Fine Structure Study of Pollen Development in Haemanthus katherinae Baker

1971 ◽  
Vol 8 (2) ◽  
pp. 303-315
Author(s):  
JEAN M. SANGER ◽  
W. T. JACKSON
Keyword(s):  
Endoplasmic Reticulum ◽  
Fine Structure ◽  
Pollen Development ◽  
Generative Cell ◽  
Structure Study ◽  
Pollen Grain ◽  
Pollen Wall ◽  
Spheroidal Shape ◽  
Oriented System

The newly formed generative cell of the pollen grain of the African blood lily is spheroidal after its detachment from the pollen wall. Plastids are almost always excluded from the generative cell, while dictyosomes, mitochondria, ribosomes, endoplasmic reticulum, and microtubules are present throughout development of the cell. During the time that the generative cell is spheroidal, microtubules are found scattered randomly throughout the cytoplasm. The cell subsequently elongates and concurrently an oriented system of microtubules appears along the wall of the cell. The microtubules are aligned with their long axes parallel to the long axis of the cell. This system of microtubules persists in the generative cell throughout its development. The microtubules can be destroyed by exposure to isopropyl N-phenylcarbamate or colchicine and as a result the generative cell reverts to a near spheroidal shape.

Fine Structure Study of Pollen Development in Haemanthus katherinae Baker

1971 ◽  
Vol 8 (2) ◽  
pp. 289-301
Author(s):  
JEAN M. SANGER ◽  
W. T. JACKSON
Keyword(s):  
Fine Structure ◽  
Vegetative Cell ◽  
Daughter Nucleus ◽  
Generative Cell ◽  
Pollen Grains ◽  
Cell Plate ◽  
Structure Study ◽  
Pollen Grain ◽  
Pollen Wall ◽  
Fibrillar Material

When microspores of the African blood lily divide, they form pollen grains which consist of 2 cells of unequal size. This is accomplished when the microspore nucleus is displaced from the centre of the grain prior to division. The displacement is always towards the side of the grain opposite the furrow, and large vacuoles form in the cytoplasm between the furrow and the nucleus. During cell division the cell plate curves around one daughter nucleus and fuses with the pollen wall to enclose the generative cell. The cell-plate attachment always occurs with the wall that is opposite the furrow of the grain. Most of the microspore's organelles become incorporated in the larger vegetative cell, whereas the generative cell has few, if any, plastids and only a small number of other organelles. The wall around the generative cell is composed of finely fibrillar material enclosed within 2 unit membranes. The generative cell eventually becomes detached from the pollen wall, becomes spheroidal, and moves to a position near the centre of the pollen grain. At the same time, the large vacuoles disappear from the vegetative cell and the number of organelles increases substantially.

Fine Structure Study of Pollen Development in Haemanthus katherinae Baker

1971 ◽  
Vol 8 (2) ◽  
pp. 317-329
Author(s):  
JEAN M. SANGER ◽  
W. T. JACKSON
Keyword(s):  
Endoplasmic Reticulum ◽  
Fine Structure ◽  
Final Stage ◽  
Structure Study ◽  
Pollen Grain ◽  
Developmental Period ◽  
Vegetative Nucleus ◽  
Lipid Bodies ◽  
Starch Granules ◽  
Flat Cisternae

The newly formed vegetative cell of the pollen grain of the African blood lily has a spheroidal nucleus, few dictyosomes, and a small amount of endoplasmic reticulum. Plastids are smaller than those of the microspore and usually lack starch granules. Mitochondria and lipid bodies are more numerous than they were in the microspores, but their appearance is unchanged. As the pollen grain matures, the vegetative nucleus becomes irregular in shape. There is a dramatic increase in the number of dictyosomes, starch accumulates in the plastids, and a moderately well developed system of endoplasmic reticulum appears in the form of flat cisternae. In the developmental period immediately preceding anthesis, the vegetative nucleus becomes lobate and small nucleoli replace the large nucleoli present earlier. Plastids lose their starch, lipid bodies disappear, and the endoplasmic reticulum becomes vesicular in this final stage before germination.

