Development and organization of the central vacuole of Acetabularia acetabulum (original) (raw)
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An analysis of morphogenesis of the reproductive whorl of Acetabularia acetabulum
Planta, 1998
Acetabularia acetabulum (Linn.) P.C. Silva, is a useful system for studying changes in shape because it is large, morphologically complex unicell. The middle, or gametophore lobe of the cap grows radially from the stalk axis as a disc and the fully grown cap can be one of several shapes:¯at, concave, convex, and saddle. The shape of the cap normally changes during the ®rst three and a half weeks of reproductive development: individual caps within a population change shape in a stereotypical progression, with the majority proceeding from concave to¯at to saddle. Marking the existing surface of caps with carbon grains revealed that the majority of growth occurs near the center, not at the perimeter, of caps. The shape of the mature cap appeared to be independent of algal height, number of gametophores per cap, and ®nal cap diameter. Removing the rhizoid, which contains the nucleus, suggested that the contribution of the nucleus may be important for changes in shape during early cap growth. Based on these data, we present a simple model of cap shape development that suggests both dierential growth and biophysical factors may contribute to the ®nal shape of caps of A. acetabulum.
Journal of morphology, 2007
One of the main characters used in acoel taxonomy is the male copulatory organ. Despite this, ultrastructural studies of this structure are scarce. We studied the ultrastructure of the copulatory organ in eight species of acoels belonging to the taxon Childia. Members of Childia possess a well-developed conical or cylindrical stylet-like structure composed of needles. Immunogold cytochemistry of tubulin was used to determine the composition of the needles. Stylet-like structures of Childia species at the ultrastructural level are basically similar. Stylet needles show intracellular differentiations. As shown both by ultrastructural and immunocytochemical methods, the stylet needles, in all species studied, are composed of long, parallel microtubules, either tightly packed or polymerized. We report unusual polymerization of microtubules, resulting in formation of a honeycomb-like structure in cross section. Variations of ultrastructure among Childia species include numbers and arrangement of stylet needles, shape of needles, needle compactness, microtubule polymerization, direction of stylet growth, and presence/absence of different types of granules. The stylet-like structures are homologous within Childia, but are likely to prove nonhomologous with the other needle-like structures found in acoel copulatory organs. Stylets in Platyhelminthes are not homologous with stylet-like structures in acoels.
Sexual Plant Reproduction, 1992
Living embryo sacs and megagametophytic cells of Nicotiana alata and Nicotiana tabacum were obtained using enzymatic maceration and microdissection. The yields of isolated embryo sacs, egg apparatus and central cells were up to 35%, 40% and 35%, respectively. Vectorial movement of organelles and undulations of tubular structures, presumably endoplasmic reticulum, were observed in eggs, synergids and central cells using video-enhanced microscopy. Despite evident viability using the fluorochromatic reaction, the egg displays much less organelle movement and therefore appears to be quiescent. The large vacuole of the central cell is traversed by mobile strands of cytoplasm through which organelles migrate. A polygonal network is located at the periphery of the central cell, which may contribute to anchorage of the cell with the embryo-sac wall. The observation of organelle movement provides direct evidence of the condition of the cell and may be a useful approach for assessing cell vigor.
Transactions of the British Mycological Society, 1977
Nuclear behaviour and fertilization tube development in gametangia of Saprolegnia furcata Maurizio have been examined by light and electron microscopy. The gametangial nuclei undergo two divisions within the nuclear envelope, successive spindles forming at right angles to each other. Evidence that this division is meiotic comes from volume changes during division and the presence of axial elements in prophase I nuclei. The pairing of these elements is not close and synaptinemal complexes are not formed. During meiosis I the centrioles double in length and their cart-wheel structure is modified. Meiotic centrioles are also associated with structures absent at mitosis. They become enveloped in an amorphous sheath and are partly enclosed by a cap of membrane. Newly differentiated oospheres are uninucleate, whereas those contacted by fertilization tubes are nearly always binucleate. Although the fertilization tube penetrates both the wall of the oogonium and that of the oosphere, it does not rupture the plasma membrane of the oosphere. After discharging its contents the penetration peg produced by the fertilization tube collapses and is sequestered between the outer and inner layers of the wall of the oospore. Karyogamy occurs during the final stages of oospore maturation and the fusion nucleus has an unusual ultrastructure.
