The mac1 mutation alters the developmental fate of the hypodermal cells and their cellular progeny in the maize anther.

In angiosperm ovules and anthers, the hypodermal cell layer provides the progenitors of meiocytes. We have previously reported that the multiple archesporial cells1 (mac1) mutation identifies a gene that plays an important role in the switch of the hypodermal cells from the vegetative pathway to the meiotic (sporogenous) pathway in maize ovules. Here we report that the mac1 mutation alters the developmental fate of the hypodermal cells of the maize anther. In a normal anther a hypodermal cell divides periclinally with the inner cell giving rise to the sporogenous archesporial cells while the outer cell, together with adjacent cells, forms the primary parietal layer. The cells of the parietal layer then undergo two cycles of periclinal divisions to give rise to three wall layers. In mac1 anthers the primary parietal layer usually fails to divide periclinally so that the three wall layers do not form, while the archesporial cells divide excessively and most fail to form microsporocytes. The centrally located mutant microsporocytes are abnormal in appearance and in callose distribution and they fail to proceed through meiosis. These failures in development and function appear to reflect the failure of mac1 gene function in the hypodermal cells and their cellular progeny.     

The dyad gene is required for progression through female meiosis in Arabidopsis

In higher plants the gametophyte consists of a gamete in association with a small number of haploid cells, specialized for sexual reproduction. The female gametophyte or embryo sac, is contained within the ovule and develops from a single cell, the megaspore which is formed by meiosis of the megaspore mother cell. The dyad mutant of Arabidopsis, described herein, represents a novel class among female sterile mutants in plants. dyad ovules contain two large cells in place of an embryo sac. The two cells represent the products of a single division of the megaspore mother cell followed by an arrest in further development of the megaspore. We addressed the question of whether the division of the megaspore mother cell in the mutant was meiotic or mitotic by examining the expression of two markers that are normally expressed in the megaspore mother cell during meiosis. Our observations indicate that in dyad, the megaspore mother cell enters but fails to complete meiosis, arresting at the end of meiosis 1 in the majority of ovules. This was corroborated by a direct observation of chromosome segregation during division of the megaspore mother cell, showing that the division is a reductional and not an equational one. In a minority of dyad ovules, the megaspore mother cell does not divide. Pollen development and male fertility in the mutant is normal, as is the rest of the ovule that surrounds the female gametophyte. The embryo sac is also shown to have an influence on the nucellus in wild type. The dyad mutation therefore specifically affects a function that is required in the female germ cell precursor for meiosis. The identification and analysis of mutants specifically affecting female meiosis is an initial step in understanding the molecular mechanisms underlying early events in the pathway of female reproductive development.     

柽柳大、小孢子发生和雌、雄配子体发育的观察

利用常规石蜡制片技术,对柽柳(Tamarix chinensis Lour.)的大、小孢子发生及雌、雄配子体发育过程进行了观察。主要结果如下:(1)花药壁由五层细胞组成,从外向内分别为表皮、药室内壁,两层中层和绒毡层。药壁的发育属于基本型。绒毡层为分泌型。(2)孢原细胞为多孢原起源。小孢子母细胞减数分裂过程中的胞质分裂为连续型,形成的四分孢子为四面体型;同一药室的小孢子母细胞减数分裂几乎完全同步。(3)成熟花粉粒为2细胞型,具3个萌发孔。(4)柽柳为三心皮构成的单室复子房,每子房具有10~20个胚珠,基底胎座,胚珠为双珠被、厚珠心、倒生型。大孢子母细胞减数分裂形成1+3排列的4个大孢子, 4个大孢子全部参与胚囊的形成。(5)胚囊发育为贝母型,反足细胞在胚囊成熟时充分发育。(6)同一朵花中,前期雄蕊的发育早于雌蕊的发育,后期当花粉成熟时,雌配子体也达到成熟,雌雄蕊发育趋于同步。     

