Embryogenesis in <Emphasis Type="Italic">Sedum acre</Emphasis> L.: structural and immunocytochemical aspects of suspensor development

The changes in the formation of both the actin and the microtubular cytoskeleton during the differentiation of the embryo-suspensor in Sedum acre were studied in comparison with the development of the embryo-proper. The presence and distribution of the cytoskeletal elements were examined ultrastructurally and with the light microscope using immunolabelling and rhodamine-phalloidin staining. At the globular stage of embryo development extensive array of actin filaments is present in the cytoplasm of basal cell, the microfilament bundles generally run parallel to the long axis of basal cell and pass in close to the nucleus. Microtubules form irregular bundles in the cytoplasm of the basal cell. A strongly fluorescent densely packed microtubules are present in the cytoplasmic layer adjacent to the wall separating the basal cell from the first layer of the chalazal suspensor cells. At the heart-stage of embryo development, in the basal cell, extremely dense arrays of actin materials are located near the micropylar and chalazal end of the cell. At this stage of basal cell formation, numerous actin filaments congregate around the nucleus. In the fully differentiated basal cell and micropylar haustorium, the tubulin cytoskeleton forms a dense prominent network composed of numerous cross-linked filaments. In the distal region of the basal cell, a distinct microtubular cytoskeleton with numerous microtubules is observed in the cytoplasmic layer adjacent to the wall, separating the basal cell from the first layer of the chalazal suspensor cells. The role of cytoskeleton during the development of the suspensor in S. acre is discussed.     

大车前胚乳发育的超微结构研究

采用透射电镜技术对大车前(Plantago major L.)胚乳发育的超微结构进行了研究。结果表明:(1)大车前为细胞型胚乳;初生胚乳核经一次横分裂产生1个珠孔室细胞和1个合点室细胞;珠孔室两次纵向分裂一次横向分裂形成2层8个细胞,位于上层的4个细胞发育为4个珠孔吸器,位于下层的4个细胞发育为胚乳本体;合点室细胞进行一次核分裂,发育为两核的合点吸器。(2)珠孔吸器呈管状插入珠被组织,珠孔端细胞壁加厚呈现少量分支并具有壁内突,壁内突周围细胞质里分布着大量线粒体、粗面内质网、高尔基体、质体等,细胞核与核仁明显,细胞质浓厚,代谢活动旺盛;球胚期,珠孔吸器的体积呈现最大值,珠孔吸器周围的珠被组织均被水解,形成明显的空腔。珠孔吸器从珠被组织吸收并转运营养物质至胚乳本体,参与胚乳的构建与营养物质的贮藏。球胚后期,珠孔吸器逐渐退化。(3)4个胚乳本体原始细胞具旺盛的分生能力,经不断的平周与垂周分裂增加胚乳细胞数目,使胚乳本体呈现圆球体状,并将胚包围其中;珠孔吸器、合点吸器以及珠被绒毡层吸收转运的营养物质贮存在胚乳本体;球胚后期,随着胚柄的退化,胚体周围的胚乳细胞被水解,为发育的胚所利用。(4)合点吸器的2个细胞核与核仁巨大,线粒体、质体、高尔基体、内质网主要绕核分布,液泡化明显;胚体与胚乳本体的体积增大,逐渐将合点吸器向胚珠合点部位挤压,合点吸器周围的合点组织逐渐被水解,形成巨大空腔。合点吸器自珠心组织吸收并转运营养物质至胚乳本体,参与胚乳的结构构建与营养物质的贮藏。球胚后期,合点吸器逐渐失去功能,呈现退化状态。     

