叶籽银杏的观察

银杏是现存种子植物中最古老的“活化石”,在植物学上占有特别重要的位置。银杏从发生、发展到现在,历史悠久,但变异甚微,至今仍保持着许多原始性状。种子着生在叶上的叶籽银杏亦被认为与银杏雄蓝具有分离下垂的花粉囊,尤以花粉粒萌发花粉管后产生具有许多纤毛能游动的精子;扇形叶具有二出分歧式的叶脉;核果状的种子具有三层种皮同样是古老的原始性状。这对进一步研究银杏的起源和演化方面具有重要价值。 1934年日本植物学家牧野富     

银杏雌配子体的发育和受精作用的研究现状

银杏的生殖过程,自发现银杏的游动精子以来,已有大量报道。但由于银杏雌配子体发育周期长（4月-9月）,受精过程又非常短暂,有关雌配子体发育及受精过程的研究报道较少。本文参考已有文献资料,并结合自己的研究,对银杏大孢子发生、雌配子体形成、颈卵器发育及受精作用的研究现状进行了综述,对尚存在的问题特别是精细胞中液泡状结构的特点及细胞核中DNA的存在状况、受精时精子如何进入雌配子体的颈卵器与卵核结合等进行了初步探讨,以期为今后此方面的研究提供参考。     

苏铁类植物传粉生物学研究进展(综述)

苏铁类植物是现存最古老的种子植物,研究其传粉特点,对于研究种子植物的起源与演化、植物与动物的协同进化以及苏铁类植物的繁殖机制、濒危机制有重要意义。本文从苏铁雌雄株开花物候学、传粉媒介及传粉机制等方面,对苏铁类植物传粉生物学相关研究进行综述,并提出今后该类植物传粉生物学研究的建议：对更多苏铁属种类未知的传粉机制进行研究;更广泛地应用排除法研究苏铁类特别是苏铁属植物的传粉媒介,进一步探讨传粉昆虫与苏铁类的共生关系问题。     

银杏雌雄配子体发育及胚胎形成的研究进展

银杏（Ginkgo biloba）是现存最古老的裸子植物之一, 其生殖过程表现出许多原始特征和独特性状, 长期以来备受国内外专家的关注。经过近100年的研究取得了显著成果： （1） 银杏雄配子体发育周期长, 经历了从平周分裂到斜背式分裂,并最终垂周分裂形成带有鞭毛的游动精子; （2） 银杏雌配子体发育经历较长的游离核期和细胞化期, 分化形成颈卵器母细胞并经平周分裂、垂周分裂和斜向分裂形成成熟的颈卵器（包括有4个颈细胞和1个卵细胞）; （3） 推测其精细胞中的液泡状结构为受精过程中的遗传物质载体; （4） 原胚的形成经历了游离核期和细胞化期。该文针对国内外最新银杏生殖生物学方面的研究进展, 对银杏雌雄配子体发育、受精过程以及胚胎形成等方面进行较为系统全面的分析和总结, 为进一步的银杏生殖生物学研究提供有价值的参考资料。     

银杏雌雄配子体发育及胚胎形成的研究进展

银杏(Ginkgo biloba)是现存最古老的裸子植物之一, 其生殖过程表现出许多原始特征和独特性状, 长期以来备受国内外专家的关注。经过近100年的研究取得了显著成果: (1) 银杏雄配子体发育周期长, 经历了从平周分裂到斜背式分裂,并最终垂周分裂形成带有鞭毛的游动精子; (2) 银杏雌配子体发育经历较长的游离核期和细胞化期, 分化形成颈卵器母细胞并经平周分裂、垂周分裂和斜向分裂形成成熟的颈卵器(包括有4个颈细胞和1个卵细胞); (3) 推测其精细胞中的液泡状结构为受精过程中的遗传物质载体; (4) 原胚的形成经历了游离核期和细胞化期。该文针对国内外最新银杏生殖生物学方面的研究进展, 对银杏雌雄配子体发育、受精过程以及胚胎形成等方面进行较为系统全面的分析和总结, 为进一步的银杏生殖生物学研究提供有价值的参考资料。     

