Showing papers on "Ultrastructure published in 1988"

Phragmites australis– A preliminary study of soil‐oxidizing sites and internal gas transport pathways

Abstract: SUMMARY The possible pathways of oxygen transport within Phragmites australis and out into the soil were investigated by means of pressurized air flow, methylene-blue dye and by anatomical studies. In most cases, gas was easily forced through the plants, thus demonstrating gas-space connexion between aerial shoot, rhizomes and roots and a relatively low resistance to flow. Gas-space connexions between the pith cavity and cortical aerenchyma in the rhizomes were also detected and were investigated anatomically they are present only in nodal regions just above the insertion of the pith diaphragm and take the form of radial channels through the stelar cylinder. Similar pathways in the culm connect the pith cavity with nodal lines of stomata and it is suggested that these regions may often form the major oxygen entry point to the rhizome-root system. A failure to effect pressurized gas-flow through some rhizomes led to the detection of secondary barriers to longitudinal gas-flow. Seemingly a response to wounding, these are an impenetrable barrier to gases, to flooding, and probably also to microorganisms, and take the form of tylosoidal growths from and within regions of stellate-and/or circumvascular-parenchymas such as those of the nodal diaphragms. Stellate parenchymas of various sorts were found to be a common feature of the gas-path in Phragmites and evidently they form an important component of the gas-space system occurring within the nodal radial channels, the nodal diaghragms and, rather unusually, the root-shoot junctions where they must confer a porosity which is higher than for most plants. As measured by methylene-blue oxidation, oxygen release from underground parts was most rapid from young adventitious and secondary roots and particularly basal tufts of fine laterals. Zones of oxidation also occurred around the sprouting tips of horizontal and vertical rhizomes. Dormant tips showed very little oxidizing power, whilst the rhizomes themselves and the older parts of adventitious roots showed none. This was associated with cuticularization of the rhizome and hypodermal suberization and lignification; oxygen-impermeable regions of the roots were also hyperdermally suberized and lignified. The findings are discussed in relation to the use of Phragmites in sewage-treatment beds.

Structural and ultrastructural disorders in cadmium‐treated bush bean plants (Phaseolus vulgaris L.)

Abstract: summary The effect of a growth reducing cadmium concentration (5 μg ml−1) on the structure and ultrastructure of leaves, stomata and plastids of bush bean plants (Phaseolus vulgaris L. cv. Contender) grown on perlite was studied using light, transmission electron and scanning electron microscopy. The structural and ultrastructural alterations observed were not directly related to the average Cd content of the whole organs. In roots, where the highest Cd concentration was found, plastid ultrastructure was hardly affected, while in the upper parts of the plant the chloroplasts showed severe alterations. Disruption of chlorophyll synthesis and plastid ultrastructure was greater in young trifoliate leaves than in primary leaves. The effects of Cd toxicity on the structure and ultrastructure and their physiological implications are discussed in relation to Cd uptake.

An ultrastructural study of amphidinium poecilochroum dinophyceae a phagotrophic dinoflagellate feeding on small species of cryptophytes

Abstract: The general ultrastructure of A. poecilochroum is typical of dinoflagellates. The proximal part of the longitudinal flagellum possesses a previously undescribed structure consisting of three dense ...

Ultrastructure and synaptic relationships of calbindin-reactive, Dogiel type II neurons, in myenteric ganglia of guinea-pig small intestine.

Abstract: Immunoreactivity for calbindin D 28K was localized ultrastructurally in nerve cell bodies and nerve fibres in myenteric ganglia of the guinea-pig small intestine. Reactive cell bodies had a characteristic ultrastructure: the cytoplasm contained many elongate, electron-dense mitochondria, numerous secondary lysosomes that were peripherally located, peripheral stacks of rough endoplasmic reticulum and dispersed Golgi apparatus. The cells were generally larger than other myenteric neurons and had mainly smooth outlines. The cytoplasmic features of these neurons were shared by a small group of immunonegative cells, but the majority of negative cells had clearly different ultrastructural appearances. Of 310 cells from 16 ganglia that were systematically examined, 38% were immunoreactive for calbindin, 10% were unreactive but similar in ultrastructure to the calbindin-reactive neurons and 51% were unreactive and dissimilar in the appearance of their cytoplasmic organelles. Immunoreactive varicosities with synaptic specializations were found on most unreactive neurons, but were markedly less frequent on the calbindin-immunoreactive cell bodies. Non-reactive presynaptic fibres were also more common on non-reactive neurons than on the calbindin-positive cell bodies. Numerous reactive varicosities, some showing synaptic specializations, were found adjacent to other fibres in the neuropil. Light microscopic studies show calbindin immunoreactive neurons to have Dogiel type-II morphology. Thus the present work links distinguishing ultrastructural features to a specific nerve cell type recognized by light microscopy in the enteric ganglia for the first time.

