胚珠发育的分子机理

胚珠是研究器官形态发生和模式建成遗传分子机理的一个理想系统.近年来,关于胚珠特征的决定、模式建成、珠被形态建成和胚囊形成等发育事件分子机理的研究取得了重要进展,初步建立了胚珠发育的基因调控模型.同时,离体花器官再生系统为研究激素调控胚珠发育的机理提供了有效途径.本文对拟南芥(Arabidopsis thaliana)胚珠发育的分子调控机制进行了综述.     

被子植物花器官发育的模型演变和分子调控

基于模式植物拟南芥(Arabidopsis thaliana)和金鱼草(Antirrhinum majus)花器官突变体研究提出的四聚体模型揭示了花同源异型蛋白的相互作用方式;进一步提出的核小体拟态模型,解释了花同源蛋白四聚体调控目标靶基因的分子机理。被子植物花器官形态多样化与MADS-box基因的表达模式和功能分化密切相关。多年生被子植物花发育的高通量转录组分析表明,多种基因参与调控花器官发育过程。本文重点综述了被子植物花器官发育的模型演变、MADS-box基因结构和基因重复、miRNA调控以及相关转录组分析的最新研究成果,并对花器官发育的研究前景进行了展望。     

水稻花器官特征决定以及数量控制的分子机制

继双子叶模式植物拟南芥之后, 单子叶模式植物水稻的生殖发育研究受到广泛的重视。随着水稻正向和反向遗传学研究的不断深入, 人们发现了一些调控水稻花器官特征以及花器官数量的重要基因, 使得对水稻花器官发育的调控机制有了更多的了解。本文着重概述和讨论水稻花器官特征决定以及花器官数量控制分子机理研究的最新进展。     

水稻花器官特征决定以及数量控制的分子机制

继双子叶模式植物拟南芥之后,单子叶模式植物水稻的生殖发育研究受到广泛的重视。随着水稻正向和反向遗传学研究的不断深入,人们发现了一些调控水稻花器官特征以及花器官数量的重要基因,使得对水稻花器官发育的调控机制有了更多的了解。本文着重概述和讨论水稻花器官特征决定以及花器官数量控制分子机理研究的最新进展。     

叶发育的遗传调控机理研究进展

叶是植物进行光合作用的主要器官。高等植物叶原基起始于顶端分生组织的周边区,在一系列基因精确调控下,叶原基建立近一远轴、基一顶轴和中．侧轴极性,引导原基细胞朝着特定的方向分裂和分化,最终发育戍一定形态和大小的叶片。近年来分子遗传学研究结果表明,数个转录因子家族基因、小分子RNA和细胞增殖相关因子组成一个复杂的遗传控制网络,调节叶片极性建成过程。此外,复叶的形态建成还受到另外一些转录因子的调控。本文对近年来叶发育遗传调控机理研究的新进展做简要介绍。     

《新发现的植物激素》书评

植物激素是植物体内合成的一批微量信号分子,通过整合不断变化的外界环境与内部发育信号,从分子、细胞、组织和器官水平上调控植物的生理生化反应和形态建成,确保植物正常的生长发育。近年来,有关植物激素作用机理的研究十分活跃,并在植物激素受体和信号转导途径等研究领域取得了重要进展,植物激素已由＂经典＂的5大类（生长素类、赤霉素类、     

花器官发育的分子机制研究进展

经典的ABC模型成功地解释了模式植物拟南芥和金鱼草因同源异型基因突变而引起的植物花器官的变异。随后,大量花器官特征基因和新突变体的研究不断完善和发展了ABC模型。该文综述了近年来花器官发育分子模型及花器官同源基因的调控机理等方面的最新研究成果,并对未来的研究方向进行了展望,以期为深入了解花发育的分子机理和遗传机制奠定基础。     

被子植物胚珠研究进展

胚珠作为被子植物的有性生殖器官一直为植物学家所关注。19世纪以来, 人们从形态结构、发生发育、起源及分子生物学等方面对胚珠进行了大量的研究。近年来, 随着研究手段的不断改进, 研究者对许多关键性的问题, 如胚珠的起源、胚珠发生发育的分子机制已经有了一定的认识, 但是这些问题并未得到圆满的解决。对此, 本文对前人的研究内容进行了回顾,并综述了最新研究进展, 在此基础上提出了今后对胚珠研究的建议。     

