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。     

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.     

Seed fertilization, development, and germination in Hydatellaceae (Nymphaeales): Implications for endosperm evolution in early angiosperms

New data on endosperm development in the early-divergent angiosperm Trithuria (Hydatellaceae) indicate that double fertilization results in formation of cellularized micropylar and unicellular chalazal domains with contrasting ontogenetic trajectories, as in waterlilies. The micropylar domain ultimately forms the cellular endosperm in the dispersed seed. The chalazal domain forms a single-celled haustorium with a large nucleus; this haustorium ultimately degenerates to form a space in the dispersed seed, similar to the chalazal endosperm haustorium of waterlilies. The endosperm condition in Trithuria and waterlilies resembles the helobial condition that characterizes some monocots, but contrasts with Amborella and Illicium, in which most of the mature endosperm is formed from the chalazal domain. The precise location of the primary endosperm nucleus governs the relative sizes of the chalazal and micropylar domains, but not their subsequent developmental trajectories. The unusual tissue layer surrounding the bilobed cotyledonary sheath in seedlings of some species of Trithuria is a belt of persistent endosperm, comparable with that of some other early-divergent angiosperms with a well-developed perisperm, such as Saururaceae and Piperaceae. The endosperm of Trithuria is limited in size and storage capacity but relatively persistent.     

Origin of facultative heterochromatin in the endosperm ofGagea lutea (Liliaceae)

Summary Facultative heterochromatin occurs not only in certain animals in connection with sex determination but also in members of at least one plant genus,Gagea (Liliaceae s. str.), but here in the course of embryo sac development, fertilization, and endosperm formation. The present contribution intends to provide undebatable photographic and cytometric evidence, previously not available, for the events in the course of which three whole genomes in the pentaploid endosperm nuclei ofGagea lutea become heterochroma-tinized. In this plant, embryo sac formation usually follows the Fritillaria type, i.e., the embryo sac is tetrasporic, and a 1 + 3 position of the spore nuclei is followed by a mitosis in which the three chalazal spindles fuse and two triploid nuclei are formed. A triploid chalazal polar nucleus is derived from one of these, which contributes to the pentaploid endosperm. These nuclei in the chalazal part of the embryo sac show stronger condensation compared with the micropylar ones. The pycnosis of the triploid polar nucleus is maintained and even enhanced during endosperm proliferation, while the micropylar polar nucleus and the sperm nucleus maintain their euchromatic condition. The origin of the heterochromatic masses in the endosperm nuclei from the three chalazal genomes of the central cell is unambiguously evident from the distribution of heterochromatic chromosomes in the first endosperm mitosis and the following interphase. DNA content measurements confirm a 3 2 relationship of heterochromatic and euchromatic chromosome sets, which is usually maintained up to the cellularized endosperm. Pycnotic nuclei in the chalazal part of megagametophytes are characteristic of several embryo sac types, but only forGagea spp. it is documented that such nuclei can take part in fertilization and endosperm formation.Dedicated to Professor Walter Gustav Url on the occasion of his 70th birthday     

西瓜胚乳吸器的发育及ATP酶的超微细胞化学定位

报道了西瓜（Citrullus lanatus)胚乳吸器发育过程,并对胚乳吸器细胞中的ATP酶进行了超微细胞化学定位,球形胚早期,胚囊合点端的壁伸长发育成一管状胚乳吸器,进而吸器靠近乳本体端膨大为囊状,球形胚晚期吸器自珠孔端向合点端逐渐细胞化,胚分化出子叶时,胚乳吸器自合点端向珠孔端退化,在刚形成的胚乳吸器细胞中,ATP酶活性反应主要分布在细胞的核膜,内质网上,胞间连丝和吸器细胞壁内的小球状物上也有较强的ATP酶活性反应;在开始退化的吸器细胞中,核膜上的ATP酶性的反应减弱较早,内质网稍晚,进一步退化的胚乳吸器细胞中,ATP酶主要集中分布在细胞壁,细胞间隙内,核上几乎没有ATP酶性反应,内质网上仅有微弱的ATP酶反应。     

