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.

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.

Megasporogenesis and megagametogenesis in Pelargonium × hortorum

1973 ◽  
Vol 51 (3) ◽  
pp. 607-612 ◽  
Author(s):  
Annie H. Tsai ◽  
Patricia M. Harney ◽  
R. L. Peterson
Keyword(s):  
Mother Cell ◽  
Megaspore Mother Cell ◽  
Outer Integument ◽  
Embryo Sac ◽  
Mature Embryo ◽  
Polar Nucleus ◽  
Archesporial Cell ◽  
Linear Tetrad ◽  
Polygonum Type ◽  
Cell Functions

The ovary of Pelargonium × hortorum contains five pairs of superposed ovules in five locules. These ovules are bitegmic and crassinucellar and the upper ovule of each pair is campylotropous while the lower one is anatropous. A single archesporial cell functions directly as the megaspore mother cell. Meiotic division of the megaspore mother cell results in the formation of a linear tetrad of megaspores of which the chalazal megaspore is functional. Embryo sac development is of the polygonum type. Rapid degeneration of the three antipodals occurs followed by the fusion of the two polar nuclei. Therefore, the mature embryo sac contains the egg, the two synergids, and the fused polar nucleus. Double fertilization takes place. Ninety-two percent of the fertilized ovules of P. × hortorum cv. ‘Purple Heart’ are found in the upper position.The two integuments are initiated before the differentiation of the archesporial cell. Cells of the outer layer of the outer integument and the inner layer of the inner integument deposit tannins. The nucellus develops through divisions of the parietal cells of the nucellar epidermal cells.

Reproductive development in two species of Darwinia Rudge (Myrtaceae)

1969 ◽  
Vol 17 (2) ◽  
pp. 215 ◽  
Author(s):  
N Prakash
Keyword(s):  
Embryo Sac ◽  
Pollen Grains ◽  
Reproductive Development ◽  
Outer Zone ◽  
Mature Embryo ◽  
Globular Embryo ◽  
Primary Endosperm Nucleus ◽  
Oil Glands ◽  
Polygonum Type ◽  
History Of

In Darwinia the floral parts are differentiated in a "calyx-orolla-gynoeciumandroecium" sequence. In individual buds stages of microsporogenesis markedly precede corresponding stages of megasporogenesis. The anther is tetrasporangiate with all sporangia lying in one plane. The secretory tapetum is one- to three-layered within the same microsporangium and a large number of Ubisch bodies are formed. The anthers dehisce by minute lateral pores and an ingenious mechanism helps disperse the twocelled pollen grains. A basal placenta in the single loculus of the ovary bears four ovules in D. micropetala and two in D. fascicularis. In both species, however, only one ovule is functional after fertilization. The fully grown ovules are anatropous, crassinucellar, and bitegmic; the inner integument forms the micropyle. The parietal tissue is most massive at the completion of megasporogenesis but is progressively destroyed later. The embryo sac follows the Polygonum type of developnlent and when mature is five-nucleate, the three antipodals being ephemeral. Following fertilization, the primary endosperm nucleus divides before the zygote. Subsequent nuclear divisions in the endosperm mother cell are synchronous and lead to a free-nuclear endosperm which becomes secondarily cellular, starting from the micropylar end at the time the globular embryo assumes an elongated shape. Embryogeny is irregular and the mature embryo is straight with a massive radicle and a hypocotyl which terminates in two barely recognizable cotyledons. Sometimes the minute cotyledons are borne on a narrow neck-like extension of the hypocotyl. A suspensor is absent. Both integuments are represented in the seed coat and only the outer layer of the outer and the inner layer of the inner integuments, with their thick-walled tanniniferous cells, remain in the fully grown seed. The ovary wall is demarcated into an outer zone containing oil glands surrounded by cells containing a tannin-like substance and an inner zone of spongy parenchyma. In the fruit this spongy zone breaks down completely but the outer zone is retained. The two species of Darwinia, while closely resembling each other in their embryology, differ significantly from other Myrtaceae. However, no taxonomic conclusions are drawn at this stage, pending enquiry into the life history of other members of the tribe Chamaelaucieae.

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.

