Morphology and histology of the digestive system of the vector leafhopper Psammotettix striatus (L.) (Hemiptera: Cicadellidae)

The vector leafhopper Psammotettix striatus (L.) (Hemiptera: Cicadellidae) is an important economic pest that is a serious threat to wheat in Northwest China, causing great losses to agricultural production by transmitting wheat blue dwarf (WBD) in a persistent circulative manner. Studies on morphology and ultrastructure of the digestive system were made using light, scanning and transmission electron microscopy. The gross morphology of the alimentary canal consists of esophagus (foregut), midgut, hindgut, and special filter chamber. The esophagus, a narrow and slender tube, runs through the whole thorax extending into the filter chamber and connecting with the anterior midgut. The midgut consists of three major regions, anterior, middle and posterior midgut. The anterior midgut is composed of exceptionally thick epithelial cells surrounding a large lumen. Numerous well-developed microvilli occur at the basal region of the epithelium. A large number of electron-lucent and lipid-like vesicles are observed under the microvilli. The posterior midgut is smaller than the anterior midgut in diameter. Numerous different concentric circular bodies are characteristic of the posterior midgut. The hindgut arises from the posterior midgut at the boundary of the filter chamber. It extends downward toward the anus where the hindgut enlarges to form the rectum. The rectum is formed by various cells typical of epithelium, whose nuclei are relatively smaller than those of the midgut. Relatively large muscle cells are present at the well-defined and thick basement membrane. There are two pairs of Malpighian tubules. Numerous mitochondria and lamellar rough endoplasmic reticulum in the cells of the anterior segment of the Malpighian tubules; the sub-anterior segment of the tubules resemble the distal segment which are wave-like, amount vesicles in the cells; numerous tightly packed large vesicles contain two types of brochosomes in the inflated segment of the Malpighian tubules. The salivary system of P. striatus contains one pair of salivary glands, which are made up of the principal and accessory gland. The principal glands are divided into anterior, mid- and posterior lobes. About nineteen acini are observed in the principal glands of P. striatus, and vary in structure and colour. Five cellular types are found in the principal glands by transmission electron microscopy, which are rich in secretory granules, modified in size, electron-dense and shape. Rough endoplasmic reticulum in the shape of vesicular and lamellar, mitochondria and Golgi complexes are observed. The accessory gland has only an oval or a rod-shaped acinus.     

Testicular structure and description of the seminal pathway in Leporinus macrocephalus (Anostomidae, Teleostei)

The present study examined the testicular structure and the seminal pathway in freshwater fish Leporinus macrocephalus (Garavello and Britski, 1988). Twenty-five specimens of this species were studied. Testicular structure was analyzed using light and transmission electron microscopy. The testicular main ducts were examined by means of conventional histology, corrosion–cast technique and scanning electron microscopy. Additional techniques were applied for polysaccharides histochemistry and immunohistochemistry for androgen receptor. The testicular parenchyma was classified as the anastomosing tubular testis type with spermatogonia occurring along the lengths of the seminiferous tubules. The seminiferous tubules emptied directly into the testicular main ducts. The wall of the testicular main ducts in L. macrocephalus consisted of three layers: epithelium, connective tissue and peritoneum. The epithelium changed from simple cuboidal to pseudostratified. The histochemical analysis revealed the presence of granules PAS positive in the epithelial cells. The immunoreactivity to androgen receptor was noted in the testicular main ducts through all cytoplasmic areas of epithelial cells.     

Characterization of self-assembled monolayers (SAMs) on silicon substrate comparative with polymer substrate for Escherichia coli O157:H7 detection

