橄榄雄株花粉形态特征观察及数量分类初探

运用扫描电镜对采自全国主要橄榄分布区的24个橄榄雄株种质的花粉超微形态特征进行观察,结果表明,观察的橄榄花粉为圆球形或近长球形(1.07

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蕨类植物孢子与种子植物花粉萌发的比较

蕨类植物孢子与种子植物花粉在有性生殖过程中都具有重要的作用。花粉作为种子植物的雄配子体, 通过萌发后极性生长的花粉管将精细胞送到胚囊完成受精作用。蕨类植物孢子作为配子体的原始细胞, 通过不对称的有丝分裂产生一大一小两个细胞, 小细胞萌发出极性生长的假根, 大细胞继续分裂发育为原叶体(配子体)。成熟的花粉和蕨类植物孢子都是代谢高度静止的细胞, 两者的萌发过程不仅都受到各种不同环境因子的影响, 而且在信号转导、极性建立和能量代谢等方面可能有着相似的调控机制。本文综述了蕨类植物孢子和种子植物花粉萌发过程的差异和保守性特征。     

中国木犀属花粉形态研究及其系统学意义

观察了中国木犀属4组21种植物的花粉形态。花粉为圆球形或近长球形,外壁表面均具网状纹饰。大多数种类都具有三孔沟的萌发孔,极少四孔沟,或六萌发孔。内孔明显或不明显,有9种植物同时存在具三孔沟和具三沟二种类型的花粉及中间过渡类型(显脉木犀同时存在具三拟孔沟和具四拟孔沟)。很多特点表明,木犀属花粉的萌发孔在木犀科中处于由简单萌发孔向复合萌发孔过渡的阶段。根据网眼从沟间区中央到沟边是否变细,可将本属花粉分为两大类型,与分组有一定的对应关系。综合一些花粉特征,可发现本属花粉形态差异较明显,与一般形态差异有一定的相关性。花粉形态在木犀属具有一定的系统学意义。     

‘东方晨曲’铁线莲小孢子发生和雄配子体发育进程的解剖学研究

以晚花铁线莲类的‘东方晨曲’为实验材料,利用常规石蜡切片技术对其小孢子发生和雄配子体发育进行观察,以探究其胚胎发育特征。结果显示:(1)‘东方晨曲’成熟花朵的雄蕊120~160枚,花药4室。(2)花药壁从外至内依次由表皮、药室内壁、中层和绒毡层组成,花药壁的发育方式是双子叶型。(3)花粉母细胞减数分裂过程中的胞质分裂为同时型,四分体中小孢子排列大部分呈四面体型,少数呈左右对称型。(4)成熟花粉是2-细胞花粉型,具3个萌发沟,扫描电镜下观察成熟花粉粒是圆球形,外壁呈光滑状或波浪状。研究发现,‘东方晨曲’铁线莲小孢子发生和雄配子体发育没有发生异常现象,可作为培育高观赏价值铁线莲杂交种的父本品种。     

蕨类植物孢子与种子植物花粉萌发的比较

蕨类植物孢子与种子植物花粉在有性生殖过程中都具有重要的作用。花粉作为种子植物的雄配子体，通过萌发后极性生长的花粉管将精细胞送到胚囊完成受精作用。蕨类植物孢子作为配子体的原始细胞，通过不对称的有丝分裂产生一大一小两个细胞，小细胞萌发出极性生长的假根，大细胞继续分裂发育为原叶体（配子体）。成熟的花粉和蕨类植物孢子都是代谢高度静止的细胞，两者的萌发过程不仅都受到各种不同环境因子的影响，而且在信号转导、极性建立和能量代谢等方面可能有着相似的调控机制。本文综述了蕨类植物孢子和种子植物花粉萌发过程的差异和保守性特征。     

