scholarly journals Ultrastructural organization of the tomato embryo sac at the time of fertilization

2014 ◽  
Vol 50 (1-2) ◽  
pp. 139-142 ◽  
Author(s):  
Franciszek Kadej ◽  
Agnieszka Kadej
Keyword(s):  
Cell Nucleus ◽  
Close Contact ◽  
Embryo Sac ◽  
Egg Cell ◽  
Ultrastructural Organization ◽  
Nucleolar Structure ◽  
Great Uniformity

In tomato embryo sac at the time of fertilization noticeable multiplication of the endosperm cytoplasm is observed. The cytoplasm of the egg cell, next to the nucleus, appears loose with distinct mitochondria and plastids. At a distance from the nucleus ribosomes become grouped into a cytoplasmic mass of great uniformity. Nucleolar structure of the egg cell nucleus displaces to its periphery. Its new position seems to he related to the process of fertilization. In the area of the endosperm two nuclei in close contact to each other are found which suggests the beginning of secondary fertilization.

scholarly journals Cytochemical study of the embryo sac of Nicotiana tabacum L.

2014 ◽  
Vol 50 (1-2) ◽  
pp. 121-125
Author(s):  
V. P. Babbikova ◽  
O. A. Khvendynich ◽  
L. S. Serdyuk
Keyword(s):  
Cell Nucleus ◽  
Mitotic Cycle ◽  
Cell Formation ◽  
Embryo Sac ◽  
Central Cell ◽  
Egg Cell ◽  
Cell Nuclei ◽  
Cytochemical Study ◽  
Male Gametes ◽  
S Period

The mitotic cycle in the egg cell and physico-chemical state of chromatin in the egg cell and central cell of the tobacco embryo sac were studied. It was revealed that during egg cell formation a change in the mitotic cycle kinetics takes place, it consists in prolongation of the S-period as compared with that of somatic cells and G1 - period as compared with that of male gametes. Egg cell and central cell nuclei differ in chromatin structure. Condensed chromatin dominates in the egg cell nucleus, diffuse chromatin in the central cell nucleus, but both show only weak metabolic activity.

scholarly journals The ultrastructure of the mature embryo sac in the natural tetraploid of red clover (Trifolium pratense L.): that has a very low rate of seed formation

2014 ◽  
Vol 66 (1) ◽  
pp. 13-20 ◽  
Author(s):  
Gönül Algan ◽  
H. Nurhan Bakar
Keyword(s):  
Endoplasmic Reticulum ◽  
Trifolium Pratense ◽  
Embryo Sac ◽  
Red Clover ◽  
Mature Embryo ◽  
Polar Nucleus ◽  
Central Cell ◽  
Egg Cell ◽  
Ultrastructural Organization ◽  
Seed Formation

In this study, ultrastructural organization of cells in the mature embryo sac of natural tetraploid <em>Trifolium pratense</em> L. was investigated. The mature embryo sac of this plant contains an egg cell with two synergids at the micropylar end, and a central cell with two polar nuclei. The ultrastructure of these cells agrees with what is known for most angiosperms studied with the electron microscope. The egg cell is a large and highly vacuolate cell, partially surrounded by a wall. Much of the cytoplasm is located around the nucleus at the chalazal end and there are few numbers of channel-shaped endoplasmic reticulum, mitochondria, plastids and numerous ribosomes distributed throughout the cytoplasm. Unlike the egg cell, much of the cytoplasm in synergid cells is located at micropylar part of the cell and the synergid cytoplasm contains especially, large numbers of rough endoplasmic reticulum, free ribosomes, mitochondria and plastids. The central cell of <em>T. pratense</em> L. contains two large polar nuclei which lie close to the egg apparatus. Each polar nucleus has a single, large, dense nucleolus that contains several nucleolar vacuoles. Much of the central cell cytoplasm consisting of granular and agranular endoplasmic reticulum, mitochondria, plastids, ribosomes, dictyosomes and lipid bodies are placed around polar nuclei.

