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.

Early embryogenesis in Arabidopsis thaliana. I. The mature embryo sac

1991 ◽  
Vol 69 (3) ◽  
pp. 447-460 ◽  
Author(s):  
S. G. Mansfield ◽  
L. G. Briarty ◽  
S. Erni
Keyword(s):  
Arabidopsis Thaliana ◽  
Endoplasmic Reticulum ◽  
Embryo Sac ◽  
Mature Embryo ◽  
Central Cell ◽  
Egg Cell ◽  
Cell Cytoplasm ◽  
Intimate Contact ◽  
Egg Apparatus ◽  
Common Wall

Arabidopsis thaliana has a seven-celled eight-nucleate megagametophyte of the Polygonum type; each cell type displays a different form of structural specialization. The egg apparatus cells are highly polarized; the egg has a large micropylar vacuole and chalazally sited nucleus, whereas the opposite is true for the synergids. At the chalazal region of the egg apparatus cells there are no cell wall boundaries, although their plasmalemmas are in intimate contact. The common wall between the two synergids is thin and irregular and contains plasmodesmatal connections. The synergid cytoplasm is rich in organelles; profiles of rough endoplasmic reticulum appear in masses of parallel stacked cisternae, and large accumulations of mitochondria occur adjacent to the filiform apparatus. The egg cell cytoplasm is quiescent; ribosome concentration and frequencies of dictyosomes and endoplasmic reticulum are noticeably lower and plastids are poorly differentiated. The central cell is long and vacuolate with a large diploid nucleus; fusion of the polar nuclei occurs prior to embryo sac maturity. The cytoplasm contains numerous starch-containing plastids accumulated in a shell around the nucleus. A high ribosome concentration and the absence of vacuoles and dictyosomes typifies the antipodal cell cytoplasm. All antipodal cells are interconnected by plasmodesmata as well as being connected to the nucellus and central cell. Key words: Arabidopsis, embryo sac, embryogenesis, cell specializations, stereology.

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.

Ultrastructural observations of the mature megagametophyte and the fertilization in wheat (Triticum aestivum)

1985 ◽  
Vol 63 (2) ◽  
pp. 163-178 ◽  
Author(s):  
Ruilin You ◽  
William A. Jensen
Keyword(s):  
Triticum Aestivum ◽  
Pollen Tube ◽  
Cell Walls ◽  
Embryo Sac ◽  
Mature Embryo ◽  
Central Cell ◽  
The Other ◽  
Egg Cell ◽  
Filiform Apparatus ◽  
Egg Apparatus

The mature embryo sac of wheat contains an egg apparatus composed of an egg cell and two synergids at the micropylar end, a central cell with two large polar nuclei in the middle, and a mass of 20 to 30 antipodals at the chalazal end. A comparison was made of the ultrastructural features of the various cells of the embryo sac. The features included the position of the nucleus and vacuoles, the number, structure, and distribution of organelles, and the extent of the cell walls surrounding each cell. The pollen tube enters one synergid through the filiform apparatus from the micropyle. The penetration and discharge of the pollen tube causes the further degeneration of that synergid, which had already undergone changes before pollination. The second synergid does not change further in appearance following the penetration of the first by the pollen-altered tube. Half an hour after pollination at 20–25 °C, two male nuclei are seen in the cytoplasm of the egg and the central cell. At about 1 h after pollination, one sperm has made contact with the egg nucleus, while the other sperm is fusing with one of the polar nuclei.

Ultrastructural studies on the embryo sac of Viscum minimum: II. Megagametogenesis

1994 ◽  
Vol 72 (11) ◽  
pp. 1613-1628 ◽  
Author(s):  
M. Zaki ◽  
J. Kuijt
Keyword(s):  
Early Stage ◽  
Light And Electron Microscopy ◽  
Embryo Sac ◽  
Mature Embryo ◽  
Mitotic Division ◽  
Central Cell ◽  
Egg Cell ◽  
Ultrastructural Studies ◽  
Stage Of Development ◽  
Final Length