Ultrastructure of the hepatopancreas of the Pacific white shrimp, Penaeus vannamei (Crustacea: Decapoda)

Abstract: Fourteen specimens of the hepatopancreas of the Pacific white shrimp, Penaeus vannamei, were prepared for examination with the transmission and scanning electron microscopes and with the light microscope. The histology and ultrastructure of this organ is similar to that seen in other Decapoda. At the ultrastructural level, it was observed that B-cells rupture at approximately the level of gap junctions located on the lateral plasma membranes of the cells, and discharge the contents of their large vacuoles into the intercellular space. This efflux of enzymatic material may be the mechanism by which cells are released from the wall of the tubule at the proximal end: the rupture and collapse of a B-cell may be analagous to the removal of the keystone which supports an arch. Deprived of support, and lacking structural adaptations for cohesion (there are no desmosomes or interdigitations in the epithelium) and with the intercellular material digested, the remaining intact cells collapse into the lumen of the tubule. The lysis of individual cells of all types - R-, F-, and B-cells - may contribute to the tubules’ total complement of digestive enzymes.

Structural and functional aspects of porcine placental microvasculature.

Abstract: The microvascular architecture of the pig placenta was studied by serial semithin histological sections for light microscopy, which were compared with scanning electron microscopy of artificially exposed materno-fetal contact surfaces as well as of vessel casts prepared from the maternal, fetal, and combined maternal and fetal sides.

An ultrastructural and morphometric analysis of the Sertoli cell during the spermatogenic cycle of the rat

Abstract: The ultrastructure of Sertoli cells from selected stages of the spermatogenic cycle was assessed by morphometric analysis which showed significant changes in the morphological features of Sertoli cell cytoplasm at the commencement of the cycle (stage II) compared to the middle (stages VII-VIII) and the completion of the cycle (stages IX-XIV). Total volume and surface area of organelles (rough and smooth endoplasmic reticulum (ER), lysosomes, mitochondria and Golgi) exhibited stage-dependent and cyclic variations as did the total surface area of Sertoli cell plasma membrane. Polarization of cytoplasmic organelles to basal or columnar regions of the Sertoli cell, exhibited particularly by the Golgi, rough ER and lysosomes also showed marked cyclic fluctuations during the spermatogenic cycle. Rough and smooth ER exhibited the most dramatic stage-dependent changes in total volume and surface area the former being respectively largest and smallest in stages VII-VIII and XIII-XIV, the latter organelle presenting the reverse pattern in these two groups of stages. Similar stage-dependent alterations of lysosome volume and surface area were also noted, being maximal during stages XIII-XIV-II and reaching a nadir at stage VIII. Although the functional role of most Sertoli cell organelles and inclusions remain largely unknown, the present study suggests that the cyclic and stage-dependent variations in ultrastructure probably reflect major changes in Sertoli cell function necessary for the regulation of the spermatogenic cycle.

Sperm Binding and Penetration during Ascidian Fertilization

Abstract: Introduction In order for the sperm to enter and fertilize the egg it must first bind to the egg vestments, a step that is usually quite species-specific. Then, the sperm must penetrate several barriers to reach the egg surface where gamete fusion finally takes place. Most of the research into the mechanisms of these processes have involved the gametes of sea urchins and mammals. Ascidians, which come from near the base of the evolutionary lineage of chordates are, nevertheless, invertebrates, sharing the deuterostome heritage of the echinoderms. Given their intermediate evolutionary position we would expect that a study of fertilization in ascidians would be similar to mammals and sea urchins in some respects, but unique in others, yielding new ways of looking at the overall process. Ascidian eggs are unusually well-guarded by coverings which are barriers to the sperm arriving at the egg surface. The sperm first encounter a layer of follicle cells which function in egg flotation in some species (37) and are necessary for fertilization in others (26, 9). After passing through the narrow clefts between these cells, the sperm binds to the surface of the vitelline coat (VC) or chorion. Sperm then pass through the VC and the perivitelline space before they finally fuse with the oocyte plasma membrane. (Within the perivitelline space are the test cells). These coverings are everybit as complex as those of the mammalian egg, yet the sperm is among the simplest known. In this review we consider how this seemingly simple sperm manages to arrive at the surface of such a well-guarded egg.

