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.     

Changes in actin organization in the living egg apparatus of Torenia fournieri during fertilization

Changes in actin organization in the living egg apparatus of Torenia fournieri from anthesis to post-fertilization have been investigated using microinjection and confocal microscopy. Our results revealed that the actin cytoskeleton displays dramatic changes in the egg apparatus and appears to coordinate the events of synergid degeneration, pollen tube arrival and gametic fusion during fertilization. Synergid degeneration occurs after anthesis and is accompanied by actin fragmentation and degradation. The actin cytoskeleton becomes organized with numerous aggregates in the chalazal end of the degenerating synergid, and some of the actin infiltrates into the intercellular gap between synergids, egg and central cell, forming a distinct actin band. An actin cap is present near the filiform apparatus after anthesis and disappears after pollen tube arrival. In the egg cell, actin filaments initially organize into a network and after pollination become fragmented into numerous patches in the cortex. These structures, along with the actin in the degenerating synergid and intercellular spaces form two distinct actin coronas during fertilization. The actin coronas vanish after gametic fusion. This is the first report of changes in actin organization in the living egg apparatus. The reorganization of the actin cytoskeleton in the egg apparatus and the presence of the actin coronas during fertilization suggest these events may be a necessary prelude to reception of the pollen tube and fusion of the male and female gametes. Received: 11 November 1999 / Accepted: 31 January 2000     

Actin coronas in normal and indeterminate gametophyte1 embryo sacs of maize

 The actin cytoskeletal organization and nuclear behavior of normal and indeterminate gametophyte1 (ig1) embryo sacs of maize were examined during fertilization. After pollination, during degeneration of one of the synergids and before arrival of the pollen tube, the cytoskeletal elements undergo dramatic changes including formation of the actin coronas at the chalazal end of the degenerating synergid and at the interface between the egg cell and central cell. The actin coronas are present only for a limited period of time and their presence is coordinated with pollen tube arrival and fusion of the gametes; they disappear before the zygote divides. This allows us to estimate the frequency of fertilized ovules along the ear. Up to 88% of the ovules on an ear contain actin coronas in the embryo sacs when observed 16–19 h after pollination, indicating the high frequency of fertilizing kernels along the ear at this stage. In the ig embryo sacs, two or more degenerated synergids containing actin coronas at their chalazal ends receive multiple pollen tubes for gametic fusion and can consequently give rise to twin or polyembryos. These findings with the monocot maize are consistent with previous reports on the dicots Plumbago and Nicotiana, suggesting that the formation of actin coronas in the embryo sac during fertilization is a universal phenomenon in angiosperms and is part of a mechanism of interaction between gametic signaling and actin cytoskeleton behavior which appears to precisely position and facilitate the access of male gametes to the egg cell and central cell for fusion. Received: 15 May 1998 / Revision accepted: 17 August 1998     

Early Events in the Penetration of the Embryo Sac in Torenia fournieri(Lind.)

At maturity, Torenia fournieri(Lind.) has an embryo sac whichprotrudes through the micropyle placing the synergids, egg celland part of the central cell within the ovary locule adjacentto the placenta. The present study utilized this unique attributein combination with confocal and light microscopy to characterizethe timing and associated structural changes during pollinationevents leading to double fertilization. The observation of spermnuclei in living gametophyte tissue is an important advancein the identification, in real time, of stages leading to fertilizationin angiosperms. A continuum of fertilization occurred between12 and 16 h after pollination (hap), with peak frequency ofegg and sperm fusion at 14 hap (43%). Movement of the spermcells through the degenerated synergid took several hours andfusion between sperm and their respective female nuclei occurredsimultaneously. Changes in embryo sac structure were also documented.Cell walls in the region between the synergids and egg cellwere poorly developed prior to pollen tube penetration. Thickenedcell walls were observed around the periphery of the synergidsand egg cell following pollination, and in the central cellwhere it lay within the body of the ovule. Starch was observedin the cells of the embryo sac, although the number and distributionof granules varied before and after pollination. These temporaland spatial observations of the embryo sac inTorenia fournieriprovide a basis for further research to determine control mechanismsoperating during specific double fertilization events in angiosperms.Copyright 2000 Annals of Botany Company Double fertilization, embryo sac, sperm nuclei, Hoechst, Torenia fournieri     

