Histopathological changes in susceptible corn inoculated with Helminthosporium maydis race O

Seedlings of a susceptible inbred line of male-fertile corn were inoculated with conidia of Helminthosporium maydis race O. Histological and ultrastructural observations of mesophyll, bundle sheath and phloem were made over a period of 8 days. Histological observations at 1 day revealed that lesions were comprised of several dead mesophyll cells bordered by a pair of vascular bundles. By 3 days lesions had developed their characteristic appearance caused by mesophyll collapse and had increased to a width of 10–12 bundles. At the ultrastructural level, the first signs of mesophyll cell change were rupture of the tonoplast and swelling of the mitochondrial matrix followed by a disintegration of the cytoplasm and swelling of the chloroplast stroma. Following these changes the cytoplasm became filled with an electron dense material and the plasmalemma ruptured leaving only partial remnants of chloroplasts as recognizable organelles. All of these changes occurred by 1 day. Bundle sheath cells were more resistant and intact cells could be observed in 3-day-old lesions. Phloem showed signs of degeneration by 1 day with distortion of the sieve-tube element membranes and disintegration of the companion cell cytoplasm. By 4 days the phloem had disintegrated.     

Unusual features of intercellular junctions in the larvacean Oikopleura dioica

Summary In the pelagic larvacean Oikopleura dioica, the epithelium lining the alimentary tract consists of ciliated and unciliated cell types. The ciliated cells also exhibit an apical border of long microvilli. Between the microvilli, the cellular membrane often projects deeply down into the cytoplasm; the membranes of these invaginations and those of apicolateral interdigitations may be associated with one another by tight junctions. Some of these junctions may be autocellular. The tight junctions are seen by freeze-fracture to be very simple in construction, composed of a single row of intramembranous particles, which may be fused into a P-face ridge. There is a dense cytoplasmic fuzz associated with these tight junctions which may extend into adjoining zonula adhaerens-like regions. The invaginations of the apical membranes are, in addition, associated by gap junctions which may also be autocellular. More conventional homocellular and heterocellular tight and gap junctions occur along the lateral borders of ciliated cells and between ciliated and unciliated cells. These gap junctions possess a reduced intercellular cleft and typical P-face connexons arranged in macular plaques, with complementary E-face pits. Both cell types exhibit extensive stacks of basal and lateral interdigitations. The tight junctions found here are unusual in that they are associated with a dense cytoplasmic fuzz which is normally more characteristic of zonulae adhaerentes.     

The fine structure of blood cells in the ascidian Perophora viridis

The fine structure of each of the blood cell types of Perophora viridis has been characterized and strong evidence for localization of vanadium in two of these types is given. There are eight cell types; phagocytes which may contain completely engulfed cells, lymphocytes with a prominant nucleolus and scanty cytoplasm packed with clustered ribosomes, and six other cell types each with distinctive granules. Morula cells contain a central nucleus and cytoplasm filled by wedged bodies, about five of which are seen in section. These bodies contain regularly spaced electron dense foci. Green cells have the same organization but contain bodies which are electron dense throughout. Granular amoebocytes contain many smaller lightly staining oval bodies and much glycogen. Another cell type (probably orange cells of light microscopy) contains numerous granular rounded bodies. Compartment cells have vacuoles containing electron dense particles and signet ring cells have usually one large vacuole which is electron dense lined and may contain electron dense particles. Developmental stages of these cell types show involvement of endoplasmic reticulum and Golgi bodies in granule formation. After glutaraldehyde fixation alone the only extremely electron dense components are particles in the compartment cells and signet ring cells implicating these as sites of vanadium localization, although not excluding other cell types.     