Biological Bulletin, 1989
A method for artificial fertilization of lance let eggs is described, and the egg coats are studied for the first time by transmission electron microscopy. Large, ovarian oocytes and spawned, unfertilized eggs (which are about 140 @tmin diameter) are surrounded by a coarsely granular vitelline layer about 1 @m thick and a jelly layer a few micrometers thick. The egg cortex is crowded with a monolayer ofcortical granules, each with an average diameter ofapproximately 3.5 sm. About 20 to 30 5 after insemination, a cortical reaction occurs al most simultaneously over the entire egg surface. The cor tical granules undergo exocytosis, and part of their con tent evidently forms a dense layer 30 nm thick against the inside of the vitelline layer: both layers together con stitute the fertilization envelope, which begins elevating from the egg surface. By 80 s after insemination, the jelly layer has disappeared, and beneath the fertilization enve lope the bulk ofthe ejected cortical granule material has become organized into a hyaline layer with a finely fi brogranular consistency. By 20 mm after insemination, the perivitelline space between the fertilization envelope and the egg surface has attained its maximum width of roughly 150 jim, and both the hyaline layer and the vitel line layer component of the fertilization envelope are much attenuated and remain so until hatching about 9 h after insemination. Egg coats are compared among ma jor deuterostome groups, and the results imply that the ancestral chordate may have been an unspecialized ap pendicularian.
Journal of phycology, 1998
The fine structure of zoosporogenesis, zoospore germination, and early gametophyte development in Cladophora surera Parodi et Cáceres were studied. Zoosporogenesis started with simultaneous meiosis in all nuclei of apical initial cells. The resulting haploid nuclei duplicated in turn by successive centric, closed mitoses. Then, each initial cell divided into two short zoosporangia. Numerous vacuoles appeared around each sporic nucleus. The delimitation of uninucleate zoosporocytes occurred by cytokinetic furrows produced by the coalescence of tiny, clear vesicles, without microtubules. Final shape of the zoospore resulted from gradual expulsion of vacuoles from the cell body. Mature biflagellate zoospores exhibited a conspicuous apical papilla containing fine granular globules, the basal apparatus, and a microtubular ''umbrella'' formed by numerous cortical microtubules that ran backward the length of the cell body. The chloroplast showed a conspicuous eyespot. The zoosporangial wall disorganized at the pore through which the zoospores were liberated. Zoospores settled on a substrate by their anterior papilla secreting an adhesive. Germination involved retraction of the apical papilla, loss of the ''umbrella'' microtubules and eyespot, and the lateral absorption of the entire flagellar apparatus, i.e. basal apparatus plus axoneme, into the cytoplasm. Early gametophyte development involved the synthesis of a thin, young cell wall, the development of outer peripheral vacuoles, the appearance of the marginal reticulate chloroplast, and the formation of the first central vacuoles derived from abundant endoplasmic reticulum. Close to the plasmalemma ran longitudinally oriented cortical microtubules. Eventually, the germling developed an achlorophylic, elongated rhizoidal portion.
Protoplasma, 1997
Motile tubular vacuole systems have been visualised using DIC optics in living hyphae ofPisolithus tinctorius without loading of any fluorescent tracer. Adding new medium, with or without the tracer CFDA, alters the motility of this system and increases the number of tubules. This response has been shown in individual hyphal tip cells and quantified in populations of tip cells. Vacuoles with motile tubules are also demonstrated in more basal cells of the hyphae, within 600 μm of the growing hyphal front. The vacuoles in these cells show more limited motility, but similarly respond to addition of new medium by increased motility and tubular activity. This demonstration that the vacuole system in more mature regions is both motile and interconnected as in the tips, and similarly responds to changes in external conditions, supports the hypothesis that the vacuole system may play a role in long-distance transport. Vacuoles in the most mature cells, more than 600 μm behind the hyphal growth zone are not motile. They do not respond to these stimuli and remain spherical and isolated. There are many explanations for this and the present lack of response does not exclude the transport hypothesis. The findings further support the concept that tubular vacuole systems are equivalent to animal endosomal/lysosomal systems and have implications for their motility, especially their plasticity in response to external stimuli, such as fluorescent tracers.
The purpose of this work was to study in detail with TEM the successive stages of pollen wall and tapetum development in Dianthus deltoides and to clarify the mechanisms underlying the developmental processes. At the young tetrad stage a thin glycocalyx layer is poorly structured, being a mixture of glycoproteins, secreted by Golgi vesicles through the process of exocytosis. At the middle tetrad stage the plasma membrane acquires a deeply invaginated profile as a result of self-assembly cellular tensegrity, and its pinnacles determine the sites of the future spines. Then, lipoid sporopollenin (SP) precursors and monomers are added into the periplasmic space. The concentrations of all substances in the periplasmic space are under genome control. As a consequence of self-assembly hydrophilic–hydrophobic interactions, " islets " of osmiophilic lipoid substances occur in the gly-cocalyx mixture, first as spherical units, then as plates, with further lateral growth and the appearance of the hexagonal reticulate pattern of the future tectum. At maturity, the reticulate pattern is not evident. At the late tetrad stage spines are initiated as outgrowths of the glycocalyx in the form of cone-like liquid-crystal " skeletons " , the latter accumulate SP. Columellae are initiated very late in ontogeny, at the stage when the tetrads separate into monads, on the base of the glycocalyx rod-like units — the cylindrical micelles. The first endexine lamella with a central white line appears at the young free microspore stage on the base of laminate micelles. The second end-exine layer is granulate and appears on the base of spherical micelles. Pollen grains are polyporate with aperturate membranes, consisting of lamellate endexine-1 and an underlying dilation – oncus – comprising gran-ulate endexine-2. The pore membranes bear large cupola-like tectal spines. The tapetum secretes a peri-tapetal membrane with Ubisch bodies, first with clusters of globules, then exine-like spines on the top of clusters. These Ubisch bodies mimic the pattern of the exine. The entire sequence of developmental events can be explained as the development of a self-assembling system under initial genomic regulation.