Embryo sac development of Viscum minimum was investigated using light and electron microscopy. Stages described involve uninucleate, binucleate, four-nucleate, and mature embryo sacs following cellularization. During the early stage of development, prior to mitosis, numerous small vacuoles are initiated in the cytoplasm of a uninucleate functional megaspore. The centrally located nucleus undergoes the first mitotic division and results in formation of two identical nuclei sharing a common cytoplasm. As the vacuole increases rapidly in size, the two nuclei become separated and move to opposite poles where the second mitotic division takes place. A remarkable elongation of the embryo sac is observed between the second and third mitotic division. Eventually, the embryo sac reaches its final length, two-thirds of the length of the ovary, at cellularization. Elongation of the embryo sac is closely related to the increase in vacuole size. Factors involved in vacuole formation and in the elongation of the embryo sac are discussed along with changes accompanying the transition from a sporophytic to a gametophytic pattern of development. Ultrastructural studies on the mature embryo sac, following cellularization, suggest that the egg cell is the least active cell in the megagametophyte. On the other hand, the synergids appear metabolically very active, being rich in plastids, mitochondria, dictyosomes, numerous vesicles, polysomes, and reserves. The central cell is the largest cell in the embryo sac. In a mature embryo sac the central cell has two adjacent nuclei, suggesting that fusion of the nuclei is completed following pollination and fertilization. The antipodals possess a complete set of organelles, numerous free and aggregated ribosomes, and endoplasmic reticulum. It is believed the antipodals play a significant nutritive role during the development of the embryo sac of V. minimum. Modification of the wall between antipodals and central cell and its role in nutrient transportations are discussed. Key words: embryo sac, embryogenesis, gametogenesis, megagametogenesis, mistletoes, ultrastructure.

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.

scholarly journals Early events during embryogenesis in Zea mays L.

2014 ◽  
Vol 50 (1-2) ◽  
pp. 289-290 ◽  
Author(s):  
A. A. Van Lammeren
Keyword(s):  
Zea Mays ◽  
Structural Changes ◽  
Zea Mays L ◽  
Mature Embryo ◽  
Early Embryogenesis ◽  
Central Cell ◽  
Egg Cell ◽  
Cellular Endosperm ◽  
Well Differentiated

The megagametophyte of <em>Zea mays</em> L. undergoes a series of structural changes after fertilization resulting in a well differentiated mature embryo and cellular endosperm at 480 hours after pollination in greenhouse conditions. In the present work emphasis was laid on the localization of the cytoplasm in the synergids, central cell-endosperm and egg cell-zygote prior to and after fertilization. The observations are discussed in relation to the process of early embryogenesis.

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.

Cytoskeletal organisation and modification during pollen tube arrival, gamete delivery and fertilisation in Plumbago zeylanica

Zygote ◽  
1993 ◽  
Vol 1 (2) ◽  
pp. 143-154 ◽  
Author(s):  
Bing-Quan Huang ◽  
Elisabeth S. Pierson ◽  
Scott D. Russell ◽  
Antonio Tiezzi ◽  
Mauro Cresti
Keyword(s):  
Pollen Tube ◽  
Embryo Sac ◽  
Central Cell ◽  
Egg Cell ◽  
Target Cells ◽  
Sperm Cells ◽  
Plumbago Zeylanica ◽  
Rhodamine Phalloidin ◽  
Male Gametes ◽  
Pollen Tube Penetration

The cytoskeletal organisation of the isolated embryo sac and egg cells of Plumbago zeylanica was examined before, during and after pollen tube penetration into the embryo sac to determine the potential involvement of microtubules and actin filaments in fertilisation. Material was singly and triply stained using Hoechst 33258 to localise DNA, fluorescein isothiocyanate (FITC)-labelled anti- α-tubulin to detect microtubules and rhodamine-phalloidin to visualise F-actin. Microtubules in the unfertilised egg cell are longitudinally aligned in the micropylar and mid-lateral areas, aggregating into bundles near the filiform apparatus. In the perinuclear cytoplasm of the egg cell, microtubules become more or less randomly aligned. F-actin bundles form a longitudinally aligned mesh in the chalazal cytoplasm of the egg cell. In the central cell, microtubules and F-actin are distributed along transvacuolar strands and are also evident in the perinuclear region and at the periphery of the cell. During pollen tube penetration, sparse microtubule bundles near the pathway of the pollen tube may form an apparent microtubular ‘conduit’ surrounding the male gametes at the delivery site. Actin aggregates become organised near the pathway of the pollen tube and at the delivery site of the sperm cells. Subsequently, actin aggregates form a ‘corona’ structure in the intercellular region between the egg and central cell where gametic fusion occurs. The corona may have a role in maintaining the close proximity of the egg and central cell and helping the two sperm cells move and bind to their target cells. The cytoskeleton may also be involved in causing the two nuclei of the egg and central cell to approach one another at the site of gametic fusion and transporting the two sperm nuclei into alignment with their respective female nucleus. The cytoskeleton is reorganised during early embryogenesis.

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.

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