MEGASPOROGENESIS AND MEGAGAMETOGENESIS IN SOYBEAN,GLYCINE MAX

Megasporogenesis and megagametogenesis were examined in Glycine max with light, fluorescence, and electron microscopy. Megasporogenesis results in a linear tetrad of four megaspores. Megagametophyte development is of the Polygonum type, with the functional chalazal megaspore undergoing three successive mitotic divisions to produce an eight-nucleate, seven-celled mature megagametophyte. The central cell becomes packed with starch. At fertilization, the antipodals are degenerate, the polar nuclei have fused, starch is diminished, and the egg occupies most of the micropylar portion of the megagametophyte. Several pollen tubes were occasionally observed at each micropyle, yet only one was involved in fertilization. Pollen tube entry occurs through a slightly reduced, viable synergid cell. Endosperm development precedes embryo growth. These results describing normal development allow important comparison with genetic mutants of soybean that affect female fertility.     

Embryo sac development in Arabidopsis thaliana II. The cytoskeleton during megagametogenesis

The microtubular and actin cytoskeletons have been investigated during megagametogenesis in Arabidopsis thaliana using immunofluorescence labelling of isolated coenocytic and mature embryo sacs. We found both actin and microtubules (MTs) to occur in abundance throughout megagametogenesis and in all constituent cells of the mature embryo sac. During many stages, the patterns of distribution of these cytoskeletal elements are congruent and may prove to be co-aligned. Many changes in the arrays of MTs and microfilaments take place and indicate varying roles of the cytoskeleton in the different stages and cell types of megagametogenesis. Two major populations of MTs recur throughout embryo sac formation: (1) Elaborate nuclear-based networks are found during the two-nucleate and four-nucleate developmental stages as well as in the egg cell. These arrays may function in positioning the nuclei. (2) Cytoplasmic MTs in longitudinal orientation in the two-nucleate embryo sac, synergids and part of the egg cell, or in a reticulate pattern in the four-nucleate embryo sac, egg and central cell probably participate in organization of the cytoplasm. Synergid MTs converge at the filiform apparatus. Preprophase bands of MTs are absent throughout megagametogenesis but phragmoplast arrays occur during cellularization of the embryo sac. Well developed arrays of cortical MTs are restricted to the antipodal cells. A large concentration of MTs in the part of the egg cell adjacent to the synergids is well placed for being involved with sperm cell movement within the degenerative synergid. On the basis of the morphology of the cytoskeleton, we concur with views that the shape of megagametophyte is largely determined by the surrounding tissues, including the integumentary tapetum.     

Origin of Megagametophytes with Supernumerary Egg Cells Occurring in Oryza sativa

Cytoembryological observations were attempted to reveal the cytological origin of megagametophyte with supernumerary egg cells. It was shown that all ovules underwent a normal megasporogenesis. The meiosis of megasporocyte consisted of two successive divisions, which gave rise to four haploid megaspores. It was the chalazal spore that developed to form the megagametophyte while the three micropylar megaspores degenerated quickly. After first mitosis in the functional megaspore the two nuclei were separated to the micropylar and chalazal poles by a large central vacuole, meanwhile a differential enlargement of the two-nucleate embryo sac was visualized. The micropylar side enlarged quickly and in contrast, the chalazal side remains almost unchanged. Immediately afterward, the second mitosis took place forming four-nucleate embryo sac. During the second mitosis, nucleus located in the narrow area of chalazal side divided transversely, with its upper sister nucleus migrating to the central or micropylar part of the embryo sac, while the nucleus in the micropylar side divided at an angle of about 45° against the micropylar-chalazal axis. Through the third mitosis, two patterns of nuclear arrangement deviating from polygonum were observed. (i) One nuclear distribution pattern was two, two, four respectively in chalazal, central and micropylar parts. And during maturation the four micropylar nuclei differentiated as egg apparatus consisting of two egg cells and two synergids. The two central nuclei, which presumably suppressed the movement of nucleus toward centre part from both micropylar and chalazal sides developed into central cell with two polar nuclei. And the two chalazal nuclei organized into antipodal cells. Rarely indeed, one nucleus of either chalazal or micropyle side did migrate to join the formation of central cell. (ii) The other nuclei arrangement pattern was two and six respectively positioned in chalazal and micropylar sides. During maturation, five micropylar nuclei differentiated into egg apparatus consisted of three egg cells and two synergids. The sixth one migrated to form the upper polar nucleus. The lower nucleus of the chalazal side developed into antipodal cell which divided quickly, and the upper nucleus became the lower polar nucleus.     