八角莲大孢子发生和雌配子体形成

首次报道了八角莲(Dysosma versipellis (Hance)M.cheng)大孢子发生和雌配子体形成的过程.结果:双珠被,多为厚珠心胚珠,少数为假厚珠心,胚珠多为横生,少数为弯生;边缘胎座,子房一室,多胚珠,珠孔由两层珠被共同形成,呈"之"字形;多为单孢原,位于珠心表皮下:偶见2～3个孢原细胞位于珠心表皮下;大孢子母细胞有两种发生方式;直线形大孢子四分体,合点端的大孢子发育为功能大孢子,蓼型胚囊;成熟胚囊中,二个极核在受精前合并为次生核;三个反足细胞不发达,较早退化;"品"字形卵器极性明显,其中卵细胞与助细胞极性相反;助细胞发达,其丝状器在不同发育时期形态及大小不同,且具吸器功能.     

EMBRYOLOGY OF CALYPSO BULBOSA. I. OVULE DEVELOPMENT

Calypso bulbosa is a terrestrial orchid that grows in north temperate regions. Like many orchids, the Calypso has ovules that are not fully developed at anthesis. After pollination, the ovule primordia divide several times to produce a nucellar filament which consists of five to six cells. The subterminal cell of the nucellar filament enlarges to become the archesporial cell. Through further enlargement and elongation, the archesporial cell becomes the megasporocyte. An unequal dyad results from the first meiotic division. A triad of one active chalazal megaspore and two inactive micropylar megaspores are the end products of meiotic division. Callose is present in the cell wall of the megaspore destined to degenerate. In the mature embryo sac the number of nuclei is reduced to six when the chalazal nuclei fail to divide after the first mitotic division. The chalazal nuclei join the polar nucleus and the male nucleus near the center of the embryo sac subsequent to fertilization.     

Studies on the Development of Male and Female Gametophytes in Sinojakia xylocarpa

Observed in this paper was the development of the microspore and megaspore, male and female gametophytes in Sinojakia xylocarpa, which is endemic to China. The anther comprises four microsporangia. Microspore wall forms simultaneously after meiotic division in PMCs. The arrangment of microspore in a tetrad is tetrahedral. Bicel lular pollen grains appear at the shedding stage. ‘They are 3-colporate, with irregular min ute-faveolate exine sculpture. The anther wall development is of the dicotyledonous type, and its endothecitum develops slight fibrous thickenings, which also form on some epidermal cells. The tapetum is glandular. The pistil with hollow style is composed of three carpels, and its ovary contains several anatropous ovules. The ovule is unitegmic, tenuinucellar, but no obturator was observed. The archesporial cell functions directly as the megaspore mother cell which forms a linear tetrad, but T-shaped tetrad was found in a few ovules. A Polygonum type embryo sac forms from the functional chalazal megaspore. In the mature embryo sac, the synergids are elongate with a large vacuole at the chalazal end, but the distrihution of vacuoles in the egg cell appears random. Two polar nuclei remain in contact with each other for a spell before the fertilization and the 3 antipodal cells may persist into early postfertilzation stages. Numerous starch gra ins occur in the embryo sac. According to the present embryological studies on Sinojakia xylocarpa and the works on embryogenesis by some early embryologist, authors consider that Styracaceae, Symplocaceae, Sapotaceae and Ebenaceae are rather closely related, and we alsoconsider it reasonable to put the 4 families mentioned above in Ebenales.     

小盐芥大孢子发生和雌配子体发育

本论文研究了小盐芥(Thellungiella halophila)大孢子发生和雌配子体发育过程及该阶段与花蕾、花、果实外部形态的相关性。结果如下: 小盐芥雌蕊由2心皮组成, 侧膜胎座, 每室胚珠多数, 弯生, 双珠被, 薄珠心。孢原细胞位于珠心表皮之下, 直接起大孢子母细胞的功能。大孢子四分体线形排列, 合点端大孢子为功能大孢子, 胚囊发育为蓼型。     

