natural plant populations. They thus support the contention that pollinators can drive the evolution of both floral display and flowering time.     

离体植物花芽和花器官的发育研究进展

在近二十几年,尤其是近十年由于离体培养技术的完善和进一步向精确的层次的发展,已使得许多种植物花序、花芽和单独花器官以及部分的花器官在体外成功地进行了培养和尝试,并且对花芽及花器官的离体发育有了更深入的认识。不同植物的花发育需要不同的植物生长调节剂以及它们的不同配比,并且不同植物在其花发育所需要的营养因子也存在着相当大的差异性。这种差异性又随植物器官及花发育的不同阶段而受到加大或缩小。通过对正常花及突变体花进行的离体培养实验研究已经对一些花器官发生过程中的调节程序有了新的了解。利用离体培养技术,包括刚发展起来的薄层细胞培养技术在阐明花发育的机理、形态建成的分子机制以及成花梯度的物质基础等问题上具有广阔的潜力。     

Bacterial evolution and silicon

This review examines the possible role of silicon in molecular evolution. It is possible silicon participated in early molecular evolution by providing a stable mineral surface or gel structure where the assembly and replication of primitive genetic information occurred. However, as molecular evolution proceeded, silicon was not required in the evolution of C-based organisms. Silicon can be accumulated by diatoms and other living organisms such as silicoflagellates, some xanthophytes, radiolarians and actinopods and plants such as grasses, ferns, horseradish, some trees and flowers, some sponges, insects and invertebrates and bacteria and fungi. Silicon also has a role in synthesis of DNA, DNA polymerase and thymidylate kinase activity in diatoms. It is not unreasonable to examine the role of silicon in early molecular evolution as it may have been part of a micro-environment in which assembly of genetic information occurred.     

Reconstructing the ancestral angiosperm flower and its initial specializations

Increasingly robust understanding of angiosperm phylogeny allows more secure reconstruction of the flower in the most recent common ancestor of extant angiosperms and its early evolution. The surprising emergence of several extant and fossil taxa with simple flowers near the base of the angiosperms-Chloranthaceae, Ceratophyllum, Hydatellaceae, and the Early Cretaceous fossil Archaefructus (the last three are water plants)-has brought a new twist to this problem. We evaluate early floral evolution in angiosperms by parsimony optimization of morphological characters on phylogenetic trees derived from morphological and molecular data. Our analyses imply that Ceratophyllum may be related to Chloranthaceae, and Archaefructus to either Hydatellaceae or Ceratophyllum. Inferred ancestral features include more than two whorls (or series) of tepals and stamens, stamens with protruding adaxial or lateral pollen sacs, several free, ascidiate carpels closed by secretion, extended stigma, extragynoecial compitum, and one or several ventral pendent ovule(s). The ancestral state in other characters is equivocal: e.g., bisexual vs. unisexual flowers, whorled vs. spiral floral phyllotaxis, presence vs. absence of tepal differentiation, anatropous vs. orthotropous ovules. Our results indicate that the simple flowers of the newly recognized basal groups are reduced rather than primitively simple.     

Evolution by acquisition: the case for horizontal gene transfers

One of the most debated questions in the field of molecular evolution is the possible role of horizontal transfer in evolution. Of all the claims that have been made over the years, those reporting transfers between eukaryotes and prokaryotes are the most controversial. Here we present the cases for and against several such possible gene acquisitions.     

THE GENETICS OF GENDER AND THE EFFECTS OF GENDER ON FLORAL CHARACTERS IN GYNODIOECIOUS PHACELIA LINEARIS (HYDROPHYLLACEAE)

The evolution of gynodioecy depends in part on the location (nucleus or cytoplasm) of gender-determining genes. Characters genetically correlated with gender also can be important in the evolution of this sexual system. For example, gender differences in the costs of flowers affect the potential for resource compensation by females for the loss of male function. This paper reports the genetics of gender and the nature of secondary sex characters of flowers in Phacelia linearis (Hydrophyllaceae), a gynodioecious annual in which females exhibit substantial compensation. A single nuclear gene has a major effect on gender, recessive homozygotes being male-sterile, but not all the data can be explained by this or other simple inheritance models. In nature, hermaphrodites have wider corollas than females and begin to flower slightly later than females. In a common environment, gender effects on corolla size are modified by genetic background and/or maternal effects. Hermaphrodite flowers have 15% greater dry biomass than female flowers, but similar ovule number and nectar sugar production. Hermaphrodite and female flowers differ in the linear dimensions and biomass allocation of several floral organs. In particular, the androecia and corollas of female flowers are smaller than those of hermaphrodite flowers, both in absolute terms and relative to the size of the rest of the flower. Corolla size reduction could be an important source of resources for compensation by females.     

