蕨类植物性别分化对环境的响应

蕨类植物是维管植物中唯一的孢子体和配子体都能独立生活的类群.同型孢子蕨类配子体的性别分化受到激素和环境因子的影响.生理学研究表明,成精子囊素与赤霉素能诱导雄配子体发育,抑制雌配子体发育;脱落酸阻止成精子囊素诱导的精子器形成;乙烯合成前体ACC促进赤霉素诱导的精子器形成,而乙烯合成抑制因子AOA通过抑制细胞分化来抑制精子器形成.光照对不同种类蕨类配子体分化的影响存在差异.糖类能够促进雄配子体形成,并可加速成熟雌配子体向两性分化.钙离子、钴离子和甲硫氨酸等分别参与了蓝光和赤霉素对配子体性别分化的调控过程.培养密度影响配子体生长及性别表达,高密度下雄性和无性配子体居多,而低密度下两性和雌性配子体居多.近年来的突变体表型分析与分子生物学研究表明,成精子囊素通过影响ANI1、HER、TRA、FEM和MAN等基因的表达调控配子体性别分化.综述了蕨类植物性别分化对环境响应的研究进展.     

单倍体在海带遗传研究中的应用

几年来从海带的遗传实验中发现海带单倍体(配子体和配子)是遗传研究的良好材料。科研工作从分离单个海带配子体开始,由此得到了雌配子体和雄配子体的无性生殖系、雌性孢子体和雄性孢子体。这些不同来源的配子体和孢子体在性质上都是“纯系”。配子体的无性生殖系寿命可以很长,它们都能保持原来的性别,而且年年可以由此得到孢子体。由于雌性孢子体能产生大量的雌配子体,完成自己的生活史,用雌配子体来分析海带孢子体性状的遗传情况,或用来研究杂种优势和突变,都很适宜。     

花粉选择的研究进展

早在本世纪20年代就有许多关于影响花粉受精 能力的遗传研究报道亡“,。配子体自交不亲和性、玉米 中影响不正常分离的配子体因子、黑麦中的B染色体 和在种间杂交的回交过程中供体亲本基因型的消除 等,都是典型的配子体选择受精的例子,Ter- Avanesian (1947）在对陆地棉等的研究中发现,生长迅 速的花粉管产生的后代显然不同于未受到选择的花粉 管产生的后代;Lewis于50年代亦报道了在番茄中 的类似观察结果,表明配子体选择可能对抱子体世代 发生影响。Mulcahy (1979）明确提出了基因表达可能 在配子体阶段和抱子休阶段相互交错重叠的概念,并 指出对雄配子阶段的选择对于被子植物的进化和改变 植物的遗传结构具重要意义〔20,5110     

不同环境因子对珍稀观赏蕨类金毛狗配子体性别分化的影响

金毛狗[Cibotium barometz(L.)J.Sm.]是珍稀观赏蕨类的重要类群,为国家二级重点保护野生植物。该研究以金毛狗孢子为试验材料,探究培养密度、外源赤霉素以及光质等不同环境因子对金毛狗配子体性别分化的影响,为金毛狗人工繁育和蕨类植物配子体性别决定机制研究提供技术支持。结果表明:(1)低配子体培养密度(1个/cm2和5个/cm2)有利于颈卵器和雌配子体形成,随着配子体培养密度增加,颈卵器平均数量及雌配子体比率下降,精子器平均数量以及雄配子体和两性配子体比例增加,但配子体培养密度过高(80个/cm2)会导致大量无性配子体产生。(2)不同配子体培养密度下,随着培养时间延长,两性配子体比率均有增加,且增加幅度基本一致。(3)外源GA4显著抑制颈卵器和雌配子体形成,并显著促进精子器和雄配子体形成;外源GA3对金毛狗配子体性别分化没有显著影响。(4)白光、红光、蓝光等不同光质对金毛狗配子体性别分化未产生显著影响,但会影响配子体的发育和形态建成。     