小麦受精过程中酸性磷酸酶的超微细胞化学定位

小麦（Ｔｒｉｔｉｃｕｍ ａｅｓｔｉｖｕｍ ）受精前成熟胚囊,除胚囊中央细胞的合点端细胞质中有酸性磷酸酶外,其余部位均未发现酸性磷酸酶。受精时期,以下部位存在酸性磷酸酶活性：卵细胞的细胞核内一部分染色质和细胞质中大部分线粒体;精、卵核融合时两核的核周腔内;退化助细胞合点端细胞质和一些液泡内;进入雌性细胞中的两个精核;胚囊各成员细胞的细胞壁及胚囊周围珠心细胞的细胞壁。二细胞原胚中未见有酸性磷酸酶。早期胚乳游离核染色质上有酸性磷酸酶。小麦受精过程酸性磷酸酶的分布特点可能与卵细胞生理状态的变化和细胞质中线粒体的改组、助细胞的退化、精核的生理状态以及精核与卵核的核膜融合等有关。     

The Ultracytochemical Localzation of Acid Phosphatase Activity in Wheat During Fertilization

No acid phosphatase activity was observed in the mature embryo sac of wheat (Triticum aestivum) except the chalazal cytoplasm Of the central cell before fertilization. During fertilization, acid phosphataseactivity was observed in the following loci: part of chromatin of the egg nucleus and most of the mitochondria in the egg cytoplasm; the perinuclear spaces of the egg and sperm nuclei at the fusion of the egg and sperm nuclei; the chalazal cytoplasm and some vacuoles of the degenerated synergid; two sperm nuclei within the cytoplasm of female cells; the cell wall of each cell of the embryo sac and that of the nucellar cells surrounding the embryo sac. No acid phosphatase was observed in the two-celled proembryo. Dense enzyme reaction product was localized in the chromatin of the free nuclei at early stage of the endosperm. The characteristic of acid phosphatase distribution during fertilization may be associated with the physiological change of the egg Cell, the reorganization of mitochondria in the egg cell cytoplasm, the degeneration of one of the two synergids, the physiological state of the sperm nuclei and the nuclear membrane fusion of the egg and sperm nuclei.     

鹤顶兰胚囊发育过程中微管变化的共焦显微镜观察

光镜的观察确定了鹤顶兰（Ｐｈａｉｕｓ ｔａｎｋｅｒｖｉｌｌｉａｅ （Ａｉｔｏｎ） Ｂｌ．）胚囊发育属单孢子蓼型。应用免疫荧光标记技术及共焦镜观察了胚囊发育过程中微管分布的变化。当孢原细胞初形成时,细胞内的微管呈网状分布。之后,孢原细胞体积增大发育为大孢子母细胞。大孢子母细胞延长,进入减数分裂Ⅰ。微管由分裂前的网状分布变为辐射状排列。二分体的两个细胞内的微管分布一样,呈辐射状。四分体的近珠孔端的３ 个大孢子解体,细胞内的微管消失。靠合点端的功能大孢子内有许多微管呈网状分布。当功能大孢子进入第一次有丝分裂时,细胞内的微管由网状变为辐射状,从核膜伸展至周质。再经两次有丝分裂形成八核胚囊。在核分裂之前微管一般是呈网状分布并紧包围着核。在分裂期间二核和四核胚囊都呈极性现象,微管系统也呈极性分布。微管在八核胚囊内的分布变化情形特别复杂。首先,八核分别作不同程度的移动,其中两个核移向胚囊中央,珠孔端和合点端的３ 个核分别互相靠拢,形成３ 个区,即中央区、反足区和卵器区。胚囊未形成区时,８ 个核都被网状分布的微管包围着。当胚囊明显分成区时,反足区内的微管仍作网状分布。中央区的微管分布则趋疏松,形成篮形结构,包围着液泡和两个极核。在     

东北地区野豌豆属VICIAL．物种生物学研究Ⅷ．幼苗形体结构动态和种间界限

在野外居群调查的启示下,本文以组件观点对柳叶野豌豆复合种和歪头菜幼苗亚单位的时序变化与开花关系进行了分析。结果发现在柳叶野豌豆复合种栽培居群中存在打破物种间形体结构特征的个体,即在复叶由一对小叶组成的植株就已开花而进入生殖时期。另外,在歪头菜的野生居群中发现由三或四枚小叶组成复叶的个体,因此,我们推测这种形体结构的变化可能暗示着柳叶野豌豆复合种和歪头菜有着共同的祖先。     

