Demonstration of succinic dehydrogenase in mitochondria of fern egg cells at electron microscope level

Summary The use of ferricyanide in the presence of Cu⁺⁺ to capture the ferrocyanide generated proved a reliable method for the location of succinic dehydrogenase in fern egg cells. The response of mitochondria-like nuclear evaginations was largely negative, but small patches of apparently authentic reaction product, absent in the controls, were occasionally encountered in their envelopes. From the point of view of deciding the nature of the nuclear evaginations the results were therefore equivocal.     

Evidence for the association of acyl transferases with the production of nuclear evaginations in maturing eggs of the fern Dryopteris filix-mas.

Utilizing the ability of free CoA to reduce ferricyanide, evidence is presented that acyl transferase activity is associated with the nuclear envelope in the maturing egg of the fern Dryopteris filix-mas. This activity is particularly marked in the nuclear evaginations. This strengthens the view that the evaginations are distinct structures formed by localized growth of the envelope, and not transient extensions of the nucleus.     

Nucleocytoplasmic Interaction During Maturation of the Egg of the Fern Histiopteris incisa (Thunb.) J. Smith

The maturing egg of Histiopteris incisa has many features incommon with that of Pteridium, with which the species may berelated. The nuclear evaginations are however conspicuous inrespect of the extensive development of internal membrane systems,involving dilatation of the perinuclear space. In some in stancesthe inner membrane of the nuclear envelope, the proliferationof which gives rise to the dilatations, was strikingly tenuous,possibly indicating an extensive interchange between the perinuclearspace and that part of the nucleoplasm sequestered in the evaginations.The evaginations frequently contain an aggregate of electron-opaquematerial resembling structurally and in staining propertiessimilar aggregates in Pteridium, but in contrast to Pteridiumthere was no evidence that these aggregates were organized inor near the nucleolus. Histiopteris inciso (Thunb.)J. Smith, Pteridophyta, egg maturation, nucleocytoplasmic interaction, ultrastructure     

The Fine Structure of the Mature Gametes of Haemoproteus columbae Kruse*

SYNOPSIS. The filiform microgamete of Haemoproteus columbae consists of an elongate double-walled nucleus paralleled by 2 axonemes embedded in a homogeneous matrix. At one end of the gamete, the axonemes are sharply flexed back on themselves, but no conventional kinetosome has been recognized. No mitochondria have been seen. Single-walled vesicles occur in the matrix, and the entire gamete is surrounded by a single membrane. The large round macrogamete has a conspicuous central nucleus with its outer membrane drawn out into anastomosing evaginations which extend to the periphery of the cell. A moderately electron dense material fills the space between the 2 nuclear membranes and the lumina of the evaginations. Nucleolar material may occur in scattered masses within the nucleus. One or 2 axonemes appear to arise endogenously next to the nuclear membrane. The cytoplasm is filled with ribosomes and perhaps glycogen granules. Typical protozoan mitochondria and vesicles containing pigment retained from the erythrocytic stage are found in the peripheral cytoplasm. Accumulations of dense-walled vesicles occur in the cytoplasm in conjunction with evaginations of the nuclear membrane. Amid these vesicles triple-ringed discs resembling the cytostomes of merozoites are frequently seen. Several distinct layers of dense material surround the micro-gamete.     

The fine structure of basidiospores of Panaeolus campanulatus (L.) Fr. revealed by freeze-etching

Summary Freeze-etch replicas of basidiospores of Panaeolus campanulatus treated for 16 hours in glycerol showed that germination processes had been initiated. The plasmalemma bore evaginations, abstricting vesicles into the paramural space, and the nuclear envelope evaginated abstricting promitochondrial initials. The significance of these results is discussed in relation to previous work on chemically-fixed spores of various fungi.     

The ultrastructural differentiation of the endoplasmic reticulum in choroidal epithelial cells of the chick embryo

During the development of the choroidal epithelium in the chick embryo, a substantial concentration of granular endoplasmic reticulum differentiates in the subnuclear cytoplasm of the epithelial cells. The formation of the membranous components of this organelle is preceded by the appearance of a dense, localized population of small, free polyribosomes. Subsequently, numerous membrane-bound vesicles appear in the perinuclear cytoplasm. These primordial ER vesicles measure from 0.1 μ to 0.5 μ or more and they originate from evaginations of the outer nuclear membrane. These vesicles commonly occur in successive rows situated around the margin of the nucleus, and they expand and/or interconnect to form incipient ER tubules. Most vesicles and early tubules are smooth to nearly smooth in appearance. With continued development nuclear evaginations cease, and ER tubules expand in Situ to form an elaborate, laminated system of 7–12 ‘bag-like’ cisternae. Throughout this period of expansive growth, small polyribosomes attach to the developing ER cisternae. As the ER cisternae progressively attain their granular appearance, the number of small, free polyribosomes diminishes. During later stages of development larger polyribosomes appear in association with the subnuclear concentration of ER, and the first accumulations of electron-dense material develop within cisternal spaces.     

