THE FINE STRUCTURAL ORGANIZATION OF NERVE FIBERS, SHEATHS, AND GLIAL CELLS IN THE PRAWN, PALAEMONETES VULGARIS

In view of reports that the nerve fibers of the sea prawn conduct impulses more rapidly than other invertebrate nerves and look like myelinated vertebrate nerves in the light microscope, prawn nerve fibers were studied with the electron microscope. Their sheaths are found to have a consistent and unique structure that is unlike vertebrate myelin in four respects: (1) The sheath is composed of 10 to 50 thin (200- to 1000-A) layers or laminae; each lamina is a cellular process that contains cytoplasm and wraps concentrically around the axon. The laminae do not connect to form a spiral; in fact, no cytoplasmic continuity has been demonstrated among them. (2) Nuclei of sheath cells occur only in the innermost lamina of the sheath; thus, they lie between the sheath and the axon rather than outside the sheath as in vertebrate myelinated fibers. (3) In regions in which the structural integrity of the sheath is most prominent, radially oriented stacks of desmosomes are formed between adjacent laminae. (4) An ~200-A extracellular gap occurs around the axon and between the innermost sheath laminae, but it is separated from surrounding extracellular spaces by gap closure between the outer sheath laminae, as the membranes of adjacent laminae adhere to form external compound membranes (ECM's). Sheaths are interrupted periodically to form nodes, analogous to vertebrate nodes of Ranvier, where a new type of glial cell called the "nodal cell" loosely enmeshes the axon and intermittently forms tight junctions (ECM's) with it. This nodal cell, in turn, forms tight junctions with other glial cells which ramify widely within the cord, suggesting the possibility of functional axon-glia interaction.     

ULTRASTRUCTURE OF THE PRAWN NERVE SHEATHS : Role of Fixative and Osmotic Pressure in Vesiculation of Thin Cytoplasmic Laminae

The sheaths from freshly teased nerve fibers of the prawn exhibit a positive radial birefringence, consistent with their EM appearance as highly organized laminated structures composed of numerous thin cytoplasmic sheets or laminae bordered by unit membranes and arranged concentrically around the axon. The closely apposed membranes in these sheaths are fragile and often break down into rows of vesicles during fixation. Desmosome-like attachment zones occur in many regions of the sheath. The membranes within these zones resist vesiculation and thereby provide a "control" region for relating the type of vesicles formed in the fragile portions of the sheaths to the specific fixation conditions. It is proposed that during fixation the production of artifactual vesicles is governed by an interplay of three factors: (a) direct chemical action of the fixative on the polar strata of adjacent unit membranes, (b) osmotic forces applied to membranes during fixation, and (c) the pre-existing natural relations between adjacent membranes. It is found that permanganate best preserves the continuity of the membranes but will still produce vesicles if the fixative exerts severe osmotic forces. These results support other reports (19) of the importance of comparing tissues fixed by complementary procedures so that systematic artifacts will not be described as characteristic of the natural state.     

The Fine Structure of Nerve Cells and Fibers, Neuroglia, and Sheaths of the Ganglion Chain in the Cockroach (Periplaneta americana)

The abdominal nerve cord of Periplaneta americana was studied utilizing light and electron microscopes. In the nerve cells, delicate granules, similar to those probably responsible for cytoplasmic basophilia, are evenly distributed in "dark" cells and clumped in "light" cells. Neuroglial cells are stained metachromatically by cresyl violet. The neuroglial cells have many processes which ramify extensively and are enmeshed to form overlapping layers. These imbricated processes ensheath the nerve cells; the inner layer of the sheath penetrates into the neuron and is responsible for the appearance of the trophospongium of Holmgren. Nerve fibers are embedded within glial cells and surrounded by extensions of the plasma membrane similar to mesaxons. Depending on their size, two or several nerve fibers may share a single glial cell. Nerve fibers near their terminations on other nerve fibers contain particles and numerous, large mitochondria. The ganglion is ensheathed by a thick feltwork of connective tissue and perilemmal cells. The abdominal connective has a thinner connective tissue sheath which is without perilemmal cells. The nerve fibers and sheaths in the connective become thinner as they pass through ganglia.     