Ultrastructural features of type II alveolar epithelial cells in early embryonic mouse lung.

Abstract: Immunofluorescence studies of type II alveolar epithelial cells indicate that they first apper in the pseudoglandular period of mouse lung development (around day 14.2). They are the only cell type to line the prospective pulmonary acinus at this time. The ultrastructural characteristics of this cell are defined by investigating embryos aged 13–16 days with transmission and scanning electron microscopy. Early embryonic type II cells appear as low-columnar or cuboid cells having large, approximately round nuclei and distinct ultrastructural features, including a welldeveloped Golgi apparatus with many associated vesicles, multivesicular bodies, dense bodies, and large apical and basal glycogen fields. These fields represent a distinctive property of the cell. Frequently, they show compartmentalization due to the presence of membrane systems, and association with dense bodies of various sizes.

The interaction between Neisseria gonorrhoeae and the human cornea in organ culture. An electron microscopic study.

Abstract: Explants of human corneas in organ culture were used to study the interaction betweenNeisseria gonorrhoeae and human corneal epithelium at an ultrastructural level. Scanning electron microscopy revealed that infection of the corneal explants withN. gonorrhoeae resulted in a rapid adherence of the bacteria to the cell surface. This attachment was probably mediated by pili since only piliated strains were able to adhere to the cells. Upon attachment the bacteria appeared to become engulfed by the epithelial cells. Transmission electron microscopy revealed gonococci apparently lying within vacuoles inside the cells within 1 h after inoculation of the bacteria. At prolonged infection (8–24 h), the thickness of the epithelium was found to be considerably reduced. This thinning of the cornea was probably caused by a continuous desquamation of infected cells. Taken together, the present data demonstrate thatNeisseria gonorrhoeae is able to adhere and penetrate into intact corneal epithelium and furthermore indicate that human cornea explants in organ culture are a useful model in studies of bacterial-epithelial cell interaction.

Effects of oxygen concentration on embryonic development in rats: a light and electron microscopic study using whole-embryo culture techniques

Abstract: By using a whole-embryo culture technique (New 1978), the effects of oxygen concentration (5%, 20% and 95% oxygen) on embryonic development in the rat were investigated by light and electron microscopy. The best embryonic development occurred when the 9.5-day-old embryos were cultured for 24 h with 5% oxygen, and the 10.5-day-old embryos with 20% oxygen (optimum oxygen concentration). When the 9.5- and 10.5-day-old embryos were cultured for 24 h with too little or too much oxygen, retardation of the embryonic growth and abnormal development was observed. Using light microscopy, numerous degenerating cells, exhibiting granular deposits in the cytoplasm, were seen, but the distribution of the degenerating cells was quite different between the two groups. With electron microscopy, the most striking feature of the degenerating cells in the embryos cultured with too little oxygen, was the extreme swelling of the mitochondria without any morphological alterations of the nucleus or the other cell organelles. On the other hand, the characteristic feature of the degenerating cells in the embryos exposed to too much oxygen, was the formation of phagolysosomes in the cytoplasm. Morphological alterations of the nucleus or mitochondria were not evident. In the present study, the possible teratogenic mechanism of too much or too little oxygen in the whole-embryo culture of the rat embryo is discussed.

The role of cellular parenchyma and extracellular matrix in the histogenesis of the paruterine organ of Mesocestoides lineatus (Platyhelminthes: Cestoda)

Abstract: The cellular parenchyma of adult Mesocestoides lineatus consists primarily of muscle cells divided into myofibrils, myocytons with numerous greatly dilated cisternae of granular endoplasmic reticulum, and glycogen-rich myocytons with lipid droplets and membranous whorl inclusions. The latter are connected to each other by numerous gap junctions. Other mesenchymally arranged cells in the parenchyma are calcareous corpuscle cells. The extracellular matrix (ECM) consists of an electron-lucent ground substance and numerous filaments. During histogenesis of the paruterine organ wall, the myocytons surrounding the posterior end of the uterus undergo extensive flattening, followed by cellular deterioration. There is a concomitant reduction in ECM/cell ratio. The paruterine organ lumen dilates and then its uterine epithelium breaks down as the wall thickens, so that the late gravid paruterine organ consists of a thick wall of membranous sheets enclosing the egg mass. Parenchymal cells in other regions of the proglottid do not undergo change. These data provide evidence for epithelial-mesenchymal-ECM interactions in the development of an epithelio-mesenchymal organ in the Platyhelminthes.

