Development of the Female Gametophyte in Hydrobryum griffithii (Podostemaceae)

The development of the female gametophyte in Hydrobryum griffithiiis of the Apinagia type. The chalazal megaspore nucleus of thetwo-nucleate embryo sac completely degenerates, and only themicropylar megaspore nucleus contributes to the four nucleipresent in the organized embryo sac. The female gametophyteconsists of two synergids, an egg and a haploid central cell.The latter degenerates before the entry of the pollen tube andthere is only syngamy. The nucellar cells below the embryo sacorganize into a nucellar plasmodium.     

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.     

The Nucellus, Embryo Sac, Endosperm, and Embryo of Aesculus and their Interdependence during Growth

Immature fruits of Aesculus yield powerful stimuli to growthand cell division. Therefore, the developing fruit of Aesculuswoerlitzensis Koehne has been investigated from pollinationto maturity. The fluid, or liquid endosperm, which containsthe growth-promoting substances is produced in a large vesiclewhich forms at the chalazal tip of the embryo sac. As the vesiclegrows, it encroaches upon the nucellus and, when the embryodevelops, one of its cotyledons penetrates into the vesicleof the embryo sac where it grows and absorbs the contents. Theembryo, which has only a vestigial suspensor, reaches the vesicleby growing along the neck of the long curved embryo sac. Thecotyledon which first penetrates the vesicle grows into a massivestructure; the other remains small. The tip of the cotyledonseems to function as an absorbing surface, for the endospermwith which it comes into contact disorganizes. Fertilizationand the presence of a viable embryo at the micropylar end ofthe embryo sac therefore sets in train a number of other events.These are the extensive development of the nucellus at the chalazalend of the embryo sac, the swelling of the vesicle and the formationof a free nuclear and some cellular endosperm, and the disorganizationof the nucellus as it is encroached upon by the vesiculate embryosac. Attention is directed to the organization of the nucellusin the vicinity of the embryo sac. Files or richly protoplasmicnucellar cells(hypostase) which converge upon the chalazal tipof the embryo sac suggest a principal route by which the vesiclemay be nourished. Special attention is drawn to the very differentsizes of cells, their nuclei and nucleoli, in the differentparts of the nucellus. The growth and development of the embryohas also been traced from the zygote to the mature seed. Thenutritive role of the veaiculate embryo sac, and the supplyof growthstimulating substances, through the function of a cotyledonas an absorbing organ, are now seen as important features ofthe development of the Aesulus embryo in the ovule. Many outstandingproblems still remain. The sequential events that follow fertilizationin the different interdependent regions (nucellus, embryo sac,cotyledon, &c.) are here described, but not casually explained.     

The Initiation, Development and Removal of Embryo Sac Wall Ingrowths in the Developing Seeds of Solanum nigrum L. An Ultrastructural Study

In developing seeds of Solanum nigrum L., wall ingrowths developedat the extreme micropylar and chalazal ends of the embryo sac.In the micropylar region, the wall ingrowths were initiatedat the three-celled endosperm stage starting at the base ofthe zygote then progressing for a short distance chalazalwards.They developed quickly with the most elaborate around the baseof the suspensor. The chalazal wall ingrowths developed alongthe surfaces of the chalazal cup, the antipodal cup and thehypostase. Those along the hypostase were initiated at the four-celled,those in the chalazal and antipodal cups at the 20-celled endospermstages. The most elaborate developed along the base of the antipodalcup; the most simple were along the base of the chalazal cup.Small electron-lucent invaginations of the plasmalemma whichlater became filled with fibrillar material, were the earliestindication of wall ingrowth formation. Removal of the wall ingrowthscommenced at the mid-globular stage of embryo development andwas completed by the mid-heart-shaped stage. In the micropylarregion, wall ingrowth removal was rapid, starting with the lossof the fibrillar component followed by the thinning of the cellwall. However, along the hypostase and antipodal cup, a heterogeneouslayer of varying electron densities and a thinner, more electrondense layer was laid down over the ingrowths. This was followedby the removal of the fibrillar component. The initiation, removaland location of the embryo sac wall ingrowths is discussed inconnection with understanding the nutritional relationshipsbetween maternal tissue, endosperm and embryo.Copyright 1995,1999 Academic Press Wall ingrowths, Solanum nigrum, transfer cells, zone of separation and secretion, hypostase     

鹤顶兰胚囊发育过程中微管变化的共焦显微镜观察

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

Ultrastructure of the Developing and Fertilized Embryo Sac of Amaranthus hypochondriacus L.

