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.

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.

The Ultrastructure and Ontogeny of Pollen in Helleborus Foetidus L

1968 ◽  
Vol 3 (2) ◽  
pp. 161-174
Author(s):  
P. ECHLIN ◽  
H. GODWIN
Keyword(s):  
Cell Wall ◽  
Tapetal Cell ◽  
Pollen Grains ◽  
Ultrastructural Level ◽  
Low Molecular Weight ◽  
Cell Organelles ◽  
Helleborus Foetidus ◽  
Ubisch Bodies ◽  
Ubisch Body ◽  
Development Proceeds

The ontogeny of the tapetum and Ubisch bodies in Helleborus foetidus L. has been examined at the ultrastructural level, and their development has been closely linked with that of the sporogenous cell and pollen grains. During development the tapetum passes through successive phases of synthesis, maturity and senescence, ending in complete dissolution. During the anabolic phase of growth, precursors of the Ubisch bodies are formed as spheroidal vesicles of medium electron density within the tapetal cytoplasm; they are associated with a zone of radiating ribosomes, which, as development proceeds, can clearly be seen to be situated on strands of endoplasmic reticulum. The callose special wall round the microspores and the tapetal cell wall now disintegrate and the pro-Ubisch bodies are extruded through the cell membrance of the tapetal cells, where they remain on the surface of the anther cavity and soon become irregularly coated with sporopollenin. Deposition of sporopollenin continues on the Ubisch bodies at the same time as upon the exines of the developing pollen grains. In both cases, the later stages of sporopollenin deposition are associated with electron-transparent layers of unit-membrane dimensions appearing in section as white lines of uniform thickness. Continuing deposition of sporopollenin leads to the formation of compound or aggregate Ubisch bodies. It is conjectured that the sporopollenin is synthesized from the compounds of low molecular weight released into the anther loculus by the breakdown of the callose special wall and the tapetal cell wall. The final stages of tapetal autolysis involve the disappearance of all the cell organelles. An attempt is made to relate the findings to those described in other recent studies on Ubisch body formation and to combine them in a common ontogenetic pattern.

scholarly journals Autoradiographic studies of DNA and histone synthesis in successive differentiation stages of pollen grain in Hyacinthus orientalis L.

2014 ◽  
Vol 50 (3) ◽  
pp. 367-380 ◽  
Author(s):  
Elżbieta Bednarska
Keyword(s):  
Dna Replication ◽  
Dna Synthesis ◽  
Vegetative Cell ◽  
Developmental Stages ◽  
Generative Cell ◽  
Pollen Grain ◽  
Cell Nuclei ◽  
Hyacinthus Orientalis ◽  
Histone Synthesis ◽  
Generative Cells

DNA and histone synthesis in five consecutive morphological stages of <em>Hyacinthus orientalis</em> L. pollen grain differentiation were studied autoradiographically. DNA synthesis was found to occur in both the generative and the vegetative cell. DNA replication in the generative cell took place when the generative cell was still adhered to the pollen grain wall but already devoid of callose wall. DNA synthesis in the generative cell slightly preceded that in the vegetative cell. Histones were synthesized in phase S of the generative and vegetative cell. In the generative cell histone synthesis also continued at a lower level after completion of DNA replication. In the developmental stages under study the nuclei of the generative cells were decidedly richer in lysine histones than vegetative cell nuclei.

scholarly journals Ultrastructural transformations in the cytoplasm of differentiating Hyacinthus orientalis L. pollen cells

2014 ◽  
Vol 57 (2) ◽  
pp. 235-245 ◽  
Author(s):  
Elżbieta Bednarska
Keyword(s):  
Vegetative Cell ◽  
Generative Cell ◽  
Pollen Grain ◽  
Border Region ◽  
Ultrastructural Changes ◽  
Grain Development ◽  
Callose Wall ◽  
Highly Active ◽  
Hyacinthus Orientalis

The sequence of ultrastructural changes in the cytoplasm during the successive stages of pollen grain development in <em>Hyacinthus orientulis</em> pollen cells was studied. The cytoplasmic transformations of the generative cell included the elimination of plastids, increase in the number of mitochondria, assumption of a spindle shape with the aid of microtubules and the characteristic development of the vacuole system with the formation of so-called colored bodies. The cytoplasmic transformations of the generative cell encompassed changes in the plastids, which began to accumulate starch soon after the cell was formed, then released it shortly before anthesis, an increase in the number of mitochondria and an increase in the number of highly active dictyosomes just before anthesis. Changes in the structure of the border region between the differentiating pollen cells were associated mainly with the periodical appearance of a callose wall and the presence of lysosome-like bodies in the cytoplasm of the vegetative cell surrounding the generative cell. They arose soon after the disappearance of the callose wall and disappeared shortly before anthesis.

