scholarly journals Female gametophyte development and embryogenesis in Taxus baccata L.

2014 ◽  
Vol 65 (1-2) ◽  
pp. 135-139 ◽  
Author(s):  
Vladimir B. Brukhin ◽  
Peter V. Bozhkov
Keyword(s):  
Early Embryo ◽  
Temperate Climate ◽  
Taxus Baccata ◽  
Linear Tetrad ◽  
Canal Cell ◽  
Nuclear Stage ◽  
Female Gametophyte Development ◽  
Ventral Canal ◽  
Embryonic Region ◽  
Suspensor Cells

Crassinucellate ovules are initiated in <em>Taxus</em>, directly from the shoot apex. The rudimentary pollen chamber is formed in the nucellus. A linear tetrad of megaspores with a functional chalazal megaspore is formed. A free-nuclear stage is charac-teristic at the beginning of megagametophyte development. Archegonia without ventral canal cell are solitary or in complexes. The embryo has a very long suspensor even after maturation. Two types of polyembryony have been revealed: i) embryogenic redifferentiation of suspensor cells and ii) cleavage of embryonic region in the early embryo. In the northern temperate climate of St. Petersburg one month delay in development of reproductive structures has been noted.

Sexual reproduction of mountain hemlock (Tsuga mertensiana)

1975 ◽  
Vol 53 (17) ◽  
pp. 1811-1826 ◽  
Author(s):  
John N. Owens ◽  
Marje Molder
Keyword(s):  
Cell Walls ◽  
Pollen Tubes ◽  
Linear Tetrad ◽  
Form Complex ◽  
Male Gametes ◽  
Canal Cell ◽  
Micropylar Canal ◽  
Tsuga Mertensiana ◽  
Mother Cells ◽  
Ventral Canal

Meiosis of pollen mother cells begins in October of the year in which cones are initiated. They reach pachytene then become dormant until the next March. Meiosis is complete and the winged pollen mature by mid-June. Meiosis of the megaspore mother cell occurs in May, forming a linear tetrad of megaspores. The female gametophyte undergoes free nuclear division at pollination in mid-June. No pollination drop is present; rather, the pollen adheres to the sticky, splayed edge of the micropyle, where it germinates and pollen tubes grow toward the nucellus. The nucellus elongates into the micropylar canal, forming a nucellar beak, which makes contact with the pollen tubes. Several pollen tubes penetrate the nucellus.At the time of fertilization early in August, each ovule contains two to four aichegonia each having two to four neck cells in one tier. Pollen tubes penetrate the neck cells and two male gametes are formed. The ventral canal cell breaks down and fusion occurs in the center of the archegonium. Four free nuclei form and migrate to the base of the archegonium. cell walls form, and a 16-celled proembryo develops. Both simple and cleavage polyembryony occur. Rosette cells divide but do not form complex embryos. The embryo and seed are mature in October and the cones dry and open during October and November. Mature cones averaged 70 seeds, of which 46% were filled.Reproduction in mountain hemlock (Tsuga mertensiana (Bong.) Carr.) is similar to that in other species of Tsuga except for the presence of winged pollen. Any attempt to place the species in the genus Picea or place it as a hybrid midway between Picea and Tsuga is unfounded based on all of the more-conservative reproductive and embryological characteristics.

Elektronenmikroskopische Untersuchungen über die Eizellbildung und Eizellreifung des Lebermooses Sphaerocarpus donnellii Aust.

1965 ◽  
Vol 20 (8) ◽  
pp. 795-801 ◽  
Author(s):  
Lothar Diers
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Phase Contrast ◽  
Lipid Droplets ◽  
Unit Membrane ◽  
Light Phase ◽  
Lamellar System ◽  
Small Bodies ◽  
Canal Cell ◽  
Ventral Canal

The formation and maturation of the egg of the liverwort, Sphaerocarpus donnellii, was investigated by light, phase contrast and particularly by electron microscopy. The division of the central cell into the egg and the ventral canal cell, and the maturation of the egg, is completed within four days. All stages of this formation and maturation were examined under the electron microscope after fixation in KMnO4 or OsO4. — In the maturing egg there always occur the endoplasmic reticulum, well recognisable plastids with a poorly developed lamellar system, numerous mitochondria and dictyosomes, a rising number of lipid droplets, unknown small bodies limited by a unit membrane, and numerous ribosomes. During maturation the nucleus considerably enlarges and forms evaginations into the cytoplasm. Starch is increasingly deposited in the plastids. A degeneration of plastids has not been found.

Embryogeny of Phaseolus coccineus: the ultrastructure and development of the suspensor

1979 ◽  
Vol 57 (2) ◽  
pp. 120-136 ◽  
Author(s):  
Edward C. Yeung ◽  
Mary E. Clutter
Keyword(s):  
Smooth Endoplasmic Reticulum ◽  
Early Embryo ◽  
Wall Thickening ◽  
Ontogenetic Changes ◽  
Early Embryo Development ◽  
Wall Ingrowths ◽  
Globular Stage ◽  
Cotyledon Stage ◽  
Suspensor Cells ◽  
Cellular Organelles

Structural specializations occur in the suspensor at the proembryo stage with the formation of wall ingrowths. Soon after the appearance of the ingrowths, mitochondria, plastids, polysomes, and smooth endoplasmic reticulum greatly increase in their abundance within the suspensor cells. By the late globular stage, wall ingrowths are extremely well developed and the cells within the suspensor are packed with cellular organelles. The nucleus of the suspensor cell at the heart stage also takes on an active appearance. The nucleus becomes highly lobed in shape and micronucleoli can also be found. There is little change in the overall ultrastructural pattern of the cell till the cotyledon stage. At this stage, wall thickening occurs in all suspensor cells and the outlines of most of the ingrowths become less obvious. The mitochondria, plastids, and polysomes become less abundant and a change in the configuration of the smooth endospermic reticulum is also observed. The ontogenetic changes of the cellular organelles suggest that the suspensor plays a role during early embryo development, i.e., globular to early cotyledon stage.

