scholarly journals Ultrastructure of the egg apparatus of Spinacia

2014 ◽  
Vol 50 (1-2) ◽  
pp. 165-168 ◽  
Author(s):  
H. J. Wilms
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Wall ◽  
Rough Endoplasmic Reticulum ◽  
Embryo Sac ◽  
Spherical Nucleus ◽  
Egg Cell ◽  
Lipid Bodies ◽  
Filiform Apparatus ◽  
Starch Grains ◽  
Egg Apparatus

The egg apparatus of <em>Spinacia</em> was studied from the time the embryo sac reaches its maximal size to just before fertilization, i.e., until about 8-9 hours after pollination. At maturity each synergid has a large elongated nucleus and prominent chalazal vacuoles, Numerous mitochondria, plastids, dictyosomes, free ribosomes, rough endoplasmic reticulum (RER), and lipid bodies are present. The cell wall exists only around the micropylar half of the synergids and each cell has a distinct, striated filiform apparatus. In general, degeneration of one synergid starts after pollination. The egg cell has a spherical nucleus and nucleolus and a large micropylar vacuole. Numerous mitochondria, some plastids with starch grains, dictyosomes, free ribosomes, and HER are present. A continuous cell wall is absent around the chalazal end of the egg cell.

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.

The development of the embryo sac of sunflower Helianthus annuus before fertilization

1973 ◽  
Vol 51 (5) ◽  
pp. 863-878 ◽  
Author(s):  
William Newcomb
Keyword(s):  
Endoplasmic Reticulum ◽  
Helianthus Annuus ◽  
Rough Endoplasmic Reticulum ◽  
Lipid Droplets ◽  
Embryo Sac ◽  
Egg Cell ◽  
Electron Microscopic ◽  
Linear Tetrad ◽  
Golgi Bodies ◽  
Large Clusters

The megaspore mother cell of sunflower Helianthus annuus L. undergoes two meiotic divisions to form a linear tetrad of haploid megaspores. The chalazal megaspore increases in size while the other megaspores and the nucellus degenerate such that the integumentary tapetum is adjacent to the embryo sac. Mitotic divisions occur forming the coenocytic two- and four-nucleate embryo sacs and the seven- or eight-nucleate six-celled embryo sac. Electron-microscopic observations suggest that the antipodals are very active synthetically but start degenerating before fertilization. Similarly the synergids are also apparently very active synthetically before fertilization as judged by the presence of extensive regions of dilated rough endoplasmic reticulum and many Golgi bodies and associated vesicles. The egg cell is characterized by the presence of many free ribosomes and small undifferentiated plastids. The central cell contains many circular strands of rough endoplasmic reticulum, lipid droplets, and large clusters of apparently active Golgi; it is a transfer cell resulting from the presence of embryo sac wall ingrowths. The development and the possible nutritional interrelationships of the megagametophyte and surrounding tissues are discussed.

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.

ULTRASTRUCTURE OF THE HYPHAE AND HAUSTORIA OF PHYTOPHTHORA INFESTANS AND HYPHAE OF P. PARASITICA

1966 ◽  
Vol 44 (11) ◽  
pp. 1495-1503 ◽  
Author(s):  
Mary A. Ehrlich ◽  
Howard G. Ehrlich
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Wall ◽  
Phytophthora Infestans ◽  
Current Literature ◽  
Lipid Bodies ◽  
Potato Varieties ◽  
Parasitic Fungi ◽  
Obligate Parasites ◽  
Tubular Endoplasmic Reticulum ◽  
Cytoplasmic Continuity

The ultrastructure of the mycelium of both Phytophthora infestans and P. parasitica is consistent with that reported for other Oomycetes. A distinct plasmalemma, porate nuclei, tubular endoplasmic reticulum, mitochondria with tubular cristae, Golgi dictyosomes, and lipid bodies are present within the protoplast. The haustoria produced by P. infestans in the leaves of susceptible potato varieties consist of an expanded haustorial head surrounded by a fungus wall which is continuous with the wall of the intercellular mycelium. The haustorium lacks the long narrow stalk or neck often associated with this organ, and there is considerable cytoplasmic continuity between the haustorium and the intercellular mycelium. All P. infestans haustoria observed were anucleate and generally contained only a few mitochondria and sparse endoplasmic reticulum. The haustorium is enclosed in an encapsulation surrounded by a membrane which is continuous with the host plasmalemma. There is no evidence, around any portion of the haustorium, of a sheath originating from the cell wall of the host. A survey of the current literature on the ultrastructure of the Eumycotinia shows that the parasitic fungi exhibit no unique cytoplasmic features when compared with non-parasitic fungi, and the ultrastructure of the haustoria-producing facultative saprophyte is similar to that of the obligate parasites.