被子植物胚珠研究进展

胚珠作为被子植物的有性生殖器官一直为植物学家所关注。19世纪以来,人们从形态结构、发生发育、起源及分子生物学等方面对胚珠进行了大量的研究。近年来,随着研究手段的不断改进,研究者对许多关键性的问题,如胚珠的起源、胚珠发生发育的分子机制已经有了一定的认识,但是这些问题并未得到圆满的解决。对此,本文对前人的研究内容进行了回顾,并综述了最新研究进展,在此基础上提出了今后对胚珠研究的建议。     

MicroRNA在植物抵御盐胁迫过程中的作用

盐胁迫是植物生长发育过程中的重要限制因子,可影响植物器官发育、形态建成、信号转导等各个环节,严重时会导致植物死亡。MicroRNA(miRNA)是一类长约19-25 nt的非编码单链RNA分子,越来越多的研究发现,在植物抵御盐胁迫过程中,miRNA可通过参与调控植物种子萌发、器官发育、形态建成、活性氧清除等过程发挥重要作用。对在植物抵御盐胁迫过程中发生响应的miRNA进行综述,旨在为植物耐盐机制研究和植物耐盐分子育种提供参考。     

Organogenesis in plants: the molecular and genetic control of ovule development

The ovule is the site of megagametogenesis and fertilization and hence is of central importance to sexual reproduction in seed plants. In recent years, the ovule has become established as an excellent model system in which to study organogenesis. Progress has been made in several aspects of ovule development: the control of ovule identity, the mechanism of primordium outgrowth, early pattern formation and the regulation of integument morphogenesis.     

BELL1 and AGAMOUS genes promote ovule identity in Arabidopsis thaliana

Molecular and genetic analyses have demonstrated that the Arabidopsis thaliana gene BELL1 (BEL1) is required for proper morphogenesis of the ovule integuments. Several lines of evidence suggest that BEL1 may act, at least in part, to repress the function of the organ identity gene AGAMOUS (AG) during ovule development. To study the relative roles of BEL1 and AG, plants homozygous for ag, bel1 or both were constructed in an ap2 mutant background where ovules form even in the absence of AG function. The loss of either BEL1 or AG led to a decrease in the number of mature ovules, accompanied by an increase in primordial outgrowths. These data suggest that BEL1 and AG gene products act early in ovule development in a partially redundant manner to direct ovule identity. Development of the abnormal integuments characteristic of the Bel1- mutant phenotype was found to be dependent on AG function. Finally, BEL1 appears to be required for embryo sac development independent of both other aspects of ovule morphogenesis and AG function. This study therefore suggests that both BEL1 and AG are required for several distinct aspects of ovule morphogenesis.     

Ovule development: genetic trends and evolutionary considerations

Much of our current understanding of ovule development in flowering pants is derived from genetic and molecular studies performed on Arabidopsis thaliana. Arabidopsis has bitegmic, anatropous ovules, representing both the most common and the putative ancestral state among angiosperms. These studies show that key genetic determinants that act to control morphogenesis during ovule development also play roles in vegetative organ formation, consistent with Goethe’s “everything is a leaf” concept. Additionally, the existence of a common set of genetic factors that underlie laminar growth in angiosperms fits well with hypotheses of homology between integuments and leaves. Utilizing Arabidopsis as a reference, researchers are now investigating taxa with varied ovule morphologies to uncover common and diverged mechanisms of ovule development.     

Cytological Observation on Megasporogenesis and Embryo Sac Development of Regenerated Ovule in Hyacinth

The morphogenesis of regenerated ovule and cytological changes of its megasporogenesis and embryo sac development were studied. Results showed as follows: 1. the differentiation of the regenerated ovule had followed a normal process in the order of inner integument , outer integument and then funiculus. But the form of the regenerated ovules in vitro was quite different from that of ovule in vivo. Most of the regenerated ovules were orthotropous and hemianatropous , only a few were anatropous which are the same with that in vivo. 2. the megasporogenesis and the embryo sac development also had normal cytological process ,and the Polygonum type-embryo sac consisted of one egg, two synergids , one central cell and three antipodals could be seen in mature regenerated ovule. These ex-perimental results make clear that the regenerated ovule differentiated directly from explant could accomplish the complex processes of megasporogenesis and embryo sac development. By this fact ,authors infer that once the differentiation of ovule primordium, the complex biochemical programs for the megasorogenesis and embryo sac development can be controlled by the ovule itself and need no more information from flower bud and /or plant.     