Quantitative ultrastructure and protein composition of date palm (Phoenix dactylifera) seeds: a comparative study of endosperm vs. embryo

Abstract: Comparative studies on the ultrastructure and protein composition of the embryo and endosperm of date palm (Phoenix dactylifera L.) were conducted. Cells of the embryo cotyledon and endosperm function in reserve storage and contained cell walls, nuclei, and cytoplasm rich in lipid and protein bodies. Morphometric analysis from light and electron micrographs showed that the cell walls of the endosperm occupied 65% of the total cell volume, but only 6% in the embryo. The protein bodies of the endosperm accounted for 11%, whereas those of the embryo occupied more than half of the total cell volume. The volume of organelles and organelle-free cytoplasm in the endosperm was negligible, suggesting that most of the extractable endosperm proteins are localized in the protein bodies. Extractable proteins in the embryo may come from cytoplasm, protein bodies, and other organelles. The endosperm contains relatively lower amounts of proteins than does the embryo. Proteins extracted from both tissues were compared using SDS-polyacrylamide gel electrophoresis, tube gel isoelectric focusing, and two-dimensional electrophoresis. Proteins of both the tissues were heterogeneous in molecular mass and charge. The majority of the proteins were similar in molecular mass and charge in the two tissues, suggesting that most of the storage proteins are probably the same. However, there were also several embryo- and endosperm-specific proteins apparent in both the first- and second-dimension gels. The endosperm-specific proteins may play an important role in germination and seedling development.

Fluorescence microscopy: An aid to the elucidation of ascomycete structures

Abstract: Freshly collected specimens and preserved herbarium material of ascomycetes from a variety of orders were dissected to obtain slide preparations of ascogenous cells, paraphyses, asci and ascospores. Phase contrast, differential interference contrast and fluorescent light microscopy were used to examine each species in a range of mountants including water, erythrosin, Melzer's reagent, lactophenol and calcofluor. Detailed results are provided for Diatrype disciformis, Hypoxylon fuscum, Peltigera horizontalis and Pleurostoma ootheca . Asci of Diatrype disciformis were found to have more than one functional wall layer, and its ascogenous cells are described and illustrated for the first time. Hitherto unknown fluorescent rings are described in asci and ascospores of Hypoxylon fuscum . In Peltigera horizontalis fluorescent light microscopy confirms an earlier TEM study of ascus structure and dehiscence in the genus, and asci of Pleurostoma ootheca are described as having lateral thickening, a strongly fluorescing base and a mode of secession from their ascogenous cells apparently previously unknown in the ascomycetes. Most of these features could not be seen at all, or only with difficulty without fluorescent light. Each appeared similar in fresh collections and herbarium specimens dried and preserved for up to one hundred years. Fluorescent light microscopy can provide new information of great value to students of the ascomycetes.

Ultrastructural Correlates of Antimycotic Treatment

Abstract: The descriptive ultrastructure of a large variety of fungal species either grown under in vitro culture conditions or in situ during infection of the host has been reported in detail. Morphologic characterization of yeasts, dimorphic fungi, and filamentous fungi has been done using scanning electron microscopy to elaborate the surface structure, transmission electron microscopy to reveal the internal subcellular organelles, and freeze-fracture electron microscopy to display some intramembranous molecular structures (2, 3, 5, 6, 12, 17, 28, 31, 45, 50, 61, 64, 66, 70, 75, 83, 85, 112, 113, 124). For a long time the detailed description of fungal substructure has been hampered by the lack of adequate methodology. From the early days of explorative research, especially the field of transmission electron microscopy has been encumbered with difficulties of clear-cut visualization, hence obscuring the interpretation of the observations (17).

Ultrastructure of human retroviruses.