Rearrangement of nuclear ribonucleoproteins and extrusion of nucleolus-like bodies during apoptosis induced by hypertonic stress

Short-term hypertonic (HT) stress induces apoptotic cell death in human EUE cells in culture, as observed by electron microscopy, agarose-gel electrophoresis of low-molecular-weight DNA, DNA flow cytometry and annexin-V-propidium iodide double-staining. During HT-induced apoptosis, nuclear ribonucleoprotein (RNP)-containing structures undergo rearrangement, with the formation of Heterogeneous Ectopic RNP-Derived Structures (HERDS) which pass into the cytoplasm, as already reported for other examples of spontaneous and drug-induced apoptosis. Of special interest was the observation that nucleolus-like bodies (NLBs) which resemble morphologically nuclear functional nucleoli may be extruded into the cytoplasm of apoptotic cells and are observed inside the cytoplasmic fragments blebbing-out at the cell surface; these NLBs still contain immunodetectable nucleolar proteins (such as fibrillarin). This is an additional example of RNP-containing structures of nuclear origin which are extruded from the nucleus, in an almost "native" form, during apoptosis.     

Morphological evidence for a probable secretory site of the male sex pheromones of Nauphoeta cinerea (blattaria,blaberidae). 2. electron microscope studies

Light and electron microscopy of the glandular epithelium of intersegmental membranes between sternites three and seven and tergites two and eight of various age groups of Nauphoeta cinerea male adults and one age group of female adults discloses differences in the epithelia of the intersternite and intertergite. The intersternal epithelium appears thicker, more glandular, and stratified. Altogether, seven cell types are recognizable, six in the male and two in the female. They are designated as types 1, 2a, 2b, 2c, 3, 4, and 5. Of these, types 1, 2a, 3, and 4 are recognizable on the sternum; types 1, 2b, and 5 on the tergum of the mature male integuments. Types 1 and 2c are found on the sternum of mature female. The cell types undergo morphological differentiation after adult emergence and show different stages of secretory activity. Type 1 are squamous cuticle-secreting cells; type 2a, 2b, and 2c are columnar-glandular and contain electron-transparent secretory vesicles of various sizes, which increase greatly in number and size in the 5-day-old adult males when the glands are most active. The vesicular size and number also differ between types 2a, 2b, and 2c cells of the same age group. The vesicles are assumed to be derived from smooth endoplasmic reticulum. The type 2 gland cells are also provided with a secretory end apparatus lined by cuticle and bordered by microvilli through which the secretion is believed to be released by exocytosis. The end apparatus leads into a cuticular ductule that opens to the surface of the cuticle as a cup-shaped receptacle, which is more conspicuous in the male intersternite. In the active gland cells, the mitochondria near the end apparatus are swollen and vacuolated. Type 3 cells are seen only on the intersternum and are believed to secrete the cuticular ductule that proceeds from the end apparatus. Type 4 cells are also recognizable only on the male intersternum and contain closely packed, electron-dense bodies, which are most numerous in mature (5-day-old) males. Type 5 cells with their dense cytoplasm are located basally in the intertergal epithelium. The functional significance of type 4 and 5 cells in the males and type 2c cells in the female is not clear. On the basis of differences in morphology, pheromone activity, and sexual behavior, it is suggested that the pheromones secreted by the intersternal and intertergal glands in the male are different, the former secreting a seducin that attracts the female to the male and the latter an “aphrodisiac” acting as a contact pheromone important in accomplishing mating.     

Cytology of the human seminiferous epithelium

The appearances in cytologic specimens of the principal cell types in the normal human seminiferous epithelium are described and illustrated. Sertoli cells, which are larger than spermatogenic cells, are characterized by a slightly basophilic, ill-defined cytoplasm of triangular, elongated or columnar shape; the cytoplasm may be vacuolated and may contain spermatozoa. The nuclei of Sertoli cells are round, with a uniformly finely granulated chromatin and a single nucleolus. Spermatogenic cells are round or oval and show scanty cytoplasm with deeper basophilia and well-defined cytoplasmic borders. Multinucleation is common in spermatogenic cells. The Sertoli cells constitute a very homogeneous cell population as compared to the spermatogenic cells, which show several distinct cell types (spermatogonia, primary and secondary spermatocytes, spermatids and spermatozoa) whose nuclear structures depend on the stage of meiosis. Both cell types may occur as naked nuclei. Some problems of cell classification are discussed.     

A histochemical study of the cells of the ventral cord ganglia of the horseshoe crab,Limulus polyphemus (L.)