Fertilization in Plumbago zeylanica: entry and discharge of the pollen tube in the embryo sac

1982 ◽  
Vol 60 (11) ◽  
pp. 2219-2230 ◽  
Author(s):  
Scott D. Russell
Keyword(s):  
Cell Wall ◽  
Pollen Tube ◽  
Female Gametophyte ◽  
Embryo Sac ◽  
Central Cell ◽  
Vegetative Nucleus ◽  
Egg Cell ◽  
Ultrastructural Organization ◽  
Plumbago Zeylanica ◽  
Male Gametes

The ultrastructural organization of the megagametophyte of Plumbago zeylanica, which lacks synergids, was examined in chemically and physically fixed ovules after entry of the pollen tube. Similar to angiosperms with conventionally organized megagametophytes, the pollen tube enters the ovule through a micropyle, formed by the inner integument, and approaches the female gametophyte by growing between nucellar cells. Unlike other described female gametophytes, however, continued pollen tube growth results in direct penetration of the base of the egg through cell wall projections forming a filiform apparatus and is completed between the egg and central cell without disrupting either of these cells' plasma membranes. A terminal pollen tube aperture forms when the pollen tube reaches an area of strong curvature near the summit of the egg; this results in the release of two sperm cells, the vegetative nucleus, and a limited amount of pollen cytoplasm. The formerly continuous chalazal egg cell wall is locally disrupted near the tip of the pollen tube and apparently is thus modified for reception of male gametes. Discharged pollen cytoplasm rapidly degenerates between the egg and central cell, but unlike pollen tube discharge in conventionally organized megagametophytes, it is unassociated with the degeneraton of any receptor cell within the female gametophyte. Sperm nuclei are transmitted, one to the egg and the other to the central cell, to effect double fertilization by nuclear fusion with their respective female reproductive nuclei. The vegetative nucleus and discharged pollen cytoplasm degenerate between the developing embryo and endosperm during early embryogenesis. The emerging concept that the egg of Plumbago possesses combined egg and synergid functions is supported by the present study and suggests that the megagametophyte of this plant displays a highly specialized egg apparatus composed exclusively of a single, modified egg cell.

Overgrowth of Pollen Tubes in Embryo Sacs of Rhododendron Following Interspecific Pollinations

1986 ◽  
Vol 34 (4) ◽  
pp. 413 ◽  
Author(s):  
EG Williams ◽  
V Kaul ◽  
JL Rouse ◽  
BF Palser
Keyword(s):  
Pollen Tube ◽  
Embryo Sac ◽  
Pollen Tubes ◽  
Egg Cell ◽  
Interspecific Crosses ◽  
Main Body

Frequent overgrowths of pollen tubes within the embryo sac are characteristic of a number of interspecific crosses in the genus Rhododendron (Ericaceae). The combined techniques of sectioning, squashing and whole-ovule clearing have confirmed that in ovules showing this phenomenon the pollen tube fails to terminate growth and release sperms on entry into a synergid; instead it continues to grow beyond the synergid and egg cell, often filling the main body of the embryo sac with a coiled and distorted mass. Such ovules fail to develop further. The occurrence and possible causes of this error syndrome are discussed.

scholarly journals Recent advances in understanding female gametophyte development

F1000Research ◽  
2018 ◽  
Vol 7 ◽  
pp. 804 ◽  
Author(s):  
Debra J Skinner ◽  
Venkatesan Sundaresan
Keyword(s):  
Cell Fate ◽  
Female Gametophyte ◽  
Cell Communication ◽  
Embryo Sac ◽  
Cell Types ◽  
Egg Cell ◽  
Male Gametes ◽  
Reproductive Unit ◽  
Genetic Mechanisms ◽  
Female Gametophyte Development

The haploid female gametophyte (embryo sac) is an essential reproductive unit of flowering plants, usually comprising four specialized cell types, including the female gametes (egg cell and central cell). The differentiation of these cells relies on spatial signals which pattern the gametophyte along a proximal-distal axis, but the molecular and genetic mechanisms by which cell identities are determined in the embryo sac have long been a mystery. Recent identification of key genes for cell fate specification and their relationship to hormonal signaling pathways that act on positional cues has provided new insights into these processes. A model for differentiation can be devised with egg cell fate as a default state of the female gametophyte and with other cell types specified by the action of spatially regulated factors. Cell-to-cell communication within the gametophyte is also important for maintaining cell identity as well as facilitating fertilization of the female gametes by the male gametes (sperm cells).