Polar distribution dynamics of Con A binding sites in embryo sacs is temporally coupled by the fertilization process

The binding site distribution of concanavalin agglutinin (Con A) and wheat germ agglutinin (WGA) on embryo sacs at various developmental stages of Torenia fournieri L was studied by using a cooled Charge Coupled Device (CCD) and fluorescent Con A and WGA probes. The distribution patterns of Con A and WGA binding sites on embryo sacs changed during the fertilization process. The fluorescent signal indicating Con A binding sites was distributed evenly on the surface of the embryo sac wall before anthesis, was much denser on the micropylar end of the embryo sac wall and looked like a corona on the day of anthesis. After pollination, stronger fluorescence was present on the micropylar end of the embryo sac wall and the filiform apparatus (FA), showing an obvious polar distribution. When the pollen tube entered the embryo sac and reached a synergid, the fluorescence was still concentrated on the micropylar end and FA, and started to appear on the synergid. After fertilization, the polar distribution of the fluorescence gradually disappeared and an even distribution pattern was observed again on the embryo sac wall. These results revealed that the dynamic distribution of Con A binding sites was temporally coupled with the process of fertilization. WGA binding site distribution on the embryo sac was also investigated and showed a simple pattern but also regularly changed during the process of fertilization. The variation of these lectin binding sites during the fertilization process suggests that lectin binding site interactions may play a role in the process.     

Fertilization in Torenia fournieri: Actin organization and nuclear behavior in the central cell and primary endosperm

Studies of the living embryo sacs of Torenia fournieri reveal that the actin cytoskeleton undergoes dramatic changes that correlate with nuclear migration within the central cell and the primary endosperm. Before pollination, actin filaments appear as short bundles randomly distributed in the cortex of the central cell. Two days after anthesis, they become organized into a distinct actin network. At this stage the secondary nucleus, which is located in the central region of the central cell, possesses an associated array of short actin filaments. Soon after pollination, the actin filaments become fragmented in the micropylar end and the secondary nucleus is located next to the egg apparatus. After fertilization, the primary endosperm nucleus moves away from the egg cell and actin filaments reorganize into a prominent network in the cytoplasm of the primary endosperm. Disruption of the actin cytoskeleton with latrunculin A and cytochalasin B indicates that actin is involved in the migration of the nucleus     

Kinetics of double fertilization in Torenia fournieri based on direct observations of the naked embryo sac

Torenia fournieri Lind. has a naked embryo sac that protrudes from the micropyle. The precise time course of the entire process of double fertilization and the kinetics of fertilization events were determined in this species by the following methods: (i) without squashing, pollen tubes on the torn stylar canal were observed by fluorescence microscopy after staining with both 4′,6-diamidino-2-phenylindole (DAPI) and aniline blue; and (ii) large numbers of living embryo sacs were observed directly by differential interference microscopy before and after fertilization. The pollen began to germinate 5 min after pollination and extruded pollen tubes which elongated at a constant rate of 2.3 mm · h⁻¹. At 4.0 h after pollination, the mitotic index of the generative cell within the pollen tube reached 88% and the two sperm cells were formed. Pollen tubes began to arrive at ovules 8.9 h after pollination and directly entered one of two synergids in the naked embryo sac. The time required for transport of sperm cells in the degenerated synergid was estimated statistically to be 1.9 ± 1.8 min for transport of the first cell and 7.4 ± 1.6 min for the second. In the nucleus of the fertilized egg cell, the male nucleolus began to emerge 10 h after pollination and the female nucleolus often decreased in size. The two nucleoli fused together prior to elongation of the zygote, which began 28 h after pollination. In the central cell, the secondary nucleus migrated to a region adjacent to the egg apparatus after pollination but prior to the arrival of the pollen tube. The primary endosperm nucleus rapidly returned to the inner region after fertilization. Prior to embryogenesis, the first division of the primary endosperm began about 15 h after pollination, at a defined site, to form the chalazal haustorium. Received: 24 October 1996 / Accepted: 13 March 1997     