An ultrastructural study of pollen development in tomato (Lycopersicon esculentum). I. Tetrad to early binucleate microspore stage

1993 ◽  
Vol 71 (8) ◽  
pp. 1039-1047 ◽  
Author(s):  
P. L. Polowick ◽  
V. K. Sawhney
Keyword(s):  
Endoplasmic Reticulum ◽  
Lycopersicon Esculentum ◽  
Ultrastructural Study ◽  
Pollen Development ◽  
Pollen Wall ◽  
Ultrastructural Changes ◽  
Dense Matrix ◽  
Tetrad Stage ◽  
Microspore Stage ◽  
Electron Dense Matrix

Microspores undergo considerable ultrastructural changes between the tetrad and early binucleate microspore stages of microsporogenesis in tomato (Lycopersicon esculentum). Pollen wall deposition began late in the tetrad stage, and by the early microspore stage a lamellar foot layer and tectum were deposited. Sculpturing of the tectum was evident by the early binucleate microspore stage. Dictyosomes and vesicles were abundant during the period of pollen wall formation. Plastids were associated with the endoplasmic reticulum (ER) to form plastid–ER complexes, from the late tetrad to the vacuolate microspore stage. At the vacuolate microspore stage, endoplasmic reticulum independent of plastids was also observed, and at the early binucleate microspore stage ER was not associated with plastids. Free ribosomes were evenly distributed throughout the cytoplasm until the vacuolate microspore stage when they were organized into polysomes. Mitochondria were spherical to ellipsoid, with an electron-dense matrix and swollen cristae, until the early binucleate microspore stage when they were highly elongate and became convoluted. Key words: Lycopersicon esculentum, microsporogenesis, pollen development, tetrads, tomato, ultrastructure.

Elektronenmikroskopische Beobachtungen an der vegetativen Zelle im auskeimenden Pollenkorn von Oenothera hookeri Torr. et Grey

1963 ◽  
Vol 18 (12) ◽  
pp. 1092-1097 ◽  
Author(s):  
Lothar Diers
Keyword(s):  
Endoplasmic Reticulum ◽  
Golgi Apparatus ◽  
Nuclear Envelope ◽  
Vegetative Cell ◽  
Generative Cell ◽  
Pollen Grain ◽  
Serial Sections ◽  
Lipid Inclusions ◽  
Intense Activity ◽  
Germinating Pollen

According to the intense activity of the vegetative cell in the germinating pollen grain, the cytoplasm shows a highly organized structure. Concerning the structure the vegetative cell differs strongly from the generative cell. In the vegetative cell the big nucleus shows a very lobed shape. Large invaginations of the cytoplasm into the nucleus can be frequently observed. Series of adjacent sections show that deep and flat vesicles which may often broaden to unusual large cisternae, extend through the vegetative plasm and form by interconnections a highly developed endoplasmic reticulum which is continuous with the nuclear envelope. The leucoplasts contain large starch grains and very few lamellae, in many sections only one lamella is visible. Sometimes, a process of a leucoplast deeply reaches into another leucoplast. In some leucoplasts and mitochondria there are concentric stripes which, according to serial sections, are the margins of invaginations of the cytoplasm or of another organell. In the numerous mitochondria the inner folds have the form of cristae, tubules are not so frequently seen. The edges of the flattened sacs of the Golgi - apparatus expand to vacuoles which seem to separate from the flattened cisternae. Typical for the vegetative plasm are numerous small vacuoles. Relatively large, ringshaped or uniform dark bodies are assumed to be lipid inclusions.

Ultrastructural aspects of the first postmeiotic mitosis and cytokinesis in the pollen grain of allium cepa l

1978 ◽  
Vol 36 (2) ◽  
pp. 428-429
Author(s):  
M.I. Rodriguez-Garcia ◽  
M.C. Risueno
Keyword(s):  
Allium Cepa ◽  
Research Work ◽  
Generative Cell ◽  
Lateral Position ◽  
Mitotic Division ◽  
Pollen Grain ◽  
Pollen Wall ◽  
Central Position ◽  
Haploid Nucleus ◽  
Allium Cepa L

This report deals with research work on first pollen grain mitosis and the formation of vegetative and generative cells in Allium cepa L.The haploid nucleus of young microspores has a long interphase period which starts when the microspores begin to free themselves from the surrounding special callose wall and finishes when a central vacuole is formed in their cytoplasm. The pollen wall (Exine and Intine) is formed during this period.Before the mitosis, a large vacuole is formed in the cytoplasm. The microspore nucleus that previously occupied a central position in the cell can now be found in a lateral position generally on the opposite side of the porus. At this moment the nucleus enters prophase and the mitotic division takes place. This is characterized by the formation of an asymmetric spindle and as a result two unequal daughter cells are formed (Fig. 1) : the vegetative cell is larger and its nucleus remains near the centre of the pollen grain, whilst the generative cell is smaller and at the beginning lies close to the pollen wall (Fig. 2, 3).