Amaranthus hypochondriacus embryo sac development was investigatedbefore and after fertilization. During the early stages of development,the young embryo sac displays three antipodal cells at the chalazalpole that degenerate very early in the maturation process, beforethe synergids and egg cell are completely differentiated. Themature embryo sac is composed only of the female germ unit.The synergid cells organize a filiform apparatus accompaniedby the presence of mitochondria and dictyosomes with numerousvesicles. The involvement of the synergids in transport andsecretory functions related to pollen tube attraction and guidance,are discussed. The egg cell is located at the micropylar polenear the synergids and displays exposed plasma membranes atthe chalazal pole. The fertilized egg cell does not exhibitmarked changes after fertilization except for the closure ofthe cell wall. The central cell is the largest cell of thisvery long embryo sac. The fused nucleus is close to the eggapparatus before fertilization and displays a remarkable chalazalmigration after gamete delivery. The ultrastructure of the centralcell cytoplasm and the numerous wall ingrowths around this cellsuggest an important role in nutrient transportation. Aftergamete delivery, the embryo sac displays electron dense bodiesthat aggregate within the intercellular space between the synergids,egg cell and central cell. These bodies, that appear in theembryo sac of several plants, are probably involved in gametedelivery for double fertilization. The possibility of biparentalinheritance of mitochondria in this plant is also discussed.Copyright 1999 Annals of Botany Company Amaranthus hypochondriacus, grain amaranth, embryo sac, fertilization.     

Abnormal Behavior of Nuclei and Microtubule (MT) Organizational Changes During Embryo Sac Development in the Poly-Egg Mutant,APⅣ of Rice

APⅣ is a rice mutant that develops poly-egg apparatus in its embryo sac. All the eggs that make up the poly-egg apparatus can be fertilized respectively resulting in the development of polyembryony. The routes taken in the development of polyembryony appear to fall mainly into three variant polygonum pattern types, designated as 5-2-1 , 5-3-0 and 6-2-0 types. Out of the embryo sacs of APⅣ studied about 50% exhibited variant polygonum type with associated abnormal nuclear behavior and microtubule organizational changes. Some of the major abnormal features shown by the three variant polygonum types were described and they included the following: For the 5-2-1 type At the beginning of the four-nucleate embryo sac development, one pair of nuclei became located to the micropylar end and the other pair to the chalazal end. As embryo sac further developed, long connecting microtubule (MT) bundles that existed between the two nuclei in the chalazal end play a role in the movement and positioning of that nucleus. As a result of the activities of these MT, one of the nuclei in the chalazal end moved to the micropylar end resulting in the micropylar end having three nuclei and the chalazal end only one. For the 5-3-0 type In the two-nucleate embryo sac of the 5-3-0 type, one nucleus remained at the micro-pylar end, while the other one became located near the central region. In the four-nucleate embryo sac, the pair of nuclei aligned in parallel to the micropylar-chalazal axis often having one of its nuclei relocated to the micropylar end as a result of associated MT activities. For the 6-2-0 type All the nuclei in the megaspore, two- and four-nucleate embryo sacs became located to the micropylar end. At the early stages of the eight-nucleate embryo sac development, the two nuclei in the central region of the embryo sac (originally at the micropylar end) became polar nuclei. All the other nuclei remained at the micropylar end were surrounded by reticulate MT. The relationship between abnormal behavior of nuclei and MT organi-zation in the development of rice embryo sac was discussed.     

Accumulation of Metabolites during Seed Development in Trifolium repens L.