Megagametogenesis, fertilization, and embryo development in Larixdecidua

1986 ◽  
Vol 16 (6) ◽  
pp. 1301-1309 ◽  
Author(s):  
Grzegorz Kosiński
Keyword(s):  
Cell Wall ◽  
Sexual Reproduction ◽  
Mother Cell ◽  
Megaspore Mother Cell ◽  
Female Gametophyte ◽  
Nuclear Stage ◽  
Empty Seed ◽  
Development Failure ◽  
Major Factors ◽  
Female Gametophyte Development

The phenology of sexual reproduction in Larixdecidua Mill, varies from year to year, and some intra- and inter-clonal differences were also found. Megaspore mother cell meiosis occurred at the time of pollination, during the second half of April, resulting in three or four megaspores. The free nuclear stage and cell wall and archegonia formation were completed in late May and the first half of June. An average of four archegonia was observed in each ovule, but the number ranged from two to six. Fertilization occurred during the first 20 days of June, about 7 weeks after pollination. A four-tiered, 16-celled proembryo formed. Meristematic regions formed in the embryo from the end of June to mid-July. Fully developed embryos were observed in mid-August. Simple polyembryony and delayed cleavage polyembryony were observed. Lack of pollination, disturbances during megasporogenesis and female gametophyte development, failure of fertilization, and embryo degeneration are the major factors resulting in empty seed.

Anther and Ovule Development in Tasmannia (Winteraceae)

1992 ◽  
Vol 40 (6) ◽  
pp. 877 ◽  
Author(s):  
N Prakash ◽  
AL Lim ◽  
FB Sampson
Keyword(s):  
Mother Cell ◽  
Female Gametophyte ◽  
Cell Plate ◽  
Basic Type ◽  
Ovule Development ◽  
Linear Tetrad ◽  
Polygonum Type ◽  
Secretory Type ◽  
Mother Cells ◽  
Female Gametophyte Development

Three species of Tasmannia R.Br. ex DC., T. glaucifolia, T. insipida and T. stipitata are studied. The anther is tetrasporangiate and its waU development conforms to the Basic type. The tapetum follows the secretory type of development. Cytokinesis in the microspore mother cells is simultaneous but an evanescent cell plate is present at telophase I and anaphase I1 during meiosis. Pollen tetrads are permanent and tetrahedral. The mature pollen is anaulcerate, reticulate and 2-celled. The ovule. is anatropous, bitegmic and crassinucellate. The micropyle in T. stipitata and T. Glaucifolia is formed by the inner integument only whereas in T. insipida it is formed by both the integuments and is zigzag in outline. Meiosis in the single megaspore mother cell produces a linear or T-shaped megaspore tetrad in T. stipitata and T. glaucifolia but only a linear tetrad in T. insipida. Female gametophyte development is of the monosporic Polygonum type. Fertilisation is porogamous; triple fusion and syngamy occur simultaneously.

On the cytological features of fertilisation and related phenomena in Pinus silvestris , L

1898 ◽  
Vol 63 (389-400) ◽  
pp. 400-401
Keyword(s):  
Pinus Silvestris ◽  
Wall Formation ◽  
Canal Cell ◽  
Cytological Features ◽  
Ventral Canal ◽  
Complete Account

This paper gives a fairly complete account of the minute cytological details of the act of fertilisation and of the processes surrounding from the formation of the ventral canal cell up to the period of cl wall formation at the base of the egg. As the oosphere nucleus, after separation of the nucleus of the ventral canal cell, moves rapidly back towards the centre of the e it increases greatly in size, as described by Strasburger. Ts increase in size is shown to be due to the appearance in the nucleus of a peculiar metaplasmic substance, which fills up the nucleus, and owing to its attraction for stains, ultimately obscures the chromatin.

Laser scanning confocal microscopic analysis of cytoskeletal and nuclear reorganization in live Drosophila embryos

1993 ◽  
Vol 51 ◽  
pp. 174-175
Author(s):  
William Theurkauf
Keyword(s):  
Laser Scanning ◽  
Microscopic Analysis ◽  
Large Cell ◽  
Early Embryo ◽  
Drosophila Embryo ◽  
Cortical Actin ◽  
Nuclear Reorganization ◽  
Cytoskeletal Elements ◽  
Microtubule Structure ◽  
Drosophila Embryos

Cell division in eucaryotes depends on coordinated changes in nuclear and cytoskeletal components. In Drosophila melanogaster embryos, the first 13 nuclear divisions occur without cytokinesis. During the final four divisions, nuclei divide in a uniform monolayer at the surface of the embryo. These surface divisions are accompanied by dramatic changes in cortical actin and microtubule structure (Karr and Alberts, 1986), and inhibitor studies indicate that these changes are essential to orderly mitosis (Zalokar and Erk, 1976). Because the early embryo is syncytial, fluorescent probes introduced by microinjection are incorporated in structures associated with all of the nuclei in the blastoderm. In addition, the nuclei divide synchronously every 10 to 20 min. These characteristics make the syncytial blastoderm embryo an excellent system for the analysis of mitotic reorganization of both nuclear and cytoskeletal elements. However, the Drosophila embryo is a large cell, and resolution of cytoskeletal filaments and nuclear structure is hampered by out-of focus signal.

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