This article presents the characterization of two substrates, silicon and polymer coated with gold, that are functionalized by mixed self-assembled monolayers (SAMs) in order to efficiently immobilize the anti-Escherichia coli O157:H7 polyclonal purified antibody.A biosurface functionalized by SAMs (self-assembled monolayers) technique has been developed. Immobilization of goat anti-E. coli O157:H7 antibody was performed by covalently bonding of thiolate mixed self-assembled monolayers (SAMs) realized on two substrates: polymer coated with gold and silicon coated with gold. The F(ab′)₂ fragments of the antibodies have been used for eliminating nonspecific bindings between the Fc portions of antibodies and the Fc receptor on cells. The properties of the monolayers and the biofilm formatted with attached antibody molecules were analyzed at each step using infrared spectroscopy (FTIR-ATR), atomic force microscopy (AFM), scanning electron microscopy (SEM) and cyclic voltammetry (CV). In our study the gold-coated silicon substrates approach yielded the best results.These experimental results revealed the necessity to investigate each stage of the immobilization process taking into account in the same time the factors that influence the chemistry of the surface and the further interactions as well and also provide a solid basis for further studies aiming at elaborating sensitive and specific immunosensor or a microarray for the detection of E. coli O157:H7.     

‘Epixenosomes’: Peculiar epibionts of the protozoon ciliate Euplotidium itoi: Do their cytoplasmic tubules consist of tubulin?

Epixenosomes, epibiontic organisms living on the protozoon ciliate Euplotidium itoi, like prokaryotes, lack a true nucleus surrounded by a nuclear envelope. However, their cytoplasm, at least in the mature state, is somehow compartmentalized by the presence of a complex extrusive apparatus surrounded by a form of basket consisting of bundles of tubules (BT), 20–24 nm in diameter, delineated by a wall made of globular subunits. The nature of these tubules was investigated by means of in vivo experiments, ultrastructural analysis and immunocytochemistry by both fluorescence and electron microscopy. It has been found that BT, besides being well preserved when fixed in the presence of tannic acid, are sensitive to factors known to depolymerize cytoplasmic microtubules in a variety of cells such as nocodazole and cold and show a positive immunoreaction against different antitubulin antibodies. On the basis of all the results obtained, the hypothesis that the epixenosomal BT consist of tubulin acquires a strong credibility. This is particularly interesting if we consider that tubulin in prokaryotes has never been conclusively demonstrated.     

Plasma sterilization using the RF glow discharge

In the present work, glow discharge oxygen plasma was used to sterilize the Pseudomonas aeruginosa on the polyethylene terephthalate (PET) sheets. In a self-designed plasma reaction equipment, active species (electron, ion, radical, UV light, etc.) were separated effectively, and the discharge area, afterglow area and remote area were plotted out in the plasma field. Before and after plasma treatment the cell morphology was studied by scanning electron microscopy (SEM). The results showed that after treatment of 30 s the germicidal effect is 4.26, 3. 84, 2.61, respectively in the three areas on the following conditions: discharge power was 40 W and gas flux was 20 cm³/min. SEM results revealed the cell morphology before and after plasma treatment. The walls or cell membrane cracking was testified by determining the content of protein using coomassie light blue technique. The results from electron spin resonance spectroscopy (ESR) and double Langmuir electron probe showed that electron, ion and oxygen free radical played important roles in sterilization in the discharge area, but only oxygen radicals acted to sterilize the bacteria in the afterglow area and the remote area.     

Effects of static magnetic fields on Escherichia coli

This paper represents the study of the biological effects of static magnetic fields (SMFs) on Escherichia coli (E. coli). The bacterial strain E. coli was exposed to SMFs in order to test its viability (evaluated by the number of colony-forming units (CFU)). In this study, we measured the dependence of CFU on the duration of exposure, on the treatment temperature T and on the value of the magnetic field induction B. The results showed that the number of CFU decreased with longer exposure time and higher treatment temperature (from 25 °C to 40 °C), whereas multiple extreme values of number of CFU were obtained when the induction B changed. In order to explain the results, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to investigate the morphology of the cells. We found obvious cell surface damage when the cells were exposed to SMFs.     

Structure and vibrational properties of carbon tubules

The structure of multilayered carbon tubules has been investigated by electron microscopy and X-ray diffraction. The structure of tubules is characterized by disorder in the stacking of cylindrical graphene sheets. Raman scattering measurements have been carried out in tubules and compared with graphite. The observed features in the Raman spectra in tubules can be understood in terms of the influence of disorder. The additional Raman modes predicted for single layer carbon tubules have not been observed.     