Ultrastructural characterization of apospory in Panicum maximum

The nucellar ultrastructure of apomictic Panicum maximum was analyzed during the meiocytic stage and during aposporous embryo sac formation. At pachytene the megameiocyte shows a random cell organelle distribution and sometimes only an incomplete micropylar callose wall. The chalazal nucellar cells are meristematic until the tetrad stage. They can turn into initial cells of aposporous embryo sacs. The aposporous initials can be recognized by their increased cell size, large nucleus, and the presence of many vesicles. The cell wall is thin with few plasmodesmata. If only a sexual embryo sac is formed, the nucellar cells retain their meristematic character. The aposporous initial cell is somewhat comparable to a vacuolated functional megaspore. It shows large vacuoles around the central nucleus and is surrounded by a thick cell wall without plasmodesmata. In the mature aposporous embryo sac the structure of the cells of the egg apparatus is similar to each other. In the chalazal part of the egg apparatus the cell walls are thin and do not hamper the transfer of sperm cells. Structural and functional aspects of nucellar cell differentiation and aposporous and sexual embryo sac development are discussed.     

Confocal Microscopic Observations on Microtubular Cytoskeleton Changes During Megasporogenesis and Megagametogenesis in Phaius tankervilliae (Aiton) Bl.

In nun orchid (Phaius tankervilliae (Alton) B1. ) embryo sac development follows the monosporic pattern. Changes in the pattern of organization of the microtubular cytoskeleton during megasporogenesis and megagametogenesis in this orchid were studied using the immunofluorescence technique and eonfocal microscopy. At the initial stage of development the microtubules in the arehesporium were randomly oriented into a network. Later the archesporial cell elongated to form the megasporocyte. The cytoskeleton in the elongated megasporoeyte was radially organized in which microtubules extending from the nuclear envelope to the peripheral region of the cell. The megasporoeyte then underwent meiosis 1 to form a dyad. The dyad cell at the chalazal end was larger than the cell at the micropylar end. Microtubules in the dyad cell were radially oriented. The dyad underwent meiosis to give rise to a linear array of four megaspores (i. e. tetrad formation). The chalazal-far most megaspore survived and became the functional megaspore, which contained a set of randomly oriented microtubules. The microtubules in the other 3 megaspore disappeared as the cells degenerated. The functional megaspore then underwent mitotic division giveing rise to a 2 nucleate embryo sac. The nuclei of the 2-nucleate embryo sac were separated by a set of longitudinally oriented microtubules which ran parallel to the long axis of the embryo sac. Each nucleus in the embryo sac was surrounded by a set of perinuelear microtubules. The gnucleate embryo sac again underwent mitotic division to form a 4-nucleate embryo sac. The division of the two nuclei was synchronous. But the orientation of the division plan of the two spindles was different (i. e. the spindle microtubules at the chalazal end ran parallel with the long axis of the embryo sac and those at the mieropylar end ran at right angle to the axis of the embryo sac). The 4 nuclei of the 4-nucleate embryo sac were all tightly surrounded by randomly oriented microtubules. Later the paired nuclei at the micropylr end and at the chalazal end as well underwent mitotic division in seguence. At this time when the embryo sac had reached the 8-nucleate embryo sac stage. The pattern of organization of the microtubules was very complex. Initially the nuclei were surrounded by a set of randomly oriented microtubules, but after the two polar nuclei had moved to the central region of the embryo sac, three different organizational zones of microtubules appeared, viz: a randomly oriented set of microtubules surrounding each nucleus in the chalazal zone: a set (in the form of a basket) of cortical microtubules which surrounded the vacuoles and the two polar nuclei in the central zone and a loosely knitted network of microtubules surrounding the nucleus that later became the egg cell nucleus in the micropylar zone. The two nuclei that would become the nuclei of the synergids were surrounded by a set of more densely packed mierotubules. Towards far the most micropylar end some microtubules formed thick bundles. The site of appearance of these thick bundles coincided with the site of development of the filiform apparatus. The pattern of microtubule organization after cellularization (i. e. at the beginning of embryo sac maturation) did not change much. The author's results indicated that various patterns of microtubule organization observed in the developing embryo sac of nun orchid reflected the complexity and dynamism of the embryo sac.     

Studies of Ultrastructure and ATPase Localization of Mature Embryo Sac in Vicia faba L.

