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

1973 ◽  
Vol 51 (5) ◽  
pp. 879-890 ◽  
Author(s):  
William Newcomb
Keyword(s):  
Helianthus Annuus ◽  
Mitotic Spindle ◽  
Embryo Sac ◽  
Endosperm Development ◽  
Primary Endosperm Nucleus ◽  
Single Row ◽  
Wall Formation ◽  
Globular Stage ◽  
Spindle Apparatus ◽  
Single Fertilization

The degeneration of one synergid denotes the initiation of embryo and endosperm development in the embryo sac of sunflower Helianthus annuus L. The other synergid, the persistent synergid, is present until the late globular stage of embryogenesis. The primary endosperm nucleus divides before the zygote nucleus forming a coenocytic nuclear endosperm. When about eight endosperm nuclei are present during the early globular stage of embryogenesis, endosperm wall formation starts at the micropylar end of the embryo sac. The walls continue to grow toward the chalazal end of the embryo sac apparently as a result of the activity of Golgi located at the tips of the growing walls. Most endosperm wall formation is not associated with a mitotic spindle apparatus in sunflower. The suspensor of the embryo consists of a large basal cell during the proembryo stages, a single row of cells during the early globular stages, and at the late globular stage a double tier of cells near the radicle end of the embryo and a single row at the micropylar end of the embryo sac. Occasionally embryo development occurs in the absence of endosperm when only single fertilization has taken place. The development and nutritional implications of post-fertilization events in the sunflower embryo sac are discussed.

LIGHT AND ELECTRON MICROSCOPIC EXAMINATION OF THE EMBRYO AND ENDOSPERM DEVELOPMENT IN THE NATURAL TETRAPLOID TRIFOLIUM PRATENSE L.

1996 ◽  
Vol 44 (4) ◽  
pp. 273-288 ◽  
Author(s):  
Goönül Algan ◽  
H.Nurhan Bakar
Keyword(s):  
Trifolium Pratense ◽  
Embryo Sac ◽  
Central Nucleus ◽  
Maturity Stage ◽  
Lipid Bodies ◽  
Globular Embryo ◽  
Primary Endosperm Nucleus ◽  
Seed Formation ◽  
Globular Stage ◽  
Embryo Cells

The ultrastructure of the embryo cells in ovules, from fertilization to the embryo maturity stage in the natural tetraploid Trifolium pratense L. that has a very low rate of seed formation, was examined. Following fertilization the vacuolar organization in the zygote changes. The zygote was a polarized cell and contained a central nucleus, mitochondria, plastids, ribosomes. and lipid bodies. Ribosomal concentration increases significantly after fertilization. The first division of the zygote was transverse or oblique and unequal. The primary endosperm nucleus divides before the zygote nucleus, forming a coenocytic nuclear endosperm; however, part of it later becomes cellular. At the earliest stage of embryo development, the cells were vacuolate, and plastids and mitochondria were simple in structure. During all stages of embryogenesis the suspensor cells were less electron dense than the adjoining embryo cells. Endosperm cellularization begins when the embryo has developed the globular embryo proper. Cellularization starts at the micropylar end of the embryo sac and progresses toward the chalazal end. Dictyosome activity, ribosomal aggregation, and the amount of rough endoplasmic reticulum were highest during the late globular embryo stage. In addition, the vacuolar volume in the cells was reduced. Lipid bodies were present up to the early globular stage, then disappeared. The inner cell walls of the embryo were thin, with many plasmodesmata. These walls begin to thicken at the late globular stage. The results show a corresponding increase in the amount and activity of the metabolic machinery as the development of the embryo progresses.