Nuclear envelope-limited chromatin sheets (ELCS) and heterochromatin higher order structure

The interphase nucleus and nuclear envelope can acquire a myriad of shapes in normal or pathological cell states. There exist a wide variety of indentations and invaginations, of protrusions and evaginations. It has been difficult to classify and name all of these nuclear shapes and, consequently, a barrier to understanding the biochemical and biophysical causes. This review focuses upon one type of nuclear envelope shape change, named “nuclear envelope-limited chromatin sheets” (ELCS), which appears to involve exaggerated nuclear envelope growth, carrying with it one or more layers of ∼30 nm diameter heterochromatin. A hypothesis on the formation of ELCS is proposed, relating higher order heterochromatin structure in an interphase nucleus, nuclear envelope growth, and nuclear envelope-heterochromatin interactions.     

Ultrastructural analysis of the effects of dominant cataract-Fr gene in mouse embryos]

An electron microscope study of lenses in 11--15 and 17 days old embryos of mice homozygous by dominant cataract-Fr (CatFr) gene has shown that ultrastructural changes in the nuclear envelope are the earliest expression of the mutant gene. The primary lens fibers of 12 days old embryos CatFr/CatFr, unlike those of the normal ones, are characterized by the decrease in the number of nuclear pores, evagination of the outer nuclear membrane, marked and unequal extension of perinuclear space which connects itself with the endoplasmic reticulum cisternae. In 14 days old embryos breaks in the outer nuclear membrane and evaginations in the inner one, fusion of nuclear membranes and breaks of the nuclear envelope are observed and resulted in the release of the nuclear contents with the nucleolus in the cytoplasm. Similar ultrastructural changes are characteristic also of the nuclei of secondary lens fibers at a comparable stage of differentiation. The destructive changes of nuclei are accompanied by the degeneration and autophagocytosis of cellular organelles and matrix.     

Freeze-etching observations of trophozoites of pathogenic Entamoeba histolytica.

Pathogenic Entamoeba histolytica trophozoites were studied by the freeze-etching (FE) technique of electron microscopy. Surface replicas of intact cell membranes were highly convoluted with numerous invaginations, evaginations, and undulations. Sperical depressions and elevations varying from 0.5 mu to 1.0 mu in diameter were commonly present on the external cell membrane and appeared to represent an extracellular secretory mechanism of trophozoites. Cleaved surfaces of amebae exhibited a granular and lumpy cytoplasm in which there were many vesicles and vacuoles that ranged in diameter from 0.2 mu to 9.0 mu. Some vacuoles contained tightly enveloped bacteria, while others contained bacteria and host cytocomponents. Occasional vesicles and vacuoles appeared to be fused to each other. Replicas of FE nucleus were enclosed by double nuclear membranes which were fenestrated by numerous sperical pores measuring approximately 640 A in diameter and spaced at intervals of 650 A. Counts of nuclear pores were possible and indicated 35 pores per square micron on the nuclear envelope. Golgi apparatus, mitochondria and well formed endoplasmic reticulum were absent in FE replicas. This was in agreement with electron microscope observations on thin sections previously reported by other investigators.     

Nuclear envelope projections from pronuclei ofSpirogyra zygotes

Summary Spirogyra zygospores were fixed in buffered 2% osmium tetroxide and embedded in Epon. Serial sectioning established that the pronuclei, in the zygotes studied, had come to lie in very close proximity but had not started to fuse.The pronuclei had interesting projections from their nuclear envelopes. These were regular finger-like structures containing both membranes of the nuclear envelope but lacking nuclear pores. The projections measured 0.22 m in diameter and had an indeterminate length around 2.0 m. They had an inner band on the nucleoplasmic side which appeared to describe a helix along the evagination maintaining a distance of 20 nm from the inner membrane, except for occasional small regions of contact.The possibility that these evaginations were important in nuclear movement or fusion was considered less likely than that they were involved in some kind of nucleocytoplasmic exchange, possibly organellogenesis like that described inPteridium.     