Formation and manipulation of regular metallic nanoparticle arrays on bacterial surface layers: an advanced TEM study

The template-directed formation of regular nanoparticle arrays on two-dimensional crystalline protein layers after their treatment with metal salt complexes was studied by transmission electron microscopy. For these investigations, bacterial surface layers (S layers), recrystallized in vitro into sheets and tube-shaped protein crystals with typical dimensions in the micrometer range, were used as the template. As identified by electron holography and scanning force microscopy, the S-layer tubes form alternating double layers when deposited onto a solid substrate surface. Two distinct pathways for the metal particle formation at the templates have been found: the site-specific growth of metal clusters by chemical reduction of the metal salt complexes, and the electron-beam induced growth of nanoparticles in the transmission electron microscope. Both mechanisms lead to regular arrays with particle densities > 6×10¹¹ cm ^-2. Nanoparticle formation by electron exposure takes exclusively place in the flat-lying double-layered protein tubes, where a sufficient amount of metal complexes can be accumulated during sample preparation. Received 6 December 2000     

Elaboration and characterization of barium silicate thin films

Room temperature depositions of barium on a thermal silicon oxide layer were performed in ultra high vacuum (UHV). In-situ X-ray photoelectron spectroscopy (XPS) analyses were carried out as well after exposure to air as after subsequent annealings. These analyses were ex-situ completed by secondary ion mass spectrometry (SIMS) profiles and transmission electron microscopy (TEM) cross-sectional images. The results showed that after air exposure, the barium went carbonated. Annealing at sufficient temperature permitted to decompose the carbonate to benefit of a barium silicate. The silicate layer was formed by interdiffusion of barium with the initial SiO₂ layer.     

Comparative sperm ultrastructure of three species in Siniperca (Teleostei: Perciformes: Sinipercidae)

Siniperca chuatsi, Siniperca kneri, and Siniperca scherzeri are three of the most economically important sinipercid species. The ultrastructure and morphology of the mature spermatozoa of them are examined using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The sperm consists of an acrosome-less head, a short midpiece and a long flagellum. Ultrastructurally, it has a homogeneously electron-dense nucleus in a granular pattern with nuclear lucent and a nuclear fossa excluding the centriolar complex. One to four mitochondria with lamellar cristae encircle the basal body of the flagellum in the midpiece. The cytoplasm surrounding the centrioles and the cylindric cytoplasmic channel contains glycogen granules and vesicles. Comprising the conventional 9 + 2 axoneme, vesicles and lateral fins, the sperm flagellum is inserted laterally on the nucleus, therefore the spermatozoon is asymmetrical. All of the spermatozoa of the three species are of the primitive or ect-aquasperm form and conform to the teleostean type II spermatozoa instead of the previously supposed type I. Variations in the shape of the heads, angles between the two centrioles, location of the cytoplasmic vesicles, mitochondrial number and structural characteristics of the lateral fins are notable among the three species. S. chuatsi is a sister-group of the other two species and is the most differentiated. The present study provides fresh insights to the comparative spermatology of Siniperca fishes and will be useful to the existing knowledge of the sinipercid fishes in systematic characters, biodiversity conservation and reproduction.     

Ultramorphology of the proventriculus in Panorpidae and Bittacidae (Mecoptera)

The proventriculus is a specialized part of the foregut in the alimentary canal in some insects, varying greatly in its structure across different insect groups. The ultramorphology of the proventriculus in Mecoptera was investigated in eight species of Panorpidae and one of the Bittacidae using light microscopy and scanning electron microscopy. The proventriculus consists of the outer circular muscles, the inner longitudinal muscles, an epithelium, and a sclerotized intima with dense acanthae. The proventricular acanthae could be divided into three categories: the anterior acanthae (AA), the main acanthae (MA), and the posterior acanthae (PA). In Panorpidae the AA are rounded in cross section and could be subdivided into two subtypes, the long AA with a polytomy apiculus and the short AA with a V-shaped or spine-like apiculus. The MA, covering the majority of the proventricular inner surface, are dense, uniform, and hollow rectangular structures in cross section with forked apiculi. Each hollow base of the MA was first found to be inserted with a cone-shaped process of the corresponding epithelial cell. The PA are very thin, with a spine-like apiculus. In Bittacidae the proventriculus is specialized by a ring of cuticular thickening within its anterior orifice, and the AA are shaped like a ring of thin spines. Six cardiac valves were observed in Panorpidae and ten in Bittacidae. The functions of the various types of acanthae in digestion and extra-oral digestion and their significance in insect systematics are briefly discussed.     