The action of digitonin on rat liver mitochondria. Electron microscopy

1. Rat liver mitochondria were examined in the electron microscope by using negative staining in the presence of 0·3m-sucrose. The intact outer membrane does not appear to be freely permeable to the stain. Where the stain penetrated through a tear it was seen that the inner membrane had randomly oriented grooves, many of which contained round structures varying between 200 and 900å in diameter. Laminar structures containing two to five layers of approx. 50å each were found at the periphery. 2. When the outer membrane was removed by treating the mitochondria with digitonin several types of inner-membrane complexes were formed and they showed a general correlation with those observed in sectioned samples of the same preparations. The main types were: (a) a condensed form looking very much like the intact mitochondrion without the outer membrane (this still showed the grooves, some of which contained the round structures, and the laminar whirls at the edges); (b) a more transparent form containing tubules of uniform width and various lengths (some of these appeared to terminate in a hole at the surface of the inner membrane); (c) a large torn sac, probably the inner membrane, containing some tubules and vesicles. 3. When the inner-membrane complex was further treated with digitonin it was disrupted and the resulting material consisted of pieces of membrane, doughnut-shaped units and lamellar structures. Most of these pieces varied in size between 500 and 1000å.     

Sox9 Expression in Canine Epithelial Skin Tumors

Sox9 is a master regulatory gene involved in developmental processes, stem cells maintenance and tumorigenesis. This gene is expressed in healthy skin but even in several skin neoplasms, where its expression patterns often resembles those of the developing hair follicle. In this study, samples from eleven different types of canine skin neoplasms (squamous papilloma, squamous cell carcinoma, infundibular keratinizing acanthoma, inferior tricholemmoma, isthmic tricholemmoma, trichoblastoma, trichoepithelioma, malignant trichoepithelioma, pilomatricoma, subungual keratoacanthoma, subungual squamous cell carcinoma) were immunohistochemically stained and evaluated for Sox9 with the aim to correlate tumor phenotype with molecular characteristics that may help to better define tumor development, contribute to its diagnosis and clinical management. Keratoacanthoma excluded, all the skin neoplasms examined showed a variable positivity to Sox9, especially in the basal layers, but with major intensity in neoplasms developing from the bulge region of the hair follicle, as trichoblastoma. According to our results, Sox9 could be employed as a stem cell marker to better assess the role of stem cells in canine epidermal and follicular tumors.Key words: Sox9; dog, epidermal tumors, hair follicle tumors, immunohistochemistry     

Neuroglia of the adult rat optic nerve in the course of wallerian degeneration

The neurological reactions in Wallerian degeneration have been studied by electron microscopy in the optic nerve of adult albino rats from 7 to 120 days after unilateral enucleation. Reactive astrocytes contained abundant dense bodies, numerous microtubules and hyperplastic glial filaments. These astrocytes also assisted phagocytosis of degenerated myelin sheaths and in glial scar formation. Oligodendrocytes disconnected their cytoplasmic extensions, which were phagocytosed by microglial cells and astrocytes, by increased production of lysosomes. Microglial cells consisted of crinkled, long, rough endoplasmic reticula, several highly-active Golgi complexes, laminar inclusions and globoid lipid droplets. Microglia engulfed and lysed the disintegrated axons and myelin sheaths.     