Morphological and embryological studies in Nymphaeaceae. II. Brasenia schreberei Gmel. and Nelumbo nucifera Gaertn

1965 ◽  
Vol 13 (3) ◽  
pp. 379 ◽  
Author(s):  
P Khanna
Keyword(s):  
Embryo Sac ◽  
Pollen Grains ◽  
Pollen Sterility ◽  
Nelumbo Nucifera ◽  
Primary Endosperm Nucleus ◽  
Polygonum Type ◽  
Globular Stage ◽  
Compound Pollen ◽  
Mother Cells ◽  
Antipodal Cells

The stamens are whorled in Brasenia schreberei and spirally arranged in Nelumbo nucifera. The anther is tetrasporangiate. Parietal layers are five-celled in thickness in B. schreberei and six-celled in N. nucifera. Endothecial cells contain a tannin-like substance and develop fibrous thickenings in N. nucifera. The middle layers are persistent in N. nucifera and ephemeral in B. schreberei. The tapetal cells become multinucleate and the layer develops cutinization on its inner walls in N. nucifera. It is secretory. Micronuclei are formed at the meiosis in the microspore mother cells. These degenerate in B. schreberei and form micropollen grains in N. nucifera. Polysporads and compound pollen grains occur frequently in the latter. Pollen sterility is common. In B. schreberei the carpel is horseshoe-shaped, unites with its margins, and bears two to three pendulous ovules with lamina1 placentation. The carpel in N. nucifera, however, remains open in its early development, unites by the growth of the interlocking hairs, and contains a single ovule. A single parietal layer is present in B. schreberei, and four to five such layers in N. nucifera. A hypostase is formed in B. schreberei. The nucellus functions as perisperm in the latter and is consumed early in N. nucifera. A linear megaspore tetrad is formed in which the chalazal megaspore is functional. The embryo sac is of the Polygonum type. The antipodal cells are ephemeral in B. Schreberei and persistent with secondary multiplication in N. nucifera. In post-fertilized ovules one of the synergids is persistent. Fertilization is non-synchronous in N. nucifera and simultaneous in B. schreberei. In N. nucifera the antipodal cells become enlarged and multinucleate, and occupy the elongated tube formed by the downward penetration of the embryo sac. They degenerate at the early globular stage of the embryo and are not persistent when the embryo is pear-shaped. In B. schreberei a transverse cytokinesis follows division of the primary endosperm nucleus and two unequal cells are formed. The small chalazal endosperm cell penetrates the nucellus below and forms a long tube-like haustorium occupying three-quarters of the length of the nucellus. Its nucleus subsequently hypertrophies and degenerates completely at the globular stage of the embryo. Endosperm is ab initio cellular in B. schreberei and free nuclear in N. nucifera.

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.

Early events in the embryo sac after intraspecific and interspecific pollinations in Rhododendron kawakamii and R. retusum

1986 ◽  
Vol 64 (2) ◽  
pp. 282-291 ◽  
Author(s):  
V. Kaul ◽  
J. L. Rouse ◽  
E. G. Williams
Keyword(s):  
Seed Set ◽  
Embryo Sac ◽  
Pollen Tubes ◽  
Interspecific Crosses ◽  
Primary Endosperm Nucleus ◽  
Kalmia Latifolia ◽  
Taxonomic Grouping ◽  
Similarities And Differences ◽  
Normal Fertilization

Early events in the embryo sac of Rhododendron kawakamii and R. retusum have been studied after compatible self-pollinations and eight interspecific crosses, using sectioned ovaries, pistil squashes, and seed-set data. Ovules of Rhododendron kawakamii and R. retusum are anatropous, unitegmic, and tenuinucellate, with a typical eight-nucleate, seven-celled embryo sac. Fertilization normally occurs 4–5 days after pollination. The zygote lays down a callose wall but remains undivided during the first 13–15 days after pollination. The primary endosperm nucleus divides soon after fertilization, and development is cellular ab initio. Crosses of R. kawakamii (♂) with R. santapaui and R. retusum and crosses of R. retusum (♂) with R. kawakamii, R. santapaui, R. ovatum, and R. tashiroi showed apparently normal fertilization in a majority of ovules entered by pollen tubes. In crosses of R. kawakamii (♂) with R. quadrasianum and Kalmia latifolia entry of pollen tubes into ovules was delayed and frequently abnormal. Apart from compatible self-pollinations of R. kawakamii an R. retusum, only the cross of R. kawakamii (♂) with R. santapaui produced healthy seedlings. Of the remaining seven interspecific crosses only three showed significant embryo development in control pistils left to mature in situ. Similarities and differences in the breeding behaviour of R. kawakamii and R. retusum are discussed with reference to their taxonomic grouping within subsection Pseudovireya.