Metabolite deposition during seed development was examined histochemicallyin Trifolium repens by light- and fluorescence microscopy. Allendosperm haustorium at the chalazal pole of the embryo sacand wall protrusions in cell walls of the suspensor and theembryo sac suggest that transfer of metabolites from maternalto offspring tissue takes place primarily at these sites. Thisis further supported by prominent cutinization of the interpolarregion of the embryo sac wall, accumulation of starch in integumentaltissue at the embryo sac poles, and breakdown of interpolarendothelial cells. Decomposition of osteosclereid starch isfollowed by accumulation in the cellular endosperm and subsequentlyin the embryo parallel to endosperm degradation. The starchaccumulates gradually inward from the subepidermal cells ofthe embryo to the stele. Protein bodies are formed in the vacuolesalong the tonoplast, later to be cut off in vesicles releasedinto the cytoplasm. At maturity the embryo is packed with proteinand starch, but without lipid reserves. Phytin is observed inthe protein bodies. The mature embryo is surrounded by a proteinand starch containing aleurone layer which originates from theendosperm.Copyright 1994, 1999 Academic Press White clover, protein, starch, cuticle, embryo sac wall     

Megasporogenesis, female gametophyte development and embryonic development of Ambrosia L. in China

The megasporogenesis, female gametophyte development and embryonic development of Ambrosia artemisiifolia L. and Ambrosia trifida L. of genus Ambrosia L. in China were studied using conventional paraffin section technology and optical microscopy. The results show that both A. artemisiifolia L. and A. trifida L. have a bilobed pistil stigma, two carpels, one chamber, basal placenta, unitegmic, tenuinucellate, anatropous ovule, and well-developed integumentary tapetum. Megaspore mother cells are directly developed from archesporial cells originated from the nucellar cells under the nucellar epidermis and further undergo meiosis to form linear tetrads. The megaspore at the chalazal end develops into a functional megaspore and the other three megaspores are degraded. The development of embryo sac is monosporic type. After three consecutive mitosis, mononucleate embryo sac becomes a mature embryo sac with two synergids and one egg cell at the micropylar end, a central cell at the center and three antipodal cells at the chalazal end. Most antipodal cells are mononucleate or binucleate, only few are trinucleate. The embryonic development process contains four stages: globular embryo, heart-stage embryo, torpedo-stage embryo and mature embryo. The development of endosperm is cellular type.     

宁夏枸杞大孢子发生和雌配子体发育的细胞学研究

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

Embryo 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.     

竹节参雌配子体发育的研究

本文报道了竹节参(Panax japonicus C.A.Mey)雌配子体(胚囊)的发育过程。竹节参大孢子母细胞减数分裂产生线形排列的大孢子四分体。胚囊发育属蓼型,由合点端大孢子发育而成。游离核胚囊时期,胚囊珠孔端的细胞器种类和数量都较胚囊合点端多;胚囊合点端相邻的珠被细胞中有含淀粉粒的小质体,与胚囊珠孔端相邻的退化中的非功能大孢子中则有含淀粉粒的大质体和大类脂体。成熟胚囊中,反足细胞较早退化;极核融合成次生核;卵细胞高度液泡化,细胞器数量较少;助细胞则有丰富的细胞器和发达的丝状器。PAS反应表明,受精前的成熟胚囊中积累淀粉粒。次生核受精后,很快分裂产生胚乳游离核,到几十至数百个核时形成胚乳细胞。卵细胞受精后则要经过较长的休眠期。     

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。     

ADVENTIVE EMBRYOGENESIS IN CITRUS AND ITS RELATION TO POLLINATION AND FERTILIZATION

Cytological and histological studies of seeds from three facultative apomictic Citrus cultivars show that adventive embryos develop, as a rule, from the first few cell layers of the nucellus adjacent to the embryo sac in the micropylar half and occasionally from the chalazal end. The adventive embryos initiated in nucellar tissue away from the embryo sac and most of those initiated from the chalazal end of the nucellus do not develop beyond the one-celled stage. When two or more embryos are developing in the same seed, the successful development of a given embryo depends on its location in relation to access to nutrients from the endosperm. The presence of a zygote and triploid endosperm in seeds with adventive embryos, the abortion of seed when endosperm degenerates, and the lack of seed set without pollination indicate that pollination and fertilization are essential for in vivo adventive embryogenesis.     

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.     

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

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

Occurrence of Endosperm Haustorium in Cannabis sativa L.: With thirteen Figures in the Text

The development and structure of the chalazal endosperm haustoriumin Cannabis sativa are described. The endosperm is nuclear anda haustorium is formed at the chalazal end. The latter remainsfree nuclear throughout. Enucleate vesicles appear in the upperpart of the endosperm but finally they merge with the cytoplasmof the haustorium. As the embryo reaches maturity it occupiesthe whole seed cavity, the haustorium collapses and the endospermpersists only as a thin layer.     

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.