CAPSELLA EMBRYOGENESIS: THE EGG,ZYGOTE, AND YOUNG EMBRYO

The ultrastructure and composition of the egg, zygote, and young embryo of Capsella bursa-pastoris were examined. The egg is a highly polarized cell; one-half to one-third of the micropylar end is filled with a large vacuole while the chalazal end contains the nucleus and much of the cytoplasm of the cell. The wall which surrounds the cell is incomplete at the chalazal end. Ribosomes fill the cytoplasm and show little or no aggregation into polysomes. The structure of the nucleolus suggests that ribosomes are not being produced. Following fertilization and the formation of the zygote, the cell decreases slightly in volume as the large central vacuole becomes smaller. The zygote soon increases in size as the small chalazal vacuoles present before fertilization begin to enlarge. The dictyosomes become active and a continuous wall forms around the zygote. Aggregation of the ribosomes begins and numerous polysomes are formed. Before division of the zygote all plasmodesmata between the zygote and the surrounding cells are lost. The first division of the zygote is unequal as a result of its marked polarity. A large basal cell and a small terminal cell are produced. The basal cell appears to contain more protein, RNA, carbohydrate, and cell organelles than the terminal cell. Ribosomal aggregation is even more pronounced at this stage. Starch accumulates in the plastids. Numerous plasmodesmata are present between the terminal and basal cells but there are no connections between the endosperm or other cells. The basal cell divides next to give rise to a three-celled linear embryo consisting of the basal cell, the suspensor cell, and the terminal cell. The terminal cell stains more intensely for protein and RNA as a result of increased numbers of ribosomes. Starch in all the cells is about equal and reaches a maximum in the embryo at this stage.     

Structure of Embryo Sac Before and After Fertilization and Distribution of Transfer Cells in Ovules of Green Gram

The structure of embryo sac before and after fertilization, embryo and endosperm development and transfer cell distribution in Phaseolus radiatus were investigated using light and transmission electron microscopy. The synergids with distinct filiform apparatus have a chalazal vacuole, numerous mitochondria and ribosomes. A cell wall exists only around the micropylar half of the synergids. The egg cell has a chalazally located nucleus, a large micropylar vacuole and several small vacuoles. Mitochondria and plasrids with starch grains are abundant. No cell wall is present at its chalazal end. There are no plasma membranes between the egg and central cell in several places. The zygote has a complete cell wall, abundant mitochondria and plastids containing starch grains. Both degenerated and persistent synergids migh.t serve as a nutrient supplement to proembryo. The wall ingrowths occur in the central cell, basal cell, inner integumentary cells, suspensor cells and endosperm cells. These transfer cells may contribute to embryo nutrition at different developmental stages of embryo.     

The specialized chalazal endosperm inArabidopsis thaliana andLepidium virginicum (Brassicaceae)

Summary Endosperm of the nuclear type initially develops into a large multinucleate syncytium that lines the central cell. This seemingly simple wall-less cytoplasm can, however, be highly differentiated. In developing seeds of members of the family Brassicaceae the curved postfertilization embryo sac comprises three chambers or developmental domains. The syncytium fills the micropylar chamber around the embryo, spreads as a thin peripheral layer surrounding a large central vacuole in the central chamber, and is organized into individual nodules and a large multinucleate cyst in the chalazal tip. Later in development, after the endosperm has cellularized in the micropylar and central chambers, the chalazal endosperm cyst remains syncytial and shows considerable internal differentiation. The chalazal endosperm cyst consists of a domelike apical region that is separated from the cellularized endosperm by a remnant of the central vacuole and a basal haustorial portion which penetrates the chalazal proliferative tissue atop the vascular supply. In the shallow chalazal depression ofArabidopsis thaliana, the cyst is mushroom-shaped with short tentacle-like processes penetrating the maternal tissues. The long narrow chalazal channel ofLepidium irginicum is filled by an elongate stalklike portion of the cyst. In both, the dome contains a labyrinth of endoplasmic reticulum, dictyosomes with associated vesicles, nuclei, and plastids. The basal portions, which lack the larger organelles, exhibit extensive wall ingrowths and contain parallel arrays of microtubules. The highly specialized ultrastructure of the chalazal endosperm cyst and its intimate association with degrading chalazal proliferative cells suggest an important role in loading of maternal resources into the developing seed.     

