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.

Ultrastructure of the fertilized embryo sac in the dwarf mistletoe Arceuthobium americanum (Viscaceae) and development of the caecum

2005 ◽  
Vol 83 (5) ◽  
pp. 459-466 ◽  
Author(s):  
Cynthia M Ross ◽  
Michael J Sumner
Keyword(s):  
Cell Walls ◽  
Embryo Sac ◽  
Central Cell ◽  
Filiform Apparatus ◽  
Dwarf Mistletoe ◽  
Primary Endosperm Nucleus ◽  
Complex Cells ◽  
Arceuthobium Americanum ◽  
Fluorescence And Electron Microscopy ◽  
Light Fluorescence

Post-fertilization changes in the seven-celled embryo sac of the parasitic angiosperm Arceuthobium americanum Nutt. ex Engelm. were investigated with light, fluorescence, and electron microscopy. Two embryo sacs, of which only one is fertilized, are found within the reduced ategmic ovule (the placental–nucellar complex). All cells of the fertilized embryo sac developed thickened cellulosic and (or) hemicellulosic bounding walls and, aside from the degenerative synergid, acquired ultrastructure reflective of metabolically active cells. The filiform apparatus became thickened in the persistent synergid, and a similar structure developed in the antipodals. Unlike the changes observed in the zygote and central cell, those in the persistent synergid and antipodals were unusual, as these cells regularly degenerate after fertilization in a typical angiosperm; therefore, in A. americanum, they likely play a role in providing nutrition to the zygote and (or) central cell. A pouch-like outgrowth (caecum) initiated from the central cell near the primary endosperm nucleus and, after vacuolar expansion and intercellular growth, reached the base of the placental–nucellar complex in three days. The observation of mitochondria clusters within the central cell, caecum, and adjacent placental–nucellar complex cells suggests the caecum functions in embryo sac expansion and haustorial nutrient absorption.Key words: Arceuthobium, caecum, cell walls, fertilized embryo sac, mistletoe, ultrastructure.

Fine structure of megagametophyte development in Zea mays

1979 ◽  
Vol 57 (10) ◽  
pp. 1093-1110 ◽  
Author(s):  
Scott D. Russell
Keyword(s):  
Zea Mays ◽  
Embryo Sac ◽  
Structural Complexity ◽  
Aniline Blue ◽  
Second Phase ◽  
Fluorescence And Electron Microscopy ◽  
Membrane Bound ◽  
Lytic Vacuole ◽  
Light Fluorescence ◽  
Functional Megaspore

Polygonum-type embryo sac development was examined in Zea mays with light, fluorescence, and electron microscopy. Megasporocyte polarity is expressed in organelle distribution, aniline blue wall fluorescence, and chalazal location of plasmodesmata. In the meiotic cytoplasm concurrent with the sporophyte–gametophyte transition, ribosome concentrations are low, and membrane-bound organelles are simplified. The functional megaspore is the largest and most chalazal cell of the resultant triad or tetrad. Aniline blue fluorescence is intense in nonfunctional megaspore walls, whereas in the functional megaspore intensity decreases from the chalazal end to that in nucellar walls. Throughout functional megaspore and two-nucleate megagametophyte, ribosome concentrations, organelle numbers, and structural complexity increase. The transition from vegetative to reproductive gametophytic growth presumably follows this biosynthetic period. In the four-nucleate stage, a second phase of mitochondrial simplification coincides with the formation of an extensive lytic vacuole containing evidence of possible organelle and cytoplasmic membrane incorporation. Near the close of intensive lytic activity, compartmentalization of lytic areas contributes to creating a prominent vacuole in the central cell as synergids, egg, and antipodals differentiate.