Abstract: We compared the ultrastructure of the human retroviruses by thin-section electron microscopy of infected lymphocytes. Virus particles form at the plasma membrane without involvement of a cytoplasmic precursor. Budding forms of human T-cell leukemia virus types I and II (HTLV-I and -II) consist of a crescent-shaped nucleoid separated from the envelope by an intermediate layer. Mature forms of these viruses are about 100 nm in diameter. The nucleoid is electron lucent and almost completely fills the virion. There is about a 10-nm space between the envelope and nucleoid. The envelope has fuzzy surface projections. HTLV-I and -II resemble other type C retroviruses in morphology. Budding forms of human immunodeficiency virus (HIV, LAV, HTLV-III) also have a crescent-shaped nucleoid but not an intermediate layer between the core and envelope. The envelope has rod-shaped surface projections. Mature forms of HIV have an electron-dense nucleoid that is eccentric and bar- or cone-shaped. Particles have the same ultrastructure as retroviruses of the Lentivirus genus. HIV is readily distinguishable from HTLV-I and -II by thin-section electron microscopy. HIV is usually found in extracellular spaces by transmission electron microscopy of thin sections, and scanning electron microscopy of HIV-infected T4 lymphocytes also shows many particles on the surface of these cells. Lymphadenopathy-associated virus type II (LAV-II) has the same internal ultrastructure as HIV, but its surface projections are more prominent, being about three times the length of those of HIV. Human T lymphotropic virus type IV (HTLV-IV) has the same morphology as LAV-II.

Mucochondroid (mucous connective) tissues in the heads of teleosts.

Abstract: The distribution and structure of mucochondroid tissues in the heads of teleosts has been studied in 56 species from 26 families. The tissues could also be called mucous connective tissue and have previously been known as basophilic gelatinous tissue. They are a heterogeneous group of tissues that contain fibroblasts (type example — the subcutaneous mucochondroid of the Cobitidae) or hyaline cells (type example — the mucochondroid around the medulla oblongata and spinal cord of Rasbora heteromorpha), embedded in a pale-staining matrix in which there are variable numbers of collagen fibres and blood vessels. Mucochondroid tissue is especially common beneath the skin, in labial folds, around olfactory and accessory olfactory sacs, in opercular valves and beneath the sensory epithelia of the stato-acoustic organ. The histochemistry of several mucochondroid tissues has been studied in Misgurnus anguillicaudatus, Acanthopsis choirorhynchus, gnathonemus petersi and Cyclopterus lumpus. They have widely different amounts and types of glycoproteins, glycosaminoglycans and connective tissue fibres. The ultrastructure of subcutaneous mucochondroid is described in Acanthophthalmus semicinctus. Its cells contain little rough endoplasmic reticulum and a small Golgi apparatus, but numerous plasmalemmal vesicles, especially in the cell processes. The matrix contains 23–35 nm diameter granules, collagen and 11–12 nm diameter microfibrils. The similarities between mucochondroid and hyaline cell chondroid (cartilage) at the ultrastructural level, are more obvious than their differences.

Arthropod immune system: I. Comparative light and electron microscopic accounts of immunocytes and other hemocytes of Blattella germanica (Dictyoptera: Blattellidae)

Abstract: Light microscopy (LM) and scanning (SEM) and transmission electron microscopy (TEM) disclose seven types of hemocytes in adults of the German cockroach, Blattella germanica (Dictyoptera: Blattellidae)-namely, prohemocytes (PR), granulocytes (GR), plasmatocytes (PL), spherulocytes (SP), adipohemocytes (AD), coagulocytes (CO), and oenocytoids (OE). Their shape, size, surface appearance, and internal ultrastructure are characterized here. The shapes and relative sizes of hemocytes noted in vitro have been compared with those flowing through the wing veins (in vivo). The GRs constitute more than 90% of the hemocyte population and have roles in the defense system such as encapsulation and phagocytosis. They are characterized by numerous cytoplasmic granules and marginal microtubular bundles, which are commonly noted in the blood cells of both vertebrates and invertebrates, but have been rarely reported in insect hemocytes. The PRs are characterized by being spherical and small, having a relatively large nucleus and a small area of cytoplasm. The polymorphic PLs have some micropapillae on the cell surface and fewer granules than the GRs. The SPs are characterized by an oblate shape, raspberrylike appearance in SEM, and many spherules in the cytoplasm. The ADs are spherical and have large, refringent fat droplets. The COs possess a distinctive cartwheellike appearance when observed by LM but resemble GRs in TEM preparations. The OEs are opaque and often have an eccentric nucleus. Of the seven types of hemocytes, all, except the COs, can be recognized both in vivo and in vitro by LM; the COs can be recognized only in vitro. SEM does not allow the COs to be distinguished from the GRs, except in samples in which coagulation has occurred. All hemocyte types can be recognized by TEM. Thus, all three types of microscopy allow the various types of hemocytes to be recognized; unequivocal discrimination among the cells is best achieved by combining all the three kinds of microscopy.