Development of the female gametophyte of Minuria cunninghamii (DC). Benth, Ccompositae)

1964 ◽  
Vol 12 (2) ◽  
pp. 152 ◽  
Author(s):  
GL Davis
Keyword(s):  
Comparative Study ◽  
Female Gametophyte ◽  
New South ◽  
Embryo Sac ◽  
Mature Embryo ◽  
Polygonum Type ◽  
South Wales ◽  
Significant Difference ◽  
Female Gametophyte Development ◽  
Two Populations

Minuria cunninghamii is widely distributed throughout the drier parts of Australia, and a comparative study was made of the female gametophyte development in two populations 300 miles apart in western New South Wales. In specimens collected 120 miles south of Menindee, the embryo sac was monosporic in origin and of the Polygonum type, whereas in those from Wanaaring it was usually bisporic and of the Allium type. No significant difference was found in mature embryo sacs from the two localities, although an unusual feature of both was the occurrence of vacuoles in the apices of the synergids.

scholarly journals Floral Biology and Embryo Development in Chestnut (Castanea sativa Mill.)

HortScience ◽  
1995 ◽  
Vol 30 (6) ◽  
pp. 1283-1286 ◽  
Author(s):  
Roberto Botta ◽  
Grazia Vergano ◽  
Giovanni Me ◽  
Rosalina Vallania
Keyword(s):  
Embryo Development ◽  
Apical Meristem ◽  
Embryo Sac ◽  
Castanea Sativa ◽  
Pistillate Flower ◽  
Floral Biology ◽  
Mature Embryo ◽  
Full Bloom ◽  
Mature Ovule ◽  
Castanea Sativa Mill

Floral biology of chestnut, from sporogenesis to mature embryo, is described. Microsporogenesis in flowers of unisexual catkins occurred in the first week of June 1991. Anthesis started in mid-June (≈70 days after budbreak) and lasted 2 weeks. In mid-June, in each pistillate flower, six to eight styles began to emerge, and 4 to 7 days later, they were extended fully (i.e., full bloom). In each flower, 10 to 16 anatropous ovules developed from the ovary axis. The megaspore mother cell had formed by the end of bloom. The mature ovule consisted of two integuments and a long, narrow nucellus with a small embryo sac of the Polygonum type. Zygotes were found 15 to 20 days after pistillate flower full bloom. Embryo development followed the Onagrad type, Trifolium variation. Seeds attained full size in mid-September, and fruit were mature in early November. The embryonal axis averaged 4.5 mm long × 2.1 mm wide. An apical meristem and the radicle were evident at opposite ends of the axis.

An embryological study of Bauera capitata with comments on the systematic position of Bauera

1977 ◽  
Vol 25 (6) ◽  
pp. 615 ◽  
Author(s):  
N Prakash ◽  
EJ McAlister
Keyword(s):  
Outer Integument ◽  
Embryo Sac ◽  
Mature Embryo ◽  
Systematic Position ◽  
Embryological Study ◽  
Anther Wall ◽  
Polygonum Type ◽  
Antipodal Cells

In Bauera capitata Ser. ex DC. the anthers are tetrasporangiate with a three- or four-layered anther wall. The tapetum is glandular and its cells remain uninucleate. Tannin accumulates in the epidermis and the endothecium, and many connective cells in addition contain druses. Simultaneous cytokinesis leads to tetrahedral and isobilateral tetrads of microspores. The pollen is shed when two-nucleate and is gorged with starch. Degeneration of contents of one or more sporangia is frequent. The ovules are anatropous, crassinucellar and bitegmic. Twin microspore tetrads and twin embryo sacs are common but only one embryo sac reaches maturity. The development of the embryo sac follows the monosporic, Polygonum type. Starch accumulates in the mature embryo sac and remains until the initiation of endosperm. The antipodal cells persist until fertilization and rarely multiply. The seeds are frequently sterile but contain a well-formed outer integument. The healthy seeds have in addition a five- or six-layered inner integument, a nuclear type of endosperm and an embryo. The embryological evidence points to a closer affinity of Bauera Banks ex Andr. to the Cunoniaceae than to the Saxifragaceae.