Summary The ventral cord ganglia of the horseshoe crab, Limulus polyphemus, contains six distinct cell types: three appear to be ordinary neurons and three exhibit the staining affinities of neurosecretory cells.The presumed neurosecretory cells have been termed neurosecretory cell I (NSC I), NSC II and NSC III. NSC I cells contain a colloid-like inclusion which may occur as a single small vacuole or occupy more than one-half of the cell volume. Colloid inclusions occur with greater frequency toward the periphery, although small cells of similar staining affinity occur in cords extending to the fibrous core. The histochemical tests suggest that the cytoplasm is positive for proteins, but contains no strong acidic groups which may have been derived from S-S or S-H groups. The presence of carbohydrate is also indicated.NSC II cells exhibit distinct secretory cycles. Early in the cycle the cytoplasm becomes phloxinophilic and progresses to a distinct fuchsinophilic stage. Small homogeneous irregular inclusions are found in the axon hillock during the latter stages of the cycle. Histochemical tests suggest the presence of a carbohydrate and strong acidic groups which may have been derived from S-S or S-H groups. There are small cells present which appear to be immature neurosecretory cells.NSC III cells are characterized by a perinuclear ring of cytoplasm which is stained by chrome alum hematoxylin but not by paraldehyde fuchsin. A secretory cycle may also be present in this cell type.The three cell types presumed to be ordinary neurons exhibit no particular staining affinity for the stains or tests used in this study.This study was supported in part by a grant from the Central Fund for Research of the Pennsylvania State University.     

Studies on rickettsia-like organism disease of the tropical marine pearl oyster I: the fine structure and morphogenesis of pinctada maxima pathogen rickettsia-like organism

The present paper reports for the first time the discovery of a rickettsia-like organism (RLO) in the cultured tropical marine pearl oyster Pinctada maxima with mass mortality in the Hainan Province of China. This organism parasitizes the cytoplasm of host cells and forms intracytoplasmic eosinophilic inclusions. These organisms are extremely pleiomorphic in shape and average 967 x 551 nm in size, as measured in cross sections of transmission electron micrographs. The organisms exhibit clearly recognizable ultrastructural characteristics of prokaryotic bacteria-like cells, including two trilaminar membranes, an increasing electron-dense periplasmic ribosome zone, and a thread-like DNA nucleoidal structure. In addition to the above prokaryotic characteristics, the following unique biological characteristics were confirmed by TEM: (i) These organisms are usually located in host cells in two ways, namely, free in the cell cytoplasm and involved within membrane-limited phagolysosomes; (ii) The organisms exist in two morphological cell types, namely a small cell variant (SCV) and a large cell variant (LCV). The most important morphological difference between two cell types is that the SCV is obviously ribosome-rich in the periphery of the body, which makes SCV more electron-dense in the cytoplasm and narrower in the central nucleoid area than the LCV; (iii) Two propagative modes of the organisms, transverse binary fission and budding, are observed in cytoplasm and phagolysosomes of host cells under TEM, in which the budding is more often seen in phagolysosomes. These characteristics indicate that the organism is a separate species in the family Rickettsiaceae and should be classified into the genus Rickettsia. On the basis of the existence of the two propagative modes and two cell types, and intracellular location, we propose a developmental cycle for this organism which includes a vegetative differentiation stage to develop LCV by transverse binary fisson and a budding differentiation stage to develop resistant SCV. Copyright 1999 Academic Press.     

FINE STRUCTURE OF THE SNOW ALGA (CHLAMYDOMONAS NIVALIS) AND ASSOCIATED BACTERIA1

Chlamydomonas nivalis (Bau.) Wille is present in red snow as large spherical resting cells. Fine structural studies reveal an abundance of clear granules in the cytoplasm and occasional starch grains in the chloroplast. Individual cells display a thick cell wall with a smooth outer surface. Cells may be surrounded by a loose fibrous network in which encapsulated bacteria are seen. The bacteria have a characteristic Gram-negative cell wall and constrictive mode of division. The algal-bacterial association appears to be characteristic of red snow populations.     