Rhinanthus serotinus (Schönheit) Oborny (Scrophulariaceae): immunohistochemical and ultrastructural studies of endosperm chalazal haustorium development

Chalazal endosperm haustorium in Rhinanthus serotinus consists of a single large binucleate cell. It originates from the primary endosperm cell dividing transversely into two unequal cells: a smaller micropylar cell and a larger chalazal cell. The chalazal cell undergoes a single mitotic division, then lengthens significantly during development and functions as a chalazal endosperm haustorium. In this paper, immunofluorescent techniques, rhodamine phalloidin assay, and electron microscopy were used to examine the actin and tubulin cytoskeleton during the development of the chalazal haustorium. During the differentiation stage, numerous longitudinally oriented bundles of microfilaments ran along the axis of transvacuolar strands in haustorium. Microtubules formed intensely fluorescent areas near the nuclear envelope and also formed radial perinuclear microtubule arrays. In the fully differentiated haustorium cell, the actin cytoskeleton formed dense clusters of microfilaments on the chalazal and micropylar poles of the haustorium. Numerous microfilament bundles occurred near wall ingrowths on the chalazal wall. There were numerous clusters of microfilaments and microtubules around the huge lobed polytenic haustorial nuclei. The microfilaments were oriented longitudinally to the long axis of the haustorium cell and surrounded both nuclei. The microtubules formed radial perinuclear systems which were appeared to radiate from the surface of the nuclear envelope. The early stage of degeneration of the chalazal haustorium was accompanied by the degradation of microtubules and disruption of the parallel orientation of microtubules in the chalazal area of the cell. The degree of vacuolization increased, autophagous vacuoles appeared and the number of vesicles decreased.     

THE DEVELOPMENT OF THE SEED IN ANDROGRAPHIS SERPYLLIFOLIA

Mohan Ram , H. Y. (U. Delhi, India.) The development of the seed in Andrographis serpyllifolia. Amer. Jour. Bot. 47(3) : 215—219. Illus. 1960.–Andrographis serpyllifolia, a member of the Acanthaceae, has an embryo sac with a bifurcated chalazal part. At the time of fertilization both synergids and antipodal cells disintegrate. Early in its development the endosperm is composed of 3 distinct parts: (1) a binucleate densely cytoplasmic chalazal haustorium; (2) a large binucleate micropylar haustorium; and (3) a central chamber which develops into the endosperm proper. The divisions in the central endosperm chamber are ab initio cellular. A few of the endosperm cells elongate enormously, ramify into the integument and destroy the surrounding cells. These cells have been termed secondary haustoria. Due to the unequal destruction of the integument, the endosperm assumes a ruminate condition. The mature seed is nearly naked because the seed coat is almost completely digested. The embryo has a long suspensor. The micropylar cells of the suspensor are hypertrophied and multinucleate. Contrary to Mauritzon's (1934) belief, the course of endosperm development is markedly different from that observed in Thunbergia. So far, albuminous seeds have been reported only in the subfamily Nelsonioideae. The present investigation provides a case of its occurrence in the Acanthoideae also.     

PATTERNS OF EMBRYO AND ENDOSPERM FORMATION IN MONOTROPA HYPOPITYS (MONOTROPACEAE) FROM NORTH AMERICA AND WESTERN SWEDEN

Within the Monotropaceae. Monotropa hypopitys L. has the widest geographical distribution with sporophytes characterized as achlorophyllous, mycotrophic, and morphologically reduced. General and histochemical observations at the light microscope level concerning the postpollination changes in the numerous anatropous, unitegmic ovules reveal a precise embryogeny and endosperm development. Following double fertilization, the primary endosperm cell produces a lipid-rich cellular endosperm situated between a micropylar and a chalazal haustorium. A cytoplasmically unequal division of the elongated zygote initiates proembryo formation. The degeneration of the basal cell of the proembryo results in an isolated terminal cell that undergoes a cytoplasmically equal, transverse division establishing a two-celled embryo embedded in endosperm. Prior to final seed maturation, proteins replace the lipids as the dominant cytoplasmic reserve material. In contrast with earlier studies that depicted the mature embryo as variable in structure, here the embryo is shown to be consistently uniform within and between those populations sampled from North America and Europe.     