Development of a Heat-Inducible Gene Expression System Using Female Gametophytes of Arabidopsis thaliana

2019 ◽  
Vol 60 (11) ◽  
pp. 2564-2572 ◽  
Author(s):  
Dukhyun Hwang ◽  
Satomi Wada ◽  
Azusa Takahashi ◽  
Hiroko Urawa ◽  
Yasuhiro Kamei ◽  
...  
Keyword(s):  
Arabidopsis Thaliana ◽  
Expression System ◽  
Embryo Sac ◽  
Gene Induction ◽  
Central Cell ◽  
Egg Cell ◽  
Dominant Negative Mutant ◽  
Nucleate Cell ◽  
Recombination System ◽  
Induction System

Abstract Female gametophyte (FG) is crucial for reproduction in flowering plants. Arabidopsis thaliana produces Polygonum-type FGs, which consist of an egg cell, two synergid cells, three antipodal cells and a central cell. Egg cell and central cell are the two female gametes that give rise to the embryo and surrounding endosperm, respectively, after fertilization. During the development of a FG, a single megaspore produced by meiosis undergoes three rounds of mitosis to produce an eight-nucleate cell. A seven-celled FG is formed after cellularization. The central cell initially contains two polar nuclei that fuse during female gametogenesis to form the secondary nucleus. In this study, we developed a gene induction system for analyzing the functions of various genes in developing Arabidopsis FGs. This system allows transgene expression in developing FGs using the heat-inducible Cre-loxP recombination system and FG-specific embryo sac 2 (ES2) promoter. Efficient gene induction was achieved in FGs by incubating flower buds and isolated pistils at 35�C for short periods of time (1–5 min). Gene induction was also induced in developing FGs by heat treatment of isolated ovules using the infrared laser-evoked gene operator (IR-LEGO) system. Expression of a dominant-negative mutant of Sad1/UNC84 (SUN) proteins in developing FGs using the gene induction system developed in this study caused defects in polar nuclear fusion, indicating the roles of SUN proteins in this process. This strategy represents a new tool for analyzing the functions of genes in FG development and FG functions.

Apospory in Paspalum thunbergii

2004 ◽  
Vol 52 (1) ◽  
pp. 81 ◽  
Author(s):  
Guohua Ma ◽  
Xuelin Huang ◽  
Nanxian Zhao ◽  
Qiusheng Xu
Keyword(s):  
Chromosome Number ◽  
Developmental Stage ◽  
Pollen Viability ◽  
Paraffin Section ◽  
Embryo Sac ◽  
Low Frequency ◽  
The Other ◽  
Egg Cell ◽  
Successive Generations ◽  
Mother Cells

The cytology, development of aposporous embryo sac, pro-embryo and pseudogamy in Paspalum thunbergii Kunth ex Steud. was studied. P. thunbergii was found to be a tetraploid cytotype, with a chromosome number of 40. Meiosis of the pollen mother cells was irregular, pollen viability was low and multiporate pollens were often observed. Megasporogenesis began normally; however, the megaspore deteriorated at the developmental stage of tetrad, while one to five specific nucellar cells became active and began enlarging, and then developed into aposporous embryo sacs. The mature aposporous sacs usually had three nuclei characterised by one egg cell and two polar nuclei. The egg cell developed spontaneously to form pro-embryos prior to anthesis. When several aposporous sacs occurred in the same ovule, usually one sac near the micropyle was involved in pseudogamy, while the other sacs were not involved. Low frequency of twin-embryo seedlings was observed after seeds matured. Examination of three successive generations by paraffin-section and clearing methods revealed that no sexual sac was present. Therefore, the species P. thunbergii is considered to be an obligate apomict that reproduces by apospory.

scholarly journals Development of generative structures of polar Caryophyllaceae plants: the Arctic Cerastium alpinum and Silene involucrata, and the Antarctic Colobanthus quitensis

2017 ◽  
Vol 38 (1) ◽  
pp. 83-104 ◽  
Author(s):  
Wioleta Kellmann-Sopyła ◽  
Justyna Koc ◽  
Ryszard J. Górecki ◽  
Marcin Domaciuk ◽  
Irena Giełwanowska
Keyword(s):  
Embryo Sac ◽  
Single Layer ◽  
Pollen Grains ◽  
The Arctic ◽  
Egg Cell ◽  
Colobanthus Quitensis ◽  
West Antarctic ◽  
The Family ◽  
Electron Microscopes ◽  
Species Specific

