Embryology of Epidendrum ibaguense. I. Ovule development

1989 ◽  
Vol 67 (8) ◽  
pp. 2219-2226 ◽  
Author(s):  
Edward C. Yeung ◽  
Sandra K. Law
Keyword(s):  
Cell Division ◽  
Mitotic Division ◽  
Archesporial Cell ◽  
Ovule Development ◽  
Meiotic Cell ◽  
Nucellar Cell ◽  
Polygonum Type ◽  
Unequal Size ◽  
Branching System ◽  
Functional Megaspore

The orchids are unique among angiosperms in that ovule development is initiated after successful pollination. The monandrous orchid Epidendrum ibaguense has three placental ridges at anthesis. After pollination, mitotic activities result in the formation of a dichotomously branching system of outgrowths. The tip of each branch consists of five to six nucellar cells covered by the epidermis. A subterminal nucellar cell differentiates into the archesporial cell approximately 12 days after pollination. By day 18, it differentiates directly into a megasporocyte. The first meiotic cell division produces a dyad in which the micropylar cell begins prompt degeneration. The second meiotic cell division results in the formation of two megaspores of unequal size. The larger cell at the chalazal end will become the functional megaspore. Callose is present in the walls of the megasporocyte, the micropylar dyad cell, and the megaspore destined to degenerate. The development of the megagametophyte conforms to the Polygonum type. One of the chalazal nuclei delays its final mitotic division until fertilization, making it appear that only two antipodals are present. The mature ovules are bitegmic and have an anatropous orientation.

scholarly journals The formation of integuments, megasporogenesis and megagametogenesis in Dendrobium catenatum, with special discussions on embryo sac types and section techniques

2021 ◽  
Vol 45 (2) ◽  
pp. 177-184
Author(s):  
Yong Chen ◽  
Xiaofeng Wang ◽  
Liang Li ◽  
Chengqi Ao
Keyword(s):  
Meiotic Division ◽  
Embryo Sac ◽  
Mitotic Cell ◽  
Mature Embryo ◽  
Archesporial Cell ◽  
Nucellar Cell ◽  
Polygonum Type ◽  
Cell Divisions ◽  
Mature Ovule ◽  
Branching System

The formation of integuments, megasporogenesis and megagametogenesis in Dendrobium catenatum, an economically important orchid, are observed. After pollination, mitotic cell divisions of the placental epidermis result in the formation of a branching system of outgrowths. The tip of each branch consists of an archesporial cell derived from the differentiation of the terminal subepidermal nucellar cell. It differentiates directly into a megasporocyte. The first division of the meiosis of the megasporocyte produces a dyad approximately equal in size, in which the micropylar cell promptly degenerates. The second meiotic division of the remaining dyad cell results in the formation of two megaspores of unequal size. The larger chalazal cell becomes functional and eventually develops into a mature megagametophyte. The development of the megagametophyte conforms to the Monosporic Polygonum type. The final arrangement of the mature embryo sac conforms to a sevencelled/ eight-nucleate structure. The mature ovule is bitegmic, tenuinucellate and has an anatropous orientation. In the present study, we also discuss the differences between three main types of embryo sac development and the improvement of section techniques.

Embryo sac and early ovule development in Oryzopsis miliacea and Stipa tortilis

1970 ◽  
Vol 48 (1) ◽  
pp. 27-41 ◽  
Author(s):  
Jack Maze ◽  
Lesly R. Bohm ◽  
Lyle E. Mehlenbacher Jr.
Keyword(s):  
Cell Division ◽  
Pollen Tube ◽  
Nuclear Division ◽  
Outer Integument ◽  
Embryo Sac ◽  
Ovule Development ◽  
Polygonum Type ◽  
Embryo Sac Development

The ovules of Stipa tortilis and Oryzopsis miliacea are hemianatropous, bitegmetic, and pseudocrassinucellate (sensu Davis 1966). The hemianatropous shape of the ovule is the result of characteristic patterns of cell division and enlargement in the chalazal area and areas alongside the embryo sac. Embryo sac development in both is Polygonum-type and both have proliferating antipodals. Endosperm is nuclear, although in O. miliacea it is atypical in that nuclear division is synchronous within one portion of the embryo sac, e.g. micropylar, but not synchronous between different portions of the embryo sac, e.g., micropylar and chalazal. Differences in ovule initiation, persistence of the outer integument, fate of the inner integument, nature of the nucellus, shape of the embryo sac, nature of the synergids, cytoplasm of the egg, polar nuclei, and endosperm exist between these two taxa. Both synergids of O. miliacea undergo changes before fertilization and one degenerates before fertilization. The pollen tube enters the embryo sac at the base of the persistent synergid. There is presently insufficient embryological data to permit meaningful speculation on relationships between Stipa and Oryzopsis. Embryologically, Stipa and Oryzopsis are festucoid grasses, as much other evidence indicates. Embryo sac development in the Gramineae is more similar to that of the Restionaceae than to that of the Cyperaceae. This is in contradiction to recent speculations on the relationships of the Gramineae.