Microbial origin of travertine fabrics—two examples from Southern Germany (Pleistocene stuttgart travertines and miocene riedöschingen Travertine)

Summary In Southern Germany, two examples of travertines of different age and depositional morphology were examined in detail. Travertines are laminated carbonate rocks formed by precipitation from mineral and/or thermal waters. They include characteristic facies types, such as bushy layers (‘shrubs’) referred to calcification of branching microbes (‘Dichothrix’-morphotype), laminar microbial mats, peloidal layers, and gas bubble layers formed within the sediment. In travertines, microbial activity is the most important factor for carbonate precipitation. Tufas differ from travertines by their abundance of molds of higher plants (leaves, reed, moss, green algae). They may be associated with travertines, but do not exhibit strict travertine facies types. Tufas are common in normal fresh water environments. Contrary to travertines and tufas, calcareous sinters usually occur in restricted areas like spring fissures, caves, or in pores, where microbial activity is not totally absent, but not of paramount importance for precipitation. Pedogenetic processes, which can alter travertine deposits, are responsible for large-scale features such as tepee-structures, and some intraclastic layers, and microscopic structures like endolithic borings andMicrocodium. Travertines may also grade into lacustrine limestones with Characeae, ostracods, and aquatic gastropods.     

THE ELECTRON MICROSCOPIC LOCALIZATION OF CHOLINESTERASE ACTIVITY IN THE CENTRAL NERVOUS SYSTEM OF AN INSECT, PERIPLANET A AMERICANAL.

The distribution of esterase activity in the last abdominal ganglion, the connectives and the cereal nerves of the cockroach Periplaneta americana has been investigated cytochemically. Activity of an unspecific eserine-insensitive esterase (or esterases) has been found in glial elements in these regions of the nerve cord. In addition, sites of cholinesterase (eserine-sensitive) activity have been found in association with (a) the glial sheaths of the axons in the cereal nerves and connectives, (b) the glial folds encapsulating the neuron perikarya in the ganglion, and (c) in localized areas along the membranes of axon branches within the neuropile, often flanked by focal clusters of synaptic vesicles. These results are discussed with particular reference to the previously reported insensitivity of the insect nerve cord to applied acetylcholine, and to the probable existence of a cholinergic synaptic mechanism in the central nervous system of this insect.     

Self-organization of local magnetoplasma structures in the upper layers of the solar convection zone

Self-organization and evolution of magnetoplasma structures in the upper layers of the solar convection zone are discussed as a process of diffuse aggregation of magnetic flux tubes. Equations describing the tube motion under the action of magnetic interaction forces, hydrodynamic forces, and random forces are written explicitly. The process of aggregation of magnetic flux tubes into magnetic flux clusters of different shapes and dimensions is simulated numerically. The obtained structures are compared with the observed morphological types of sunspot groups. The quantitative comparison with the observational data was performed by comparing the fractal dimensions of the photospheric magnetic structures observed in solar active regions with those of structures obtained in the numerical experiment. The model has the following free parameters: the numbers of magnetic flux tubes with opposite polarities on the considered area element (Nn and Ns), the average radius of the cross section of the magnetic flux tube (a), its effective length (l), the twist factor of the tube field (k), and the absolute value of the average velocity of chaotic tube displacements (d). Variations in these parameters in physically reasonable limits leads to the formation of structures (tube clusters of different morphological types) having different fractal dimensions. Using the NOAA 10488 active region, which appeared and developed into a complicated configuration near the central meridian, as an example, it is shown that good quantitative agreement between the fractal dimensions is achieved at the following parameters of the model: Nn = Ns = 250 ± 50; a = 150 ± 50 km; l ～ 5000 km, and d = 80 ± 10 m/s. These results do not contradict the observational data and theoretical estimates obtained in the framework of the Parker “spaghetti” model and provide new information on the physical processes resulting in the origin and evolution of local magnetic plasma structures in the near-photospheric layers of the solar convection zone.     

ELECTRON MICROSCOPE STUDIES ON SOMA-SOMATIC INTERNEURONAL JUNCTIONS IN THE CORPUS PEDUNCULATUM OF THE WOOD ANT (FORMICA LUGUBRIS ZETT.)