Studies of ultrastructure and ATPase localization of the mature embryo sac in Vicia faba L. show that the egg cell has no cell wall at thechalazal end, it has a chalazally located nucleus and a large micropylar vacuole. There are many nuclear pores in the nuclear membrane. The cytoplasm is restricted around the nucleus. Dictyosome and mitochondria are few. There are some starch grains and lipid grains in the egg cytoplasm. There are no obvious differences between two synergids. No cell wall is seen at the chalazal end either, but there are some vesicles which project to vacuole of the central cell and fuse with its vacuolar membrane. Plasmodesmata connections occur within the synergid wall where it is adjacent to the central cell. The synergid has a micropylarly located nucleus and a chalazal vacuole, the nucleus is irregularly shaped. The synergid cytoplasm is rich in organelles. The filiform aparatus is of relatively heterogeneous structure. The central cell is occupied by a large vacuole and its cytoplasm is confined to a thin layer along the empryo sac wall, but is rich in various organelles, starch grains and lipid bodies. Nucleolar vacuoles are often present two polar nuclei. The nuclear membranes of two polar nuclei have partly fused. ATPase reactive product was located obviously at the endoplasmic reticulum in cytoplasm of the egg cell and central cell. The embryo sac wall consists of different density of osmiophilic layer. There are some wall ingrowths in chalazal region of the embryo sac. The long-shaped and cuneate cells of chalazal region are peculiar. Special tracks of ATPase reactive products are visible at their intercellular space which may be related to transportation of nutrients.     

宁夏枸杞大孢子发生和雌配子体发育的细胞学研究

采用半薄切片技术和组织化学染色法对宁夏枸杞大孢子发生和雌配子体发育过程中的细胞结构变化及营养物质积累特征进行了观察。结果表明,(1)宁夏枸杞为中轴胎座,多室子房,倒生胚珠,单珠被,薄珠心类型。(2)位于珠心表皮下的孢原细胞可直接发育为大孢子母细胞,减数分裂后形成直线型大孢子四分体,合点端第一个大孢子发育为功能大孢子,胚囊发育类型为蓼型,具有珠被绒毡层。(3)初形成的胚囊外周组织中没有营养物质积累,成熟胚囊时期出现了大量的淀粉粒且呈珠孔端明显多于合点端的极性分布特征。(4)助细胞的珠孔端具有明显的丝状器结构,呈PAS正反应表现出多糖性质,成熟胚囊具有承珠盘结构。     

EMBRYO SAC LACKING ANTIPODAL CELLS IN ARABIDOPSIS THALIANA (BRASSICACEAE)

Ultrastructure of the embryo sac lacking antipodals in prefertilization stages in Arabidopsis thaliana has been examined 2 hr before and 5 hr after manual cross pollination. The cytoplasm of both synergids before fertilization is rich in ribosomes, mitochondria, and rough endoplasmic reticulum, and also contains several microbodies and spherosomes. The filiform apparatus includes electron-dense material and a fibrous part. Many cortical microtubules appear in the filiform apparatus area. One of the two synergids degenerates before fertilization. The synergids, the egg cell, and central cell have a rich cytoskeleton of microtubules; only the synergids appear to contain microfilaments. At the chalazal end, the antipodals are initially present but degenerate by the time of pollination in most embryo sacs in the starchless line studied. The embryo sac is completely surrounded by a wall containing an electron-dense layer, separating it from the nucellus, including the chalazal end. When the antipodals have degenerated, the electron-dense layer disappears at the chalazal end only, and the wall between the central cell and the nucellus is homogeneous. Between the central cell and nucellar cells no plasmodesmata are found. The membranes of both antipodal cells at the chalazal end of the embryo sac appear sinuous, like those of transfer cells. The central cell has plastids preferentially distributed around the nucleus, but the other organelles are randomly distributed. The central cell in the embryo sac and the adjacent chalazal nucellar cells show a transfer-cell function in the embryo sac after the antipodals degenerate.     

Egg cell signaling by the secreted peptide ZmEAL1 controls antipodal cell fate

Unlike in animals, female gametes of flowering plants are not the direct products of meiosis but develop from a functional megaspore after three rounds of free mitotic divisions. After nuclei migration and positioning, the eight-nucleate syncytium differentiates into the embryo sac, which contains two female gametes as well as accessory cells at the micropylar and chalazal pole, respectively. We report that an egg-cell-specific gene, ZmEAL1, is activated at the micropylar pole of the eight-nucleate syncytium. ZmEAL1 translation is restricted to the egg cell, resulting in the generation of peptide-containing vesicles directed toward its chalazal pole. RNAi knockdown studies show that ZmEAL1 is required for robust expression of the proliferation-regulatory gene IG1 at the chalazal pole of the embryo sac in antipodal cells. We further show that ZmEAL1 is required to prevent antipodal cells from adopting central cell fate. These findings show how egg cells orchestrate differentiation of the embryo sac.     