国产爵床科山牵牛属6种、叉柱花属和老鼠簕属各1种植物的花粉形态

报道了国产爵床科Acanthaceae山牵牛属Thunbergia(山牵牛亚科Thunbergioideae)6种、叉柱花属Staurogyne(瘤子草亚科Nelsonioideae)和老鼠簕属Acanthus(老鼠簕亚科Acanthoideae)各1种植物在扫描电镜下的花粉形态。山牵牛属植物的花粉粒为圆球形,均具螺旋状萌发孔,外壁纹饰以光滑或颗粒状为主,偶具棒状突起。具螺旋状萌发孔被认为是该科独特而较原始的花粉特征。叉柱花属的花粉粒为圆球形,具3孔沟,外壁平滑。老鼠簕属的花粉粒为长球形,具3沟,外壁具细网状纹饰或具小穿孔。花粉形态特征支持传统上将上述3属置于3个不同亚科的处理。     

中国钩藤属9种植物的花粉形态

利用光学显微镜和扫描电镜对中国钩藤属(Uncaria Schreb)9种植物的花粉形态进行了观察.结果表明,钩藤属植物的花粉为单粒,小型,辐射对称,赤道面观圆球形至近长球形,极面观3-裂圆形,具3孔沟,萌发沟裂缝状,长达两极.萌发沟中央有"内壁加厚突出"结构.外壁具条纹至细网纹饰,表面光滑无附属物.钩藤属花粉大小、形状、萌发沟和纹饰类型都较接近,属于单一型花粉.钩藤属植物的花粉形态特征是茜草科(Rubiaceae)中较为原始的类型.     

水鳖科9属15种植物花粉形态的研究

应用光学显微镜、扫描电镜和透射电镜对水鳖科Hydrocharitaceae 9属15种植物的花粉形态进行 了观察。水鳖科植物花粉为圆球形至近椭球形,无萌发孔或偶为单沟萌发孔,外壁纹饰通常为小刺状纹 饰,刺密集或稀疏,花粉表面具瘤状、疣状、颗粒状、皱波状突起或光滑。外壁由覆盖层、柱状层和基层组 成。覆盖层厚或较薄,柱状层小柱发育不明显,基层薄。水鳖科植物在花粉大小、纹饰类型、刺的长短、 密度、形态、萌发孔的有无以及花粉壁的结构等方面表现出了较为明显的差异,这些特征对探讨类群间 关系具有较重要意义。由于黑藻属Hydrilla和Stratiotes属花粉较为特殊,支持将它们各自作为一个独立 的族处理。水鳖科植物花粉外壁纹饰和结构特点表明该科与水雍科Aponogetonaceae、泽泻科Alismataceae 和花蔺科Butomaceae等近缘,而该科植物花粉大多无萌发孔等则反应了该科与茨藻目Najadales植物有密切联系。     

芸苔属脱外壁花粉作为研究花粉萌发的新实验系统

脱外壁花粉的分离与人工萌发已在芸苔属(Brassica L.)中取得成功。由于其缺乏外壁与萌发沟这一特点,脱外壁花粉是研究花粉萌发的有用的实验系统。作者重点研究了脱外壁花粉分离与萌发过程中有关极性形成、萌发位点预定及新壁的合成等问题。结果表明在外壁脱离之前花粉已经活化并预先建立了极性;脱外壁后的萌发位点仍位于原萌发沟处;在萌发位点处合成的新壁可能起限定花粉管直径的作用。由此推论,脱外壁花粉可在花粉生物学研究中广泛加以应用。     

烟草幼嫩花粉原生质体分离与早期离体发育

建立了两种分离烟草（Ｎｉｃｏｔｉａｎａ ｔａｂａｃｕｍ ）幼嫩花粉原生质体的方法：一为通过花药漂浮培养释放出外壁裂开的花粉,后者转入酶液彻底脱去外壁,内壁降解而分离出原生质体（简称“花药预培养法”）;二为花粉经饥饿处理后,转入酶液释放原生质体（简称“花粉饥饿预处理法”）。对影响分离效果的主要因素作了研究。用花药预培养法分离的幼嫩花粉原生质体,在Ｋ３ 培养基中可再生细胞壁,启动１ 次细胞分裂,或萌发花粉管。表明具有孢子体发育与配子体发育的潜能。观察到花粉原生质体分裂成二细胞后,其中１ 个子细胞又长出花粉管的稀有现象,暗示其开始启动孢子体发育后又重新恢复配子体发育途径     