1. The corpora pedunculata of the wood ant (Formica lugubris Zett.) contain densely packed neuron perikarya which are separated by ultrathin glial sheaths. 2. These glial sheaths are occasionally interrupted by round holes with an average surface area of 2.64 µ². The holes are designated glial windows since they represent intracellular gaps of glial cytoplasm. 3. The glial windows allow soma-somatic interneuronal junctions. Of all adjacent neurons in a selected neuron pool, only 42% were interconnected by such junctions. 4. The intercellular space at the soma-somatic junctions has an average diameter of 30 A; occasionally, it is collapsed and an external compound membrane ensues. The junctional membranes are characterized by the presence of a subunit pattern of cross-directional electron-opaque lines with a 50- to 70-A periodicity. 5. Morphological signs of chemical transmission are absent in these junctions. On the other hand, there is a striking similarity in structural organization between soma-somatic junctions and electrical synapses described in other species. Therefore, it is suggested that these cell contacts of the ant's "cerebral cortex" are another form of electrical junction. 6. The close proximity of the junctions to the cell nucleus is noted. Its significance could not be ascertained. 7. The suggestion is made that glial windows may have dynamic properties and may intervene in the regulation of interneuronal transfer of information.     

FINE STRUCTURAL LOCALIZATION OF CHOLESTEROL-1,2-3H IN DEGENERATING AND REGENERATING MOUSE SCIATIC NERVE

The localization of ³H-labeled cholesterol in nerves undergoing degeneration and regeneration was studied by radioautography at the electron microscope level. Two types of experiments were carried out: (a) Cholesterol-1,2-³H was injected intraperitoneally into suckling mice. 5 wk later, Wallerian degeneration was induced in the middle branch of the sciatic nerve, carefully preserving the collateral branches. The animals were then sacrificed at various times after the operation. During degeneration, radioactivity was found over myelin debris and fat droplets. In early stages of regeneration, radioactivity was found in myelin debris and regenerating myelin sheaths. Afterwards, radioactivity was found predominantly over the regenerated myelin sheaths. Radioactivity was also associated with the myelin sheaths of the unaltered fibers, (b) Wallerian degeneration was induced in the middle branch of the sciatic nerves of an adult mouse, preserving the collateral branches. Cholesterol-1,2-³H was injected 24 and 48 hr after the operation and the animal was sacrificed 6 wk later. Radioactivity was found in the myelin sheaths of the regenerated and unaltered fibers. The results from these experiments indicate that: (a) exogenous cholesterol incorporated into peripheral nerve during myelination remains within the nerve when it undergoes degeneration. Such cholesterol is kept in the myelin debris as an exchangeable pool from which it is reutilized for the formation of the newly regenerating fibers, especially myelin. (b) exogenous cholesterol incorporated into the nerves at the time that degeneration is beginning is also used in the formation of new myelin sheaths during regeneration, (c) mature myelin maintains its ability to incorporate cholesterol.     

Mutational Profile of GNAQ Q209 in Human Tumors

Background

Frequent somatic mutations have recently been identified in the ras-like domain of the heterotrimeric G protein α-subunit (GNAQ) in blue naevi 83%, malignant blue naevi (50%) and ocular melanoma of the uvea (46%). The mutations exclusively affect codon 209 and result in GNAQ constitutive activation which, in turn, acts as a dominant oncogene.

Methodology

To assess if the mutations are present in other tumor types we performed a systematic mutational profile of the GNAQ exon 5 in a panel of 922 neoplasms, including glioblastoma, gastrointestinal stromal tumors (GIST), acute myeloid leukemia (AML), blue naevi, skin melanoma, bladder, breast, colorectal, lung, ovarian, pancreas, and thyroid carcinomas.

Principal Findings

We detected the previously reported mutations in 6/13 (46%) blue naevi. Changes affecting Q209 were not found in any of the other tumors. Our data indicate that the occurrence of GNAQ mutations display a unique pattern being present in a subset of melanocytic tumors but not in malignancies of glial, epithelial and stromal origin analyzed in this study.     