Life history of Tetragonia tetragonioides (Pall.) O. Kuntze

1967 ◽  
Vol 15 (3) ◽  
pp. 413 ◽  
Author(s):  
N Prakash
Keyword(s):  
Cell Formation ◽  
Embryo Sac ◽  
Pollen Grains ◽  
Mature Embryo ◽  
Polygonum Type ◽  
Innermost Layer ◽  
Glandular Cells ◽  
History Of ◽  
Mother Cells ◽  
Tetragonia Tetragonioides

Accessory flowers arise from the surface of inferior ovaries in 25 % of the flowers of Tetragonia, suggesting an axial nature of the inferior ovary. The ovary is six to nine-loculed, with a single pendulous ovule in each locule. The anther is tetrasporangiate. The innermost layer of the four-layered wall constitutes a secretory tapetum with multinucleate cells. Cytokinesis in microspore mother cells is simultaneous and results in tetrahedral or decussate tetrads. The pollen grains are shed at the three-celled stage. The ovules are bitegminal, crassinucellar, and anacampylotropus. The funiculus is long and bears an obturator of glandular cells. The inner integument forms the micropyle and forms a collar at the distal end. A nucellar cap is present. The nucellus persists in the seed as perisperm. The archesporium is multicelled, although only a single cell develops. Following meiosis the megaspore mother cell gives rise to a linear row of three or four megaspores, of which only the chalaza1 functions to form an embryo sac of the Polygonum type. The endosperm is of the Nuclear type and eventually assumes a horseshoe shape. Cell formation is restricted to the micropylar region, the rest remaining nuclear until consumed by the embryo. The embryogeny is of the Solanad type, and the mature embryo is curved and dicotyledonous.

scholarly journals Mixed segregation of chromosomes during single-division meiosis of Saccharomyces cerevisiae.

Genetics ◽  
1990 ◽  
Vol 125 (3) ◽  
pp. 475-485
Author(s):  
G Sharon ◽  
G Simchen
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Meiotic Division ◽  
Chromosome Pair ◽  
Yeast Cells ◽  
Cell Divisions ◽  
Dyad Analysis ◽  
Normal Meiosis ◽  
Segregation Of Chromosomes

Abstract Normal meiosis consists of two consecutive cell divisions in which all the chromosomes behave in a concerted manner. Yeast cells homozygous for the mutation cdc5, however, may be directed through a single meiotic division of a novel type. Dyad analysis of a cdc5/cdc5 strain with centromere-linked markers on four different chromosomes has shown that, in these meioses, some chromosomes within a given cell segregate reductionally whereas others segregate equationally. The choice between the two types of segregation in these meioses is made individually by each chromosome pair. Different chromosome pairs exhibit different segregation tendencies. Similar results were obtained for cells homozygous for cdc14.

scholarly journals Apical Constriction Reversal upon Mitotic Entry Underlies Different Morphogenetic Outcomes of Cell Division

2019 ◽  
Author(s):  
Clint S. Ko ◽  
Prateek Kalakuntla ◽  
Adam C. Martin
Keyword(s):  
Cell Division ◽  
Cell Shape ◽  
Mitotic Cell ◽  
Signal Interference ◽  
Apical Constriction ◽  
Mitotic Entry ◽  
Cell Divisions ◽  
Cell Shape Changes ◽  
Shape Changes ◽  
Mitotic Cells

AbstractDuring development, coordinated cell shape changes and cell divisions sculpt tissues. While these individual cell behaviors have been extensively studied, how cell shape changes and cell divisions that occur concurrently in epithelia influence tissue shape is less understood. We addressed this question in two contexts of the early Drosophila embryo: premature cell division during mesoderm invagination, and native ectodermal cell divisions with ectopic activation of apical contractility. Using quantitative live-cell imaging, we demonstrated that mitotic entry reverses apical contractility by interfering with medioapical RhoA signaling. While premature mitotic entry inhibits mesoderm invagination, which relies on apical constriction, mitotic entry in an artificially contractile ectoderm induced ectopic tissue invaginations. Ectopic invaginations resulted from medioapical myosin loss in neighboring mitotic cells. This myosin loss enabled non-mitotic cells to apically constrict through mitotic cell stretching. Thus, the spatial pattern of mitotic entry can differentially regulate tissue shape through signal interference between apical contractility and mitosis.

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