Ultrastructure of an exocrine dermal gland in the gills of the grass shrimp,Palaemonetes pugio: Occurrence of transitory ciliary axonemes associated with the sloughing and reformation of the ductule

Exocrine dermal glands, comparable to the class 3 glandular units of insects, are found in the gills of the grass shrimp, Palaemonetes pugio. The dermal glands are composed of three cells: secretory cell, hillock cell and canal cell. Originating as a complex invagination of the apical cytoplasm of the granular secretory cell, a duct ascends through the hillock and canal cells to the cuticular surface. The duct is divisible into four regions: the secretory apparatus in the granular secretory cell, the locular complex, the hillock region within the hillock cell and the canal within the canal cell. A tubular ductule is contained within the latter two regions. As the ductule ascends to the cuticular surface, its constitution gradually changes from one of a fibrous material to one which possesses layers of epicuticle. During the proecdysial period, the ductule is extruded into the ecdysial space and this is followed by the secretion of a new ductule. Temporary ciliary structures, located near the secretory apparatus of the secretory cell, are associated with the extrusion and reformation of the ductule. Characterized only by a basal body and rootlets throughout most of the intermolt cycle, the ciliary organelles give rise to temporary axonemic processes which ascend through the ductule toward the ecdysial space at the onset of proecdysis. Subsequently, the old ductule is sloughed off and a new ductule is reformed around the ciliary axonemes. Following this reformation, the ciliary axonemes degenerate. The function of cytoplasmic processes, derived from the apical cytoplasm of the secretory cell, is also discussed.     

Early death at medium acidification and survival after low pH adaptation inCryptococcus neoformans

WhenCryptococcus neoformans was grown in yeast nitrogen base (YNB) supplemented with 0.5% glucose, the medium was acidified to below pH 3 during the exponential growth phase, which caused early growth-phase death in susceptible strains. Even in resistant strains, 30–70% cells died if incubated for 2 d in YNB supplemented with 1.5% glucose, whereas the remaining cells survived long. Two types of fatal alterations have been observed in dead cells. In the first type, release of cytoplasm occurred through weakened parts of the cell wall; structures attached to cell walls of dead cells were shown to be rich in proteins by FITC staining, indicating their cytoplasmic origin. In the second type, cells shrank distinctly with no sign of wall rupture. The shrinkage may be due to dysfunction of the plasma membrane at low pH. The mechanism of cell survival in medium below pH 3 was also examined. Aniline blue alone, or calcofluor together with methylene blue, allowed cell wall glucan or chitin and dead cell cytoplasm to be stained simultaneously. In the later stages of incubation, cells showing bright staining for cell wall glucan and chitin emerged. These changes in cell wall synthesis could be considered as an adaptation mechanism to acidification of the medium, because such cells survived longer than cells showing no change in the cell wall staining pattern.     

Cytochemical Observations on Proteins,Alkaline and Acid Phosphatases,Adenosine Triphosphatase,and 5′-Nucleotidase in Chick Liver Cell Cultures Infected with Trichomonas vaginalis*, †

