The development of the ovule and megagametophyte in Rhexia mariana

1968 ◽  
Vol 46 (2) ◽  
pp. 133-139 ◽  
Author(s):  
Albert L. Etheridge ◽  
J. M. Herr Jr.
Keyword(s):  
Parietal Cell ◽  
Nuclear Division ◽  
Close Contact ◽  
Egg Cell ◽  
Sporogenous Cell ◽  
Egg Apparatus ◽  
Chalazal Megaspore ◽  
Subsequent Separation ◽  
Similarities And Differences

The ovules of Rhexia mariana are bitegmic and anatropous or rarely atropous. Periclinal divisions in the nucellar epidermis at the micropylar end produces a nucellar cap. A terminal pore in the nucellus is formed by the suppression of anticlinal divisions in the epidermis and subsequent separation of the cells during nucellar enlargement. A single hypodermal archesporium divides, producing a primary parietal cell and primary sporogenous cell. The primary parietal cell establishes a prominent parietal tissue as the primary sporogenous cell differentiates into the megasporocyte. Two prominent nucleoli that consistently appear in the archesporium persist in the primary sporogenous cell and the megasporocyte. Meiosis produces a tetrad of megaspores in either linear or approximately T-shaped arrangement. Cells of the nucellus adjacent to the sporogenous cell, megasporocyte, and tetrad rarely give rise to megagametophytes aposporically. The chalazal megaspore functions in megagametogenesis. Shortly after the first nuclear division, vacuoles migrate and coalesce between the nuclei. Two more nuclear divisions establish the four- and eight-nucleate megagametophytes. The chalazal nuclei are situated laterally and are noticeably smaller than the micropylar nuclei in both four- and eight-nucleate stages. The two polar nuclei remain in close contact, usually near the egg apparatus, but sometimes near the center of the megagametophyte. The three antipodal nuclei are ephemeral with degeneration completed by the time the egg apparatus is established. Orientation of the egg apparatus places the synergids on the side of the megagametophyte adjacent to the funiculus and the egg cell on the opposite side. The similarities and differences in ovule and megagametophyte development between Rhexia mariana and the tropical representatives of Melastomataceae previously investigated are discussed.

Metaphorical application and interpretation of animal terms

2015 ◽  
Vol 15 (2) ◽  
pp. 280-293
Author(s):  
Mitra Shahabi ◽  
Maria Teresa Roberto
Keyword(s):  
Close Contact ◽  
Physical Characteristics ◽  
The Other ◽  
Daily Lives ◽  
Surrounding World ◽  
Behavioural Characteristics ◽  
Descriptive Approach ◽  
Similarities And Differences ◽  
Animal Names ◽  
Determining Factor

The present research adopts a contrastive and descriptive approach aiming at discovering the reason for similarities and differences between the metaphorical meanings of animal terms between the two languages of English and Persian. For this purpose the most popular animal metaphors in both languages are compared and contrasted. The animals are mostly those with which we have close contact in our daily lives. It is believed that if we could learn how metaphors have originated across languages we could find some explanations for similarities and differences of the metaphorical meanings across languages and cultures. Contrasting the origins of metaphorical concepts is believed to be an appropriate framework for this goal. The results of this study reflect how English and Persian people conceptualize their surrounding world across cultures and how they lexicalize them. It is found that although the physical characteristics and behaviour of animals are the basis for the metaphorical applications or interpretations of animal terms, they are not the only determining factor. The other factors in metaphorical meanings of animal names are culture, language-specificity, and also those behavioural characteristics of animals which are attributed to culture (culturally salient features).

The ultrastructure and cytochemistry of the egg apparatus of Brassica campestris

1989 ◽  
Vol 67 (1) ◽  
pp. 177-190 ◽  
Author(s):  
M. J. Sumner ◽  
L. Van Caeseele
Keyword(s):  
Plasma Membrane ◽  
Cell Walls ◽  
Brassica Campestris ◽  
Positive Response ◽  
Uv Light ◽  
Egg Cell ◽  
Filiform Apparatus ◽  
Egg Apparatus ◽  
Large Numbers ◽  
Acidic Polysaccharides

The egg apparatus of Brassica campestris L. cv. Candle (canola-rapeseed) is composed of an egg and two synergids juxtaposed at the extreme micropylar end of the megagametophyte with the egg cell displaced in a chalazal direction. The cell walls of the synergids and egg are uniformly PAS and PA–TCH–SP-positive, but contained β-linked glucans only in the micropylar region. The number and development of the cytoplasmic organelles suggested that the egg cell is relatively inactive metabolically while the synergid cells are active. The synergids contain large numbers of dictyosomes with PA–TCH–SP-positive vesicles at the maturing face. These vesicles appear to fuse with the plasma membrane in the region of the filiform apparatus. The filiform apparatuses of the synergids are micropylar finger-like projections that extend into the cytoplasm of the synergid. These are PAS and PA–TCH–SP-positive, fluoresce in uv light when stained with Calcofluor, and show a positive response for acidic polysaccharides when stained with alcian blue. After treatment with cellulase, fluorescence was not observed. The incipient degenerate synergid was intensely stained by cationic dyes 24–36 h after anthesis.

