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.

scholarly journals A CLEM approach to access to the ultrastructure at the graft interface in Arabidopsis thaliana

2021 ◽  
Author(s):  
Clément Chambaud ◽  
Sarah Jane Cookson ◽  
Nathalie Ollat ◽  
Emmanuelle M. F. Bayer ◽  
Lysiane Brocard
Keyword(s):  
Electron Microscopy ◽  
Arabidopsis Thaliana ◽  
Endoplasmic Reticulum ◽  
Cell Wall ◽  
Light And Electron Microscopy ◽  
Three Dimensional ◽  
Cellular Events ◽  
Membrane Tethering ◽  
Secondary Plasmodesmata ◽  
Graft Interface

Despite recent progress in our understanding of the graft union formation, we still know little about the cellular events underlying the grafting process. This is partially due to the difficulty of reliably targeting the graft interface in electron microscopy to study its ultrastructure and three-dimensional architecture. To overcome this technological bottleneck, we developed a correlative light electron microscopy approach (CLEM) to study the graft interface with high ultrastructural resolution. Grafting hypocotyls of Arabidopsis thaliana lines expressing YFP or mRFP in the endoplasmic reticulum allowed the efficient targeting of the grafting interface for under light and electron microscopy. To explore the potential of our method to study sub-cellular events at the graft interface, we focused on the formation of secondary plasmodesmata (PD) between the grafted partners. We showed that 4 classes of PD were formed at the interface and that PD introgression into the call wall was initiated equally by both partners. Moreover, the success of PD formation appeared not systematic with a third of PD not spanning the cell wall entirely. Characterizing the ultrastructural characteristics of these failed PD gives us insights into the process of secondary PD biogenesis. We showed that the thinning of the cell wall and the endoplasmic reticulum-plasma membrane tethering seem to be required for the establishment of symplastic connections between the scion and the rootstock. The resolution reached in this work shows that our CLEM method offer a new scale to the study for biological processes requiring the combination of light and electron microscopy.

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.

scholarly journals THE FINE STRUCTURE OF DIFFERENTIATING XYLEM ELEMENTS

1965 ◽  
Vol 24 (3) ◽  
pp. 415-431 ◽  
Author(s):  
James Cronshaw ◽  
G. Benjamin Bouck
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Wall ◽  
Fine Structure ◽  
Secondary Wall ◽  
Osmium Tetroxide ◽  
Light And Electron Microscopy ◽  
Wall Thickening ◽  
Direction Parallel ◽  
Secondary Wall Thickening ◽  
Xylem Elements

Differentiating xylem elements of Avena coleoptiles have been examined by light and electron microscopy. Fixation in 2 per cent phosphate-buffered osmium tetroxide and in 6 per cent glutaraldehyde, followed by 2 per cent osmium tetroxide, revealed details of the cell wall and cytoplasmic fine structure. The localized secondary wall thickening identified the xylem elements and indicated their state of differentiation. These differentiating xylem elements have dense cytoplasmic contents in which the dictyosomes and elements of rough endoplasmic reticulum are especially numerous. Vesicles are associated with the dictyosomes and are found throughout the cytoplasm. In many cases, these vesicles have electron-opaque contents. "Microtubules" are abundant in the peripheral cytoplasm and are always associated with the secondary wall thickenings. These microtubules are oriented in a direction parallel to the microfibrillar direction of the thickenings. Other tubules are frequently found between the cell wall and the plasma membrane. Our results support the view that the morphological association of the "microtubules" with developing cell wall thickenings may have a functional significance, especially with respect to the orientation of the microfibrils. Dictyosomes and endoplasmic reticulum may have a function in some way connected with the synthetic mechanism of cell wall deposition.

scholarly journals The haustorial synergids of Cortaderia (Gramineae) at maturity

2014 ◽  
Vol 50 (1-2) ◽  
pp. 151-160 ◽  
Author(s):  
Melva N. Philipson
Keyword(s):  
Cell Wall ◽  
Plasma Membrane ◽  
Pollen Tube ◽  
Pollen Tube Growth ◽  
Central Cell ◽  
Transfer Cell ◽  
Tube Growth ◽  
Transport Activity ◽  
Cell Cytoplasm ◽  
Cortaderia Selloana

The ultrastructure of synergids which extend through the micropyle as haustoria and lie against 'the ovary wall are described in <em>Cortaderia selloana</em> and its F<sub>l</sub> hybrid with <em>C. araucana</em>. These haustoria bear typical transfer cell wall invaginations closely associated with the plasma membrane and with mitochondria. Their function seems to be one involved in the absorption and conduction of nutrients to the synergids which are atypical in their highly vacuolate structure, degenerate nuclei and few organelles. The synergids appear to act as repositories of nutrients which are, readily accessible to the central cell by virtue of deep intrusions made into them by the central cell cytoplasm. Enzymatic secretion could also be a function of the distal end of the haustorial synergids, both in facilitating tissue peneration during its outward growth and in directing pollen tube growth. At anfhesis, the haustorium - synergid complex appears to be past its peak of absorption and transport activity, and to be involved in a seeretory or degenerative phase.