AbstractThe embryology of three polar flowering plants of the family Caryophyllaceae was studied using the methods and techniques of the light, normal and fluorescence microscopes, and the electron microscopes, scanning and transmission. The analyzed species wereColobanthus quitensisof West Antarctic (King George Island, South Shetlands Islands) as well asCerastium alpinumandSilene involucrataof the Arctic (Spitsbergen, Svalbard). In all evaluated species, flowering responses were adapted to the short Arctic and Australian summer, and adaptations to autogamy and anemogamy were also observed. The microsporangia of the analyzed plants produced small numbers of microspore mother cells that were differentiated into a dozen or dozens of trinucleate pollen grains. The majority of mature pollen grains remained inside microsporangia and germinated in the thecae. The monosporous Polygonum type (the most common type in angiosperms) of embryo sac development was observed in the studied species. The egg apparatus had an egg cell and two synergids with typical polarization. A well-developed filiform apparatus was differentiated in the micropylar end of the synergids. In mature diaspores of the analyzed plants of the family Caryophyllaceae, a large and peripherally located embryo was, in most part, adjacent to perisperm cells filled with reserve substances, whereas the radicle was surrounded by micropylar endosperm composed of a single layer of cells with thick, intensely stained cytoplasm, organelles and reserve substances. The testae of the analyzed plants were characterized by species-specific primary and secondary sculpture, and they contained large amounts of osmophilic material with varied density. Seeds ofC. quitensis,C. alpinumandS. involucrataare very small, light and compact shaped.

scholarly journals Meiosis and Development of the Embryo Sac in Gunnera insignis (Oersted) D.C. (Halorhagaceae)

1969 ◽  
Vol 46 (4) ◽  
pp. 254-268
Author(s):  
Niilo Virkki
Keyword(s):  
Costa Rica ◽  
Chromosome Complement ◽  
Embryo Sac ◽  
Mature Embryo ◽  
Egg Cell ◽  
Acrocentric Chromosomes ◽  
Antipodal Cells ◽  
Giant Species

Gunnera insignis (Oersted) D.C. is a halorhagacean plant from the mountains of Costa Rica, a giant species which can be considered as a potential ornamental. The chromosome relations of the whole genus Gunnera have been practically unknown. The diploid chromosome complement of Gunnera insignis consists of 34 acrocentric chromosomes of quite differ ent size. Both PMC and MMC meiosis are normal and vigorous, showing 17 bivalents in the first division. Absolute procentric localization of the first (or only) chiasma occurs in MMC. In PMC, the same tendency is seen in a couple of big bivalents. The rate of terminalization of chiasmata in the remaining PMC bivalents is low. The mature embryo sac of Gunnera insignis is tetrasporic, 16-nucleate, 2-phasic, and multipolar. It consists of an egg cell, a giant polyploid nucleus formed by fusion of 7 polar nuclei, and 6 antipodal cells. In exceptional cases 2 smaller fusion nuclei may occur instead of 1 large. This is considered a sign of an incomplete repolarization of the embryo sac nuclei.

Embryological studies on hybridization between Theobroma cacao and Theobroma grandiflora

1972 ◽  
Vol 50 (11) ◽  
pp. 2117-2124 ◽  
Author(s):  
Veronica A. Martinson
Keyword(s):  
Theobroma Cacao ◽  
Interspecific Cross ◽  
Embryo Sac ◽  
Egg Cell ◽  
Interspecific Crosses ◽  
Seed Formation ◽  
Contributory Factors ◽  
Poor Seed ◽  
Endosperm Formation ◽  
Species Hybridization

In a comparative study of embryo development in intraspecific (U6 × K5/353) and interspecific (U6 × T33) crosses of Theobroma, the development of the embryo sac as described by previous authors was confirmed. Disintegration of synergids showed that the growth of the pollen through the style was slightly quicker in intraspecific than in interspecific crosses, but the number of embryo sacs which had received male nuclei 3 days after pollination was about the same. Although gametic fusion and endosperm formation in the intraspecific cross was in advance of those in interspecific cross, the major blockage in species hybridization occurred subsequent to fertilization, and in most instances, well after the proembryo stage. Abnormal cell division and cell differentiation were contributory factors to poor seed formation. Possible causes of the abnormality have been discussed.Autonomous enlargement and the binucleate appearance of the egg cells in the unpollinated flower suggested a tendency to parthenogenesis and diploidization of the egg cell, under special conditions. Although a large proportion of the cacao seeds observed in the species crosses are most probably intraspecific seedlings arising from contamination after controlled pollinations, the occurrence of a small number of true maternal seeds cannot be ruled out altogether.

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