scholarly journals Apomictic development during different flower development stages in Crataegus tanacetifolia (Lam.) Pers., endemic to Turkey

2021 ◽  
Vol 13 (2) ◽  
pp. 10911
Author(s):  
Aslıhan ÇETİNBAŞ-GENÇ ◽  
Meral ÜNAL
Keyword(s):  
Flower Development ◽  
Cell Formation ◽  
Embryo Sac ◽  
Development Stage ◽  
Egg Cell ◽  
Filiform Apparatus ◽  
Initial Cell ◽  
Development Stages ◽  
Antipodal Cells ◽  
Regular Meiosis

In this study, aposporic apomictic development and its relation to the different flower development stages were investigated by light and fluorescence microscopy in Crataegus tanacetifolia (Lam.) Pers. (Rosaceae). At pre-anthesis stage, aposporic initial cell differentiated at the somatic nucellus tissue shortly after the megaspore mother cell formation. The volume of aposporic initial cell increased during the generation of dyad and megaspore tetrad respectively by regular meiosis. At this stage, linear megaspore tetrad and vacuolated aposporic initial cell were located side by side into the same ovule. At anthesis stage, before pollination, four nucleated aposporic embryo sac was formed while sexual development came to end by atrophy of megaspores completely. At this stage, atrophied megaspores and two nucleated aposporic embryo sac were located side by side into the same ovule. At post-anthesis stage, pollination still had not begun and ovule contained only eight nucleated aposporic embryo sac. Mature aposporic embryo sac was composed of two synergid cells and one egg cell on the micropylar side, three antipodal cells on the chalazal side and a central cell with two polar nuclei in the middle of the sac. The absence of filiform apparatus in the synergid cells was quite remarkable. No callose accumulation around the aposporic initial cell was observed in any development stage. Pollination started shortly after the proembryo formation. Embryo and endosperm developed without fertilization due to the problems encountered in reaching pollen tubes to the ovary.

scholarly journals Meiosis and Development of the Embryo Sac in Gunnera insignis (Oersted) D.C. (Halorhagaceae)

1969 ◽  
Vol 46 (4) ◽  
pp. 254-268
Author(s):  
Niilo Virkki
Keyword(s):  
Costa Rica ◽  
Chromosome Complement ◽  
Embryo Sac ◽  
Mature Embryo ◽  
Egg Cell ◽  
Acrocentric Chromosomes ◽  
Antipodal Cells ◽  
Giant Species

Gunnera insignis (Oersted) D.C. is a halorhagacean plant from the mountains of Costa Rica, a giant species which can be considered as a potential ornamental. The chromosome relations of the whole genus Gunnera have been practically unknown. The diploid chromosome complement of Gunnera insignis consists of 34 acrocentric chromosomes of quite differ ent size. Both PMC and MMC meiosis are normal and vigorous, showing 17 bivalents in the first division. Absolute procentric localization of the first (or only) chiasma occurs in MMC. In PMC, the same tendency is seen in a couple of big bivalents. The rate of terminalization of chiasmata in the remaining PMC bivalents is low. The mature embryo sac of Gunnera insignis is tetrasporic, 16-nucleate, 2-phasic, and multipolar. It consists of an egg cell, a giant polyploid nucleus formed by fusion of 7 polar nuclei, and 6 antipodal cells. In exceptional cases 2 smaller fusion nuclei may occur instead of 1 large. This is considered a sign of an incomplete repolarization of the embryo sac nuclei.

scholarly journals Cytochemical study of the embryo sac of Nicotiana tabacum L.

2014 ◽  
Vol 50 (1-2) ◽  
pp. 121-125
Author(s):  
V. P. Babbikova ◽  
O. A. Khvendynich ◽  
L. S. Serdyuk
Keyword(s):  
Cell Nucleus ◽  
Mitotic Cycle ◽  
Cell Formation ◽  
Embryo Sac ◽  
Central Cell ◽  
Egg Cell ◽  
Cell Nuclei ◽  
Cytochemical Study ◽  
Male Gametes ◽  
S Period

The mitotic cycle in the egg cell and physico-chemical state of chromatin in the egg cell and central cell of the tobacco embryo sac were studied. It was revealed that during egg cell formation a change in the mitotic cycle kinetics takes place, it consists in prolongation of the S-period as compared with that of somatic cells and G1 - period as compared with that of male gametes. Egg cell and central cell nuclei differ in chromatin structure. Condensed chromatin dominates in the egg cell nucleus, diffuse chromatin in the central cell nucleus, but both show only weak metabolic activity.