假瘤蕨属植物配子体与幼孢子体发育的比较形态学研究

配子体及幼孢子体发育过程对蕨类植物的系统学研究具有重要意义,但在假瘤蕨属植物中较少报道.本研究比较了3种假瘤蕨属植物的配子体及幼孢子体发育过程:孢子均为单裂缝,萌发类型为书带蕨型.原叶体发育为槲蕨型.丝状体2～6细胞,成熟配子体心形,中肋明显加厚.配子体两性,在播种后48 ～ 55 d产生精子器,之后15 ～ 18 d产生颈卵器.播种后80 ～ 100 d,形成胚胎,后者分化出第一叶、第一根和茎端,发育为幼孢子体.配子体边缘分布有单细胞毛状体,配子体腹面分布有单列多细胞的毛状体,以中肋处最多,围绕并保护胚胎和幼孢子体.本属3个种的配子体和幼孢子体,在孢子体积、萌发时间、丝状体和成熟配子体特征以及性器产生时间等方面存在差异.土培条件下的配子体发育不同步,即配子体分批发育,原因为配子体的营养繁殖或孢子萌发不整齐.     

植物雄配子体发生和发育的遗传调控

植物雄配子体发生和发育是有性生殖的关键步骤之一,是高等植物通过有性生殖进行世代交替所必需的。近几年来,随着分离和鉴定配子体型突变体技术的发展,雄配子体遗传机制研究取得了很大进展,发现了一些调控雄配子体发生和发育过程中细胞分化和互作的重要基因。本文着重概述和讨论植物雄性生殖细胞和雄配子体发生及其与周边细胞互作遗传机制研究的最新进展。     

植物雄配子体发生和发育的遗传调控

植物雄配子体发生和发育是有性生殖的关键步骤之一, 是高等植物通过有性生殖进行世代交替所必需的。近几年来,随着分离和鉴定配子体型突变体技术的发展, 雄配子体遗传机制研究取得了很大进展, 发现了一些调控雄配子体发生和发育过程中细胞分化和互作的重要基因。本文着重概述和讨论植物雄性生殖细胞和雄配子体发生及其与周边细胞互作遗传机制研究的最新进展。     

宽礁膜的生活史

在国内首次观察描述了宽礁膜(Monostroma latissimum Wittrock)生活史各阶段的形态结构特征和发育变化,并对其单性生殖进行了周年培养和观察.大型的雌雄异体的膜状配子体成熟后,放散双鞭毛的配子,小型的球状孢子体成熟后放散四鞭毛的游孢子,其生活史是单倍体的配子体与二倍体的孢子体互相交替的异形世代交替.另外,在生活史中还发现合子和孢子囊的二分裂增殖方式,一年生配子体和二年生孢子囊等现象.未接合的雌、雄配子固着后变成球状单细胞体,室内培养后发育成成熟的单性孢子囊,并放散四鞭毛的游孢子,这些游孢子固着后,可直接发育成膜状的配子体,单性生殖也可以用来进行人工育苗.     

关于"世代交替"的一些疑惑

世代交替是指一些生物的生活史中有双倍体的孢子体世代与单倍体的配子体世代交替出现的现象, 由于涉及孢子、配子、孢子体、配子体等概念,学生常常容易混淆,并产生一些疑惑,现分析如下:     

宽礁膜的生活史

在国内首次观察描述了宽礁膜(Monostroma latissimum Wittrock)生活史各阶段的形态结构特征和发育变化,并对其单性生殖进行了周年培养和观察。大型的雌雄异体的膜状配子体成熟后,放散双鞭毛的配子,小型的球状孢子体成熟后放散四鞭毛的游孢子,其生活史是单倍体的配子体与二倍体的孢子体互相交替的异形世代交替。另外,在生活史中还发现合子和孢子囊的二分裂增殖方式,一年生配子体和二年生孢子囊等现象。未接合的雌、雄配子固着后变成球状单细胞体,室内培养后发育成成熟的单性孢子囊,并放散四鞭毛的游孢子,这些游孢子固着后,可直接发育成膜状的配子体,单性生殖也可以用来进行人工育苗。     

Overlap of gametophytic and sporophytic gene expression in barley

Summary The overlap of gametophytic and sporophytic gene expression in barley was studied by means of enzyme electrophoresis. Of the isozymes found, 60% were expressed in both gametophyte and sporophyte, 30% were sporophyte specific, and 10% were gametophyte specific. A considerable amount of the barley genome is thus potentially amenable to gametophytic selection. The estimated sizes of the common, sporophytic and gametophytic domains in barley gene expression correspond with the estimates obtained in other plant species.     