“Tight” junctions in the sheath of normal and regenerating motor nerves of the crayfish,Orconectes virilis

Summary Tight or occluding intercellular junctions occur between adjacent glial processes in normal and regenerating crayfish motor nerve sheaths. Although infrequent, these junctions possess the ridge and groove configuration characteristic of freeze-cleaved occluding junctions. When present, nerve sheath tight junctions consist of a single, or at most a few, parallel intramembrane ridges situated on the EF membrane face of the glial plasma membrane. Consequently, such contacts are rarely recognized in thin sections of plasticembedded nerve sheaths. Crayfish nerve sheath tight junctions are of the fascia occludens type and, therefore, do not impede solute flow across the nerve sheath. Fasciae occludentes of regenerating nerve sheaths occur in close proximity to discoid plaque-like aggregates of particles assumed to represent maculae adhaerentes. This relationship, which was not observed in normal nerve sheaths, suggests a functional association between the two types of junctions, perhaps developmental transformation of one junction type into the other. Although ridges and grooves of tight junctions occur next to crossfractured trans-glial channels, no functional significance is proposed for this relationship. This study is the first report of tight intercellular junctions in crustacean glial nerve sheaths.Supported by the National Research Council of Canada     

Apolipoprotein D expression in primary brain tumors: analysis by quantitative RT-PCR in formalin-fixed, paraffin-embedded tissue.

Apolipoprotein D (apoD) expression has been shown to correlate both with cell cycle arrest and with prognosis in several types of malignancy, including central nervous system astrocytomas and medulloblastomas. ApoD expression was investigated by real-time quantitative RT-PCR using RNA extracted from 68 formalin-fixed, paraffin-embedded brain specimens. Glyceraldehyde phosphate dehydrogenase was used as an internal control. Quantitation was achieved on all specimens. Sixteen poorly infiltrating WHO grade I glial neoplasms (i.e., pilocytic astrocytomas and gangliogliomas) showed an average 20-fold higher apoD expression level compared with the 20 diffusely infiltrating glial neoplasms (i.e., glioblastoma, anaplastic astrocytoma, oligodendrogliomas; p=0.00004). A small number of exceptions (i.e., two high-expressing glioblastomas and three low-expressing gangliogliomas) were identified. Analyzed as individual tumor groups, poorly infiltrating grade I pilocytic astrocytomas and gangliogliomas differed significantly from each tumor type within the diffusely infiltrating higher-grade category (p<0.05 for each comparison) but not from each other (p>0.05). Conversely, each individual tumor type within the diffusely infiltrating category differed significantly from both pilocytic astrocytomas and gangliogliomas (p<0.05) but did not vary from other infiltrating tumors (p>0.05). Ependymomas, non-infiltrating grade II neoplasms, expressed levels of apoD similar to or lower than levels expressed by the diffusely infiltrating gliomas. Ten medulloblastomas with survival longer than 3 years averaged slightly higher apoD expression than four fatal medulloblastomas; however, this result was not statistically significant and individual exceptions were notable. In 17 of the medulloblastomas, MIB-1 proliferation rates quantitated by image cytometry did not correlate with apoD expression. In addition, apoD expression was 5-fold higher in the slowly proliferating grade I glial neoplasms compared with non-proliferating normal brain tissue (p=0.01), suggesting that apoD expression is not simply an inverse measure of proliferation. ApoD expression measured by quantitative RT-PCR may be useful in the differential diagnosis of primary brain tumors, particularly pilocytic astrocytomas and gangliogliomas.     