DEVELOPMENT OF THE SEED AND FRUIT IN RHINANTHUS MAJOR AND R. SEROTINUS

There are seven sessile, campylotropous, discoid ovules in each loculus of the anteroposteriorly flattened bilocular ovary. They are arranged alternately in two rows in each chamber on the axile placenta which is nodular where the ovules are borne. Nucellus degenerates early except at the chalazal end of the curved embryo sac, and the inntermost layer of the integument functions as endothelium. The aggressive, multinucleate micropylar haustorium grows as a tubular body through the micropylar canal and ramifies in the placenta while the two-nucleate chalazal haustorium creates a large space by digesting a good deal of the chalazal tissue. Endosperm is differentiated into three regions: the middle storage, the haustorial micropylar, and the chalazal. Thickness of the integument is considerably added to by the endothelium and by its surrounding meristematic zone of the integument. There are two prominent wings on the dorsal and smaller ones on the lateral faces of the cochlidiospermous seed, its ventral face being occupied by a prominent basal body. A heavily cutinized envelope, formed by the endothelium, surrounds the ovoid storage endosperm. Testa of the seed is mainly composed of the thickened epidermis and the endothelium. The micropylar and the chalazal parts of the endosperm become tanniferous and serve to plug the two ends of the seed. Embryo is straight, and it bears two cotyledons and two plumular leaves.     

Embryology and taxonomical position of Retzia capensis (Retziaceae)

The ovules of Retzia capensis are anatropous, unitegmic and tenuinucellate. A well-developed hypostase of concentric layers of cells is present. Embryo sac formation follows Polygonum type. The central part of the mature embryo sac contains rich amounts of starch grains, which disappear at the beginning of the endosperm development. The endosperm formation results in a chalazal haustorium of a great number of long, narrow, densely plasmatic cells, a micropylar haustorium of loosely plasmatic cells, and a middle region which in the beginning is only partly cellular, but later the whole endosperm consists of long, narrow cells. The hypostase prevents the chalazal endosperm haustorium from penetrating to the lower part of the ovule, while the micropylar haustorium is able to grow upwards into the long micropyle. The cellular endosperm formation, the formation of endosperm haustoria, of which the micropylar is most distinctive, and formation of a well-developed hypostase all indicate a close relationship to Buddleiaceae and part of Scrophulariaceae. Therefore, both Retziaceae and Buddleiaceae should be placed in the order Scrophulariales.     

Cytoskeletal organization of the micropylar endosperm in Coronopus didymus L. (Brassicaceae)

Summary. The micropylar chamber of the mustard Coronopus didymus is a developmental domain distinct from the contiguous central chamber and the more extreme chalazal chamber. Early in syncytial development the micropylar endosperm surrounding the embryo becomes populated with unusual fusiform to multilobed nuclei. These nuclei are sheathed by unique parallel arrays of microtubules that focus at tips of the nuclei and flare to connect with a reticulate network in the common cytoplasm. F-actin does not closely invest the nuclei but instead forms an extensive but separate cytoplasmic reticulum. When the embryo is in the early heart stage, the cytoskeleton of the endosperm undergoes a remarkable transition in preparation for cellularization. Microtubules become reorganized into radial arrays emanating from the nuclei, which themselves become spherical. Radial microtubule systems (RMSs), which replace both the parallel microtubules and the cytoplasmic reticulum, organize the common cytoplasm into evenly spaced nuclear cytoplasmic domains (NCDs). F-actin gradually becomes coaligned with the RMSs. Phragmoplasts are initiated adventitiously at the interfaces of opposing RMSs in the absence of mitosis. Cell plate deposition, which is initiated at multiple sites, results in a network of walls formed more or less simultaneously around the densely packed NCDs. The walls, which are rich in 1–3-β-glucans, join with one another and with the existing walls of both the central cell and embryo to complete cellularization in the micropylar chamber. In the adjacent central chamber where the syncytium is restricted to a thin peripheral layer by the large central vacuole, basic organization of the syncytium into NCDs is followed by alternating cycles of alveolation and periclinal cell division resulting in cellularization. Received July 19, 2001 Accepted October 16, 2001     