银杏传粉生物学研究进展

银杏(Ginkgo biloba L.)是最古老裸子植物之一,其传粉受精过程表现出许多特殊的原始性状和特征,在种子植物的系统演化上具有重要研究价值;同时,银杏种实经济价值高,但栽培上由于授粉受精不良而导致落花落果现象严重,因此了解银杏传粉生物学特性对于其种实的优质高产具有实际意义.本文从银杏雌雄株开花物候学、雌雄花形态结构特征、花粉和胚珠发育进程、花粉和胚珠生物学特性、传粉机制及花粉在胚珠内萌发生长进程等方面,对银杏传粉生物学相关研究进行综述,为银杏的系统演化、授粉受精和种实发育研究提供参考.     

种子植物受精摆脱水束缚应归因于花粉管的起源吗？——植物学教材质疑(一)

几乎所有中文植物学教材都把花粉管当成是种子植物对受精摆脱水束缚的适应特征,并得出粉管受精使种子植物更适应于陆生生活的结论。但是,某些灭绝的(种子蕨和科得荻植物)和一些现存的(银杏和苏铁)裸子植物行游动受精,需要特别指出的是其受精并不需要液态水。种子蕨和科得荻植物不形成花粉管,银杏和苏铁的花粉管是吸器而无输送精子的功能。其实,正是小孢子在小孢子囊中的原位发育导致植物演化出花粉和传粉,花粉的形成及其传播才使受精真正摆脱了水的限制。澄清花粉管的功能可作为植物学批判性教学的案例,以促进学生们科学精神和科学思维的发展。     

古韵明珠傍仙湖——深圳仙湖植物园

苏铁类植物是现存最原始的一类裸子植物，也是一群曾与恐龙同时代的古老植物，从而被称为古韵明珠，如今它们已成为濒临灭绝的“活化石”。因此，它们对深入探讨古生态、古气候、古地理以及种子植物起源与演化、种子植物区系的演变等有着重要的科学价值。同时，苏铁类植物还是常见的园林观赏植物和重要的经济与药用植物。     

古韵明珠傍仙湖——深圳仙湖植物园苏铁种质资源保护中心

苏铁类植物是现存最原始的一类裸子植物,也是一群曾与恐龙同时代的古老植物,从而被称为古韵明珠,如今它们已成为濒临灭绝的“活化石”。因此,它们对深入探讨古生态、古气候、古地理以及种子植物起源与演化、种子植物区系的演变等有着重要的科学价值。同时,苏铁类植物还是常见的园林观赏植物和重要的经济与药用植物。然而,经过     

中国特产2种濒危水韭雄性发育的比较研究

采用透射电镜和光镜比较观察了中华水韭和云贵水韭雄配子体及其精子的发育特征。结果显示:(1)2种水韭的雄配子体的寿命只有15~30d,终生都在小孢子壁内发育。(2)雄配子体只含有1个原叶体细胞、1个精子器壁细胞和4个精细胞,前2个细胞内含有丰富的营养物质。(3)精子由精核、微管带、鞭毛、细胞质等4部分构成。(4)中华水韭雄配子体发生率为4.5%,平均每个雄配子体产生0.46个精子,精子游动速度约53μm/s,寿命8min;云贵水韭雄配子体发生率和产精量略高于中华水韭,但精子游动速度和寿命略低于中华水韭。研究认为,中国水韭濒危的主要原因之一是雄配子体产精率低、受到生殖生态限制、水污染对精子的危害等;雄性特征表明水韭在石松类中占有较高的进化地位;结合前人的研究成果绘出了水韭雄配子体的发育模式。     

Secretions from the female gametophyte and their role in spermatozoid induction in Cycas revoluta