水稻PDER品系的特点和二倍体孢子生殖胚囊的形成和发育

对水稻（ＯｒｙｚａｓａｔｉｖａＬ．）早发生胚ＰＤＥＲ（ｐｒｅ－ｄｅｖｅｌｏｐｅｄｅｍｂｒｙｏｏｆｒｉｃｅ）品系的特点和细胞胚胎学研究表明,ＰＤＥＲ是二倍体植物２ｎ＝２４,约有５０％胚囊的卵细胞未经受精能自行发育形成胚,成熟种子的萌发和生长速度较常规正常水稻快。ＰＤＥＲ的大孢子母细胞经有丝分裂产生未减数的胚囊,即无融合生殖中的二倍体孢子生殖类型。在胚囊形成和发育过程中有如下几个特点：（１）孢原细胞至大孢子母细胞分裂前的过渡期持续时间较长,孢原细胞和大孢子母细胞的细胞质比周围的珠心细胞质稀淡。（２）大孢子母细胞经二次有丝分裂后形成直线排列的三个细胞（三分体）,珠孔端的两个解体,合点端的一个发育为功能细胞,有少数胚囊的三个细胞全部解体形成败育胚囊。（３）功能细胞经三次连续核分裂形成具八核七个细胞的成熟胚囊,它的结构与常规正常水稻基本相同,但助细胞呈长形而没有回抱着卵细胞。     

小盐芥大孢子发生和雌配子体发育

本论文研究了小盐芥（Thellungiella halophila）大孢子发生和雌配子体发育过程及该阶段与花蕾、花、果实外部形态的相关性。结果如下：小盐芥雌蕊由2心皮组成,侧膜胎座,每室胚珠多数,弯生,双珠被,薄珠心。孢原细胞位于珠心表皮之下,直接起大孢子母细胞的功能。大孢子四分体线形排列,合点端大孢子为功能大孢子,胚囊发育为蓼型。     

海南山薯雌花发育及胚胎发育的研究

通过研究山薯的雌花及胚胎发育,为山薯的胚胎学研究以及杂交育种奠定基础。结果表明:山薯大部分为雌雄异株,海南岛的山薯雌花花期约3个月,为9月初至11月末。子房3室,每室有2个倒生胚珠;胚珠具厚珠心,双珠被。珠孔一端表皮下的孢原细胞逐渐发育为大孢子母细胞。大孢子母细胞减数分裂形成4个呈线形排列的大孢子,其中只有1个可以发育为功能大孢子。成熟的胚囊为7胞8核胚囊,其胚囊发育类型为蓼型。卵细胞的受精属于有丝分裂前型。其胚的发育类型为柳叶菜型,经过二细胞原胚、倒T型原胚、棒状胚、球形胚和梨形胚这5个发育阶段。胚乳的发育为核型。     

Development of Ovules and Embryo sacs in Ostrya virginiana (Betulaceae) and Its Systematic Significance

The development of ovules and embryo sacs in Ostrya virginiana was studied for the first time. Most ovaries had two ovules which were anatropous, unitegmic and crassinucellate. The ovule usually possessed several archesporial ceils which divided periclinally into the upper parietal cell and the lower sporogenous cell. The sporogenous cell functioned directly as megaspore mother cell. The tetrad of megaspores was linear in arrangement, and every megaspore might be functional. One ovule often contained 2- 6 embryo sacs and the embryo sac belongs to Polygonum type. It can be concluded from the present data that all ovules among the genera of the Betulaceae are unitegrnic. There are more groups with the phenomenon of multiple embryo sacs in anemophic plants such as Betulaceae, Casuarinaceae, Graminae, Jnglandaceae, Myricaceae, Simaroubaceae, Ulmaceae, than in entomophilous plants. Multiple embryo sacs also occur among some parasitic plants and saprophytes, e.g. Orobanchaceae, Cassytha in Lauraceae, Cuscuta in Convolvulaceae and Utricularia in Lentibulariaceae. It may be inferred that the characteristic of multiple embryo sacs be an evolutionary adaptation of those plants with lower pollination rate to increase the rate of fertilization. Finally, a comparison of embryological characters among the genera of the Betulaceae shows that the family is of a number of common embryological characters, such as multicellular archesporium, multiple embryo sacs in one ovule, and a long interval between pollination and fertilization. The diversity and systematic significance of several embryological characters among the “higher” hamamelid families are also discussed. It is still hard to explain the phy-logenetic relationships among those families clearly only with.     