The Ultrastructure and Ontogeny of Pollen in Helleborus Foetidus L

1972 ◽  
Vol 11 (1) ◽  
pp. 111-129
Author(s):  
P. ECHLIN
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Wall ◽  
Vegetative Cell ◽  
Generative Cell ◽  
Ultrastructural Level ◽  
Mitotic Division ◽  
Tube Formation ◽  
Pollen Grain ◽  
Granular Body ◽  
Development Proceeds

The final stages of Helleborus pollen-grain ontogeny, which culminate in maturation and germination of the grain, have been investigated at the ultrastructural level. Following the deposition of primary and secondary exine, and during the early stages of intine formation, the microspore passes through a vacuolate phase, in which the cytoplasm appears devoid of most organelles other than the prominent nucleus. The formation of the vacuole results in the displacement of the nucleus to one side of the pollen grain. The vacuole quickly disappears and a number of organelles reappear in the cytoplasm, in particular the dictyosomes and strands of endoplasmic reticulum, with associated grey bodies. Following mitotic division of the pollen grain, the first signs of the generative cell wall appear as a pair of tightly appressed unit membranes in the narrow strand of cytoplasm separating the two newly formed generative and vegetative nuclei. As development proceeds, the space between the two membranes gradually fills with an electron-transparent material similar to the substance found in the numerous dictyosome-derived vesicles which, together with the endoplasmic reticulum, are both closely associated with the developing cell wall. The generative cell wall fuses with the cellulosic intine, which has gradually increased in amount during these stages, and the cell division is complete. The smaller generative cell contains a prominent nucleus and a small amount of cytoplasm devoid of plastids and most other organelles. The larger vegetative cell also contains a prominent nucleus and a large amount of cytoplasm containing amyloplasts, mitochondria, dictyosomes and endoplasmic reticulum, and abundant ribosomes, many of which are in a polysome configuration. The final stages in development are characterized by a progressive decrease in the amount of starch in the vegetative cell and an increase in the size of grey bodies, many of which are invested in multilayered shrouds of endoplasmic reticulum. The generative cell wall disappears and a multivesicular/granular body gradually appears at the periphery of the pollen grain. The granular-vesicular material, which is formed from the dictyosomes and/or the degenerating plastids, is thought to represent metabolic reserves necessary for pollen-tube formation. One or more pollen tubes emerge from the apertural sectors of the pollen grain, and maturation of the grain is complete.

scholarly journals Elektronenmikroskopische Beobachtungen an der generativen Zelle von Oenothera hookeri Torr. et Gray

1963 ◽  
Vol 18 (7) ◽  
pp. 562-566 ◽  
Author(s):  
Lothar Diers
Keyword(s):  
Endoplasmic Reticulum ◽  
Inclusion Bodies ◽  
Generative Cell ◽  
Cytoplasmic Inclusion ◽  
Pollen Grain ◽  
Lipid Bodies ◽  
Lamellar System ◽  
Varying Thickness ◽  
Cytoplasmic Inclusion Bodies ◽  
Germinating Pollen

In the germinating pollen grain the generative cell shows the structure of a meristematic cell. It is separated from the cytoplasm of the vegetative cell by a clearly visible wall, on the average about 30 — 60 mµ thick. This wall appears to be formed by two darkly stained membranes including a lighter region of varying thickness. In the generative cell there are a big nucleus, plastids which show a scarcely developed lamellar system but no starch grains, mitochondria, dictyosomes. very probably lipid bodies and unidentified cytoplasmic inclusion bodies. The endoplasmic reticulum is continuous with the membranes of the nuclear encelope and extends through the cytoplasmic substance in which no vacuoles are recognizable.

Structure study of the chalcogens and chalcogenides by X-ray absorption fine structure

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Hiroyuki Ikemoto ◽  
Takafumi Miyanaga
Keyword(s):  
Fine Structure ◽  
Covalent Bond ◽  
Narrow Channel ◽  
Structure Study ◽  
Chain Structure ◽  
Covalent Bonds ◽  
X Ray ◽  
Absorption Fine ◽  
Amorphous States ◽  
X Ray Absorption

AbstractIn this review, we make a survey of the structure studies for the chalcogen elements and several chalcogenides in liquid, amorphous and nanosized state by using X-ray absorption fine structure (XAFS). The chalcogen elements have hierarchic structures; the chain structure constructed with the strong covalent bond as a primary structure, and the weaker interaction between chains as a secondary one. Existence of these two kinds of interactions induces exotic behaviors in the liquid, amorphous and nanosized state of the chalcogen and chalcogenides. XAFS is a powerful structure analysis technique for multi-element systems and the disordered materials, so it is suitable for the study of such as liquid, amorphous and nanosized mixtures. In section 2, the structures for the liquid state are discussed, which show the interesting semiconductor-metal transition depending on their temperatures and components. In section 3, the structure for the amorphous states are discussed. Especially, some of chalcogens and chalcogenides present the photostructural change, which is important industrial application. In section 4, the structures of nanosized state, nanoparticles and isolated chain confined into the narrow channel, are discussed. The studies of the nanoparticle and the isolated chain reveal the alternative role between the intrachain covalent bonds and the interchain interaction.

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