Fertilization and embryogeny in Agapanthus praecox ssp. orientalis (Leighton) Leighton

Fertilization and embryogeny in Agapanthus praecox ssp. orientalis are described for the first time, and embryogenic characters of Agapanthus are discussed. The main results are: (1) The pollen tube enters the embryo sac and discharges two sperm 44?C48?h after pollination. (2) The sperm fuse with the egg cell and polar nuclei, forming zygote and primary endosperm nucleus, approximately 50?h after pollination. The zygote then enters a short period of dormancy. (3) Seven days after pollination, the zygote starts division. The first division of the zygote is transversal. (4) The embryo undergoes globular stage, rod-shaped stage, and finally forms a monocotyledonous embryo. (5) The suspensor cells are ephemeral and degenerate at the globular embryo stage. (6) Endosperm cells contain massive starch grains as nutrition for embryo development. (7) Embryogeny conforms to the Onagrad type, and endosperm formation is of the nuclear type; the whole process of embryogeny and endosperm development needs approximately 60?days in A. praecox ssp. orientalis. (8) Dicotyledonous together with monocotyledonous forms of embryo morphogenesis in Agapanthus supports the concept of homology of monocots and dicot cotyledons.     

北柴胡胚和胚乳的发育及对其种子萌发的影响

利用常规石蜡制片技术对北柴胡胚和胚乳的发育及对其种子萌发的影响进行了观察。结果表明北柴胡胚的发育属于茄型,基细胞进行一次横分裂后不再分裂,因而胚柄不发达,且很早解体。胚乳的发育属于核型,初生胚孔核的分裂远远早于受精卵的分裂。对果实采收时期胚发育状况进行统计发现,在被测采收期果实中有20%的果实的胚处于球形胚阶段,70%处于心形胚,只有10% 处于鱼雷胚,说明北柴胡种子采收时胚处于不同的发育阶段,存在形态后熟现象,这是北柴胡种子萌发难、萌发率低且出苗不整齐的主要因素。     

侧金盏胚和胚乳发育的细胞胚胎学研究

利用石蜡切片技术对毛茛科植物侧金盏胚及胚乳发育进行了研究,以明确其胚胎发育的特征,为毛茛科植物的系统研究提供资料。结果表明:(1)侧金盏胚的发育属于柳叶菜型,胚乳发育为核型;初生胚乳核的分裂早于合子的第一次分裂。(2)种子成熟时,种胚尚未分化完全,尚处于球形胚后期或心形胚早期阶段,整个胚发育大约需要50~60d。(3)侧金盏种子存在明显的形态生理休眠现象,经后熟作用逐渐完成种胚的分化与生长,形成子叶形胚;侧金盏种子在相同处理条件下胚分化和发育的速度存在差异。     

The Fertilization and Early Development of Embryo and Endosperm in Stevia rebaudiana Bertani

The mature embryo sac is surrounded by endothelium tapetum. It is composed or an egg apparatus, one central cell with secondary nucleus, and 1–6 antipodal cells. About the 6th hour after pollination, female and male nuclei fuse with each other. The syngamy occurred almost simultaneously with the fusion of an other sperm nucleus and the secondary nucleus, but the velocity of the latter is faster than that of the syngamy. The fertilization of Stevia rebaudiana Bertani belongs to the premitotic type. About the 8th hour after pollination, primary endosperm nucleus is in mitosis, its dividing orientation may parallel or at right angle to the long axis of the embryo sac, and gives rise to two initial endosperm cells. The first five divisions of the endosperm cells are of synchronism. At the stage of heart-shaped embryo, the endosperm cells show the signs of digestion and absorbed. The endosperm development is of the cellular type. About the 10th hour after pollination, zygote divides for the first time. The division of the zygote is always transverse. The embryo development conforms to the Asterad type.     