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.

scholarly journals SPERMIOGENESIS IN CANCER CRABS

1969 ◽  
Vol 43 (3) ◽  
pp. 575-603 ◽  
Author(s):  
Susan G. Langreth
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Nucleic Acid ◽  
Sperm Cell ◽  
Periodic Acid ◽  
Light And Electron Microscopy ◽  
Mature Sperm ◽  
Periodic Acid Schiff ◽  
The Core ◽  
Inner Region

Spermiogenesis in Cancer crabs was studied by light and electron microscopy. The sperm are aflagellate, and when mature consist primarily of a spherical acrosome surrounded by the nucleus with its short radiating arms. The acrosome forms by a coalescence of periodic acid-Schiff-positive (PAS-positive) vesicles. During spermiogenesis one edge of the acrosomal vesicle invaginates to form a PAS-negative central core. The inner region of the acrosome bounding the core contains basic proteins which are not complexed to nucleic acid. The formation of an elaborate lattice-like complex of fused membranes, principally from membranes of the endoplasmic reticulum, is described. These membranes are later taken into the nucleus and subsequently degenerate. In late spermatids, when most of the cytoplasm is sloughed, the nuclear envelope and the cell membrane apparently fuse to become the limiting boundary over most of the sperm cell. In the mature sperm the chromatin of the nucleus and arms, which is Feulgen-positive, contains no detectable protein. The chromatin filaments appear clumped, branched, and anastomosed; morphologically, they resemble the DNA of bacterial nuclei. Mitochondria are absent or degenerate in mature sperm of Cancer crabs, but the centrioles persist in the nucleoplasm at the base of the acrosome.

Ligule development and fine structure in two heterophyllous species of Selaginella

1975 ◽  
Vol 53 (2) ◽  
pp. 127-143 ◽  
Author(s):  
Harry T. Horner Jr. ◽  
Carolyn K. Beltz ◽  
Richard Jagels ◽  
R. E. Boudreau
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Fine Structure ◽  
Light And Electron Microscopy ◽  
Early Ontogeny ◽  
Transfer Cell ◽  
Active Structure ◽  
Golgi Bodies ◽  
Sheath Cells

Ligules of Selaginella pilifera and S. uncinata were studied by light and electron microscopy. These ligules can be anatomically divided into tip, neck, and basal regions. The upper part of the ligule base is composed of very dense polygonal cells containing many ribosomes, endoplasmic reticulum (ER), and Golgi bodies. In S. pilifera, callose-like walls are secreted around these cells. The lower part of the base consists of wedge-shaped glossopodial cells and the adjacent two layers of sheath cells. Transfer-cell-like walls separate the glossopodium and upper sheath layer, whereas walls containing prominent plasmodesmata separate the two sheath layers. A continuous cuticle covers the entire ligule. During early ontogeny, all ligule cells are highly RNA positive, whereas later only the polygonal base cells stain densely. The anatomy and development of the ligule suggest that it is an active structure. The results of this study are compared with previous studies, especially in relation to ligular function.

Ultrastructure of the Parotid Gland of the Nine-Banded Armadillo

1977 ◽  
Vol 35 ◽  
pp. 640-641
Author(s):  
J. R. Ruby
Keyword(s):  
Endoplasmic Reticulum ◽  
Parotid Gland ◽  
Periodic Acid ◽  
Acinar Cells ◽  
Duct System ◽  
Parotid Glands ◽  
Dasypus Novemcinctus ◽  
Anterior Portion ◽  
Periodic Acid Schiff ◽  
Thin Sections

Parotid glands were obtained from five adult (four male and one female) armadillos (Dasypus novemcinctus) which were perfusion-fixed. The glands were located in a position similar to that of most mammals. They extended interiorly to the anterior portion of the submandibular gland.In the light microscope, it was noted that the acini were relatively small and stained strongly positive with the periodic acid-Schiff (PAS) and alcian blue techniques, confirming the earlier results of Shackleford (1). Based on these qualities and other structural criteria, these cells have been classified as seromucous (2). The duct system was well developed. There were numerous intercalated ducts and intralobular striated ducts. The striated duct cells contained large amounts of PAS-positive substance.Thin sections revealed that the acinar cells were pyramidal in shape and contained a basally placed, slightly flattened nucleus (Fig. 1). The rough endoplasmic reticulum was also at the base of the cell.

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