Male gametophytic selection in maize

Summary There is evidence that male gametophyte selection is a widespread phenomenon in higher plants. The pollen tube growth rate is one of the main components of gametophyte selective value; genetic variability for this trait, due to the effect of single genes or to quantitative variation, has been described in maize. However, indication of gametophytic selection has been indirectly obtained; its effect was revealed by the positive relation observed between gametophyte competitive ability and sporophyte metrical traits.This paper considers the results of selection applied to gametophyte populations produced from single plants. The competitive ability of the lines was evaluated in comparison with that of a standard line by means of the pollen mixture technique. Sporophytic traits were measured in the hybrid progeny obtained by crossing selected S₃ and S₄ families with an unrelated single cross and an inbred line. Gametophyte selection produced inbred lines with high gametophyte competitive ability. In view of the selection procedure adopted, this result was interpreted as an indication of haploid expression of genes involved in the control of pollen tube growth. Moreover, this gametophytic trait was positively correlated with sporophytic traits (seedling weight, kernel weight and root tip growth in vitro), indicating that both groups of characters have a common genetic basis.     

The Transformer Genes of the Fern Ceratopteris Simultaneously Promote Meristem and Archegonia Development and Repress Antheridia Development in the Developing Gametophyte

The sex of the haploid gametophyte of the fern Ceratopteris is determined by the presence or absence of the pheromone antheridiogen, which, when present, promotes male development and represses female development of the gametophyte. Several genes involved in sex determination in Ceratopteris have been identified by mutation. In this study, the epistatic interactions among new and previously described sex-determining mutants have been characterized. These results show that sex expression is regulated by two sets of genes defined by the FEM1 and TRA loci. Each promotes the expression of either male or female traits and simultaneously represses the expression of the other. A model describing how antheridiogen regulates the expression of these genes and the sex of the gametophyte is described. The observation that some gametophytic sex-determining mutants have phenotypic effects on the sporophyte plant indicates that sex determination in the Ceratopteris gametophyte is regulated by a mechanism that also regulates sporophyte development.     

Generating Autotetraploid Sporophytes and Their Use in Analyzing Mutations Affecting Gametophyte Development in the Fern Ceratopteris

The haploid gametophytes of the fern Ceratopteris richardii are autotrophic and develop independently of the diploid sporophyte plant. While haploid genetics is useful for screening and characterizing mutations affecting gametophyte development in Ceratopteris, it is difficult to assess whether a gametophytic mutation is dominant or recessive or to determine allelism by complementation analysis in a haploid organism. This report describes how apospory can be used to produce genetically marked polyploid sporophytes whose gametophyte progeny are heterozygous for mutations affecting sex determination in the gametophyte and a known recessive mutation affecting the phenotype of both the gametophyte and sporophyte. The segregation ratios of wild-type to mutant phenotypes in the gametophyte progeny of polyploid sporophyte plants indicate that all of the mutations examined are recessive. The presence of many multivalents and few univalents in meiotic chromosome preparations of spore mother cells confirm that the sporophyte plants assayed are polyploid. The DNA content of the sperm of their progeny gametophytes was also found to be approximately twice that of sperm from wild-type haploid gametophytes.     

Life history variation in gametophyte populations of the moss Ceratodon purpureus (Ditrichaceae)

The life cycles of mosses and other bryophytes are unique among land plants in that the haploid gametophyte stage is free-living and the diploid sporophyte stage is ephemeral and completes its development attached to the maternal gametophyte. Despite predictions that populations of haploids might contain low levels of genetic variation, moss populations are characterized by substantial variation at isozyme loci. The extent to which this is indicative of ecologically important life history variation is, however, largely unknown. Gametophyte plants from two populations of the moss Ceratodon purpureus were grown from single-spore isolates in order to assess variation in growth rates, biomass accumulation, and reproductive output. The data were analyzed using a nested analysis of variance, with haploid sib families (gametophytes derived from the same sporophyte) nested within populations. High levels of life history variation were observed within both populations, and the populations differed significantly in both growth and reproductive characteristics. Overall gametophytic sex ratios did not depart significantly from 1:1 within either population, but there was significant variation among families in both populations for progeny sex ratio. Some families produced predominantly male gametophytes, while others yielded predominantly females. Because C. purpureus has a chromosomal mechanism of sex determination, these observations suggest differential (but unpredictable) germination of male and female spores. Life history observations showed that male and female gametophytes are dimorphic in size, maturation rates, and reproductive output.     