The embryology of Kunzea capitata Reichb

1969 ◽  
Vol 17 (1) ◽  
pp. 97 ◽  
Author(s):  
N Prakash
Keyword(s):  
Outer Integument ◽  
Cell Formation ◽  
Embryo Sac ◽  
Pollen Grains ◽  
Basic Type ◽  
Ring Stage ◽  
Polygonum Type ◽  
Signet Ring ◽  
Mother Cells ◽  
Antipodal Cells

The anther is tetrasporangiate and the development of its wall is of the Basic type. Ubisch granules are formed on the surface of the tapetum at the signet-ring stage of the pollen grains. The anther dehisces by longitudinal slits, and pollen grains are shed at the two-celled stage. The female archesporium is subepidermal and cuts off the primary parietal cell. A six-layered parietal tissue is formed below the nucellar epidermis by the time megasporogenesis is completed. The flowers are protandrous, and in any given bud meiosis in megaspore mother cells follows that in microspore mother cells. Embryo sac development is of the Polygonum type and the antipodal cells are ephemeral. Cell formation in the nuclear endosperm commences at the micropylar end and proceeds towards the chalaza. Embryogeny corresponds to the Onagrad type and no evidence of polyembryony was found. Both the integuments take part in the formation of the seed coat, in which the cells of the outer layer of the outer integument are conspicuously elongated. A comparison is made with the embryological findings in other myrtaceous plants.

scholarly journals Developmental, ultrastructural and cytochemical investigations of the female gametophyte in Sedum rupestre L. (Crassulaceae)

PROTOPLASMA ◽  
2020 ◽  
Author(s):  
Emilia Brzezicka ◽  
Małgorzata Kozieradzka-Kiszkurno
Keyword(s):  
Female Gametophyte ◽  
Current Knowledge ◽  
Embryo Sac ◽  
Main Function ◽  
Filiform Apparatus ◽  
Electron Dense Material ◽  
Reported Data ◽  
Functional Megaspore ◽  
Sedum Rupestre ◽  
Antipodal Cells

AbstractThis article describes the development of female gametophyte in Sedum rupestre L. New embryological information about the processes of megasporogenesis and megagametogenesis provided in this paper expand the current knowledge about the embryology of the studied species. S. rupestre is characterized by monosporic megasporogenesis and the formation of Polygonum–type embryo sac. The process of megasporogenesis is initiated by one megaspore mother cell, resulting in the formation of a triad of cells after meiosis and cytokinesis. The functional megaspore, which is located chalazally, is a mononuclear cell present next to the megaspore in the centre of the triad. Only one of the two non-functional cells of the triad is binucleate, which occur at the micropylar pole. In this paper, we explain the functional ultrastructure of the female gametophytic cells in S. rupestre. Initially, the cytoplasm of the gametophytic cells does not differ from each other; however, during differentiation, the cells reveal different morphologies. The antipodals and the synergids gradually become organelle-rich and metabolically active. The antipodal cells participate in the absorption and transport of nutrients from the nucellar cells towards the megagametophyte. Their ultrastructure shows the presence of plasmodesmata with electron-dense material, which is characteristic of Crassulaceae, and wall ingrowths in the outer walls. The ultrastructure of synergid cells is characterized by the presence of filiform apparatus and cytoplasm with active dictyosomes, abundant profiles of endoplasmic reticulum and numerous vesicles, which agrees with their main function—the secretion of pollen tube attractants. Reported data can be used to resolve the current taxonomic problems within the genus Sedum ser. Rupestria.

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.