Thinking about Bacillus subtilis as a multicellular organism

Initial attempts to use colony morphogenesis as a tool to investigate bacterial multicellularity were limited by the fact that laboratory strains often have lost many of their developmental properties. Recent advances in elucidating the molecular mechanisms underlying colony morphogenesis have been made possible through the use of undomesticated strains. In particular, Bacillus subtilis has proven to be a remarkable model system to study colony morphogenesis because of its well-characterized developmental features. Genetic screens that analyze mutants defective in colony morphology have led to the discovery of an intricate regulatory network that controls the production of an extracellular matrix. This matrix is essential for the development of complex colony architecture characterized by aerial projections that serve as preferential sites for sporulation. While much progress has been made, the challenge for future studies will be to determine the underlying mechanisms that regulate development such that differentiation occurs in a spatially and temporally organized manner.     

The molecular and genetic control of ovule development

A genetic approach has resulted in an extensive framework for the methodical analysis of ovule development. The most recent progress was accomplished in the areas of primordium formation and integument morphogenesis. Furthermore, systematic screens have identified a number of gametophytic mutations disrupting several distinct steps of embryo sac ontogenesis.     

Ovule morphogenesis in Ranunculaceae and its systematic significance

BACKGROUND AND AIMS: Ranunculaceae has a prominent phylogenetic position in Ranunculales which appears at the base of eudicots. The aims of the present paper are to reveal the features of ovule morphogenesis in different taxa and gain a better understanding of the systematics of Ranunculaceae. METHODS: Flowers of 17 species from three subfamilies, nine tribes and 16 genera of Ranunculaceae, at successive developmental stages, were collected in the wild and studied with a scanning electron microscope. KEY RESULTS: The integuments in the unitegmic ovules in Helleborus, Ranunculus and Oxygraphis, as well as the inner integuments in the bitegmic genera, initiate annularly and eventually become cup-shaped. However, the integuments in the unitegmic ovules in Anemone and Clematis, as well as the outer integuments in the bitegmic genera, arise semi-annularly and eventually become hood-shaped. Different kinds of appendages appear on the ovules during development. In Coptis of subfamily Coptidoideae, a wrap-shaped appendage arises outside the ovule and envelopes the ovule entirely. In the genera of subfamily Thalictroideae and tribe Anemoneae of subfamily Ranunculoideae, appendages appear on the placenta, the funicle or both. In tribe Helleboreae of subfamily Ranunculoideae, an alary appendage is initiated where the integument and the funicle join and becomes hood-shaped. CONCLUSIONS: Ovule morphogenesis characteristics are significant in classification at the levels of subfamilies and tribes. The initiation patterns of the integuments and the development of appendages show diversity in Ranunculaceae. The present observations suggest that the bitegmic, hood-shaped outer integument and endostomic micropyle are primitive while the unitegmic, cupular-shaped outer integument and bistomic micropyle are derivative.     

Differentiation of mucilage secretory cells of the Arabidopsis seed coat

In some plant species, including Arabidopsis, fertilization induces the epidermal cells of the outer ovule integument to differentiate into a specialized seed coat cell type with a unique morphology and containing large quantities of polysaccharide mucilage (pectin). Such seed coat mucilage cells are necessary for neither viability nor germination under normal laboratory conditions. Thus, the Arabidopsis seed coat offers a unique system with which to use genetics to identify genes controlling cell morphogenesis and complex polysaccharide biosynthesis and secretion. As a first step in the application of this system, we have used microscopy to investigate the structure and differentiation of Arabidopsis seed coat mucilage cells, including cell morphogenesis and the synthesis, secretion, and extrusion of mucilage. During seed coat development in Arabidopsis, the epidermal cells of the outer ovule integument grow and differentiate into cells that produce large quantities of mucilage between the primary cell wall and plasma membrane. Concurrent with mucilage production, the cytoplasm is shaped into a column in the center of the cell. Following mucilage secretion the cytoplasmic column is surrounded by a secondary cell wall to form a structure known as the columella. Thus, differentiation of the seed coat mucilage cells involves a highly regulated series of events including growth, morphogenesis, mucilage biosynthesis and secretion, and secondary cell wall synthesis.