Mating system shifts a species’ range

Understanding the ecological and evolutionary mechanisms that shape a species’ range is an important goal in evolutionary biology. Evidence indicates that mating system is an effective predictor of the global range of native species or naturalized alien plants, but the mechanisms underlying this predictability are not elaborated. Here, we develop a theoretical model to account for the ranges of plants under different mating systems based on migration‐selection processes (an idea proposed by Haldane). The model includes alternation of gametophyte and sporophyte generations in one life cycle and the dispersal of haploid pollen and diploid seeds as vectors for gene flow. We show that the interaction between selfing rates and gametophytic selection determines the role of mating system in shaping a species’ range. Selfing restricts the species’ range under gametophytic selection in nonrandom mating systems, but expands the species’ range under the absence of gametophytic selection in any mating system. Gametophytic selection slightly restricts the species’ range in random mating. Both logarithmic and logistic models of population demography yield similar conclusions in the case of fixed or evolving genetic variance. The theory also helps to explain a broader relationship between mating system and range size following biological invasion or plant naturalization.     

Epigenetic control of cell specification during female gametogenesis

In flowering plants, the formation of gametes depends on the differentiation of cellular precursors that divide meiotically before giving rise to a multicellular gametophyte. The establishment of this gametophytic phase presents an opportunity for natural selection to act on the haploid plant genome by means of epigenetic mechanisms that ensure a tight regulation of plant reproductive development. Despite this early acting selective pressure, there are numerous examples of naturally occurring developmental alternatives that suggest a flexible regulatory control of cell specification and subsequent gamete formation in flowering plants. In this review, we discuss recent findings indicating that epigenetic mechanisms related to the activity of small RNA pathways prevailing during ovule formation play an essential role in cell specification and genome integrity. We also compare these findings to small RNA pathways acting during gametogenesis in animals and discuss their implications for the understanding of the mechanisms that control the establishment of the female gametophytic lineage during both sexual reproduction and apomixis.     

How was apical growth regulated in the ancestral land plant? Insights from the development of non-seed plants

Land plant life cycles are separated into distinct haploid gametophyte and diploid sporophyte stages. Indeterminate apical growth evolved independently in bryophyte (moss, liverwort, and hornwort) and fern gametophytes, and tracheophyte (vascular plant) sporophytes. The extent to which apical growth in tracheophytes co-opted conserved gametophytic gene networks, or exploited ancestral sporophytic networks, is a long-standing question in plant evolution. The recent phylogenetic confirmation of bryophytes and tracheophytes as sister groups has led to a reassessment of the nature of the ancestral land plant. Here, we review developmental genetic studies of apical regulators and speculate on their likely evolutionary history.

The combined results of recent developmental genetics and phylogenetics studies suggest that the ancestral sporophyte was more complex than previously thought.     

Comparative development of the sporophyte–gametophyte junction in six moss species

Developmental anatomy of the sporophyte–gametophyte junction in six moss species is described with special reference to sporophyte penetration into the gametophytic tissue. The sporophyte–gametophyte junction in mosses is classified into two types based on vaginula morphology: in the “true vaginula” type, the junction involves only an epigonium derived from the archegonium, and in the other “shoot vaginula” type, it involves a shoot and an epigonium. In both of the types, the sporophyte penetrates into an epigonial tissue accompanied by degeneration of epigonium cells under the developing sporophyte. In the “shoot vaginula” type, the sporophyte further penetrates into the conducting strand or similar cells that seem to be induced by stimulation of fertilization. It is likely that the difference in growth rate between the epigonium and the capped sporophyte is a mechanical force for sporophyte penetration.