EMBRYO SAC DEVELOPMENT IN THE CV. KS MALE-STERILE,FEMALE-STERILE LINE OF SOYBEAN (GLYCINE MAX)

Light microscopic observations were made on 22 ovules from fertile plants and 108 ovules from sterile plants of the cv. KS synaptic mutant, a highly male-sterile, female-sterile line of soybean [Glycine max (L.) Merr.] (2n = 2x = 40). Ovules of fertile siblings contained normal embryo sacs and embryos. Ovules from sterile plants contained various irregularities. The most consistent abnormality was the failure of the embryo sac to attain normal size. Small megasporocytes of irregular shape were seen; only one megasporocyte of normal shape and size was noted. No linear tetrads were found. However, two ovules contained nonlinear triads. A range from zero to 28 cells and nuclei, of various sizes, were identifiable in small megagametophytes and embryo sacs. Degeneration of these nuclei and cells was noted as early as the four-nucleate gametophyte stage. Other ovules contained degenerated nucellar centers without embryo sacs. Two ovules appeared to be normal. Late postpollination stages were marked by shrunken nucellus and integuments. The presence of pollen tube traces, endosperm, and aborting embryos in ovules of hand-pollinated flowers from sterile plants suggested that no incompatibility was involved. Degeneration of the gametophyte and embryo sac contents at many developmental stages indicated a wide array of effects, possibly resulting from meiotic irregularities similar to those seen in microsporogenesis of this mutant.     

Confocal microscopy of whole ovules for analysis of reproductive development: the elongate1 mutant affects meiosis II

Analysis of female meiosis (megasporogenesis) and embryo sac development (megagametogenesis) in angiosperms is technically challenging because the cells are enclosed within the nucellus and ovule tissues of the female flower. This is in contrast to male sporogenesis and gametogenesis where development can readily be observed through the easily dissectable developing anthers. Observation of embryo sac development is a particular problem in crassinucellate ovules such as those of maize. To overcome the problems in observing reproductive development, we developed a simple Feulgen staining procedure optimized for use with confocal microscopy to observe reproductive progression in the crassinucellate ovules of maize. The procedure greatly facilitates the observation of nuclei and cell structures of all stages of megasporogenesis and embryo sac development. The high resolution obtained using the technique enabled us to readily visualize chromosomes from individual cells within ovule tissue samples of maize. A propidium iodide staining technique was also used and compared with the Feulgen-based technique. Static cytometry of relative DNA content of individual nuclei was possible using Imaris software on both Feulgen and propidium iodide-stained samples. The techniques also proved successful for the observation of Arabidopsis and Hieracium aurantiacum female gametophyte and seed development, demonstrating the general applicability of the techniques. Using both staining methods, we analysed the maize meiotic mutant elongate1, which produces functional diploid instead of haploid embryo sacs. The precise defect in meiosis from which diploid embryo sacs arise in elongate1 has not previously been reported. We used confocal microscopy followed by static cytometry using Imaris software to show that the defect by which diploid embryo sacs arise in the maize mutant elongate1 is the absence of meiosis II with one of the dyad cells directly initiating megagametogenesis.     