Embryology ofCymbidium sinense:the Microtubule Organization of Early Embryos

InCymbidium sinense, the pattern of embryo development is unusualin that oblique cell divisions result in the formation of severalsuspensor cells prior to the development of the embryo proper.Characteristic changes in microtubular distribution can be foundwithin the zygote and the proembryo during their development.After fertilization, the ellipsoid-shaped zygote has randomlydistributed microtubules within its cytoplasm. As the zygotetakes on a more rounded appearance, microtubules organize intoa dense meshwork. Furthermore, microtubule bundles appear atthe chalazal region of the cell prior to the first mitotic divisionof the zygote. At the preprophase stage of mitosis, a preprophaseband of microtubules appears in the cytoplasm of the zygote.The zygote divides obliquely and unequally and gives rise toan apical cell and a slightly larger basal cell. Many randomly-alignedmicrotubules can be found in the cortex of the basal cell. Theincrease in the abundance of microtubules coincides with theisotropic expansion of the basal cell. The early division ofthe basal cell and subsequent division of the apical cell resultsin the formation of a four-celled embryo, of which three cellsnear the micropylar pole develop as suspensor cells. In thesuspensor cells, the microtubules tend to orient in the samedirection as the long axis of the cell. In addition, prominentmicrotubules can also be found near the adjoining cell wallsof the four-celled embryo. The terminal cell is highly cytoplasmicwith abundant microtubules within the cell. Subsequent divisionsof the terminal cell give rise to additional suspensor cellsand the embryo proper. In the mature embryo, five suspensorcells are usually present; one eventually grows through themicropyle of the inner integument and four grow towards thechalazal pole. The cortical microtubules of suspensor cellsredistribute from a longitudinal to a transverse direction asthey grow towards their respective poles.Copyright 1998 Annalsof Botany Company Embryogenesis, endosperm, microtubules, preprophase band, suspensor cells,Cymbidium sinense(Andr.) Willd.     

New data about the suspensor of succulent angiosperms: Ultrastructure and cytochemical study of the embryo-suspensor of Sempervivum arachnoideum L. and Jovibarba sobolifera (Sims) Opiz

The development of the suspensor in two species ?? Sempervivum arachnoideum and Jovibarba sobolifera ?? was investigated using cytochemical methods, light and electron microscopy. Cytological processes of differentiation in the embryo-suspensor were compared with the development of embryo-proper. The mature differentiated suspensor consists of a large basal cell and three to four chalazal cells. The basal cell produces haustorial branched invading ovular tissues. The walls of the haustorium and the micropylar part of the basal cell form the wall ingrowths typical for a transfer cells. The ingrowths also partially cover the lateral wall and the chalazal wall separating the basal cell from the other embryo cells. The dense cytoplasm filling the basal cell is rich in: numerous polysomes lying free or covering rough endoplasmic reticulum (RER), active dictyosomes, microtubules, bundles of microfilaments, microbodies, mitochondria, plastids and lipid droplets. Cytochemical tests (including proteins, insoluble polysaccharides and lipids are distributed in the suspensor during different stages of embryo development) showed the presence of high amounts of macromolecules in the suspensor cells, particularly during the globular and heart-shaped phases of embryo development. The protein bodies and lipid droplets are the main storage products in the cells of the embryo-proper. The results of Auramine 0 indicate that a cuticular material is present only on the surface walls of the embryo-proper, but is absent from the suspensor cell wall. The ultrastructural features and cytochemical tests indicate that in the two species ?? S. arachnoideum and J. sobolifera ?? the embryo-suspensor is mainly involved in the absorption and transport of metabolites from the ovular tissues to the developing embryo-proper.     

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.     