Polarity and competition between megaspores in the ovule ofOenothera hybrids

New data on the development of polarity in the ovules during megasporogenesis and early stages of embryo sac development inOenothera-hybrids are presented. It is confirmed that allOe. hookeri-hybrids show a strong tendency to form heteropolar tetrads, with the micropylar megaspore developing into an embryo sac. This preference is seen in the delay of the second meiotic division on the chalazal side, the absence of callose in the lateral wall of the micropylar megaspore, and the accumulation of starch in this megaspore. However, homopolar tetrads, chalazal preference, and ovules with two developing embryo sacs are also observed with considerable frequency. Quantitative data on the frequency of the different developmental types are compared with earlier genetic results about competition in the haplophase. There is sufficiently good agreement to support the hypothesis ofRenner that there is a correlation between the developmental processes in the megaspore tetrad and the genetic phenomena of competition in the haplophase.     

Structure and biochemistry of endosperm breakdown in date palm (Phoenix dactylifera L.) seeds

Summary The zone of endosperm breakdown in the germinated date seed (Phoenix dactylifera L.) is a narrow area immediately adjacent to the surface of the enlarging cotyledon, or haustorium. The zone width is correlated with the amount of cell division in the adjacent region of the haustorium. The sequence of endosperm breakdown is: 1. protein bodies vacuolate, 2. storage cell walls become electron-transparent immediately adjacent to the protoplast of each endosperm cell, 3. all remaining cytoplasm and lipid bodies disappear, and 4. the remaining cell walls become electron-transparent and collapse against the haustorium surface. Two cell wall hydrolases are present—endo-mannanase (EC3.2.1.78) and -mannosidase (EC3.2.1.25). -mannosidase is detectable in the endosperm before germination. At germination, the major portion of activity is found in the softened endosperm. -mannanase is only detectable from germination and there is always hundreds of fold greater activity in the softened endosperm than elsewhere. Proteinase is detectable in trace amounts at germination in the softened endosperm but is also found in the haustorium at later stages. Isolated haustoria, incubated in extracted ivory nut (Phytelephas macrocarpa) mannan in buffer, cause no mannan breakdown. Haustoria, incubated in a solution of locust bean galactomannan, cause no decrease in galactomannan viscosity. Our observations suggest that although haustoria probably regulate mannan breakdown in the endosperm, they do not seem to secrete the hydrolytic enzymes concerned.     

Nuclear fusions contribute to polyploidization of the gigantic nuclei in the chalazal endosperm of<Emphasis Type="Italic"> Arabidopsis</Emphasis>

Somatic polyploidization is recognized as a means to increase gene expression levels in highly active metabolic cells. The most common mechanisms are endoreplication, endomitosis and cell fusion. In animals and plants the nuclei of multinucleate cells are usually prevented from fusing. Here, we report that the nuclei from the syncytial cyst of the chalazal endosperm of Arabidopsis thaliana (L.) Heynh. are polyploid with some intermediate ploidy levels that cannot be attributed to endoreplication, suggesting nuclear fusion. Analysis of isolated nuclei, together with fluorescent in situ hybridization (FISH), revealed that nuclei from the chalazal endosperm are two or three times bigger than the nuclei from the peripheral endosperm and have a corresponding increase in ploidy. Together with the consistent observation of adjoined nuclei, we propose that nuclear fusion contributes, at least in part, to the process of polyploidization in the chalazal endosperm. Confocal analysis of intact seeds further suggested that free nuclei from the peripheral endosperm get incorporated into the chalazal cyst and likely participate in nuclear fusions.Abbreviations BAC Bacterial artificial chromosome - CZE Chalazal endosperm - DAPI 4,6-Diamino-2-phenylindole - FISH Fluorescent in situ hybridization - NOR Nucleolar organizing region - NCD Nuclear cytoplasmic domain - PEN Peripheral endosperm     