Introduction

2019 ◽  
pp. 1-16
Author(s):  
Philomen Probert
Keyword(s):  
Close Contact ◽  
First Century ◽  
Greek Text ◽  
Late Antique ◽  
Similarities And Differences ◽  
The Relationship

Chapter 1 introduces the relationship between Greek and Latin discussions of prosody, beginning with exchanges of ideas that took place between figures such as Cicero, Varro, and the elder Tyrannio in the Rome of the first century BC. With reference to Quintilian’s work from the 90s AD, Chapter 1 then shows that the Greek and Latin traditions remained in close contact for a time. The chapter goes on to discuss how Latin authors from Quintilian onwards recognize both similarities and differences between Greek and Latin accentuation; a comparison is offered between a late antique introduction to Latin accents (from Donatus’ Ars maior) and a Greek text ultimately related in content. Chapter 1 concludes with a statement of the aims and structure of the book.

Early embryogenesis in Arabidopsis thaliana. I. The mature embryo sac

1991 ◽  
Vol 69 (3) ◽  
pp. 447-460 ◽  
Author(s):  
S. G. Mansfield ◽  
L. G. Briarty ◽  
S. Erni
Keyword(s):  
Arabidopsis Thaliana ◽  
Endoplasmic Reticulum ◽  
Embryo Sac ◽  
Mature Embryo ◽  
Central Cell ◽  
Egg Cell ◽  
Cell Cytoplasm ◽  
Intimate Contact ◽  
Egg Apparatus ◽  
Common Wall

Arabidopsis thaliana has a seven-celled eight-nucleate megagametophyte of the Polygonum type; each cell type displays a different form of structural specialization. The egg apparatus cells are highly polarized; the egg has a large micropylar vacuole and chalazally sited nucleus, whereas the opposite is true for the synergids. At the chalazal region of the egg apparatus cells there are no cell wall boundaries, although their plasmalemmas are in intimate contact. The common wall between the two synergids is thin and irregular and contains plasmodesmatal connections. The synergid cytoplasm is rich in organelles; profiles of rough endoplasmic reticulum appear in masses of parallel stacked cisternae, and large accumulations of mitochondria occur adjacent to the filiform apparatus. The egg cell cytoplasm is quiescent; ribosome concentration and frequencies of dictyosomes and endoplasmic reticulum are noticeably lower and plastids are poorly differentiated. The central cell is long and vacuolate with a large diploid nucleus; fusion of the polar nuclei occurs prior to embryo sac maturity. The cytoplasm contains numerous starch-containing plastids accumulated in a shell around the nucleus. A high ribosome concentration and the absence of vacuoles and dictyosomes typifies the antipodal cell cytoplasm. All antipodal cells are interconnected by plasmodesmata as well as being connected to the nucellus and central cell. Key words: Arabidopsis, embryo sac, embryogenesis, cell specializations, stereology.

scholarly journals Voiceless nasal sounds in three Tibeto-Burman languages

2018 ◽  
Vol 49 (1) ◽  
pp. 1-32 ◽  
Author(s):  
Katia Chirkova ◽  
Patricia Basset ◽  
Angélique Amelot
Keyword(s):  
Reference Point ◽  
Southwest China ◽  
Close Contact ◽  
Total Duration ◽  
Regional Feature ◽  
Similarities And Differences

This paper focuses on two types of voiceless nasal sounds in Xumi, a Tibeto-Burman language: (i) the voiceless aspirated nasals // [] and // [], and (ii) the voiceless nasal glottal fricative []. We provide a synchronic description of these two types of sounds, and explore their similarities and differences. Xumi voiceless nasal consonants are described with reference to the voiceless nasal consonants // and // in Burmese and Kham Tibetan because Burmese voiceless nasals are the best described type of voiceless nasals, and are therefore used as a reference point for comparison; voiceless nasals in Kham Tibetan, which is in close contact with Xumi, represent a characteristic regional feature. The synchronic description is based on acoustic and aerodynamic measurements (the total duration of the target phonemes, the duration of the voiced period during the target phonemes, mean nasal and oral flow). Our study (i) contributes to a better understanding of voiceless nasals as a type of sound, (ii) provides a first-ever instrumental description (acoustic and aerodynamic) of the voiceless nasal glottal fricative [], as attested in a number of Tibeto-Burman languages of Southwest China, and (iii) suggests a possible phonetic basis for the observed dialectal and diachronic variation between voiceless nasals and [] in some Tibeto-Burman languages.