scholarly journals Uncommon patterns of antinuclear antibodies recognizing mitotic spindle apparatus antigens and clinical associations

Medicine ◽  
2018 ◽  
Vol 97 (34) ◽  
pp. e11727
Author(s):  
Juan Felipe Betancur ◽  
Adriana Londoño ◽  
Victoria Eugenia Estrada ◽  
Sandra Liliana Puerta ◽  
Sandra Marcela Osorno ◽  
...  
Keyword(s):  
Mitotic Spindle ◽  
Antinuclear Antibodies ◽  
Spindle Apparatus ◽  
Clinical Associations

scholarly journals Abnormal Micronuclear Telomeres Lead to an Unusual Cell Cycle Checkpoint and Defects in Tetrahymena Oral Morphogenesis

2008 ◽  
Vol 7 (10) ◽  
pp. 1712-1723 ◽  
Author(s):  
Karen E. Kirk ◽  
Christina Christ ◽  
Jennifer M. McGuire ◽  
Arun G. Paul ◽  
Mithaq Vahedi ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Mitotic Spindle ◽  
Tetrahymena Thermophila ◽  
Germ Line ◽  
Cell Cycle Checkpoint ◽  
Dna Damage Checkpoint ◽  
Telomeric Dna ◽  
Spindle Apparatus ◽  
Cycle Checkpoint

ABSTRACT Telomere mutants have been well studied with respect to telomerase and the role of telomere binding proteins, but they have not been used to explore how a downstream morphogenic event is related to the mutated telomeric DNA. We report that alterations at the telomeres can have profound consequences on organellar morphogenesis. Specifically, a telomerase RNA mutation termed ter1-43AA results in the loss of germ line micronuclear telomeres in the binucleate protozoan Tetrahymena thermophila. These cells also display a micronuclear mitotic arrest, characterized by an extreme delay in anaphase with an elongated, condensed chromatin and a mitotic spindle apparatus. This anaphase defect suggests telomere fusions and consequently a spindle rather than a DNA damage checkpoint. Most surprisingly, these mutants exhibit unique, dramatic defects in the formation of the cell's oral apparatus. We suggest that micronuclear telomere loss leads to a “dynamic pause” in the program of cortical development, which may reveal an unusual cell cycle checkpoint.

Embryology of Isotoma petraea

1970 ◽  
Vol 18 (2) ◽  
pp. 213 ◽  
Author(s):  
IC Beltran
Keyword(s):  
Mother Cell ◽  
Embryo Sac ◽  
Endosperm Development ◽  
Ovule Development ◽  
Polygonum Type ◽  
Development Patterns ◽  
Embryo Formation ◽  
Ring Bivalents ◽  
Form Ring ◽  
Embryo Sac Formation

Ovule development, embryo sac formation, and embryogeny of I. Petraea are described. The ovules are anatropous, unitegmic, and tenuinucellar. Meiosis in the megaspore mother cell is regular and the chromosomes with terminalized chiasmata form ring bivalents at metaphase 1. The Polygonum type embryo sac, Scutellaria type endosperm development, and Solanad embryo formation correspond with development patterns in other members of the Lobeliaceae.

Helianthus annuus Embryogenesis: Embryo Sac Wall Projections Before and After Fertilization

1971 ◽  
Vol 132 (4) ◽  
pp. 367-371 ◽  
Author(s):  
William Newcomb ◽  
Taylor A. Steeves
Keyword(s):  
Helianthus Annuus ◽  
Embryo Sac ◽  
Before And After

Mitotic Spindle Apparatus Autoantibodies

1996 ◽  
pp. 501-506
Author(s):  
Jerome B. Rattner ◽  
Marvin J. Fritzler
Keyword(s):  
Mitotic Spindle ◽  
Spindle Apparatus
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