scholarly journals The amounts and rates of export of polysaccharides found within the membrane system of maize root cells

1974 ◽  
Vol 142 (1) ◽  
pp. 139-144 ◽  
Author(s):  
Dianna J. Bowles ◽  
D. H. Northcote
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Wall ◽  
Golgi Apparatus ◽  
Cell Surface ◽  
Rough Endoplasmic Reticulum ◽  
Membrane System ◽  
Maize Root ◽  
Wall Material ◽  
Cell Wall Material ◽  
Root Cells

1. Maize seedling roots were incubated in vivo with d-[U-14C]glucose for 2, 5, 10, 15, 30 and 45min. The total incorporation of radioactivity into polysaccharide components in isolated fractions was investigated, and the pattern of incorporation into different polysaccharide components within the rough endoplasmic reticulum, Golgi apparatus and exported material was analysed. 2. The membrane compartments reached a saturation value of radioactivity in polysaccharide components by 30min incubation. Radioactivity in exported polysaccharide continued to increase after that time. The latter was formed and maintained by a steady-state turnover of polysaccharide synthesis and transport from the membrane system. 3. If the only access of the slime polysaccharide to the cell surface is via dictyosome-derived vesicles, the amount of slime components in the Golgi apparatus would have to be displaced every 0.3min in order to maintain the observed rates of increase in slime. This is in contrast with a displacement time of about 2.5min that is necessary for polysaccharide components in the Golgi apparatus to produce the observed increase in cell-wall material. The activity of the membrane system in the production of maize root slime is 8 times as great as that of the membrane system involved in cell-wall synthesis. 4. If the amount of polysaccharide material in the Golgi apparatus is maintained only by inflow of polymeric material from the rough endoplasmic reticulum the total amount of slime components in the rough endoplasmic reticulum would have to be displaced every 7min to maintain a constant amount in the Golgi apparatus. If the endoplasmic reticulum contributed directly to the cell surface in the synthesis of cell-wall material, displacement times necessary to maintain the observed rate of polymer production would be very slow.

Ultrastructure of basidiospore germination in Fomes fomentarius

1978 ◽  
Vol 56 (22) ◽  
pp. 2865-2872 ◽  
Author(s):  
Ichiko Tsuneda ◽  
Lorene L. Kennedy
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Wall ◽  
Germ Tube ◽  
Early Stage ◽  
Dense Layer ◽  
Lipid Bodies ◽  
Fomes Fomentarius ◽  
Additional Cell ◽  
Thin Electron ◽  
Germ Tubes

Germination of basidiospores in Fomes fomentarius (Fries) Kickx is bipolar with germ tubes emerging at both ends. Ungerminated spores are smooth with a thick cell wall consisting of two layers: an outer thin, electron-dense layer and an inner thick, electron-light layer. During the early stage of germination, two additional cell wall layers are formed: a very thin, electron-dense layer and a relatively thick, electron-light layer. Germ tube walls originate from these newly formed, inner layers. Ungerminated spores are uninucleate and contain numerous lipid bodies, ribosomes, and cisternae of endoplasmic reticulum. Germinated spores have distinct mitochondria and an invaginated plasma membrane and are usually devoid of endoplasmic reticulum.

The ultrastructure and cytochemistry of the egg apparatus of Brassica campestris

1989 ◽  
Vol 67 (1) ◽  
pp. 177-190 ◽  
Author(s):  
M. J. Sumner ◽  
L. Van Caeseele
Keyword(s):  
Plasma Membrane ◽  
Cell Walls ◽  
Brassica Campestris ◽  
Positive Response ◽  
Uv Light ◽  
Egg Cell ◽  
Filiform Apparatus ◽  
Egg Apparatus ◽  
Large Numbers ◽  
Acidic Polysaccharides

The egg apparatus of Brassica campestris L. cv. Candle (canola-rapeseed) is composed of an egg and two synergids juxtaposed at the extreme micropylar end of the megagametophyte with the egg cell displaced in a chalazal direction. The cell walls of the synergids and egg are uniformly PAS and PA–TCH–SP-positive, but contained β-linked glucans only in the micropylar region. The number and development of the cytoplasmic organelles suggested that the egg cell is relatively inactive metabolically while the synergid cells are active. The synergids contain large numbers of dictyosomes with PA–TCH–SP-positive vesicles at the maturing face. These vesicles appear to fuse with the plasma membrane in the region of the filiform apparatus. The filiform apparatuses of the synergids are micropylar finger-like projections that extend into the cytoplasm of the synergid. These are PAS and PA–TCH–SP-positive, fluoresce in uv light when stained with Calcofluor, and show a positive response for acidic polysaccharides when stained with alcian blue. After treatment with cellulase, fluorescence was not observed. The incipient degenerate synergid was intensely stained by cationic dyes 24–36 h after anthesis.