ULTRASTRUCTURE OF THE DEVELOPING MEGASPORE MOTHER CELL OF GINKGO BILOBA

The immature megaspore mother cell of Ginkgo biloba is essentially spherical and is surrounded by a thick, complex wall. A large nucleus occupies the central region of the cell, and the organelles appear to be randomly arranged in the cytoplasm. With approaching maturity and the onset of meiosis, the cell elongates in the direction of the ovular axis. An extensive system of ER develops at the micropylar pole of the cell during elongation, and the plastids and mitochondria migrate to the opposite or chalazal pole. The micropylar end of the mature megaspore mother cell is usually devoid of plastids and mitochondria, but these organelles are densely packed in the chalazal end of the cell below the nucleus. The dictyosomes and dense spherosome-like bodies do not show such polarity in their distribution. At meiosis I plastids and mitochondria are, as a rule, restricted to the chalazal dyad cell that is destined to produce the functional megaspore. The wall of the megaspore mother cell consists of a middle lamella which is irregularly thickened, an outer wall layer resembling the walls of the surrounding nutritive cells, and an inner layer resembling the middle lamella in appearance.     

Capsella embryogenesis: The suspensor and the basal cell

Summary The suspensor and basal cell ofCapsella were examined with the electron microscope and analyzed by histochemical procedures. The suspensor cells are more vacuolate and contain more ER and dictyosomes, but fewer ribosomes and stain less intensely for protein and nucleic acids than the cells of the embryo. The end walls of the suspensor cells contain numerous plasmodesmata but there are no plasmodesmata in the walls separating the suspensor from the embryo sac. The lower suspensor cells fuse with the embryo sac wall and the lateral walls of the lower and middle suspensor cells produce finger-like projections into the endosperm. At the heart stage the suspensor cells begin to degenerate and gradually lose their ability to stain for protein and nucleic acids.The basal cell is highly vacuolate and enlarges to a size of 150 X 70. An extensive network of wall projections develops on the micropylar end wall and adjacent lateral wall. The nucleus becomes deeply lobed and suspended in a strand of cytoplasm traversing the large vacuole. The cytoplasmic matrix darkens at the late globular stage and histochemical staining for protein becomes very intense. The basal cell remains active after the suspensor cytoplasm has degenerated. It is proposed that the suspensor and basal cell function as an embryonic root in the absorption and translocation of nutriments from the integuments to the developing embryo.Research supported by NSF grant GB 3460 and NIH grant 5-RO 1-CA-03656-09.     

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.     

Development of Embryo and Endosperm and Nutrient Accumulation in Vigna sesquipedalis (L.) Fruwirth

The structure of embryo sac, fertilization and development of embryo and endosperm in Vigina sesquipedalis (L.) Fruwirth were investigated. Pollization occures 7–10h before anthesis, and fertilization is completed 10 h after anthesis. After fertilization, wall ingrowths are formed at the micropylar and chalazal ends of the embryo sac. Embryo development conforms to the Onagrad type, and passes through 2 or more celled proembryo, long stick-shaped, globular, heart shaped, torpedo, young embryo, growing and enlarging embryo and mature embryo. Wall ingrowths are formed on the walls of basal cells and outer walls of the cells at basal region of suspenser. The suspensor remains as the seed reaches maturity. The starch grains accumulate in the cells of cotyledons by 9–16 days after anthesis, and proteins accumulate by 12–18 days after. The endosperm development follows the nuclear type. The endosperm ceils form at the micropylar end, and remain free nuclear phase at chalazal end. The outer cells are transfer cells. Those cells at the micropylar end form folded cells with wall ingrowths. At heartembryo stage, the endosperm begins to degenerate and disintegrates before the embryo matures.     