The Development of Embryo and Endosperm of Nelumbo nucifera Gaertn

The development of the embryo and endosperm of Nelumbo nucifera Gaertn can be summarized as follows: 1. Embryogenesis of N. nucifera belongs to Solanad type; the 1st mitotic division of the zygote takes place later than that of the primary endosperm nucleus. 2. The development of endosperm basically conforms to the Helobial endosperm. After fertilization, the primary endosperm nucleus divides first transversely. This division results in the formation of two cells. The wall of this division is a little oblique to the longitudinal axis of the embryo sac. In accordance with the character of the endospermic development, it can be divided into, three stages: (1) two-celled endosperm stage, (2) multicellular endosperm stage, and (3) the stage of the endospermic nutrition being absorbed and cells atrophy. The developments of the embryo and endosperm are well correlated. This relation is relatively stable. 3. The cotyledons of the mature embryo are comparatively developed, but the radicle is extremely reduced. 4. As the seed is ripening, a thin membrane remains outside the plumule, which is the remainder of the endosperm. Therefore, the seed of N. nucifera is exalbuminous.     

Cytological study of pollen tube growth and early seed development inPetunia inflata

Pollen tube growth from the stigma into the ovule, and the early fruit and seed development following fertilization were examined using fluorescence microscopy, scanning electron microscopy and light microscopy inPetunia inflata. After growing intercellularly in the transmitting tract for 24–36 hr, the pollen tubes emerged into the top part of the ovary cavity and grew along the surface of the septum to reach the ovule. It grew around the furnicle and penetrated the micropyle to enter the embryo sac for fertilization. After fertilization, the endosperm nucleus divided first before the embryo, and the cell wall formation occurred following the division, exhibiting the pattern of cellular type of endosperm development. The first division of the zygote did not occur until 3 days after pollination. At 6 days after pollination, the seeds grew considerably and the endosperm has gone through multiple rounds of cell division. High starch formation in the integument, especially around the embryo sac, was also observed.     

北柴胡胚和胚乳的发育及对其种子萌发的影响

利用常规石蜡制片技术对北柴胡胚和胚乳的发育及对其种子萌发的影响进行了观察。结果表明北柴胡胚的发育属于茄型,基细胞进行一次横分裂后不再分裂,因而胚柄不发达,且很早解体。胚乳的发育属于核型,初生胚孔核的分裂远远早于受精卵的分裂。对果实采收时期胚发育状况进行统计发现,在被测采收期果实中有20％的果实的胚处于球形胚阶段,70％处于心形胚,只有10％处于鱼雷胚,说明北柴胡种子采收时胚处于不同的发育阶段,存在形态后熟现象,这是北柴胡种子萌发难、萌发率低且出苗不整齐的主要因素。     

黄花油点草胚胎发育研究

利用石蜡切片技术对百合科植物黄花油点草[Tricyrtis maculata(D.Don)Machride]双受精、胚及胚乳发育进行了研究,以明确其胚胎发育的特征,为百合科植物的系统研究提供生殖生物学资料。结果表明:(1)黄花油点草为珠孔受精;进入胚囊的2枚精子分别与卵细胞和中央细胞进行正常的双受精,其受精作用属有丝分裂前型。(2)受精后的初生胚乳核立即分裂,其发育方式为核型胚乳;早期的游离胚乳核沿胚囊的边缘分布,胚囊中央部位主要为胚乳细胞质,随着游离胚乳核数量的增加,胚乳核慢慢充满整个胚囊;当发育至球形胚早期阶段,在各胚乳核周围产生胚乳细胞壁,形成完整的胚乳细胞。(3)合子有较长的休眠时间,胚的发育方式为茄型;合子第一次有丝分裂为横裂,分裂后形成基细胞和顶细胞;基细胞经过3次横裂,形成一列胚柄细胞;顶细胞经过分裂形成胚体,依次形成球形胚、棒状胚和盾形胚。(4)种子成熟时胚无器官分化;成熟种子由种皮、胚和胚乳三部分组成。     

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.     

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.     

EMBRYOLOGY AND DEVELOPMENT OF THE ENDOSPERM HAUSTORIUM OF ARCEUTHOBIUM DOUGLASII

Arceuthobium douglasii develops a dome-like structure, the ovarian papilla, in which 2 megasporocytes are formed. The papilla is not a true ovule, for no integuments are formed, and it is forced aside by the developing endosperm. Megasporocytes are differentiated in the spring, but meiosis does not occur until the following spring. A tetrasporic embryo sac is developed which is 8-nucleate at maturity. Pollination and fertilization occur approximately 13–14 months after initiation of the inflorescence. Only 1 of the 2 embryos develops after fertilization. After fertilization, the embryo sac segregates into 2 parts, one containing the zygote and the disintegrating synergids, the other the primary endosperm nucleus and the degenerating antipodals. This primary endosperm cell elongates toward the base of the ovarian papilla. Cytokinesis then forms an endosperm cell, adjacent to the zygote, and a haustorial cell. The haustorial cell forms several tiers of cells which persist during the development of the embryo and endosperm. The zygote, while still contained within the ovarian papilla, divides, forming a 2-celled sphere. It remains unchanged until after it is conveyed out of the ovarian papilla by the developing endosperm. The development of the embryo and endosperm is arrested in the autumn approximately 3 months after their initiation. They complete their development the following spring and summer.     