莴苣助细胞发育过程中钙的分布研究

用焦锑酸盐沉淀法对莴苣助细胞中的钙分布进行了观察。结果表明,开花前3天刚形成的助细胞中的钙颗粒很少:开花前2天助细胞壁中的钙颗粒增加;开花前1天助细胞珠孔端细胞壁加厚,其中积累了许多钙颗粒:开花当天助细胞珠孔端的丝状器中聚集了大量的钙颗粒。授粉后1h时两个助细胞的结构和钙分布发生差异,一个呈退化状,其中的钙颗粒明显增多,另一宿存助细胞中的钙分布与授粉前相似。去雄不授粉1天后两个助细胞均保持完好,且两助细胞中的钙分布没有明显差异,表明由花粉管引起一个助细胞中钙含量增加进而导致了助细胞退化。退化助细胞在卵细胞与中央细胞之间形成一薄层。助细胞退化后不同部位的钙颗粒呈现出与受精作用密切有关的变化:授粉后1h时,钙主要聚集在近合点端部位;授粉后2.5h卵细胞即将受精,这时许多细小的钙颗粒主要聚集在卵细胞与中央细胞之间的薄层中;授粉后4h精、卵细胞已融合,这时退化助细胞合点端的钙颗粒明显减少,而在其珠孔端又聚集了较多的钙。上述助细胞中的钙含量变化与吸引花粉管进入胚囊和促使精卵细胞融合密切有关。     

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。     

西瓜不同发育时期的助细胞超微结构的变化（简报）

The ultrastructure of synergids of watermelon (Citrullus Lanatus L.) was investigated using transmission electron microscopy at following stages of embryo sacs: 1. Unpollination, on the first flowering day. 2. Unpollination, on 2nd day after anthesis (DAA). 3. Fertilization, on DAA 2. The synergids with distinct filiform apparatus at the micropylar end have abundant organelle, such as mitochondria, endoplasmic reticulum, and plastids in cytoplasm, which indicate that they are active on the first flowering day. No wall is present at the chalazal part of synergid, and there are some flocculent materials and vesicles in the spaces of cytoplasma membranes among synergid, egg cell and central cell in embryo sacs at the first and the second stages. On DAA 2, in unpollinated embryo sacs, the central large vacuole of synergid is divided into several smaller ones and the starch grains decrease in cytoplasm. There is no newly synthesized wall at the chalazal end of persistent synergid in fertilized embryo sacs. The contents of degenerated synergid, in the form of electron dense granules, are located in the wide space among central cell, zygote and persistent synergid, and some of them migrate into central cell through cytoplasma membrane. Therefore, it is deduced that the contents of synergid might serve as a nutrient supplement to the development of endosperm, but not embryo.     

Symplastic communication between the central cell and the egg apparatus cells in the embryo sac of Torenia fournieri Lind. before and during fertilization

 Various membrane-impermeable, water-soluble fluorescent tracers with different molecular weights were microinjected into the central cell of the embryo sac of Torenia fournieri Lind. before and during fertilization. Before anthesis, there was high symplastic permeability between the central cell and the egg apparatus cells. In this stage, fluorescent tracers up to 10 kDa could pass from the central cell into the egg apparatus cells, whereas those with larger molecular weight remained in the central cell. As the embryo sac matured, symplastic permeability decreased such that 2 d after anthesis only tracers less than 3 kDa could spread from the central cell into the egg cell. There appeared to be no symplastic permeability between the primary endosperm and zygote after fertilization, since tracers as small as 521 Da could not pass into the zygote in about half of the microinjected embryo sacs. This is the first report of a change in cell-to-cell communication among the cells of the female germ unit before and after fertilization. Received: 16 December 1999 / Accepted: 4 February 2000     

Fertilization in maize indeterminate gametophyte1 mutant

Summary. Mature embryo sacs of the maize mutant indeterminate gametophyte1 displayed different cellular patterns compared to those of the wild type. About 40% of the ig1 embryo sacs contained three or more synergids and two or more egg cells at the micropylar end. During fertilization in embryo sacs with two synergids, both of them frequently degenerated and were penetrated by two pollen tubes. 75% of the embryo sacs containing three or more synergid cells were penetrated by two or more pollen tubes, although most of them had only one degenerated synergid. Multiple fusions between the sperm cells and eggs frequently occurred in the same embryo sac, which subsequently generated multiple embryos. There were two or more central cells in about 33% of ig1 embryo sacs. The largest central cell was usually adjacent to the egg apparatus and contained two unfused polar nuclei, while those extra central cells located at the chalazal end usually had a single nucleus. Fertilization occurred only between the male gamete and the largest binucleate central cell. The extra central cells eventually degenerated after fertilization.Present address: GI Basic Research Center, Mayo Clinic, Rochester, Minnesota, U.S.A.Correspondence and reprints: State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Science, China Agricultural University, Beijing 100094, Peoples Republic of China.     