Pollen germination in Welwitschia mirabilis Hook. f.: differences between the polyplicate pollen producing genera of the Gnetales

Pollen grains of the seed plant genera Ephedra L. and Welwitschia Hook. f. (Gnetales) are of similar size, shape, and have a polyplicate exine with alternating thicker and thinner regions. Ephedra pollen is considered inaperturate and the exine is shed during germination, leaving the male gametophyte naked. The shed exine curls up and forms a characteristic structure with transverse striations. Such upcurled exines have been found in situ in Early Cretaceous seeds with affinities to Ephedra. The purpose of this study was to document the germination of Welwitschia pollen and investigate whether they also discard their exine during this process.

The pollen grains of Welwitschia are monoaperturate with a distinct, distal sulcus. During germination, the sulcus splits open and the gametophyte expands to a spherical form that extends out of the exine. The pollen tube starts to grow one or two hours later and as in Ephedra, it is displaced towards one side. The exine is not shed but remains as a “cap” that partly covers the male gametophyte. Thus, in this respect the germination process is distinctly different from that in Ephedra and this study demonstrates that discharging the exine during pollen germination is unique to Ephedra, among the polyplicate pollen producing genera in the Gnetales.     

Polarity, aperture condition and germination in pollen grains ofEphedra (Gnetales)

Pollen grain polarity, aperture condition and pollen tube formation were examined inEphedra americana, E. foliata, E. rupestris, E. distachya, andE. fragilis using LM, SEM and TEM. In the characteristic oblate pollen, as seen in situ in the tetrad configuration, the polar axis is the minor one and the equatorial plane runs between the two narrow ends of the microspore. The intine is thick in fresh fixed mature pollen but we have seen no indication of regions having an exceptionally thick intine that could be considered associated with an aperture or apertures. About three minutes after transferring fresh pollen to the germinating medium the ridged exine splits and twists away from the intine and its enclosed protoplast. The shed exine spreads out and curls into a scroll-like configuration that is as distinctive as that of the pollen shape had been but now having the ridges and valleys perpendicular to the long axis. The pollen tube develops, in our experience with more than a hundred germinating pollen grains, near one of the narrow tips of the pollen grain's equatorial plane. The location of the pollen tube initiation probably is related to the position of the tube cell nucleus. The pollen tube starts to grow about one hour after the exine was shed. The pollen tube emerges close to the narrow end (equator) of the gametophyte. This end emerged first as the exine is shed and is opposite to the prothallial cells. The stout pollen tube is c. 10µm in diameter grown in vitro on agar. In our germination medium the stout tube continued to elongate for about 24 hours reaching a length of c. 100 µm. With respect to exine morphology the aperture condition could be considered as inaperturate. The pollen tube, however, is formed in a germination area near one end of the exineless gametophyte.     

Establishment of the male germline and sperm cell movement during pollen germination and tube growth in maize

Two sperm cells are required to achieve double fertilization in flowering plants (angiosperms). In contrast to animals and lower plants such as mosses and ferns, sperm cells of flowering plants (angiosperms) are immobile and are transported to the female gametes (egg and central cell) via the pollen tube. The two sperm cells arise from the generative pollen cell either within the pollen grain or after germination inside the pollen tube. While pollen tube growth and sperm behavior has been intensively investigated in model plant species such as tobacco and lily, little is know about sperm dynamics and behavior during pollen germination, tube growth and sperm release in grasses. In the March issue of Journal of Experimental Botany, we have reported about the sporophytic and gametophytic control of pollen tube germination, growth and guidance in maize.1 Five progamic phases were distinguished involving various prezygotic crossing barriers before sperm cell delivery inside the female gametophyte takes place. Using live cell imaging and a generative cell-specific promoter driving α-tubulin-YFP expression in the male germline, we report here the formation of the male germline inside the pollen grain and the sperm behaviour during pollen germination and their movement dynamics during tube growth in maize.Key words: male gametophyte, generative cell, sperm, pollen tube, tubulin, fertilization, maize     

Cytoskeleton in Pollen and Pollen Tubes of Ginkgo biloba L.