Embryo and Endosperm Development in Isatis Tinctoria L. and the Histochemical Study of Its Storage Reserve

The ovule is anatropous and bitegmic. The nuceIlar cells have disorganized except the chalazal proliferating tissue. The curved embryo sac comprises an egg apparatus and a central cell with two palar nuclei and wall ingrowths on its micropylar lateral wall. The antipodal cells disappear. Embryo development is of the Onagrad type. The filament suspensor grows to a length of 785 μm and degenerats at tarpedo embryo stage. The basal cell produces wall ingrowths on the micropylar end wall and lateral wall. The cells of mature embryo contain many globular protein bodies, 2.5–7.5 μm in diameter, composed of high concentration of protein and phytin, insoluble polysaccharide and lipid. The cells, except procambium, also contain many small starch grains. Some secretory cavities scattered in the ground tissue have liquidlike granules composed of protein, ploysacchaide and lipid. Endosperm development follows the nuclear pattern. At the late heart embryo stage, the endosperm around the embryo and the upper suspensor and the peripheral endosperm of the basal region of the U-shaped embryo sac becomes cellular. The endosperm at micropylar and chalazal ends remains free nuclear phase until the late bended cotyledon stage. Wall ingrowths at both micropylar and chalazal end wall and lateral wall of the embryo sac become more massive during endosperm development. Wall ingrowths also occur on the outer walls of the outer layer endosperm cells at both ends and lateral region of the embryo sac. When the embryo matures, many layers of chalazal endosperm ceils including 2–4 layers of transfer cells, a few of micropylar endosperm cells and 1–5 layers of peripheral endosperm cells are present. The nutrients of the embryo and endosperm at different stages of development are also discussed.     

Three-dimensional organization and dynamic changes of the actin cytoskeleton in embryo sacs ofZea mays andTorenia fournieri

Summary Actin organization was observed inm-maleimidobenzoic acid N-hydroxysuccinimide ester(MBS)-treated maize embryo sacs by confocal laser scanning microscopy. The results revealed that dynamic changes of actin occur not only in the degenerating synergid, but also in the egg during fertilization. The actin filaments distribute randomly in the chalazal part of the synergid before fertilization; they later become organized into numerous aggregates in the chalazal end after pollination. The accumulation of actin at this region is intensified after the pollen tube discharges its contents. Concurrently, actin patches have also been found in the cytoplasm of the egg cell and later they accumulate in the cortical region. To compare with MBS-treated maize embryo sacs, we have performed phalloidin microinjection to label the actin cytoskeleton in living embryo sacs ofTorenia fournieri. The results have extended the previous observations on the three-dimensional organization of the actin arrays in the cells of the female germ unit and confirm the occurrence of the actin coronas in the embryo sac during fertilization. We have found that there is an actin cap occurring near the filiform apparatus after anthesis. In addition, phalloidin microinjection into the Torenia embryo sac has proved the presence of intercellular actin between the cells of the female germ unit and thus confirms the occurrence of the actin coronas in the embryo sac during fertilization. Moreover, actin dynamic changes also take place in the egg and the central cell, accomplished with the interaction between the male and female gametes. The actin filaments initially organize into a distinct actin network in the cortex of the central cell after anthesis; they become fragmented in the micropylar end of the cell after pollination. Similar to maize, actin patches have also been observed in the egg cortex after pollination. This is the first report of actin dynamics in the living embryo sac. The results suggest that the actin cytoskeleton may play an essential role in the reception of the pollen tube, migration of the male gametes, and even gametic fusion.     