Fertilization inNicotiana tabacum: Cytoskeletal modifications in the embryo sac during synergid degeneration

The cytoskeletal organization of the embryo sac of tobacco (Nicotiana tabacum L.) was examined at maturity and during synergid degeneration, pollen-tube delivery and gamete transfer using rapid-frozen, freeze-substituted and chemically fixed material in combination with immunofluorescence and immunogold electron microscopy. Before fertilization, the synergid is a highly polarized cell with dense longitudinally aligned arrays of microtubules adjacent to the filiform apparatus at the micropylar end of the cell associated with major organelles. The cytoskeleton of the central cell is less polarized, with dense cortical microtubules in the micropylar and chalazal regions and looser, longitudinally oriented cortical microtubules in the lateral region. In the synergid and central cell, F-actin is frequently found at the surface of the organelles and co-localizes with either single microtubules or microtubule bundles. Egg cell microtubules are frequently cortical, randomly oriented and more abundant at the chalazal end of the cell; actin filaments are associated with microtubules and the cortex of the egg cell. At 48 h after pollination and before the pollen tube arrives, the onset of degeneration is evident in one of the two synergids: the electron density of cytoplasmic organelles and the ground cytoplasm increases and the nucleus becomes distorted. Although synergids otherwise remain intact, the vacuole collapses and organelles degenerate rapidly after pollen-tube entry. Abundant electron-dense material extends from the degenerated synergid into intercellular spaces at the chalazal end of the synergid and between the synergids, egg and central cell. Rhodamine-phalloidin and anti-actin immunogold labeling reveal that electron-dense aggregates in this region contain abundant actin forming two distinct bands termed coronas. This actin is part of a mechanism in the egg apparatus which appears to precisely position and facilitate the access of male gametes to the egg and central cell for fusion.Abbreviations ES embryo sac - FA filiform apparatus - Mf microfilament - Mt microtubule - PT pollen tube - RF-FS rapid-freeze freeze-substitution - TEM transmission electron microscopy We thank Gregory W. Strout for technical assistance in the use of the RF-FS technique and Dr. Hongshi Yu for providing Fig. 1. This research was supported by U.S. Department of Agriculture grants 88-37261-3761 and 91-37304-6471. We gratefully acknowledge use of the Samuel Robert Noble Electron Microscopy Laboratory of the University of Oklahoma.     

Fertilization in Torenia fournieri: Actin organization and nuclear behavior in the central cell and primary endosperm

Studies of the living embryo sacs of Torenia fournieri reveal that the actin cytoskeleton undergoes dramatic changes that correlate with nuclear migration within the central cell and the primary endosperm. Before pollination, actin filaments appear as short bundles randomly distributed in the cortex of the central cell. Two days after anthesis, they become organized into a distinct actin network. At this stage the secondary nucleus, which is located in the central region of the central cell, possesses an associated array of short actin filaments. Soon after pollination, the actin filaments become fragmented in the micropylar end and the secondary nucleus is located next to the egg apparatus. After fertilization, the primary endosperm nucleus moves away from the egg cell and actin filaments reorganize into a prominent network in the cytoplasm of the primary endosperm. Disruption of the actin cytoskeleton with latrunculin A and cytochalasin B indicates that actin is involved in the migration of the nucleus in the central cell. Our data also suggest that the dynamics of actin cytoskeleton may be responsible for the reorganization of the central cell and primary endosperm cytoplasm during fertilization.     