Ultrastructural studies on the embryo sac ofViscum minimum I. Megasporogenesis

Summary Changes taking place during megasporogenesis of a mistletoe (Viscum minimum) were examined at both light and electron microscopy levels. No distinct ovules, integuments, or ovarian cavity are present at any stage of development. The multicellular archesporium originates in the center of a solid ovary. Several functional megasporocytes are developed from the archesporial cells, either adjacent to each other or separated by unspecialized cells. The megasporocyte is much larger than surrounding cells, is invested by a thick wall, and possesses a large nucleus and amyloplasts. Although plasmodesmata are absent even between the adjacent megasporocytes, cells enter meiosis simultaneously. Following meiosis a linear tetrad is formed. Double and treble linear tetrads are frequently observed. The development of the embryo sac conforms to the monosporic or Polygonum type of megasporogenesis. However, the bisporic or Allium type of development is occasionally observed in preparations. Factors determining the pattern of development are discussed. As in other plant species which follow the monosporic type of development, only one functional megaspore cell undergoes further development while others degenerate. Unlike the healthy functional megaspore cell, the degenerating cells have large starch grains and electron-dense cytoplasm. At a later stage of development, the degraded cells are absorbed by the surrounding tissue.     

西南獐牙菜的胚胎学及其系统学意义

报道了西南獐牙菜的大、小孢子发生及雌,雄配子体发育过程,并以此讨论了獐牙菜属宽丝组和多枝组的分类等级和系统演化关系,西南獐牙菜花药四室;药壁发育为双子叶型;绒毡层二型起源,腺质型;中层细胞2层;药室内壁纤维状加厚,药壁表皮宿存,小孢子母细胞减数分裂为同时型;小孢子四分体的排列为四面体形,成熟花粉为3-细胞型,孔子房为3心皮,1室,胚珠12列,故为超侧膜胎座,薄珠心,单珠被,倒弯生胚珠,大孢子母细胞减数分裂形成4个大孢子呈直线形排列,合点端的大孢子具功能,胚囊发育为蓼型,两极核在受精前融合为次生核,3个反足细胞次生增殖为5-8个,宿存,比较宽丝组和多枝组的胚胎党性一状表明宽丝组从多枝组中分出是合理的,在系统位置上宽丝组较多枝组进化。     

Ovule Development and Determination of Seed Number Per Pod in Oilseed Rape (Brassica napus L.)

Seed number per pod at maturity over the terminal raceme ofsingle plants of oilseed rape is closely correlated to the percentageof ovules with complete embryo sacs (ovule fertility) at floweropening. Approximately one-third of the ovules did not containan embryo sac and sterility, due to the absence of embryo sac,accounted for most of the difference between the numbers ofovules and seeds. Within the terminal raceme, both a decreasedproportion of fertile ovules and a lower number of ovules perovary in apical flowers contributed to the lower number of seedsper pod in the mature apical pods compared to the basal ones.A study of ovule development before flower opening showed thatdifferences in the differentiation of the embryo sacs arosebefore the buds were 40 mm long and probably involved the stagesof meiosis II and/or differentiation of the chalazal megaspore. Key words: Oilseed rape, ovule development, seed number per pod     

Megasporogenesis,Microsporogenesis and Development of Gametophytes in Eleutherococcus senticosus (Araliaceae)