The distribution of F-actin and microtubules was investigated in pollen and pollen tubes of Ginkgo biloba L. using a confocal laser scanning microscope after fluorescence and immunofluorescence labeling. A dense F-actin network was found in hydrated Ginkgo pollen. When Ginkgo pollen was germinating,F-actin mesh was found under the plasma membrane from which the pollen tube would emerge. After pollen germination, F-actin bundles were distributed axially in long pollen tubes of G. biloba. Thick F-actin bundles and network were found in the tip of the Ginkgo pollen tube, which is opposite to the results reported for the pollen tubes of some angiosperms and conifers. In addition, a few circular F-actin bundles were found in Ginkgo pollen tubes. Using immunofluorescence labeling, a dense microtubule network was found in hydrated Ginkgo pollen under confocal microscope. In the Ginkgo pollen tube, the microtubules were distributed along the longitudinal axis and extended to the tip. These results suggest that the cytoskeleton may have an essential role in the germination of Ginkgo pollen and tube growth.     

Role of ethylene in the control of gametophyte-sporophyte interactions in the course of the progamic phase of fertilization

We investigated dynamics of the content of 1-aminocyclopropane-1-carboxylic acid (ACC) and ethylene production in male gametophyte development and germination in fertile (self-compatible and selfincompatible) and sterile clones of petunia. Fertile male gametophyte development was accompanied by two peaks of ethylene production by anther tissues. The first peak occurred during the microspore development simultaneously with the degeneration of both the tapetal tissues and the middle layers of the anther wall. The second peak coincided with dehydration and maturation of pollen grains. In the anther tissues of the sterile line of petunia, tenfold higher ethylene production was observed at the meiosis stage compared with that in fertile male gametophytes. This fact correlated with the degeneration of both microsporocytes and tapetal tissues. Exogenously applied ethylene (1–100 ppm) induced a degradation of the gametophytic generation at the meiosis stage. According to the obtained data, ethylene synthesis in germinating male gametophyte is provided by a 100-fold ACC accumulation in mature pollen grains. The male gametophyte germination, both in vitro, on the culture medium, and in vivo, on the stigma surface, was accompanied by an increase in ethylene production. Depending on the type of pollination, germination of pollen on the stigma surface and the pollen tube growth in the tissues of style were accompanied by various levels of ACC and ethylene release. The male gametophyte germination after self-compatible pollination was accompanied by higher content of ACC as compared with the self-incompatible clone, whereas, after the self-incompatible pollination, we observed a higher level of ethylene production compared with compatible pollination. For both types of pollination, ACC and ethylene were predominantly produced in the stigma tissues. Inhibitor of ethylene action, 2,5-norbornadiene (NBN), blocked both the development and germination of the male gametophyte. These results suggest that ethylene is an important factor in male gametophyte development, germination, and growth at the progamic phase of fertilization.     

Temperature as a determinant factor for increased and reproducible in vitro pollen germination in Arabidopsis thaliana

Despite much effort, a robust protocol for in vitro germination of Arabidopsis thaliana pollen has been elusive. Here we show that controlled temperatures, a largely disregarded factor in previous studies, and a simple optimized medium, solidified or liquid, yielded pollen germination rates above 80% and pollen tube lengths of hundreds of microns, with both Columbia and Landsberg erecta (Ler) ecotypes. We found that pollen germination and tube growth were dependent on pollen density in both liquid and solid medium. Pollen germination rates were not substantially affected by flower or plant age. The quartet1 mutation negatively affected pollen germination, especially in the Ler ecotype. This protocol will facilitate functional analyses of insertional mutants affecting male gametophyte function, and should allow detailed gene expression analyses during pollen tube growth. Arabidopsis thaliana can now be included on the list of plant species that are suitable models for physiological studies of pollen tube elongation and tip growth.     