SYNOPSIS. By means of the ninhydrin-Schiff method for proteins a diffuse reaction as well as one localized in granular inclusions can be shown in the cytoplasm of fibroblasts, epithelial cells, and macrophages in trypsin-dispersed chick liver cell cultures. Nuclei and nucleoli also take the specific stain. A progressive loss of cytoplasmic and nuclear staining occurs in the fibroblasts in cultures infected with a relatively pathogenic strain of T. vaginalis. A loss occurs in epithelial cells in advanced stages of degeneration, but in less damaged cells, while the diffuse reaction disappears, the number and staining intensity of the cytoplasmic inclusions remain unchanged or possibly may increase somewhat. The intensity of the diffuse reaction and the number and size of the characteristic inclusions increase in the active, parasite-free, experimental macrophages, but phagocytes with trichomonads closely applied to their external surfaces and those containing the flagellates within their cytoplasm typically retain only a few weak-staining inclusions. Similar distribution of alkaline and acid phosphatases occurs in preparations treated according to Gomori's and Burstone's methods, except that no nuclear staining is obtained with the latter. Activity of both enzymes is localized primarily in inclusions which are dispersed thruout the cytoplasm of fibroblasts and epithelial cells and tend to accumulate along the cell membranes and around the nuclei. In the course of infection with T. vaginalis there is a progressive loss of alkaline phosphatase from both cell types; however, the acid phosphatase activity increases. In the control macrophages both enzymes are localized in mostly rather large, rounded cytoplasmic inclusions. The number of such inclusions increases in the parasite-free experimental macrophages, but only a few weak-staining granules remainin phagocytes with engulfed trichomonads and in those whose external surfaces are in direct contact with the parasites. The loss of the inclusions is less apparent in macrophages containing degenerated flagellates than in the ones with healthy trichomonads, but regardless of the condition of the parasites, the highest enzymatic activity is found around them. ATPase and 5′-nucleotidase are localized in small granules dispersed thruout the cytoplasm of fibroblasts and epithelial cells. The granules tend to accumulate along the periphery of the cells and around the nuclei. A diffuse cytoplasmic reaction is present in preparations processed for 5′-nucleotidase. Nuclei and nucleoli give positive reactions for both enzymes. In the course of infection with trichomonads, activity of the 2 enzymes declines in both culture cell types. Control macrophages have diffuse cytoplasmic reaction for ATPase and 5′-nucleotidase and these enzymes are localized also in rounded cytoplasmic inclusions. Activity of both enzymes increases in the parasite-free experimental phagocytes, but little if any diffuse staining and only a few characteristic inclusions are left in macrophages with engulfed healthy trichomonads and in those whose external surfaces are invested with the flagellates. The ninhydrin-Schiff-positive inclusions found in the macrophages appear to be the same as some of those which have acid phosphatase activity and may well be identical with the glycolipoprotein bodies noted by us previously. On the grounds of their chemical constitution and behavior it seems likely that the inclusions are lysosomes.     

Asexual reproduction in the suctorianDiscophrya collini

Summary Discophrya collini reproduces asexually through the formation of a ciliated swarmer by evaginative budding. This process is initiated by the repeated replication of a single subcortical kinetosome to form a kinetosome field. The epiplasm of the multilayered cortex covering this field becomes reduced in thickness and the whole cortex invaginates to produce an internal embryonic cavity. The kinetosomes become organised into rows, and each produces a cilium which projects into the cavity. On completion of the embryonic cavity its walls are extruded through the cavity opening to form an external ciliated swarmer connected to the parent by a thin bridge of cytoplasm. It is suggested that this evagination is induced by a rapid breakdown of supporting microtubules in the cavity wall and the subsequent hydrostatic pressure exerted by the body cytoplasm. The connecting bridge shows no specialised ultrastructural features and separation of swarmer from parent probably is achieved by the active movement of the swarmer. The cytoplasm of the swarmer is similar in structure to that of the adult cell but contains a number of primordia of tentacle axonemes. The infraciliature resembles that of other suctorian swarmers. On settling, the cilia of the swarmer are lost, at least some by resorption, a stalk may be secreted and the axoneme primordia are extended to form functional tentacles.     

Transmission of male cytoplasm during fertilization in Nicotiana tabacum

Serially sectioned embryo sacs of Nicotiana tabacum were examined during fertilization events using transmission electron microscopy. After pollen tube discharge, the outer membrane of the sperm pair is removed, the two sperm cells are deposited in the degenerate synergid and the sperm cells migrate to the chalazal edge of the synergid where gametic fusion occurs. During fertilization, the male cytoplasm, including heritable organelles, is transmitted into the female reproductive cells as shown by: (1) the cytoplasmic confluence of one sperm and the central cell during cellular fusion, (2) the occurrence of sperm mitochondria (distinguished by ultrastructural differences) in the zygote cytoplasm and adjacent to the sperm nucleus, (3) the presence of darkly stained aggregates which are found exclusively in mature sperm cells within the cytoplasm of both female cells soon after cell fusion, and (4) the absence of any large enucleated cytoplasmic bodies containing recognizable organelles outside the zygote or endosperm cells. The infrequent occurrence of plastids in the sperm and the transmission of sperm cytoplasm into the egg during double fertilization provide the cytological basis for occasional biparental plastid inheritance as reported previously in tobacco. Although sperm mitochondria are transmitted into the egg/zygote, their inheritance has not been detected genetically. In one abnormal embryo sac, a pair of sperm cells was released into the cytoplasm of the presumptive zygote. Although pollen tube discharge usually removes the inner pollen-tube plasma membrane containing the two sperm cells, this did not occur in this case. When sperm cells are deposited in a degenerating synergid or outside of a cell, this outer membrane is removed, as it apparently is for fertilization.     