Abnormal manchette development in spermatids of azh/azh mutant mice

A study of manchette development during spermiogenesis in azh/azh mutant mice was carried out by thin-section transmission electron microscopy with the goal of determining which of the initial steps in spermatid development are aberrant. In the homozygous mutant, spermatogenesis was quantitatively normal; but 100% of the sperm nuclei produced had abnormal shapes. The first defect, observed in steps 8-9, was the abnormal positioning of many manchette microtubules. These microtubules were directed towards regions of the plasma membrane not normally associated with manchette formation, in addition to being located at the caudal rim of the acrosome in the normal region of manchette formation. At steps 10-12, sheets of manchette microtubules were often in ectopic positions along the plasma membrane, rather than in association with the nuclear membrane as well. The fine structural appearance of the manchette was generally normal; the defect appeared to be in its positioning within the cell. In many step 8-10 spermatids nuclear invaginations and evaginations were observed, always associated with irregularities in the position of some of the manchette microtubules; these illustrate the capacity of manchette microtubules to deform nuclear shape. The nuclear irregularities remained throughout spermiogenesis. These observations are consistent with the hypothesis that the manchette is involved in at least some aspects of sperm nuclear shaping and that the improper positioning of manchette formation is a likely candidate for the primary abnormality resulting from a defective allele at the azh locus.     

蕨受精作用的细胞学观察

为了阐明进化蕨类受精作用的特点和细胞学机制,该文采用透射电镜观察了蕨(Pteridium aquilinum var.latiusculum)受精作用的主要过程,观察结果显示:(1)蕨精子通过受精孔进入卵细胞,多数情况下,该精子的螺旋运动先在受精孔的下方产生一个受精腔,然后精子再与卵细胞质融合。(2)第一个精子的这种延迟的螺旋运动和因精子的钻入而引起的卵细胞固缩反应可能是阻止多精受精的重要因素。(3)卵发育时期产生的核外突在受精后仍能持续12 h,然后与核本体分离,逐渐在细胞质中消解。(4)合子通过其后方细胞质的液泡化而建立了水平极性,此后再进行细胞分裂。该研究观察到了进化蕨类受精作用过程中的一些新现象,包括产生受精腔、卵细胞固缩反应、核外突的命运以及合子极性建立等,这有助于理解蕨类植物的受精作用机制及有性生殖的演化。     

普通针毛蕨颈卵器和卵的发育

蕨类植物卵发生是有性生殖研究的重要内容。真水龙骨类II的卵发生尚无人研究, 本文对该类群中的普通针毛蕨(Macrothelypteris torresiana)卵发生过程进行了光镜和透射电镜研究。结果显示: 卵细胞刚形成时, 与腹沟细胞紧密相连, 随着卵进一步发育, 卵细胞和腹沟细胞之间逐渐形成分离腔, 但孔区处卵细胞和腹沟细胞始终相连。随后, 卵细胞上表面有不定型物质堆积在质膜外, 形成一层加厚的卵膜, 孔区处没有卵膜覆盖的位置最后形成受精孔。在卵发育后期, 卵细胞核变得不规则, 近成熟时卵核产生大量核外突。卵发育过程中卵膜的出现、受精孔的产生以及核外突等特征, 与进化的真水龙骨类中其他蕨类植物的卵发生研究结果相似, 与薄囊蕨类中原始基部类群的卵发生现象有显著差别。由此可见, 普通针毛蕨属于进化类型。依据卵发生中卵膜和受精孔等特征推测原始薄囊蕨类经过里白类、桫椤类, 最终演化为水龙骨类。     

Ultrastructural study ofErwinia amylovora strains: Effect of culture conditions and fixation procedures

Summary Modifications of the ultrastructure of the plant pathogenic bacteriumErwinia amylovora were analyzed according to growth conditions and fixation procedures. Six bacterial strains with various virulence characteristics were examined. Cultures were grown either in Yeast Peptone Glucose medium (YPG) or in a medium containing asparagine (ASP) supplemented with sorbitol (1% or 5% sorbitol). When grown in ASP + 1% sorbitol or in YPG, the strains, structurally similar to each other in ASP + 5% sorbitol, presented different frequencies of small evaginations which were observed arising from the cell surface mainly after an OsO₄ fixation step. There was no correlation between the frequency of evaginations and the virulence of the strain. An overnight storage at 4 °C considerably enhanced the frequency of the evaginations. It was suggested that the OsO₄ fixation step visualized differences in the bacterial outer membrane structure.List of abbreviations used ASP synthetic medium containing asparagine (see Materials and Methods) - CM cytoplasmic membrane - EPS exopolysaccharide - OM outer membrane - RT room temperature - YPG yeast peptone glucose medium (see Materials and Methods)     

Plasmatubules: an alternative to transfer cells?