scholarly journals Plant egg cell fate determination depends on its exact position in female gametophyte

2021 ◽  
Vol 118 (8) ◽  
pp. e2017488118 ◽  
Author(s):  
Yang Sun ◽  
Xiu Wang ◽  
Lin Pan ◽  
Fei Xie ◽  
Bo Dai ◽  
...  
Keyword(s):  
Cell Fate ◽  
Sperm Cell ◽  
Female Gametophyte ◽  
Imaging System ◽  
Egg Cell ◽  
Cell Identity ◽  
Auxin Level ◽  
Egg Apparatus

Plant fertilization involves both an egg cell, which fuses with a sperm cell, and synergid cells, which guide pollen tubes for sperm cell delivery. Therefore, egg and synergid cell functional specifications are prerequisites for successful fertilization. However, how the egg and synergid cells, referred to as the “egg apparatus,” derived from one mother cell develop into distinct cell types remains an unanswered question. In this report, we show that the final position of the nuclei in female gametophyte determines the cell fate of the egg apparatus. We established a live imaging system to visualize the dynamics of nuclear positioning and cell identity establishment in the female gametophyte. We observed that free nuclei should migrate to a specific position before egg apparatus specialization. Artificial changing in the nuclear position on disturbance of the actin cytoskeleton, either in vitro or in vivo, could reset the cell fate of the egg apparatus. We also found that nuclei of the same origin moved to different positions and then showed different cell identities, whereas nuclei of different origins moved to the same position showed the same cell identity, indicating that the final positions of the nuclei, rather than specific nucleus lineage, play critical roles in the egg apparatus specification. Furthermore, the active auxin level was higher in the egg cell than in synergid cells. Auxin transport inhibitor could decrease the auxin level in egg cells and impair egg cell identity, suggesting that directional and accurate auxin distribution likely acts as a positional cue for egg apparatus specialization.

Development of the unfertilized embryo sac and pollen tubes in the dwarf mistletoe Arceuthobium americanum (Viscaceae)

2004 ◽  
Vol 82 (11) ◽  
pp. 1566-1575 ◽  
Author(s):  
Cynthia M Ross ◽  
Michael J Sumner
Keyword(s):  
Embryo Sac ◽  
Pollen Tubes ◽  
Wall Material ◽  
Egg Cell ◽  
Dwarf Mistletoe ◽  
Egg Apparatus ◽  
Arceuthobium Americanum ◽  
Fluorescence And Electron Microscopy ◽  
Light Fluorescence ◽  
Functional Megaspore

Megasporogenesis, embryo sac development, and pollen tubes in Arceuthobium americanum Nutt. ex Engelm. were investigated with light, fluorescence, and electron microscopy. The orthotropous ovular structure of A. americanum lacked integuments and possessed a nucellus that was largely continuous with and indistinguishable from the placenta; we coined this structure the placental–nucellar complex (PNC). Two megasporocytes became evident in the tenuinucellate PNC by mid-April, and had undergone bisporic megasporogenesis by mid-May. The upper cell from each dyad (distal to the base of the PNC) became a functional megaspore, although only one would develop into a seven-celled embryo sac. Like typical angiosperm embryo sacs, that of A. americanum possessed an egg cell having the ultrastructure reflective of a quiescent cell, and lacked cellulosic and (or) hemicellulosic wall material between the egg apparatus and central cell. However, the egg apparatus arose at the lower embryo sac pole, not at the upper as expected for an orthotropous ovule. A hypothetical model for the development of Arceuthobium ovules is the ancestral fusion and subsequent reduction of two anatropous ovules to form two embryo sacs within the PNC, of which only one completes development. The synergids have no role in pollen tube guidance, as tubes could be seen below each functional megaspore prior to megagametogenesis.Key words: Arceuthobium, embryo sac, megasporogenesis, mistletoe, pollen tubes, ultrastructure.

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.

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 Ultrastructural organization of the tomato embryo sac at the time of fertilization

2014 ◽  
Vol 50 (1-2) ◽  
pp. 139-142 ◽  
Author(s):  
Franciszek Kadej ◽  
Agnieszka Kadej
Keyword(s):  
Cell Nucleus ◽  
Close Contact ◽  
Embryo Sac ◽  
Egg Cell ◽  
Ultrastructural Organization ◽  
Nucleolar Structure ◽  
Great Uniformity

In tomato embryo sac at the time of fertilization noticeable multiplication of the endosperm cytoplasm is observed. The cytoplasm of the egg cell, next to the nucleus, appears loose with distinct mitochondria and plastids. At a distance from the nucleus ribosomes become grouped into a cytoplasmic mass of great uniformity. Nucleolar structure of the egg cell nucleus displaces to its periphery. Its new position seems to he related to the process of fertilization. In the area of the endosperm two nuclei in close contact to each other are found which suggests the beginning of secondary fertilization.

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