Mouse hepatoblastomas: a histologic, ultrastructural, and immunohistochemical study.

Abstract: Hepatoblastomas from B6C3F1 and BALB/c mice were examined by light and electron microscopy and by immunohistochemical reactions for alpha-fetoprotein, keratin, and vimentin. Tumors occurred in one group of a chronic bioassay for the interaction of diet, genetic strain, and the carcinogen, 2-acetylaminofluorene. Tumors had several populations (including epithelial and mesenchymal cells) in various stages of differentiation. Neoplastic epithelial cells had features of embryonal hepatocytes, such as sparse cytoplasmic organelles, absence of glycogen, abundant free ribosomes, occasional bile canaliculi, and peroxisome-like dense bodies. Embryonal fibroblast-like cells had pleomorphic and folded nuclei with prominent perinuclear chromatin and dispersed cytoplasmic organelles. Fibroblast-like cells were surrounded by bundles of collagen fibrils. Intermediate or transitional types of cells were seen. No tumor cells were immunoreactive for mouse alpha-fetoprotein (AFP) antibody, unlike those in hepatocellular adenomas or carcinomas. Epithelial and mesenchymal tumor cells contained intermediate filaments throughout the cytoplasm; some of these cells stained for keratin but not for vimentin. These findings suggest that mouse hepatoblastomas are derived from bipotential liver blastema cells and are composed of a mixture of several cell populations.

The ultrastructure and possible relationships of four obligate anaerobic chytridiomycete fungi from the rumen of sheep.

Abstract: Zoospores and vegetative growth phases of three cellulolytic rumen chytridiiomycetes, Piromonas, Sphaeromonas and NF1 have been examined by electron microscopy and compared with published and new data on Neocallimastix. The four genera have some 16 distinctive ultrastructural features in common, which collectively may be used to define the group. Some of the common features may individually be sufficient to distinguish these obligate anaerobes from facultative and aerobic chytridiomycetes. These features are the presence of hydrogenosomes at all stages of the life cycle, the presence in rhizoids and sporangia of characteristic crystals coated with hexagonal arrays of particles, and in zoospores the presence of distinct surface layers on the motility organelles and cell body respectively, the organization of the ribosomes into helical and globular arrays and the structures associated with the kinetosomes.

Ultrastructure of the cell envelope of Bacteroides forsythus strain ATCC 430377T

Abstract: The Ultrastructure of the cell envelope of Bacteroides forsythus strain ATCC 43037T was studied by electron microscopy. The thin-sectioned cells had a surface layer (S-layer) consisting of serrated subunits (appr. 10 nm) outside the outer membrane. The bulk of the negatively stained, freeze-etched and metal-shadowed specimens showed an orthogonal lattice. However, lines parallel to the long axis of the cell were aacentuated, suggesting an oblique symmetry, though occasional fragments of the S-layer showed a typical tetragonal pattern. Preliminary image processing studies could not exclude either type of symmetry. The presence of periodically arranged inner cell envelope structures reported earlier could not be confirmed.

Ultrastructural features of Aloe ciliaris pollen

Abstract: Both the internal anatomy and the external morphology of the mature pollen grain of Aloe ciliaris have been studied, together with the cytological changes occurring during pollen activation. In mature pollen, the generative cell (GC) and the vegetative nucleus (VN) are closely associated with each other, and both can be found in the central part of the grain. In the generative cytoplasm, some organelles and microtubular bundles are present. In the vegetative cell, dictyosomes, stacks of rough endoplasmic reticulum, mitochondria, plastids, vacuoles, ribosomes, and masses of fibrillar material have been described. During pollen activation, important changes occur in both the generative and vegetative cells (VC). In the GC, the microtubular bundles become clearly visible, and the GC and VC gradually move towards the germ pore. The RER cisterns become free from the stacks, and organelles, such as dictyosomes, become very active. The fibrillar masses gradually decrease in number, and the individual fibrils become more evident and clearer in resolution.