A CYTOCHEMICAL STUDY OF EMBRYO SAC DEVELOPMENT IN STELLARIA MEDIA

Megasporogenesis and embryo sac development in Stellaria media were investigated using cytochemical methods for the demonstration of nucleic acids, proteins, and polysaccharides. RNA concentrations were high in the archesporial cells, low in the megaspore mother cell, and increased again to high concentrations with the formation of the megaspore and 2-, 4-, and early 8-nucleate embryo sac. RNA levels were also high in the egg and primary endosperm nucleus but low in the synergid and antipodal cells. Nucleolar size and vacuolation were indicative of RNA synthetic activity. Protein concentrations were parallel in concentration and distribution to those observed for RNA. Polysaccharides were conspicuously absent from all stages except the synergids and nucellar cells. Feulgen-stained DNA was demonstrable in the antipodal cells, megaspore mother cell, and megaspore cell, but was not visible in the 2-, 4-, or early 8-nucleate embryo sac. Feulgen staining was also absent from the egg and primary endosperm nucleus but was visible in the synergids and antipodals. Histones were difficult to visualize anywhere except in the egg cytoplasm and the nuclei of the antipodals.     

Different patterns of callose wall formation during megasporogenesis in two species ofOenothera (Onagraceae)

The homozygousOenothera hookeri Torr. etGray shows the typical pattern ofOnagraceae with ± callose on the external walls of megaspore mother cells and tetrads. Megasporogenesis is heteropolar, and the micropylar megaspore is the mother-cell of the 4-celled embryo sac. The complex-heterozygousOenothera biennis L. during megasporogenesis generally has callose not on the external cell walls but only on the transversal walls of the tetrad. In 95% of the ovules both the external chalazal and the micropylar megaspores develop to embryo sac mother-cells. Megasporogenesis is homopolar, and competition between two developing embryo sacs for nutrition in the ovule occurs. The embryo sac with the stronger genotype wins the race against the other one. Polarity phenomena during ontogeny of the female gametophyte are related to nutritional supply and hormonal induction from the ovule. The introduction of a developmental-physiological point of view into the discussion about the evolution of the embryo sac inOnagraceae is therefore justified.Stipendiatin der Alexander von Humboldt-Stiftung 1974/76.     

甜菜无融合生殖单体附加系M14成熟胚囊的超微结构特征

以甜菜无融合生殖单体附加系M14（Betavulgaris,2n=18＋1）为实验材料,利用电子显微镜技术对成熟胚囊及其超微结构进行研究。结果表明：M14成熟胚囊包括1个卵细胞、2个退化的助细胞、1个具有次生核的中央细胞和3-6个反足细胞。其卵细胞具有3种不同的形态：（1）极性正常的卵细胞,细胞核位于合点端,细胞质含有大量核糖体、线粒体、内质网等细胞器;（2）细胞核位于细胞中央;（3）细胞核位于珠孔端,且后2种形态细胞器的种类与数量少。大多数胚囊中的2个助细胞在开花前已退化。中央细胞的次生核位于反足细胞附近;未经受精自发分裂前的卵细胞与中央细胞的细胞核大、核仁明显,细胞器的种类与数量多,呈现旺盛代谢活动特征,成为二倍体孢子无融合生殖过程中,卵细胞与次生核自发分裂的细胞学标志。     

The mature embryo sac of the sugar beet, Beta vulgaris: A structural investigation

The mature embryo sac of Beta vulgaris consists of one egg cell, one persistent and one degenerated synergid, one cental cell with two fused polar nuclei, and five to six antipodals. The degeneration of one of the synergids appears before pollination in the maturing process. The two fused polar nuclei are located in the chalazal part of the central cell. The antipodals may have secretory activities. It is suggested that the embryo sac of the sugar beet completes the maturing process independently of pollination.     

水稻胚囊超微结构的研究

水稻(Oryza sativa L.)胚囊成熟时,卵细胞的合点端无细胞壁,核居细胞中部,细胞器集中在核周围,液泡分散于细胞周边区域。助细胞珠孔端有丝状器,合点端无壁,核位于细胞中部贴壁处,细胞器主要分布在珠孔端,液泡主要分布在合点端。开花前不久,一个助细胞退化。中央细胞为大液泡所占,两个极核靠近卵器而部分融合,细胞器集中在极核周围和靠近卵器处,与珠心相接的胚囊壁上有发达的内突。反足细胞多个形成群体,其增殖主要依靠无丝分裂与壁的自由生长,反足细胞含丰富活跃的细胞器,与珠心相接的壁上有发达的内突。开花后6小时双受精已完成,合子和两个助细胞合点端均形成完整壁。合子中开始形成多聚核糖体、液泡减小。退化助细胞含花粉管释放的物质,其合点端迴抱合子。极核已分裂成数个胚乳游离核,中央细胞中细胞器呈活化状态。反足细胞仍在继续增殖。讨论了卵细胞的极性、助细胞的退化、卵器与中央细胞间界壁的变化、反足细胞的分裂特点等问题。