In cycads, spermatozoids are released from pollen tubes and swim in fluid toward the archegonia. The source of this fluid was examined using Cycas revoluta Thunb. ovules placed in culture. Dissected female gametophytes just before fertilization produced copious fluid on their upper surface. The fluid first appeared around the archegonial chamber and then on the inside of the archegonial chamber. When this fluid was applied to dry turgid pollen tubes, they discharged spermatozoids 12 h later. The archegonial neck appeared as two semi-spherical swellings, whereas the four neck cells later became visible and they separated in a schizogenous manner. Many globose particles appear on the top of the archegonial neck cells when the fluid is present. The contents of pollen tubes, spermatozoids and surrounding liquid intermingle with the secreted fluid. The female gametophyte differs in ultrastructure during the stages before and after fluid secretion, the latter showing changes suggestive of fluid secretion from the female gametophyte.     

A Contribution to the Embryology of Ginkgo with a Discussion on the Affinity of the Ginkgoales

The ancestry of Ginkgoales or Ginkgophyta can be traced back to the Paleozoic. But today this order is represented only by a single species, Ginkgo biloba. Seward (1838) considered Ginkgo as one of the wonders of the world; it has persisted with little change until the present through a long succession of ages when the earth was inhabited by animals and plants for the most part far removed, in kind as in time, from their living descendents. Ginkgo is generally believed to be native to China, but so far it has not been found in wild state. A number of studies concerning the embryogeny of Ginkgo have been reported, on the basis of the materials accumulated during the past years and supplemented in 1978–1980, the embryogeny of Ginkgo is here described. Finally the phylogeny of Ginkgoales is discussed by comparing with the embryogeny of other groups of the living gymnosperms. Pollination usually takes place from the end of April to the first days of May and fertilization occurs around August 16–20 in the suburbs of Peking. Thus, the interval between pollination and fertilization is a few days less than four months. The embryo of Ginkgo is generally considered as suspensorless. In authors’ opinion, however, the somewhat elongated and much enlarged cells at the micropylar end of the embryo may be considered as the reduced suspensor cells though they are not the typical ones. There is no distinct demarcation between the proembryo and the young embryo in Ginkgo. In comparison with the embryogenesis in Coniferales, the tissue differentiation of the late embryo of Ginkgo is rather indistinct. Many authors such as Chamberlain (1935), Florin (1949), Delevoryas (1963), Sporne (1965) and others divide the gymnosperms into two major groups, Cycadophyta and Coniferophyta. From the point of view of morphological structure there are many significant common features shared by Ginkgoales and Coniferales. For example, Ginkgo possesses long shoot and short shoot while some conifers also have long and short shoots. The anatomical features of the stem of Ginkgo such as the well-developed secondary xylem, relatively small pith and the presence of bordered pits on the tracheids are also similar to those of the Coniferales. Not only Ginkgo has its characteristic leaf shape and the dichotomous venation but also they are quite different from the fronds of cycads. From the reproductive structure, on the other hand, Ginkgo and Cycadales are rather similar: both of them having one sulcate pollen grains, the pollen tube being of haustorial nature, the sperms being released from the base and not from the tip of the pollen tube, the presence of mulficiliate and rather large sperms, development of large female gametophyte bearing archegonia with exceptionally large eggs, more divisions of the free nuclear stage in the proembryo and less distinct differentiation of the ate embryo. All these features are primitive embryological characters. Thus, from the point of view of embryology the Ginkgo is close related to the Cycadales rather than to the Coniferales. Since Ginkgophyta are related to Cycadophyta in reproductive structures on one hand and similar to Coniferophyta in morphological and anatomical characters of the vegetative organs the Ginkgophyta are related to Cycadophyta in reproductive structures on one hand and similar to Coniferophyta in morphological and anatomical characters of the vegetative organs on the other hand, it indicates the interrelationship among these groups is clearly shown. Recently the discovery and studies on the progymnospermopsida (Beck, 1976) are worth notice, this fossil group contains the plants with certain characters of some conifers and certain characters of some cycads and this kind of plants bearing both homosporous and heterosporous forms are similar to ferns. They link the gymnosperms to the ferns. The present evidence, therefore, shows that the gymnosperms are very probably monophyletic and the progymnosperms might be the ancester of all the gymnosperms. The embryological characteristics supports the monophyletic origin of the gymnosperms.     