Comparative gene expression analysis of the engulfment and cell motility (ELMO) protein family in the mouse brain

Engulfment and cell motility (ELMO) proteins bind to Dock180, a guanine nucleotide exchange factor (GEF) of the Rac family, and regulate GEF activity. The resultant ELMO/Dock180/Rac module regulates cytoskeletal reorganization responsible for the engulfment of apoptotic cells, cell migration, and neurite extension. The expression and function of Elmo family proteins in the nervous system, however, are not yet fully understood. Here, we characterize the comparative gene expression profiles of three Elmo family members (Elmo1, Elmo2, and Elmo3) in the brain of C57BL/6J mice, a widely used inbred strain, together with reeler mutant mice to understand gene expression in normal laminated brain areas compared with abnormal areas. Although all three Elmo genes showed widespread mRNA expression over various mouse tissues tested, Elmo1 and Elmo2 were the major types expressed in the brain, and three Elmo genes were up-regulated between the first postnatal week (infant stage) and the third postnatal week (juvenile, weaning stage). In addition, the mRNAs of Elmo genes showed distinct distribution patterns in various brain areas and cell-types; such as neurons including inhibitory interneurons as well as some non-neuronal cells. In the cerebral cortex, the three Elmo genes were widely expressed over many cortical regions, but the predominant areas of Elmo1 and Elmo2 expression tended to be distributed unevenly in the deep (a lower part of the VI) and superficial (II/III) layers, respectively, which also changed depending on the cortical areas and postnatal stages. In the dentate gyrus of the hippocampus, Elmo2 was expressed in dentate granule cells more in the mature stage rather than the immature-differentiating stage. In the thalamus, Elmo1 but not the other members was highly expressed in many nuclei. In the medial habenula, Elmo2 and Elmo3 were expressed at intermediate levels. In the cerebellar cortex, Elmo1 and Elmo2 were expressed in differentiating-mature granule cells and mature granule cells, respectively. In the Purkinje cell layer, Elmo1 and Elmo2 were expressed in Purkinje cells and Bergmann glia, respectively. Disturbed cellular distributions and laminar structures caused by the reeler mutation did not severely change expression in these cell types despite the disturbed cellular distributions and laminar structures, including those of the cerebrum, hippocampus, and cerebellum. Taken together, these results suggested that these three Elmo family members share their functional roles in various brain regions during prenatal-postnatal development.     

Feinstrukturelle und mikroanalytische Untersuchungen an den Kristallen und Lithosomen des CiliatenEuplotes vannus

Summary In the cytoplasm of the marine ciliateEuplotes vannus, there exist two conspicuous types of membrane bound inclusions: 1. irregularly shaped crystals which are highly anisotropic; 2. globular lithosomes characterized by concentrically arranged layers of deposits which exhibit only faint birefringence. Normally, both structures form distinct accumulations. Energy dispersive X-ray microanalysis of these accumulations reveals a high content of calcium and phosphorus, besides magnesium, sulphur and chlorine. Analysis of cell areas devoid of the inclusions show significantly lower calcium- and phosphorus-peaks.

     

Tracing cells throughout development: Insights into single glial cell differentiation

In the article “Predetermined embryonic glial cells form the distinct glial sheaths of the Drosophila peripheral nervous system” we combined our expertise to identify glial cells of the embryonic peripheral nervous system on a single cell resolution with the possibility to genetically label cells using Flybow. We show that all 12 embryonic peripheral glial cells (ePG) per abdominal hemisegment persist into larval (and even adult) stages and differentially contribute to the three distinct glial layers surrounding peripheral nerves. Repetitive labelings of the same cell further revealed that layer affiliation, morphological expansion, and control of proliferation are predetermined and subject to an intrinsic differentiation program. Interestingly, wrapping and subperineurial glia undergo enormous hypertrophy in response to larval growth and elongation of peripheral nerves, while perineurial glia respond to the same environmental changes with hyperplasia. Increase in cell number from embryo (12 cells per hemisegment) to third instar (up to 50 cells per hemisegment) is the result of proliferation of a single ePG that serves as transient progenitor and only contributes to the outermost perineurial glial layer.     