Der Nucleolus und seine Beziehungen zu den Ribosomen des Cytoplasmas. Eine Untersuchung an den Malpighischen Gefässen von Drosophila melanogaster

Summary The investigation described herein is concerned with the structure and the behavior of the nucleolus of the cells of the Malpighian tubules of Drosophila melanogaster (see Fig. 16).Primarly the nucleolus consists of ribonucleic-acid granules about 150 Å in diameter which, with electron microscope, are not distinguishable from the ribosomes of the cytoplasm; they lie on or within the structural network of the nucleolus (Fig. 9). During the stages of the life history of the insect the nucleolus shows correspondingly characteristic peculiarities in structure which reflect the varying functional stages of the cell: The structure is loose in the cells of the larva (Fig. 2) and imago (Fig. 12), whereas it is compact in the pupa (Fig. 8, 9). In pupa sufficiently mature for emergence, the nucleolus contains a large central vacuole (Fig. 8, 9). The nucleolus of the larva has a similar appearance after a decrease in assimilation induced by starvation (Fig. 10, 11).There are smaller vacuoles in the nucleolus which mostly are filled with parts of the nucleolus-chromosome. In the pupal stage some of the peripheral constituents of the nucleolus separate and move to the nuclear membrane through which they pass via pores into the cytoplasm (Fig. 3, 4).Larger pieces reach the cytoplasm by local dissolution of the nuclear membrane (Fig. 5). During this process the extruded nucleolar material is dispersed into its structural components. Because the cytoplasm becomes richer in ribosomes during the period of nucleolar extrusion (Fig. 1b), it can be assumed, that the nucleolus must be a source of ribosomes, and that through such an extrusion which has been demonstrated to be a natural process (Fig. 7) the cytoplasm can be provided with ribosomes rapidly.The importance of this phenomenon in the synthesis of imaginal body is discussed.In the nucleus there are many vacuoles with a diameter of about 425 Å (Fig. 15a, b) which pass through the pores of membrane in the cytoplasm (Fig. 15c).

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Die Untersuchung wurde mit Unterstützung der Deutschen Forschungsgemeinschaft durchgeführt.     

Co-Localization of Particle Transport with Microtubules in Cytoplasmic Exudates of the Siphonous Green Alga Bryopsis

Organelles in the cortical cytoplasm of the siphonous green alga Bryopsis display various types of motile activities. One of them, saltatory movement along axially oriented linear tracks is typical for mitochondria and other small particles. A method is described which allows in vitro observation of such movements in thin layers of cytoplasm extruded from the alga and attached to a poly-l -lysine coated glass surface. By comparing video recordings of motile activities with the position of cytoskeletal elements visualized by immunofluorescence in the same area of a cytoplasmic exudate, it can be shown that tracks along which particles have moved in vitro are identical with microtubules (MTs). Depolymerization of MTs in the cytoplasmic exudates by MT-specific inhibitors stops particle movement, whereas depolymerization of actin filaments with cytochalasin D disrupts actin bundles but has little effect on particle motility. These data are consistent with the model of MT guided particle transport.     