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.

The development of the central cell of Brassica campestris prior to fertilization

1990 ◽  
Vol 68 (12) ◽  
pp. 2553-2563 ◽  
Author(s):  
M. J. Sumner ◽  
L. van Caeseele
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Wall ◽  
Brassica Campestris ◽  
Periodic Acid ◽  
Light And Electron Microscopy ◽  
Lateral Wall ◽  
Polar Nucleus ◽  
Central Cell ◽  
Transfer Cell ◽  
Egg Apparatus

The development of the central cell of Brassica campestris cv. Candle (canola-rapeseed) was examined using techniques of light and electron microscopy and cytochemistry. The mature central cell is devoid of the large central vacuole characteristic of the early cellular stage of megagametophyte development. Prior to anthesis, cell wall projections, of the transfer cell type, develop on the lateral wall of the central cell. These central cell wall projections extend from the midregion of the megagametophyte to the egg apparatus and are immediately adjacent to the starch-containing region of the inner and outer integuments. The cell wall projections are periodic acid – thiocarbohydrazide – silver proteinate positive as are the contents of dictyosome vesicles that appear to contribute to their formation. Mitochondria are associated with the wall projections as is a network of central cell endoplasmic reticulum that extends from the wall projections to the egg apparatus. Microtubules are associated with the migrating chalazal polar nucleus. The two polar nuclei partially fuse prior to double fertilization, united by nuclear bridges and endoplasmic reticulum interconnections. Proplastids are a characteristic feature of the immature cellular megagametophyte. By anthesis, the proplastids of the mature central cell develop into chloroplasts with stacked thylakoids and starch deposits. Microbodies are frequently found associated with lipid bodies, and polysomes with the endoplasmic reticulum of the mature central cell. Key words: Brassica, central cell, megagametophyte, ovule, transfer cell.

Embryology of Brassica campestris: the entrance and discharge of the pollen tube in the synergid and the formation of the zygote

1992 ◽  
Vol 70 (8) ◽  
pp. 1577-1590 ◽  
Author(s):  
M. J. Sumner
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Wall ◽  
Plasma Membrane ◽  
Pollen Tube ◽  
Brassica Campestris ◽  
Periodic Acid ◽  
Outer Integument ◽  
Central Cell ◽  
Egg Cell ◽  
Intense Staining

The postanthesis synergids and zygote of Brassica campestris cv. Candle were examined using techniques of light, fluorescence, and electron microscopy. The pollen tube enters the degenerate synergid by way of the filiform apparatus. A degeneration of one of the two synergids occurs after anthesis and is independent of pollination. The first sign of synergid degeneration is a more intense staining of one of the synergids, followed by a loss of organelle membrane integrity. There is a disappearance of the plasma membrane and dictyosome cisternae; however, profiles of degenerate synergid mitochondria, plastids, and dilated endoplasmic reticulum remain along with dictyosome vesicles that contain periodic acid – thiocarbo-hydrazide – silver proteinate positive substances. The zygote, shortly after fertilization, is reduced in size and lacks the large micropylar vacuole characteristic of the mature unfertilized egg cell. Plastids and mitochondria are concentrated around the centrally located nucleus of the zygote, and dictyosomes, active in vesicle production, are located in the lateral and chalazal regions of the cell, adjacent to the cell wall. The lateral cell walls are periodic acid – Schiff's and Calcofluor positive, while the ampulliform chalazal tip of the cell is weakly periodic acid – Schiff s positive and Calcofluor negative. Microtubules, with the long axis perpendicular to the long axis of the zygote, are abundant in the ampulliform chalazal tip of the cell. Following fertilization the central cell becomes highly vacuolate. There is continuity between the zygote – central cell plasma membrane, the central cell vacuole tonoplast, and membranes of the central cell endoplasmic reticulum. Central cell wall projections, of the transfer cell type, are located in the lateral regions of the megagametophyte adjacent to the developing zygote cell and are positioned adjacent to the region of inner and outer integument starch. Key words: Brassica, ultrastructure, synergid, megagametophyte, pollen tube, zygote.

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