Pollen and pistil in the progamic phase

The progamic phase, the period of pollen tube growth through the pistil, is a period of specific interactions between the male gametophyte and the pistil. Understanding of pollen germination and pollen tube growth are relevant for the study of pollen-pistil interactions and for understanding the function of components specifically accumulated in the transmitting tissue cell walls and intercellular matrix that may interact with pollen tubes. Received: 18 January 2001 / Accepted: 19 June 2001     

The Arabidopsis mutant feronia disrupts the female gametophytic control of pollen tube reception

Reproduction in angiosperms depends on communication processes of the male gametophyte (pollen) with the female floral organs (pistil, transmitting tissue) and the female gametophyte (embryo sac). Pollen-pistil interactions control pollen hydration, germination and growth through the stylar tissue. The female gametophyte is involved in guiding the growing pollen tube towards the micropyle and embryo sac. One of the two synergids flanking the egg cell starts to degenerate and becomes receptive for pollen tube entry. Pollen tube growth arrests and the tip of the pollen tube ruptures to release the sperm cells. Failures in the mutual interaction between the synergid and the pollen tube necessarily impair fertility. But the control of pollen tube reception is not understood. We isolated a semisterile, female gametophytic mutant from Arabidopsis thaliana, named feronia after the Etruscan goddess of fertility, which impairs this process. In the feronia mutant, embryo sac development and pollen tube guidance were unaffected in all ovules, although one half of the ovules bore mutant female gametophytes. However, when the pollen tube entered the receptive synergid of a feronia mutant female gametophyte, it continued to grow, failed to rupture and release the sperm cells, and invaded the embryo sac. Thus, the feronia mutation disrupts the interaction between the male and female gametophyte required to elicit these processes. Frequently, mutant embryo sacs received supernumerary pollen tubes. We analysed feronia with synergid-specific GUS marker lines, which demonstrated that the specification and differentiation of the synergids was normal. However, GUS expression in mutant gametophytes persisted after pollen tube entry, in contrast to wild-type embryo sacs where it rapidly decreased. Apparently, the failure in pollen tube reception results in the continued expression of synergid-specific genes, probably leading to an extended expression of a potential pollen tube attractant.     

Coherent electromagnetic fields in the remote intercellular interaction

The distant interactions various organisms and their communities and the effect of coherent electromagnetic radiation on intercellular relations were studied. The ability of fruit crops male gametophyte to control the germination of pollen tube at the field level (nonchemical) was established. The cooperative character of this process is shown. It is stimulated directly or indirectly, by low-intensity coherent radiation through a bioinductor. The conclusion is made that spontaneous chemiluminescence cannot be considered as an information channel of distant intercellular interaction.     

DEVELOPMENT OF THE POLLEN TUBE OF ZAMIA FURFURACEA (ZAMIACEAE) AND ITS EVOLUTIONARY IMPLICATIONS

Compared with pollen tubes of conifers, gnetophytes, and angiosperms, the pollen tube of cycads is exclusively a vegetative structure, uninvolved with the siphonogamous conduction of sperm to an egg. The cycad pollen tube appears to function primarily to obtain nutrients for the extensive growth and development of the male gametophyte. Previous workers have suggested that, similar to an haustorial fungus, the cycad pollen tube penetrates the reproductive tissues of the sporophyte by enzymatically destroying nucellar cells. These earlier studies did not document the precise structural relationship between the growing male gametophyte and its “host” tissue, the nucellus. Pollen tube growth, and its relation to the nucellus, was examined in Zamia furfuracea with light and transmission electron microscopy. Following germination, the pollen tube of Zamia furfuracea grows intercellularly through the subepidermal layers of the micropylar apex of the nucellus. Electron micrographs clearly show additional localized outgrowths of the pollen tube penetrating the walls of individual nucellar cells. Intracellular haustorial growth ultimately leads to the complete destruction of each penetrated cell, and appears to induce the degeneration of proximal unpenetrated nucellar cells. This pattern of intracellular penetration of the sporophyte by the male gametophyte in Zamia furfuracea is fundamentally different from what has been described in any other major group of seed plants (where intercellular growth of the male gametophyte is the rule), and suggests that the heterotrophic and tissue-specific relationships that male gametophytes of seed plants have with their host sporophytes are substantially more diverse than had previously been known.