Embryological studies in the compositae. IV. Sporogenesis, gametogenesis, and embryogeny in Brachycome ciliaris (Labill.) Less

1964 ◽  
Vol 12 (2) ◽  
pp. 142 ◽  
Author(s):  
GL Davis
Keyword(s):  
New South ◽  
Embryo Sac ◽  
Pollen Grains ◽  
Egg Cell ◽  
Male Sterile ◽  
Morphological Variations ◽  
Secondary Nucleus ◽  
South Wales ◽  
Mother Cells ◽  
Antipodal Cells

Material of two varieties of Brachycome ciliaris was obtained from several localities in southern Queensland and western New South Wales, and no embryological differences were found between populations in spite of considerable morphological variations. The plant was highly male-sterile, and although development of the anthers was normal up to the formation of microspore mother cells, presumed meiotic abnormalities resulted in failure to form microspore tetrads except in one instance. The formation of plasmodial microspore mother cells and unreduced pollen grains is described and the occurrence of normal pollen grains in two capitula is recorded. In the ovule, meiosis is suppressed and the megaspore mother cell becomes vacuolate and functions directly as the uninucleate embryo sac. Three nuclear divisions precede the formation of an eight-nucleate embryo sac in which the antipodal cells undergo secondary multiplication. There is circumstantial evidence that the polar nuclei divide simultaneously to form the fist four endosperm nuclei and do not first fuse to form a secondary nucleus. The egg cell develops parthenogenetically and cleavages follow the asterad type of development. The eariy stages of embryogeny are completed before the opening of the florets.

Ultrastructural observations of the mature megagametophyte and the fertilization in wheat (Triticum aestivum)

1985 ◽  
Vol 63 (2) ◽  
pp. 163-178 ◽  
Author(s):  
Ruilin You ◽  
William A. Jensen
Keyword(s):  
Triticum Aestivum ◽  
Pollen Tube ◽  
Cell Walls ◽  
Embryo Sac ◽  
Mature Embryo ◽  
Central Cell ◽  
The Other ◽  
Egg Cell ◽  
Filiform Apparatus ◽  
Egg Apparatus

The mature embryo sac of wheat contains an egg apparatus composed of an egg cell and two synergids at the micropylar end, a central cell with two large polar nuclei in the middle, and a mass of 20 to 30 antipodals at the chalazal end. A comparison was made of the ultrastructural features of the various cells of the embryo sac. The features included the position of the nucleus and vacuoles, the number, structure, and distribution of organelles, and the extent of the cell walls surrounding each cell. The pollen tube enters one synergid through the filiform apparatus from the micropyle. The penetration and discharge of the pollen tube causes the further degeneration of that synergid, which had already undergone changes before pollination. The second synergid does not change further in appearance following the penetration of the first by the pollen-altered tube. Half an hour after pollination at 20–25 °C, two male nuclei are seen in the cytoplasm of the egg and the central cell. At about 1 h after pollination, one sperm has made contact with the egg nucleus, while the other sperm is fusing with one of the polar nuclei.

scholarly journals Ethylene and 1-methylcyclopropene action over senescence of nasturtium flowers

2015 ◽  
Vol 33 (4) ◽  
pp. 453-458 ◽  
Author(s):  
Tania P Silva ◽  
Fernando L Finger
Keyword(s):  
Floral Development ◽  
Development Stage ◽  
Flower Senescence ◽  
Premature Senescence ◽  
Flower Opening ◽  
Development Stages ◽  
Post Harvest ◽  
The Third ◽  
Exogenous Ethylene ◽  
Floral Bud

ABSTRACT: This work describes ethylene and 1-methylcyclopropene (1-MCP) action on post-harvest shelf life of four development stages of nasturtium flowers. To reach this goal, we carried out three experiments. In the first and second experiments, we studied five ethylene (0; 0.1; 1; 10; 100 and 1000 μL/L) and three 1-MCP concentrations (0.25; 0.5 and 0.75 μL/L), respectively. In the third experiment, 1-MCP was followed by combined with ethylene (only 1-MCP; only ethylene; and 24 hours of exposure to 0.75 μL/L 1-MCP followed by 24 hours of exposure to 100 μL/L ethylene). All experiments had two control treatments, one keeping non-exposed flowers inside and another outside exposure chambers. Experiments were set in factorial design, in complete blocks at random, with four 10-flower replications each. Flower senescence was determined by a pre-established visual scale and by observing floral bud development. Ethylene dose above 10 μL/L induced flower wilting and premature senescence from the second floral development stage. Furthermore, higher concentrations of exogenous ethylene promoted irregular flower opening and/or morphological abnormalities in opened flowers. 1-MCP effectively extended post-harvest longevity of nasturtium flowers, independent of the concentration and even in the presence of exogenous ethylene.

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