Early Endosperm Development in Ovules of Soybean, Glycine max (L) Merr. (Fabaceae)

Endosperm development was studied in normally setting flowersand pods of soybean from anthesis to a pod length of 10–20mm. The free-nuclear stage following double fertilization istypified by loss of starch and increasing vacuolation. The cytoplasmprovides evidence of extensive metabolic activity. Wall ingrowths,already present at the micropylar end of the embryo sac wallprior to fertilization, develop along the lateral wall of thecentral cell as well as at the chalazal endosperm haustorium.Endosperm cellularization begins when the embryo has developeda distinct globular embryo proper and suspensor. Cellularizationstarts at the micropylar end of the embryo sac as a series ofantidinal walls projecting into the endosperm cytoplasm fromthe wall of the central cell. The free, growing ends of thesewalls are associated with vesicles, microtubules, and endoplasrnicreticulum. Pendinal walls that complete the compartmentalizalionof portions of the endosperm cytoplasm are initiated as cellplates formed during continued mitosis of the endosperm nuclei.Endosperm cell walls are traversed by plasmodesmata. This studywill provide a basis for comparison with endosperin from soybeanflowers programmed to abscise. Glycine max, soybean, endosperm, ovules     

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。     

Unusual electron-dense dome associates with compound plasmodesmata in the embryo-suspensor of genus Sedum (Crassulaceae)

Plasmodesmata ensure the continuity of cytoplasm between plant cells and play an important part in the intercellular communication and signal transduction. During the development of the suspensor of both Sedum acre L. and Sedum hispanicum L., changes in the ultrastructure of plasmodesmata and adjoining cytoplasm are observed. Numerous simple plasmodesmata are present in the inner wall of the two-celled embryo separating the basal cell from the apical cell. From the early-globular to the torpedo stage of embryo development, the part of the wall separating the basal cell from the first layer of the chalazal suspensor cells is perforated by unusual, compound plasmodesmata. The role and the sort of transport through these plasmodesmata are discussed.     

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.     

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.     

Embryology and embryogenesis of Spiranthes L.C.M. Richard (Orchidaceae): S. spiralis (L.) Cheval and S. aestivalis (Poiret) L.C.M. Richard

Abstract

The various stages of female gametophyte development and embryogenesis in S. spiralis and S. aestivalis are described. In both species the reproductive cycle is sexual. Some peculiarities are present: the female gametophyte is usually 6-7-8-nucleate; after double fertilization a single endospermatic cell is formed; the proembryo appears differentiated and is made up of different cells in the chalazal and micropylar ends; a single basal cell in the proembryo acts as suspensor.     

Polarity of nuclear and organellar DNA during megasporogenesis and megagametogenesis in Plumbago zeylanica

Summary Megasporogenesis and megagametogenesis of Plumbago zeylanica were studied using isolated megasporocytes, megaspores, and embryo sacs labeled with Hoechst 33258 for nuclear and organellar (presumably plastid) DNA. Megasporogenesis conforms to the tetrasporic Plumbago type, producing a coenomegaspore with four megaspore nuclei. Organeller DNA is polarized in the micropylar end of the coenomegaspore and embryo sac, reflecting the site of egg cell formation. The three remaining nuclei are somewhat displaced to the chalazal pole, producing a variable number of accessory cells and a 4N secondary central cell nucleus. Ultimately, the mature embryo sac consists of two to five cells including an egg cell, a central cell, zero to two lateral cells, and zero to one antipodal cell depending on the degeneration of the lateral or chalazal nuclei during megagametogenesis.     

毛竹实时荧光定量PCR内参基因的筛选及成花基因PheTFL1表达分析

通过qRT-PCR对毛竹相关成花基因PheTFL1的表达进行研究,为毛竹开花机理的研究提供理论依据.从毛竹UBC18、PP2A和EF1α等9个候选内参基因中筛选出在叶、幼嫩花序、花序轴、枝、竹青等11个组织器官中都稳定表达的PP2A用于毛竹PheTFL1基因qRT-PCR结果的校正.结果显示:PheTFL1基因在开花竹叶、枝和竹青中低丰度表达,与未开花竹差异不显著,但在花和花序轴中高丰度表达;在实生苗叶和根中高丰度表达,在实生苗茎中低丰度表达.PheTFL1基因在具有分生能力的幼嫩组织中高丰度表达,说明其不仅参与花发育的调控,还参与了分生组织生长的调控.