柽柳胚和胚乳发育的观察

利用常规石蜡制片技术,对柽柳（Tamarix chinensis Lour.）胚和胚乳的发育过程进行了观察。结果表明,胚发育属茄型,其基细胞先行纵裂。胚柄基部发育迅速,具吸器作用,球形胚期胚柄最为发达,其细胞质丰富,贮藏淀粉类物质,至晚心形胚期胚柄依然存在。助细胞被受精产生多胚现象。胚乳发育属核型,初生胚乳核常常晚于合子分裂,胚乳核的分裂速度慢于胚体细胞的分裂速度。当胚乳游离核为 32个时,以自由生长细胞壁的方式进行胚乳细胞化。胚乳细胞进一步增殖极少。珠心细胞只有两层,细胞核大,胞质丰富,内含贮藏物质,至心形胚期逐渐解体。     

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.     

Genotype effects of Brassica napus on its reproductive behavior after pollination with B. juncea

To investigate the cause of variation in the interspecific crossability of Brassica napus, three different genotypes were studied in respect of their reproductive behavior after pollination with B. juncea. There were great differences among maternal genotypes in allowing foreign pollen to germinate on and penetrate into their stigmas, leading to a wide diversity of interspecific fertilization. The division of the hybrid primary endosperm nucleus and zygote appeared normal in all combinations of crosses. While the abundant free nuclei of the endosperm developed properly and never became cellular, the embryos degenerated as early as 10 days after pollination when the cultivar Rucabo, which had the highest fertilization record with species of B. juncea, was involved. When 81007 was used as female parent, the endosperm grew a little but the embryo halted at the heart-torpedo stage. Lack of nourishment might be responsible for the observed embryo abortion. Among the sic hybrid combinations, the cross 84014A x Changyang hunagjie was the only one where endosperm tissue was observable and an abnormal embryo occurred prior to cellular endosperm formation. Apart from the three typical embryological features, significant variation was also demonstrated among each of the cross combinations. Genetic diversity appears to exist not only between varieties, but also within cultivars. In addition, methods for developing interspecific crossable lines are discussed.     

Observations on Fertilization in Sugar Beet

The whole process of double fertilization in sugar beet has been observed, the main results are as follows: About 2 hours after pollination, the pollen grains germinate, the sperms in the pollen tube are long-oval. 15 hours after pollination, the pollen tube destroys a synergid and releases two sperms on one side or at the chalazal end of the egg cell. The sperms are spherical each having a cytoplasmic sheath. 17 hours after pollination, one sperm enters the egg cell, and the sperm nucleus fuses with the egg nucleus rapidly. 21 hours after pollination, the zygote is formed. In the meantime, the primary endosperm nucleus has divided into two free endosperm nuclei. 25 hours after pollination, the zygote begins to divide, forming a two-celled proembryo. The dormancy stage of the zygote is about 4 hours. In the meantime the endosperm is at the stage of four free nuclei. 17 hours after pollination, the sperm nucleus comes into contact and fuses with the secondary nucleus. The sperm nucleus fuses with the secondary nucleus, faster than the sperm with the egg. he first division of the primary endosperm nucleus is earlier than that of the zygote, it takes place about 20 hours after pollination, the dormancy stage of the primary endosperm is about 2 hours. The endosperm is free nuclear. The fertilization of sugar beet belongs to premitotic type of syngamy. From the stage of zygote to the two-celled proembryo, it can be seen that addition- al sperms enter the embryo sac, but polyspermy has not been observed yet.     