An embryological study and systematic significance of the primitive gymnosperm Ginkgo biloba

Ginkgo biloba L.is considered one of the most ancient seed plants,with several primitive features of plant reproductive process.However,the phylogenetic position of Ginkgo and its relationship with other extant seed plants remain unclear.To gain a better understanding of these issues,we observed the embryological development of G.biloba using semi-thin sections and scanning electron microscopy.In late August,the zygote moved from the end of the micropylar to the middle of the archegonium,and mitosis resulted in many free nuclei distributed randomly in the archegonium.Afterwards,the cell wall was formed and the proembryo began to differentiate into the embryonal region and the underdeveloped presuspensor region.In early October,the embryo differentiated into two cotyledons,plumule,hypocotyl,radicle,and suspensor tissues.Subsequently,the two cotyledons grew rapidly,but the undeveloped suspensor began to degenerate and gradually disappear,indicating that the embryo had begun to mature.During early embryo development,the main supply of nutrients was carbohydrate in the cells of the jacket,tentpole,and surrounding endosperm,whereas endosperm provided nutrients during embryo maturation.Our results indicate that Ginkgo is extremely similar to cycads in terms of embryology but more similar to conifers in macromorphology and vegetative anatomy,suggesting that the Ginkgo lineage may have an intermediate phylogenetic position between cycads and conifers.     

DIVISION OF THE GENERATIVE CELL AND LATE DEVELOPMENT IN THE MALE GAMETOPHYTE OF GINKGO BILOBA

Division of the generative cell in the male gametophyte of Ginkgo biloba to yield the sterile cell and spermatogenous cell was examined in vivo and in vitro. Evidence is presented in support of a new interpretation of development in which the sterile cell and spermatogenous cell arise from an unusual anticlinal ringlike division of the generative cell. This type of cell division is only known to occur during antheridial development in leptosporangiate ferns and stomatal development among certain ferns in the Schizaeaceae and Polypodiaceae. The strong similarities in development and cell arrangement within the male gametophytes of cycads and Ginkgo suggest that division of the generative cell in cycads may be the same as in Ginkgo. Although the ringlike (conically annular) divisions in the antheridia of leptosporangiate ferns and the male gametophytes of Ginkgo (and probably cycads) are remarkably similar and result in the production of a central spermatogenous cell, it is conjectural as to whether these patterns represent a striking convergence or evolutionary homology.     

GROWTH AND DEVELOPMENT OF THE MALE GAMETOPHYTE OF GINKGO BILOBA WITHIN THE OVULE (IN VIVO)

The mature male gametophyte of Ginkgo biloba can be divided into two regions: a large saccate structure that is suspended within the fertilization chamber above the archegonia, and a pervasive, highly branched haustorial system that ramifies through the intercellular air spaces of the apex of the nucellus. This morphology appears to differ in many ways from the simpler more typical male gametophytes of most other groups of seed plants. Growth and development of the male gametophyte of Ginkgo biloba were studied using computer reconstruction techniques to generate images of the gametophyte from data derived from serial sections through the ovule. These investigations reveal that morphological development of the male gametophyte of Ginkgo biloba is divided into three distinct phases: 1) Germination, characterized by an initial brief period of diffuse growth. This phenomenon has not been described for any other seed plant male gametophyte; 2) Initiation of tip growth and the formation of a tubular body, as typifies all seed plant male gametophytes. In Ginkgo, this is accompanied by a high degree of branching, giving rise to an extensively branched haustorial system; 3) Late swelling of the proximal unbranched portion of the gametophyte resulting in formation of the saccate structure that is characteristic of the mature gametophyte. This process appears to be very similar to late development in cycad male gametophytes. Thus, despite the seemingly anomalous morphology of the mature male gametophyte of Ginkgo biloba, specific patterns of growth and development are in many ways similar to growth processes expressed by the male gametophytes of some or all major groups of seed plants.     