CELL DIVISION PATTERNS AND DIURNAL CYCLE OF PORPHYRA ABBOTTAE (RHODOPHYTA,BANGIALES) CARPOGONIAL AND CARPOSPORE DEVELOPMENT1

Post-fertilization development of carpospores in Porphyra is a well-documented phenomenon. Development of the pre-fertilization carpogonial cells from vegetative cells, however, has not been previously described. In Porphyra abbottae Krishn., a rock? intertidal monostromatic species occurring from British Columbia to central California, large cells, designated hue CIS “procarpogonial mother cells” (PMCs), initiated the formation of the carpogonial cells. The PMCs formed during late night mitoses beginning at 0200 h with cytokinesis from 0300-0500 h during short day periods of 10:14 h LD in northern California (38°20′N, 123°03′W and 36°37′N, 121°55′W). The PMC cut off numerous smaller cells which in turn divided equal. Approximately 12 h Inter, at 1500 h (day 1) the Smaller cells were recognizable as carpogonial cells by the presence of trichogynes growing from the cytoplasm out through the cell wall to the thallus surface. In another 24 h (day 2), the fertilized carpogonia had divided into carpospore packets. Spores were released at 1500 h the following day (day 3), their projection creating escape channels through the cell walls.     

含笑花药发育的超微结构研究

对含笑花药发育中的超微结构变化进行观察,结果显示:(1)花粉发育中有三次液泡变化过程——第一次是小孢子母细胞在形成时内部出现了液泡,这可能与胼胝质壁的形成有关;第二次是在小孢子母细胞减数分裂之前,细胞内壁纤维素降解区域形成液泡,它的功能可能是消化原有的纤维素细胞壁;第三次是在小孢子液泡化时期,形成的大液泡将细胞核挤到边缘,产生极性。(2)含笑花粉在小孢子早期形成花粉外壁外层,花粉外壁内层在小孢子晚期形成,而花粉内壁是在二胞花粉早期形成;花粉成熟时,表面上沉积了绒毡层细胞的降解物而形成了花粉覆盖物。研究认为,含笑花粉原外壁的形成可能与母细胞胼胝质壁有关,而由绒毡层细胞提供的孢粉素物质按一定结构建成了花粉覆盖物。     

鹅掌楸油细胞的发育解剖学研究

鹅掌楸油细胞比相邻组织细胞分化,因而在叶肉细胞未完全分化的叶原基、幼叶以及未完全分化的幼茎中,都可看到已分化的油细胞。通常,在第二叶原基中可发现油细胞原始细胞,由于其染色深、细胞核大而易与周围组织的细胞相区别。以后,油细胞逐步液泡化,直至形成一个大的液泡,此时,细胞核呈扁平状,并与细胞质一起成为一薄层围绕着大液泡。当油细胞发育成熟后,细胞质及核开始解体,整个油细胞的腔由大液泡充满,成为油囊,在部分     

Seasonal changes in the ultrastructure of the kidney collecting tubule in the lizard Podarcis ( = Lacerta) taurica

In female Podarcis taurica the kidney collecting tubule always consists entirely of mucous-secreting cells. In males it has a seasonally variable sexual segment and a non variable mucous-secreting segment. In April the sexual segment is composed of columnar cells with cytoplasm rich in ribosomes and Golgi bodies and apical clusters of large vesicles with fibrous contents. The terminal region of the sexual segment also has pillar-shaped cells resembling those of the mucous-secreting segment. By May the accumulation of apical vesicles reaches a maximum, and many cells have apparently extruded their secretion into the lumen. In July all the cells are pillar shaped with dilated endoplasmic reticulum but with few apical vesicles. In September the sexual segment has some cells resembling those of the mucous-secreting segment and others the sexual segment pillar cells in April. It is suggested that during sexual activity in the spring the sexual segment secretes a spermatozoon-nutrient protein but subsequently reverts to mucous secretion. The non variable mucous-secreting regions in both males and females consist of mucous, intermediate, and dark cells. Mucous cells have apical masses of closely packed droplets, whereas dark cells have dense cytoplasm and small, loosely associated apical vesicles. Intermediate cells have some dark cell features but mucous cell apical vesicles. The dark, intermediate, and mucous cells probably represent activity states of a single type. The mucous secretion is interpreted as a protective material which lines the urinary passage and coats the secreted solid urates. Elaborated intercellular spaces in the mucous-secreting regions may indicate a water absorption capacity in urine concentration.