延龄草(Trillium tschonoskii Maxim.)的胚胎学研究(二)——胚乳发育的研究

多年来,由于对延龄草的营养叶的脉序和花被片的分化趋势的研究,引起众多学者对延龄草的系统位置发生了兴趣。我们已发表过延龄草的大孢子发生及雌配子体的形成,本文发表的是延龄草的胚乳发育,并在此基础上,对延龄草的系统位置谈一些看法。延龄草的胚乳发育始于合点端。受精极核第一次分裂形成二个子细胞,两细胞间由一弧形壁将胚囊分隔成珠孔端室与合点端室,前者大于后者。通常珠孔端室核先于合点端室核分裂。游离核沿胚囊边缘向中央分布,且由珠孔端开始形成胚乳细胞,其速度也快于合点端。胚乳发育为沼生目型。     

Development of endosperm in Arabidopsis thaliana

 The process of endosperm development in Arabidopsis was studied using immunohistochemistry of tubulin/microtubules coupled with light and confocal laser scanning microscopy. Arabidopsis undergoes the nuclear type of development in which the primary endosperm nucleus resulting from double fertilization divides repeatedly without cytokinesis resulting in a syncytium lining the central cell. Development occurs as waves originating in the micropylar chamber and moving through the central chamber toward the chalazal tip. Prior to cellularization, the syncytium is organized into nuclear cytoplasmic domains (NCDs) defined by nuclear-based radial systems of microtubules. The NCDs become polarized in axes perpendicular to the central cell wall, and anticlinal walls deposited among adjacent NCDs compartmentalize the syncytium into open-ended alveoli overtopped by a crown of syncytial cytoplasm. Continued centripetal growth of the anticlinal walls is guided by adventitious phragmoplasts that form at interfaces of microtubules emanating from adjacent interphase nuclei. Polarity of the elongating alveoli is reflected in a subsequent wave of periclinal divisions that cuts off a peripheral layer of cells and displaces the alveoli centripetally into the central vacuole. This pattern of development via alveolation appears to be highly conserved; it is characteristic of nuclear endosperm development in angiosperms and is similar to ancient patterns of gametophyte development in gymnosperms. Received: 21 September 1998 / Revision accepted: 17 November 1998     

Endopolyploidy and structures of the nuclei in the endosperm of theCucurbitaceae

Summary In the endosperm ofEchinocystis lobata the endopolyploid nuclei show structural changes of chromocentres typical of the process of endomitosis in Angiosperms.The cytological differentiation of the endosperm proper and the chalazal haustorium in three further representatives of theCucurbitaceae: Sicyos angulata, Cyclanthera pedata andCitrullus colocynthis is also connected with endomitotic polyploidisation. The nuclei of the endosperm proper attain in the different species different levels of polyploidy, 384n, as a maximum. In the nuclei of the chalazal haustorium the degree of polyploidy is lower (as a maximum 24n).The structure of polyploid nuclei which did not undergo postendomitotic mitoses shows some differences in the species studied in the course of the present work.Sicyos angulata has prochromosomic diploid nuclei, whereas those ofCitrullus colocynthis andCyclanthera pedata can be assigned to chromomeric nuclei with a dense structure. Endopolyploid nuclei of all three species studied are characterized by the occurence of compact chromocentres of different size; besides in some nuclei ofSicyos angulata andCyclanthera pedata the chromocentres within the resting nucleus reveal their chromomere structure. In addition, inCitrullus colocynthis nuclei with numerous thin threads of various degrees of spiralisation have been observed. — In all three species the endopolyploid nuclei after mitotic divisions have notably higher numbers of nucleoli and small chromocentres.Dedicated to Professor L.Geitler on the occasion of his 70th birthday.     