Structure and function of the neck cell during fertilization in Ginkgo biloba L.

Key message

Neck cells in Ginkgo biloba contribute to archegonial opening through morphological changes and might be involved in the production of fertilization liquid to attract spermatozoids toward archegonia.

Abstract

Neck cells are an essential part of the archegonium in archegoniate gymnosperms, but their function in the sexual reproductive process remains unclear, particularly in zoidogamous gymnosperms. To clarify the structural characteristics of neck cells and their role in fertilization, we examined the neck cells of Ginkgo biloba L. by means of scanning electron microscopy and transmission electron microscopy. The two curved inner neck cells, which are covered imbricately by the two turgid outer neck cells, were pushed to two sides during fertilization, which indicated that morphological changes in these cells contribute to archegonial opening. The neck cells contained many secretory organelles with some material accumulated outside the cell wall, thus the neck cells might be involved in the production of fertilization liquid to attract spermatozoids toward the archegonium. In addition, the surrounding surface cells of the female gametophyte also cooperate to produce the liquid. Taken together, these results indicate that the neck cells provide an effective mechanism by which zoidogamous gymnosperms achieve reproductive success through altering the morphology and cellular physiology of the neck cells.     

Cell Divisions During Microsporogenesis and Development of the Male Gametophyte in Ginkgo biloba

During meiosis of the microsporocyte of Ginkgo biloba L., the nucleoids, after going through a serios of regular dynamic changes, had primarily established an axial polarity from the proximal face to the distal face of the cell. In the consequent germination, the microspore went through three consecutive polar periclinal mitotic divisions, which may be considered as further intensifying the primary polarity. In terms of structural change, lacking of plasmodesmas in the walls between the daughter cells, may set forth in isolating all the daughter cells in which fine differentiation took place. The anticlinal ring-like division observed in the generative cell might play an important role in polarity regulation in the male gametophyte, eventually leading to the anticlinal division in the spennatogenous cell to produce two back-to-back positioned spermatozoids.     

The evolutionary history of the seed plant male gametophyte

The role of the male gametophyte in the early history of seed plants remains an underappreciated but critical part of the evolution of a suite of characters that ultimately came to define seed plants. Recent paleobotanical discoveries and studies of extant primitive seed plant male gametophytes, when coupled with phylogenetic analyses of seed plants, provide insight into many hey events that occurred during the early evolution of seed plants. These discoveries are changing our ideas concerning the multiple origins of the sulcus (pollen grain germinal aperture) and pollen tube, the structural and physiological relationships of the male gametophyte with the host sporophyte tissues in primitive seed plants, and the evolution of siphonogamy (conduction of non-motile sperm via a pollen tube) from a zooidogamous (swimming sperm) condition.     

银杏雄配子体发生发育过程中的细胞分裂

银杏（ＧｉｎｋｇｏｂｉｌｏｂａＬ．）小孢子母细胞减数分裂中,拟核经过规律性的变化后,初步建立了由近极面到远极面间的轴向极性,因而,雄配子体萌发时的３次分裂都是典型的极性平周分裂;这些极性平周分裂很可能是对原有极性的进一步加强;在结构上,各子细胞间的细胞壁缺少胞间连丝,因而,这些细胞壁可能起着使子细胞孤立化的作用,从而完成雄配子体中各细胞间的精细分化。生殖细胞的分裂很可能是斜背式环形分裂（ａｎｔｉｃｌｉｎａｌｒｉｎｇｌｉｋｅｄｉｖｉｓｉｏｎ）,这种分裂可能是对最初极性方向的重大调整。结果,精原细胞的分裂方向为垂周分裂,产生两个背靠背排列的精子。