Dynamics of <Emphasis Type="Italic">Pseudomonas putida</Emphasis> biofilms in an upscale experimental framework

Exploitation of biofilms for industrial processes requires them to adopt suitable physical structures for rendering them efficient and predictable. While hydrodynamics could be used to control material features of biofilms of the platform strain Pseudomonas putida KT2440 there is a dearth of experimental data on surface-associated growth behavior in such settings. Millimeter scale biofilm patterns formed by its parental strain P. putida mt-2 under different Reynolds numbers (Re) within laminar regime were analyzed using an upscale experimental continuous cultivation assembly. A tile-scan image acquisition process combined with a customized image analysis revealed patterns of dense heterogeneous structures at Re = 1000, but mostly flattened coverings sparsely patched for Re < 400. These results not only fix the somewhat narrow hydrodynamic regime under which P. putida cells form stable coatings on surfaces destined for large-scale processes, but also provide useful sets of parameters for engineering catalytic biofilms based on this important bacterium as a cell factory.     

Leaf anatomy of c(3)-c(4) species as related to evolution of c(4) photosynthesis

This study was undertaken to examine the degree of Kranz anatomy development in the species intermediate to C₃ and C₄ types (C₃-C₄) in Panicum, Neurachne, Flaveria, and Moricandia. In each genus, C₃ and/or C₄ species were used for comparison. Leaf transections from each species were examined by light and transmission electron microscopy. The percentages of leaf photosynthetic cell profiles partitioned to bundle sheaths were higher in C₄ than in C₃ species, while C₃-C₄ species tended to be in between. However, percentages for C₃-C₄ species in Moricandia and some C₃-C₄Flaveria species were not greater than C₃. When expressed on a cell profile area basis, C₃-C₄ species partitioned more photosynthetic tissue to bundle sheaths than C₃ species in Moricandia, but not in Flaveria. Neurachne minor S. T. Blake (C₃-C₄) partitioned a very small portion of cell profile area to the inner bundle sheaths (5%) compared to Neurachne munroi F. Muell (C₄) (21%). The percentage of organelles partitioned to bundle sheaths was much greater in C₃-C₄ than in C₃ species. The average C₃ percentages for mitochondria plus peroxisomes were 19, 8, and 19.5% for Neurachne, Flaveria, and Moricandia, respectively, compared to 41, 29, and 46.5% for the C₃-C₄ species. The CO₂ compensation concentration was negatively related to the partitioning of tissue to bundle sheaths and to the percentage of organelles in bundle sheaths. It is concluded that all of the C₃-C₄ species examined have developed some degree of Kranz anatomy and that this altered anatomy is involved in their reduced apparent photorespiration.     

The In Vitro Self-Assembly of Supramolecular Structures after the Spontaneous Disassembly of Carotovoricins

The self-assembly of supramolecular structures (empty sheaths and polysheaths of the macromolecular Erwinia carotovora bacteriocins) was studied by electron microscopy in the course of 1- to 2-year incubation of phage particles at 4°C. This study showed that the empty sheaths and polysheaths of the bacteriocins of eight E. carotovora strains spontaneously assemble at the self-assembly centers (or crystallization centers), which have a diameter of 26–65 nm and contain a dense proteinaceous material. The self-assembly center consists of two components, a primer and the structural protein of contracted sheaths. Empty sheaths assembled in the crystallization centers are polar structures synthesized through the stepwise head-to-tail polymerization of monomeric units. The supramolecular structures of two E. carotovora 62A bacteriocins are assembled in a different way. At the early stages of their self-assembly, a reticular structure is formed, which then transforms into very long polysheaths composed of monomers. Along with polysheaths, rounded or lamplike structures 33–117 nm in size composed of the subunits of contracted sheaths are produced. Carotovoricins may serve as suitable objects for the study of the self-assembly of elementary biological structures.