西瓜不同发育时期的助细胞超微结构的变化

被子植物胚囊的“雌性生殖单位”,已在多种植物上进行了超微结构的观察,但大多都以卵细胞受精前后的结构变化为主要研究内容。对于“雌性生殖单位”中的另一重要成员——助细胞,在不同发育状态下其结构变化的详细资料不多,尤其是助细胞退化后的物质去向,少见报道。本研究主要观察了西瓜不同发育时期(受精前后)、不同发育状态(柱头授粉和未授粉)的助细胞超微结构,以期为研究助细胞在双受精中所起作用提供新的资     

Abnormalities Occurring during Female Gametophyte Development Result in the Diversity of Abnormal Embryo Sacs and Leads to Abnormal Fertilization in indica/japonica Hybrids in Rice

Embryo sac abortion is one of the major reasons for sterility in indica/japonica hybrids in rice. To clarify the causal mechanism of embryo sac abortion, we studied the female gametophyte development in two indica/japonica hybrids via an eosin B staining procedure for embryo sac scanning using confocal laser scanning microscope. Different types of abnormalities occurred during megasporogenesis and megagametogenesis were demonstrated. The earliest abnormality was observed in the megasporocyte. A lot of the chalazal-most megaspores were degenerated before the mono-nucleate embryo sac stage. Disordered positioning of nucleus and abnormal nucellus tissue were characteristics of the abnormal female gametes from the mono-nucleate to four-nucleate embryo sac stages. The abnormalities that occurred from the early stage of the eight-nucleate embryo sac development to the mature embryo sac stage were characterized by smaller sizes and wrinkled antipodals. Asynchronous nuclear migration, abnormal positioning of nucleus, and degeneration of egg apparatus were also found at the eight-nucleate embryo sac stage. The abnormalities that occurred during female gametophyte development resulted in five major types of abnormal embryo sacs. These abnormal embryo sacs led to abnormal fertilization. Hand pollination using normal pollens on the spikelets during anthesis showed that normal pollens could not exclude the effect of abnormal embryo sac on seed setting.     

Abnormalities Occurring during Female Gametophyte Development Result in the Diversity of Abnormal Embryo Sacs and Leads to Abnormal Fertilization in indicaljaponica Hybrids in Rice

Embryo sac abortion is one of the major masons for sterility in indicaljaponica hybrids In rice. To clarify the causal mechanism of embryo sac abortion, we studied the female gametophyte development in two indicaljaponica hybrids via an eosin B staining procedure for embryo sac scanning using confocal laser scanning microscope. Different types of abnormalities occurred during megasporogenesis and megagamatogenesis were demonstrated. The earliest abnormality was observed in the megasporocyte. A lot of the chalazal-most megaspores were degenerated before the mono-nucleate embryo sac stage. Disordered positioning of nucleus and abnormal nucallus tissue were characteristics of the abnormal female gametes from the mono-nucleate to four-nucleate embryo sac stages. The abnormalities that occurred from the early stage of the eight-nucleate embryo sac development to the mature embryo sac stage were characterized by smaller sizes and wrinkled antipodals. Asynchronous nuclear migration, abnormal positioning of nucleus, and degeneration of egg apparatus were also found at the eight-nucleate embryo sac stage. The abnormalities that occurred during female gametophyte development resulted in five major types of abnormal embryo sacs. These abnormal embryo sacs led to abnormal fertilization. Hand pollination using normal pollens on the spikelets during anthesis showed that normal pollens could not exclude the effect of abnormal embryo sac on seed setting.     

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.     

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。     

The Ultrastructural Study on the Early Embryonic Development of Radish

The ultrastructure of the mature embryo sac, the early stages of the embryo and endosperm development of common radish, Raphanur sativus was examined. The embryo sac consists of 7 cells with antipodal ceils disappeared when it matures. The egg cell is highly polarized. The wall surrounded the chalazal end of the egg cell is incomplete, showing a discontinuous structure of an electron dense material deposited intermittently in the space between the two plasma membranes of the egg cell and central cell. The synergid has filiform apparatus, rich in organelles and well developed ER. The two polar nuclei of the central cell are located near the egg apparatus because of the big vacuole, and the finger-like protrutions from the cell wall, as that in synergid, are found. The first division of the zygote occurs 4–5 days after pollination and the development of the embryo follows the Onagrad type, and the structure of the embryo cell is quite simple for containing small quantity of ER, plastids and other organelles. The primary endosperm nucleus deviates 2 days earlier than zygote. The endosperm is of nuclear-endosperm containing chloroplasts, well developed ER, and plentiful of mitochondria and golgi bodies and the nodule-like aggregation in both. the chalazal and micropylar ends of the embryo sac during the early development appeared, and cell wall starting at the micropylar end by freely-growing forms about 16 days after pollination.