This paper describes megasporogenesis, microsporogenesis, and development of female and male gametophytes in Eleutherococcus senticosus. The main results are as follows: Flowers of E. senticosus are epigynous, pentamerous. Anthers are 4 -microsporangiate. An ovary has 5 loculi. Each ovary loculus has 2 ovules: the upper ovule and the lower ovule. The upper one is orthotropous and degenerates after the formation of archesporial cell, while the lower one is anatropous, unitegmic and crassinucellar, and able to continue developing. In male plants, microsporogenesis and development of male gametophytes took place in regular way, but a series of abnormal phenomena were found in megasporogenesis and development of female gametophytes. The microspore mother cells gave rise to tetrahedral tetrads by meiosis. Cytokinesis was of the simultaneous type. The mature pollen was 3-celled and shed singly. The anther wall formation belonged to the dicotyledonous type. At the stage of microspore mother cell, the anther wall consisted of four layers, i.e. epidermis, endothecium, middle layer, and tapetum. The tapetum was of glandular type and its most cells were binucleate. When microspores were at the uninucleate stage, the tapetum began to degenerate in situ. When microspores developed into 3-celled pollen grains, the tapetum had fully degenerates. In the lower ovule of male flower, the megaspore mother cell gave rise to a linear or “T” -shaped tetrad. In some cases, a new archesporial cell over the tetrad or two tetrads parallel or in a series were observed. Furthermore, the position of functional megaspore was variable; any one or two megaspores might be functional, or one megaspore gave rise to a uninucleate embryo sac, but two other megaspores also had a potentiality of developing into the embryo sac. In generally, on the day when flowers opened, female gametophytes contained only 4 cells: a central cell, two irregular synergids and one unusual egg cell. In female plants, microspore mother cells and secondary sporogenous cells were observed. But at the stage of secondary sporogenous cell, the newly differentiated tapetum took the appearance of degeneration. Later, during the whole stage of meiosis, the trace of degenerative tapetum could be seen. At last, the microsporangium degenerated and no tetrad formed. On the blossom day, all anthers shriveled without pollen grains. In female flowers, megasporogenesis and development of female gametophytes were normal: the tetrad of megaspores was linear or “T”-shaped; the chalazal megaspore was usually functional; the development of embryo sac was of the Polygonum type. On the blossom day, most embryo sacs consisted of 7 cells with 8 nuclei or 7 cells with 7 nuclei; but the egg apparatus was not fully developed. In hermaphroditic plants, microsporogenesis was normal but the development of male gametophytes was partially abnormal. When the hermaphroditic flowers blossomed, there were more or less empty pollen grains in the microsporangium and these pollen grains were quite different in size. The development of most gynoecia was normal but numerous abnormal embryo sacs could be seen. On the blossom day, female gametophytes were mainly 7-celled with 8-nuclei or with 7-nuclei or 4-celled with antipodal cells degenerated; the egg apparatus wasnot fully developed either.     

Sexual and apomictic reproduction in Hieracium subgenus pilosella are closely interrelated developmental pathways

Seed formation in flowering plants requires meiosis of the megaspore mother cell (MMC) inside the ovule, selection of a megaspore that undergoes mitosis to form an embryo sac, and double fertilization to initiate embryo and endosperm formation. During apomixis, or asexual seed formation, in Hieracium ovules, a somatic aposporous initial (AI) cell divides to form a structurally variable aposporous embryo sac and embryo. This entire process, including endosperm development, is fertilization independent. Introduction of reproductive tissue marker genes into sexual and apomictic Hieracium showed that AI cells do not express a MMC marker. Spatial and temporal gene expression patterns of other introduced genes were conserved commencing with the first nuclear division of the AI cell in apomicts and the mitotic initiation of embryo sac formation in sexual plants. Conservation in expression patterns also occurred during embryo and endosperm development, indicating that sexuality and apomixis are interrelated pathways that share regulatory components. The induction of a modified sexual reproduction program in AI cells may enable the manifestation of apomixis in HIERACIUM:     

小叶兜兰的果实生长和雌配子体发育

为了解濒危兰科植物小叶兜兰(Paphiopedilum barbigerum Tang et Wang)胚珠和雌配子体的发育过程,采用常规石蜡切片技术对其果实的生长动态进行了研究。结果表明,授粉后60~75 d的蒴果内种子数量迅速增加,到授粉后120 d时种子充满整个蒴果。授粉后40 d的胎座上分化形成多数由1层表皮细胞包被1列细胞的胚珠原基;授粉后60 d时位于胎座指状结构末端处紧靠表皮细胞下方的孢原细胞分化为大孢子母细胞。之后,大孢子母细胞经过减数分裂和有丝分裂最终形成成熟胚囊;授粉后135 d胚囊发育成熟,附着在胎座上的种子个体分化明显。小叶兜兰胚囊的发育类型为双孢子葱型,胚珠为倒生胚珠,薄珠心,单珠被,成熟胚囊为8核。这为小叶兜兰的生殖生物学及繁殖体系的建立提供理论依据。