Overgrowth of Pollen Tubes in Embryo Sacs of Rhododendron Following Interspecific Pollinations

1986 ◽  
Vol 34 (4) ◽  
pp. 413 ◽  
Author(s):  
EG Williams ◽  
V Kaul ◽  
JL Rouse ◽  
BF Palser
Keyword(s):  
Pollen Tube ◽  
Embryo Sac ◽  
Pollen Tubes ◽  
Egg Cell ◽  
Interspecific Crosses ◽  
Main Body

Frequent overgrowths of pollen tubes within the embryo sac are characteristic of a number of interspecific crosses in the genus Rhododendron (Ericaceae). The combined techniques of sectioning, squashing and whole-ovule clearing have confirmed that in ovules showing this phenomenon the pollen tube fails to terminate growth and release sperms on entry into a synergid; instead it continues to grow beyond the synergid and egg cell, often filling the main body of the embryo sac with a coiled and distorted mass. Such ovules fail to develop further. The occurrence and possible causes of this error syndrome are discussed.

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 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.

scholarly journals Ovary Signals for Pollen Tube Guidance in Chalazogamous Mangifera indica L.

2021 ◽  
Vol 11 ◽  
Author(s):  
Jorge Lora ◽  
Veronica Perez ◽  
Maria Herrero ◽  
Jose I. Hormaza
Keyword(s):  
Pollen Tube ◽  
Pollen Tube Growth ◽  
Mangifera Indica ◽  
Embryo Sac ◽  
Pollen Tubes ◽  
Tube Growth ◽  
Transmitting Tissue ◽  
Egg Apparatus ◽  
Pollen Tube Elongation

Most flowering plants show porogamy in which the pollen tubes reach the egg apparatus through the micropyle. However, several species show chalazogamy, an unusual pollen tube growth, in which the pollen tubes reach the embryo sac through the chalaza. While ovary signals for pollen tube growth and guidance have been extensively studied in porogamous species, few studies have addressed the process in chalazogamous species such as mango (Mangifera indica L.), one of the five most important fruit crops worldwide in terms of production. In this study, we characterize pollen–pistil interaction in mango, paying special attention to three key players known to be involved in the directional pollen tube growth of porogamous species such as starch, arabinogalactan proteins (AGPs), and γ-aminobutyric acid (GABA). Starch grains were observed in the style and in the ponticulus at anthesis, but their number decreased 1 day after anthesis. AGPs, revealed by JIM8 and JIM13 antibodies, were homogenously observed in the style and ovary, but were more conspicuous in the nucellus around the egg apparatus. GABA, revealed by anti-GABA antibodies, was specifically observed in the transmitting tissue, including the ponticulus. Moreover, GABA was shown to stimulate in vitro mango pollen tube elongation. The results support the heterotrophic growth of mango pollen tubes in the style at the expense of starch, similarly to the observations in porogamous species. However, unlike porogamous species, the micropyle of mango does not show high levels of GABA and starch, although they were observed in the ponticulus and could play a role in supporting the unusual pollen tube growth in chalazogamous species.

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 Unusual behavior of growing pollen tubes in the ovary of plum culture (Prunus domestica L.)

2010 ◽  
Vol 62 (1) ◽  
pp. 137-142 ◽  
Author(s):  
Milena Djordjevic ◽  
R. Cerovic ◽  
D. Nikolic ◽  
Sanja Radicevic
Keyword(s):  
Embryo Sac ◽  
Pollen Tubes ◽  
Prunus Domestica ◽  
Unusual Behavior ◽  
Egg Apparatus

Unusual behavior of growing pollen tubes in different combinations of pollination was observed in the ovary of the plum (Prunus domestica L.) cv 'Cacanska Lepotica'. It primarily refers to several issues, i.e. the curling up of pollen tubes within the micropyle, the growth of two pollen tubes into the nucellus of an ovule, the occurrence of a bundle above the nucellar cap and fluorescence of the part of the embryo sac containing the egg apparatus. Upon the growth of pollen tubes into the nucellus of the ovule, subsequently penetrating pollen tubes form a bundle either above the micropyle entrance or above the nucellus. Branching and bending of pollen tubes by 180o upon their growth into the micropyle was also observed.

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.

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