Tubular evaginations of the plasmalemma of the scutellar epithelial cells of barley are described. The evaginations are similar to those present at other sites where solute flux occurs for a limited period only and wall development of the transfer-cell form has not occured. Differential uptake of the fluorescent dyes fluorescein, which moves into the symplast, and 8-anilino-1-naphthalene sulphonic acid, which remains in the apoplast only, indicates that the scutellar epithelial cells contain the boundary between the apoplast and symplast. We suggest that i) the plasmalemma evaginations, which have a specific form and localisation, may be referred to as plasmatubules rather than by the general term plasmalemmasome, and that ii) the plasmatubules may act in membrane amplification in a short-term structural modification which is an alternative to transfer cells.Abbreviation ANS 8-anilino-1-naphthalene sulphonic acid     

Cauda epididymal spermatozoa of the rufous hare wallaby, Lagorchestes hirsutus (Metatheria, Mammalia) imaged by electron and confocal microscopy

The ultrastructure of mature Lagorchestes hirsutus spermatozoa is described for the first time, revealing unusual aspects of sperm structure in macropodid species. The sperm head is ovoid rather than cuneiform, lacks a ventral nuclear groove and has an acrosomal distribution over approximately 85–90% of its dorsal surface. Immediately adjacent to the nuclear membrane the peripheral nucleoplasm in most spermatozoa form an irregular series of distinctive evaginations previously not described in the spermatozoa of any other marsupial. The midpiece is extremely thickened and short, containing no helical network or peripheral plasma membrane specializations. Axonemal structure is unspecialized with no connecting lamellae; dense outer fibres are closely adherent to axonemal doublets. The sperm morphology of this species is highly aberrant in comparison to other macropod taxa and supports the retention of Lagorchestes as a distinctive genus. In light of this new information, skeletal and serological data should be re‐evaluated to determine the true taxonomic and phylogenetic position of this species.     

Ultrastructural findings of congenital dyserythropoietic sickle cell beta thal-associated anemia.

The ultrastructural findings of erythroblasts and reticulocytes in one case of congenital dyserythropoiethic anemia (CDA) associated with a haemoglobinopathy, sickle cell beta thalassemia minor (Type V CDA), is described. The observations can be summarized as follows: 1) A lot of large breaks are present in the erythroblast nuclear envelope. 2) Nuclear membrane evaginations are filled with dense loose chromatin. 3) Electron-transparent areas (moth eaten chromatin) are evident in dense chromatin. 4) Electron-dense granular material, related to altered haemoglobin chain storage, is evident in the nucleus and in the cytoplasm. 5) Iron deposits are present in mitochondrial matrix. 6) Myelinic figures are present in reticulocyte cytoplasm. For the first time the ultrastructural findings in this type of associated CDA are described and related to the double origin of clinical symptoms.     

Electron microscopy of zygospore formation inChlamydomonas reinhardii

Summary After the disappearance of flagella and associated organelles, and nuclear fusion and chloroplast fusion, zygotes grow considerably. Growth is preceded by an extensive proliferation of rough endoplasmic reticulum from the outer membrane of the nuclear envelope. Nuclear fusion involves the fusion of the outer membranes (or of these endoplasmic reticulum evaginations), and then of the inner membranes. During zygospore formation on agar a complex 4–8 layered wall is formed. Precursors of two of the layers are detectable in the cytoplasm before secretion, one in the Golgi cisternae. Two types of storage granules are formed and fill much of the cytoplasm which undergoes extensive dedifferentiation. Endoplasmic reticulum and Golgi apparatus disappear. The chloroplast undergoes extensive dedifferentiation, losing its chlorophyll and most of its disc membranes. The resulting leucoplast retains its envelope, some starch grains and a tiny pyrenoid. In liquid culture developing zygospores become joined together in a multicellular mass. This disrupts wall formation, partially inhibits cytoplasmic and chloroplast dedifferentiation, and greatly reduces the zygospores' ability to germinate. The significance of these observations is discussed.     

The spatial association of the sperm cells and vegetative nucleus in the pollen grain ofBrassica

Summary In mature viable pollen ofBrassica oleracea, the pair of sperm cells and the nucleus of the vegetative cell are linked to form a structured unit we term the male germ unit. The sperm cells are held within a common periplasm and have no cell walls. Each sperm cell has a central globular body containing the nucleus surrounded by several evaginations which provide the means for linkage between them. One sperm cell, usually that closest to the nucleus of the vegetative cell contains most of mitochondria profiles (plastids are absent). This sperm cell appears to be linked by its protoplasmic evaginations to the envelope of the vegetative nucleus. The role of this unit in interactions with the female gametic complex is considered.