Sexual Plant Reproduction, 2005
Quantitative cell and organelle dynamics of the male gamete-producing lineage of Plumbago zeylanica were examined using serial transmission electron microscopic reconstruction at five stages of development from generative cell inception to sperm cell maturity. The founder population of generative cell organelles includes an average of 3.88 plastids, 54.9 mitochondria, and 3.7 vacuoles. During development the volume of the pollen grain increases from 6,200 lm 3 in early microspores to 115,000 lm 3 at anthesis, cell volume of the male germ lineage decreases more than 67% from 362.3 lm 3 to 118.4 lm 3. By the time the generative cell separates from the intine, plastid numbers increase by >600%, mitochondria by 250%, and vesicles by 43 times. A cellular projection elongates toward and establishes an association with the vegetative nucleus; this leading edge contains plastids and numerous mitochondria. When the generative cell completes its separation from the intine, organellar polarity is reversed and plastids migrate to the opposite pole of the cell. Cytoplasmic microtubules are common in association with cellular organelles. Plastids accumulate at the distal end of the cell as a linked mass, apparently adhered by lateral electron dense regions. Before division of the highly polarized generative cell, plastids decrease in number by 16%, whereas mitochondria increase by 9090% and vacuoles increase by 90140% from the prior stage. After mitosis, the resultant sperm cells differ in size and organelle content. The sperm cell associated with the vegetative nucleus (S vn) contains 62.7% of the cytoplasm volume, 87% of the mitochondria, 280.4 vesicles (79% of those in the generative cell), and 0.6% of the plastids. At maturity, the S vn mitochondria increase by 31% and the cell contains an average of 0.4 plastids, 158.9 vesicles, and 0.36 microbodies. The mature unassociated sperm (S ua) contains 39.8 mitochondria (up 3.3%), 24.3 plastids (down 31%), 91.1 vesicles (up 54.9%), and 3.18 microbodies. The small number of organelles initially in the generative cell, followed by their rapid multiplication in a shrinking cytoplasm suggests a highly competitive cytoplasmic environment that would tend to eliminate residual organellar heterogeneity. Cell and cytoplasmic volumes vary as a consequence of fluctuations in the number and size of large vesicles or vacuoles, as well as loss of cytoplasmic volume by (1) formation of ''false cells'' involving amitotic cytokinesis, (2) ''pinching off'' of cytoplasm, and (3) dehydration of pollen contents prior to anthesis.
Journal of Cell Science, 1983
Antibody against tubulin from porcine brain was used to examine the distribution of tubulin in developing spermatids of Polytrichum and mature spermatozoids of Sphagnum. Cells were prepared for indirect immunofluorescence microscopy after fixation in buffered paraformaldehyde and brief incubation in cellulase. Pretreatment with cold methanol resulted in considerably enhanced immunofluorescence but exposure to Triton X-100, with or without sonication, had no effect. The antibody showed similar immunological cross-reactivity with the flagella (both basal bodies and axonemes) and the spline microtubules of the multilayered structure. This is the first direct evidence that this rigid array of stable cytoskeletal microtubules consists of tubulin. Particularly intense fluorescence from the lamellar strata of the MLS in developing spermatids provides strong support for the notion that the lamellae comprise a highly structured microtubule organizing centre (MTOC), responsible for the ordered assembly of the overlying spline tubules. The demonstration of immunological cross-reactivity with antitubulin from porcine brain tubulin, within a plant structure other than fully formed microtubules, suggests that immunocytochemistry may have considerable potential for the detection of other MTOCs. By contrast, no detectable fluorescence emanated from the granular matrix cementing the flagellar basal bodies to the spline or the spindle-shaped sheath of fibres present in the spermatozoids of Sphagnum. Disruption of the mature gametes by sonication and treatment with Triton X-100 reveals the presence of particularly strong links between the spline and subjacent nuclear envelope.