Ultrastructure of primary spermatocyte in fish (Tilapia: Oreochromis niloticus): The synaptonemal complex

1986 ◽  
Vol 44 ◽  
pp. 288-289
Author(s):  
T. Guha ◽  
A. Q. Siddiqui ◽  
P. F. Prentis
Keyword(s):  
Fine Structure ◽  
Electron Microscope ◽  
Synaptonemal Complex ◽  
Oreochromis Niloticus ◽  
Short Communication ◽  
Primary Spermatocyte ◽  
Mitotic Division ◽  
Meiotic Cell ◽  
Electron Microscope Level ◽  
Homologous Chromosomes

The Primary Spermatocytes represent a stage in spermatogenesis when the first meiotic cell division occurs. They are derived from Spermatogonium or Stem cell through mitotic division. At the zygotene phase of meiotic prophase the Synaptonemal complex appears in these cells in the space between the paired homologous chromosomes. Spermatogenesis and sperm structure in fish have been studied at the electron microscope level in a few species? However, no work has yet been reported on ultrastructure of tilapia, O. niloticus, spermatozoa and spermatogenetic process. In this short communication we are reporting the Ultrastructure of Primary Spermatocytes in tilapia, O. niloticus, and the fine structure of synaptonemal complexes seen in the spermatocyte nuclei.

Embryological studies in the compositae, I. Sporogenesis, Gametogenesis, and Embryogeny in Cotula australis (Less.) Hook. F

1962 ◽  
Vol 10 (1) ◽  
pp. 1 ◽  
Author(s):  
GL Davis
Keyword(s):  
Mother Cell ◽  
Megaspore Mother Cell ◽  
Embryo Sac ◽  
Subsequent Development ◽  
Pollen Grains ◽  
Archesporial Cell ◽  
Polygonum Type ◽  
Wall Formation ◽  
Chalazal Megaspore

Cotula australis has a discoid heterogamous capitulum in which the outermost three whorls of florets are female and naked. The bisexual disk florets are fully fertile and have a four-lobed corolla with four shortly epipetalous stamens. The anthers contain only two microsporangia. Wall formation and microsporogenesis are described and the pollen grains are shed at the three-celled condition. The ovule is teguinucellate and the hypodermal archesporial cell develops directly as the megaspore mother cell. Megasporogenesis is normal and the monosporio embryo sac develops from the chalazal megaspore. Breakdown of the nucellar epidermis takes place when the embryo sac is binucleate and its subsequent development follows the Polygonum type. The synergids extend deeply into the micropyle and one persists until late in embryogeny as a haustorium. The development of the embryo is of the Asterad type, and the endosperm is cellular. C. coronopifolia agrees with C. australis in the presence of only two microsporangia in each anther and the development of a synergid haustorium.

scholarly journals Polarized Myosin Produces Unequal-Size Daughters During Asymmetric Cell Division

Science ◽  
2010 ◽  
Vol 330 (6004) ◽  
pp. 677-680 ◽  
Author(s):  
Guangshuo Ou ◽  
Nico Stuurman ◽  
Michael D’Ambrosio ◽  
Ronald D. Vale
Keyword(s):  
Cell Division ◽  
Asymmetric Cell Division ◽  
Unequal Size

Monensin blocks the first meiotic cell division of the Xenopus oocyte: Effect at the nuclear membrane level

1984 ◽  
Vol 9 (3) ◽  
pp. 339-349 ◽  
Author(s):  
J. Marot ◽  
J. Tso ◽  
D. Huchon ◽  
O. Mulner ◽  
R. Ozon
Keyword(s):  
Cell Division ◽  
Nuclear Membrane ◽  
Xenopus Oocyte ◽  
Meiotic Cell ◽  
Membrane Level

Morphogenesis in hydra

Development ◽  
1970 ◽  
Vol 24 (1) ◽  
pp. 21-32
Author(s):  
Sondra C. Corff ◽  
Allison L. Burnett
Keyword(s):  
Nervous System ◽  
Cell Division ◽  
Hydrostatic Pressure ◽  
Low Temperature ◽  
Low Temperatures ◽  
Mitotic Division ◽  
Basal Disc ◽  
Dividing Cells ◽  
Short Time ◽  
Disc Formation

When Hydra oligactis is excised below the tentacles and incubated for a short time in concentrations of colchicine that inhibit spindle formation in dividing cells, a peduncle and basal disc subsequently form at the cut distal end, where hypostome and tentacles normally form (Corff & Burnett, 1969). Since recent reports suggest a similarity in the action of colchicine and low temperature, in this study the effects of low temperatures on regenerating hydra were investigated. High hydrostatic pressure and low temperature have been shown to act synergistically with colchicine to inhibit the first mitotic division in sea urchin eggs (Marsland, 1968). Colchicine and cooling have also been shown to cause disintegration of the microtubule system in Actinosphaerium (Tilney, 1965). We have previously discussed peduncle and basal disc formation at the distal end in terms of colchicine inhibition of cell division and the possible action of colchicine on the nervous system (Corff & Burnett, 1969).

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