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).

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.

An ultrastructural and Nomarski-interference study of the sperms of barley

1973 ◽  
Vol 51 (3) ◽  
pp. 601-605 ◽  
Author(s):  
David D. Cass
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Wall ◽  
Light Microscope ◽  
Vegetative Cell ◽  
Small Cells ◽  
Unit Membrane ◽  
Light Microscope Level ◽  
Male Gametes ◽  
Interference Study ◽  
Common Cell

Male gametes of barley are small cells with conspicuous nuclei and compact cytoplasm. The cytoplasm is limited by a unit membrane. Between sperm and vegetative cell unit membranes is a thin, relatively homogeneous region which failed to stain with common cell wall specific reagents at the light microscope level. Cytoplasmic contents include mitochondria, ribosomes, dictyosomes, endoplasmic reticulum, and microtubules. Microtubules occur nearly around the entire periphery of a transected sperm, sometimes occurring in clusters of up to 16 tubules. Their chief orientation is longitudinal. No plastids or plastid-like organelles were observed. Chromatin in the nucleus is condensed; when present, there are two nucleoli. Living sperms observed with Nomarski-interference optics exhibited marked cytoplasmic activity, but no directional motility. Observed transitions from spindle-shaped to more spherical sperms could be facilitated by changes in disposition of sperm microtubules.

The Formation of the Generative Cell in the Pollen Grain of Endymion Non-Scriptus (L)

1968 ◽  
Vol 3 (4) ◽  
pp. 573-578
Author(s):  
R. E. ANGOLD
Keyword(s):  
Cell Wall ◽  
Somatic Cells ◽  
Generative Cell ◽  
Cell Plate ◽  
Pollen Grain ◽  
Generative Nucleus ◽  
A Cell ◽  
Generative Nuclei

The generative cell wall in the pollen grain of Endymion non-scriptus is formed, as in somatic cells, from a cell plate between the vegetative and generative nuclei. This wall curves around the generative nucleus, and fuses with the intine to enclose the generative cell. The generative cell is subsequently freed from the intine by the constriction of the generative cell wall between the generative nucleus and the intine.

scholarly journals Optical and ultrastructural study of the pollen grain development in hermaphrodite papaya tree (Carica papaya L.)

2008 ◽  
Vol 51 (3) ◽  
pp. 539-545 ◽  
Author(s):  
Lídia Márcia Silva Santos ◽  
Telma Nair Santana Pereira ◽  
Margarete Magalhães de Souza ◽  
Pedro Correa Damasceno Junior ◽  
Fabiane Rabelo da Costa ◽  
...  
Keyword(s):  
Carica Papaya ◽  
Generative Cell ◽  
Pollen Grains ◽  
Male Gamete ◽  
Mitotic Division ◽  
Pollen Grain ◽  
Grain Development ◽  
Normal Pattern ◽  
Papaya Tree ◽  
Mother Cells

The objective of this study was to describe the pollen grain development in hermaphrodite papaya tree. The flower buds were collected at different stages of the development and the anthers were treated chemically for observation under optical and electronic transmission microscopes. The pollen grain development followed the normal pattern described for the Angiosperms. The pollen grain development was described from meiocyte to the mature pollen grain. In the microsporogenesis, the microspore mother cells or the meiocytes underwent meiosis giving rise to the tetrads that were enclosed by the calose. Later, the tetrads were released by the dissolution of the calose by calase activity and microspores underwent mitosis. Microgametogenesis was characterized by asymmetrical mitotic division of each microspore giving rise to bi-nucleate pollen grains. The structures similar to the plastids were found in the cytoplasm and close to the nucleus of the generative cell. Gradual degeneration was observed in the tapetum during the male gamete development.

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