Alisma embryogenesis: The development and ultrastructure of the suspensor

Summary The development of the suspensor (consisting of a basal cell and a few chalazal cells) inAlisma plantagoaquatica andA. lanceolatum was investigated using cytochemical methods, light and electron microscopy. The basal cell becomes differentiated during the first three days of embryo development. As a result of endopolyploidization the volume of the nucleus rapidly increases, as does the quantity of chromatin it contains and the size of the nucleolus. As basal cell grows, its cytoplasm increases in volume and the number of organelles increase, and wall ingrowths begin to form on the walls at the micropylar pole of the cell. The full development and functioning of the suspensor occurs during the next three days. The enormous basal cell then attains its maximum degree of differentiation: its nucleus reaches a ploidy of 256n or 512n, the micropylar transfer wall is fully developed, as is the cytoplasm, rich in proteins, ribonucleic acids (RNA) and organelles, particularly dictyosomes and long cisternae of the rough endoplasmic reticulum. The chalazal suspensor cells joining the embryo proper to the basal cell also become differentiated. In the seven-day embryo the suspensor begins to degenerate which coincides with the cellularization of the endosperm at the micropylar pole of the embryo sac. The senescence of the suspensor involves the degradation of the nucleus, increasing cytoplasmic vacuolization, and a distinct decrease in protein and RNA content, first in the basal cell, then in the chalazal suspensor cells. Analysis of the development and ultrastructure of the basal suspensor cell suggests that it plays the role of an active metabolic transfer cell, translocating nutrients from the maternal tissues via the chalazal suspensor cells to the growing embryo proper.     

西瓜胚和胚乳的发育

应用显微技术对西瓜胚和胚乳的发育过程进行了观察并分析了西瓜胚珠败育的原因。西瓜胚发育属紫菀型。合子第一次分裂为不均等分裂 ,形成的基细胞体积明显较顶细胞大 ,两细胞均含有多个液泡。原胚发育过程中没有明显的胚柄。最外层的原胚细胞 ,与胚乳细胞相邻的壁上被胼胝质物质包围 ,且无外连丝存在 ;与胚囊壁相接的壁上无壁内突结构。胚的子叶体积增长的同时 ,子叶细胞内积累蛋白质和脂类物质 ,多糖物质的含量下降。胚乳发育属核型 ,在球形胚期开始自珠孔端向合点端细胞化 ,胚子叶分化出后开始自珠孔端向合点端退化。胚乳合点端在球形胚早期形成发达的胚乳吸器 ,开始呈游离核状态 ,后细胞化 ,在心型胚期之后退化。     

POSTFERTILIZATION CHANGES IN OVULES OF MONOTROPA UNIFLORA L. (MONOTROPACEAE)

Monotropa uniflora is an achlorophyllous angiosperm consisting of a mycorrhizae-dependent root system that produces floriferous, aerial shoots. Each of the numerous, minute ovules is anatropous, unitegmic, and contains a Polygonum type female gametophyte. Following double fertilization, a lipid-rich, cellular endosperm develops in association with both chalazal and micropylar haustoria. The vacuolate zygote elongates prior to a cytoplasmically unequal division resulting in a small terminal cell subtended by a larger, vacuolate basal cell. The basal cell eventually degenerates, isolating the terminal cell which is completely surrounded by endosperm. The terminal cell undergoes a cytoplasmically equal transverse division resulting in a two-celled embryo embedded in endosperm. In final stages of seed maturation, lipids decrease and reserve proteins increase in the cytoplasm of both the endosperm and embryo. The morphological reduction of the mature embryo may be associated with a specialized mode of nutrition.