The Studies on Embryology in Fritillaria ussuriensis Maxim

The development of the anther wall follows Basic-type. The cytokinesis at the time of pollen mother cell meiosis conforms to successive type. The arrangement of the microspores in the tetrad is referred to isobilateral. The primary wall between the generative cell and the vegetative cell is callose. The callose wall is easily detected under the fluorescence microscope. The mature pollen grain is 2-celled type. The ovule is bitegminous, tenui-nucellar and anatropous. The development of the female gametophyte follows Fritillaria-type. The mature embryo sac. consists of the six cells including the seven nuclei. The fertilization is referred to the premitotic syngamy type. The fusion of the female and male nucleoli is not observed at the end of the fertilization. The division of the primary endosperm nucleus is earlier than that of the zygote. The development of the endosperm is referred to nuclear type. The division of the zygote is transverse of longitudinal, the development of the embryo conforms to Onagradtype. When the seed is mature, the embryo is at the proembryo stage without differentiation and the endosperm cells are not absorbed.     

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.     

Embryology of barley: Time course and analysis of controlled fertilization and early embryo formation based on serial sections

The aim of this work was to determine the sequences and their time schedule in fertilization, embryo and endosperm development in a barley strain grown under controlled conditions. This study involved controlled pollinations and serial sectioning of material embedded in glycol methacrylate.
In Hordeum vulgare cv. Bomi the pollen tube reaches the nucellus in the course of 40 minutes after pollination (m.a.P). In the next minutes the tube advances between the nucellar cells, through the filiform apparatus of the degenerating synergid and releases its contents, which is characterized by rod-shaped starch grains. One of the sperm nuclei is fused with the egg nucleus 45 m.a.P., the second is in contact with the two polar nuclei 50–60 m.a.P., but the real connection between one of the polar nuclei and the sperm nucleus does not occur before 10 hours after pollination (h.a.P.). Triple fusion between all three nuclei takes place about 13 h.a.P. The first division in the zygote takes place 22–24 h.a.P. The embryo has got 3 cells at 34 h.a.P., 4 cells at 38 h. and 52 h.a.P. the embryo is composed of 7 cells. Protoderm formation takes place from a 14-celled embryo stage at 72–80 h.a.P The primary endosperm nucleus divides 14 h.a.P. The next division takes place soon after the first; therefore the endosperm is 4-nucleated already 18. h.a.P. Further divisions are synchronized, and 30–38 h.a.P. there will be more than 32 nuclei. The synchronous divisions continue, and the cellularisation begins at about 70 h.a.P. There is a tight correlation between the enlargement of the ovule and the embryo sac in the first days of the embryo development.     

An Ultrastructural Study of The Embryo/Endosperm Interface in the Developing Seeds of Solanum nigrum L. Zygote to Mid Torpedo Stage

The early developmental sequences in the formation of the Zoneof Separation and Secretion in a hexaploid species of Solanumnigrum L. are described. Ultrastructural changes which occurredduring the development of the embryo/endosperm interface couldbe related to the different stages in the embryo's development.The first step was the completion of the cell wall around thechalazal end of the zygote; a thin wall was formed along theendosperm cell(s) abutting the zygote. From the mature zygotestage to the quadrant stage, minute plasmalemma invaginationsoccurred along the endosperm wall facing the zygote. These invaginationsenlarged, and from the mid-globular stage onwards became filledwith a fine fibrillar material; this material accumulated betweenthe endosperm cell wall and the plasmalemma before being releasedinto the developing periembryonic and intercellular spaces tobecome the extracellular matrix. Cell wall development in theendosperm cells abutting the embryo followed an unusual path.During the quadrant stage, whilst the outer embryo wall increasedin thickness due to vesicle fusion, the endosperm cell wallfacing the embryo showed a loosening of the wall fibrils aswell as partial separation of these same endosperm cells fromeach other. From the early-globular stage, the endosperm cellwalls opposite the embryo became electron-translucent, disappearinginto the extracellular matrix. Enzymic secretions by the embryomay account for the alteration in the abutting endosperm cellwalls. Enzymic activity may also explain the development ofa homogenous electron-opaque layer over the outer embryo wallas well as the differences in the width of the fibrillar layerwhich accumulated around the cotyledons as the embryo grew throughthe Zone of Separation and Secretion. The potential roles ofthe extracellular matrix are briefly discussed. Solanum nigrum L.; embryo/endosperm interface; Zone of Separation and Secretion; embryo development; cellular endosperm     

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.