Phylogenetic insights into the correlates of dioecy in meadow-rues (Thalictrum, Ranunculaceae)

Numerous studies have examined the evolution of sexual systems in angiosperms, but few explore the interaction between these and the evolution of pollination mode. Wind pollination is often associated with unisexual flowers, but which evolved first and played a causative role in the evolution of the other is unclear. Thalictrum, meadow-rues (Ranunculaceae), provides a unique opportunity to study the evolution of these traits because it contains insect and wind pollination and four sexual systems. We used a phylogenetic approach to reconstruct ancestral states for sexual system, pollination mode, and geographic distribution in Thalictrum, and tested for correlations to uncover the factors involved in the evolution of unisexuality and wind pollination. Our results show that dioecy, andro- and gynomonoecy evolved at least twice from hermaphroditism. Wind pollination, unisexual flowers, and New World distribution were all significantly correlated. Wind pollination may have evolved early in the genus, followed by multiple losses and gains, and likely preceded the origin of unisexual flowers in several cases; we found no evidence for unisexual flowers evolving prior to wind pollination. Given a broad scale study showing the evolution of dioecy before wind pollination, our results from a finer scale analysis highlight that different evolutionary pathways are likely to occur throughout angiosperms.     

SHORT-TERM EVOLUTION IN THE SIZE AND SHAPE OF PEA APHIDS

Phenotypic evolution in contemporary populations can generally be witnessed only when novel selective forces produce rapid evolution. Examples of conditions that have led to rapid evolution include drastic environmental change, invasion of a new predator, or a host-range expansion. In cyclical parthenogens, however, yearly cycles of phenotypic evolution may occur due to the loss of adaptation during recombination in the sexual phase (genetic slippage), permitting an opportunity to observe adaptive evolutionary change in contemporary populations that are not necessarily subject to new patterns of natural selection. In insect herbivores, comparative studies suggest that morphological features that aid individuals in remaining on the plant or exploiting it as a food source are likely targets for selection. Here, we estimated the genetic variability of morphological traits in a cyclical parthenogen, the pea aphid (Acyrthosiphon pisum), to determine the potential for their evolution and we tested the hypothesis that size and/or shape evolves by clonal selection during one season of parthenogenetic reproduction. Genetic variation in a set of morphological traits was estimated using laboratory-reared descendents of clones collected from a single alfalfa field in May 1988 and April 1989 (henceforth, the “early” collections). In both years, there was significant clonal heritability early in the season both for overall morphology and for several individual aspects of size and shape. Because the course of short-term evolutionary change in the multivariate phenotype is a function of patterns of genetic covariance among characters, genetic correlations between size and 12 shape variables were also estimated for these early collections. A comparison between the mean phenotype of each early collection and that of a corresponding “late” collection made from the same field seven to eight clonal generations later in the same years revealed qualitatively similar changes in the average multivariate morphological phenotypes between the time periods in both years, although the difference was only significant for the 1989 samples. The pattern of genetic correlations that we estimated early in the 1989 season between overall size and various shape variables suggests that the observed short-term evolutionary changes in shape could have been due to natural selection acting only to increase overall size. We tested this hypothesis by estimating selection on size using a separate data set in which both demographic and morphological variables were measured on individuals reared under field conditions. Highly significant regressions of individual relative fitness on size were found for two major fitness components. Thus, it is likely that the evolutionary change in morphology that we observed is attributable to natural selection, possibly acting primarily through body size. A shift back to smaller size between the late 1988 and early 1989 collections from the same field suggests that either a cost of recombination or opposing selective forces during overwintering may produce persistent yearly cycles of morphological evolution in this cyclically parthenogenetic species.