Measurement of Light and pH Dependence of Single-Cell Photosynthesis by Fluorescence Microscopy

Measurement of algal photosynthetic performance with conventional methods requires thousands of cells obtained by isolation and subsequent cultivation. This is a time-consuming process for many species. We describe a new method to study photosynthetic performance of single algal cells under various environmental conditions by a combination of modulated chlorophyll fluorescence, light microscopy, and sample manipulation techniques. Single cell fluorescence was measured with a modulated microfluorometer integrated in an inverted microscope. The algal cell was sucked onto the tip of a glass microcapillary and positioned in the center of the field of view of the microscope by a micromanipulator. A superfusion device was used to generate a flow of experimental solution of variable composition along the alga. The light dependence of Scenedesmus obtusiusculus single-cell photosystem II (PSII) electron flow was measured at various pH. At a high light intensity PSII electron flow was inhibited at pH 6.5 and higher, while at a low light inhibition occurred at pH 9.5. This is in agreement with inhibition of photosynthesis by substrate (CO₂) limitation at alkaline pH. This approach can easily be extended to study the in vivo effects of other abiotic parameters (temperature, nutrients, toxicants, oxygen) on the photosynthetic performance of algae.     

Microstructures of patterned nc-Si superlattices made by pulsed laser interference crystallization

We employed atomic force microscopy, cross-section transmission electron microscopy and high-resolution electron microscopy to investigate the microstructures and surface morphology of laser interference crystallized a-Si : H/a-SiN_x : H superlattices. The experimental results show that Si nanocrystallites (nc-Si) are formed within the initial a-Si : H sublayers and are patterned in certain regions with the same periodicity of 2.0 μ m as the phase-shifting mask grating. The size of nc-Si is limited by adjacent a-SiN _x: H sublayers due to the constrained crystallization effect so it is possible to use this crystallization method to get a three-dimensional ordered nc-Si array.     

In situ observation of carbon-nanopillar tubulization caused by liquidlike iron particles

The tubulization process of amorphous carbon nanopillars was observed in situ by transmis-sion electron microscopy. Amorphous carbon nanopillars were transformed into graphitic tubules by annealing at 650-900 degrees C in the presence of iron nanoparticles. A molten catalyst nanoparticle penetrated an amorphous carbon nanopillar, dissolving it, and leaving a graphite track behind. An iron nanoparticle moved with its shape changing like an earthworm. We concluded that the tubulization mechanism is a solid-(quasiliquid)-solid mechanism where the carbon phase transformation is a kind of liquid phase graphitization of amorphous carbon catalyzed by liquefied metal-carbon alloy nanoparticles.     

Template synthesis of well-aligned titanium dioxide nanotubes

TiO₂ nanotubes of the anatase form have been synthesized by sol-gel chemical method using anodic aluminum oxide (AAO) as a template. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction were used to investigate the structure and morphology of the TiO₂ nanotubes. The results showed that TiO₂ nanotubes obtained are highly ordered and uniform. The diameter and length of the obtained nanotubes were determined by the pore size and the thickness of AAO template. It was found that through control of immersion time of AAO membrane in sol, both tubules and fibrils can be prepared. PACS 61.46.+w     

Impact of growth temperature on the crystal habits,forms and structures of VO<Subscript>2</Subscript> nanocrystals

We investigated the impact of the process temperature on the habits, forms and crystal structure of VO₂ nanocrystals grown by a vapor-transport method on (0001) quartz substrates. Four distinct growth regimes were discerned: orthorhombic nanowires, sheets, hemispheres, and nanowires with a monoclinic structure. The nanostructures were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). I/V characterization of individual nanowires was enabled by Ti/Au contact formation via electron beam lithography and lift-off techniques. The expected metal–insulator transition (MIT) was found in monoclinic VO₂ nanowires.     

Direct observation of laser-induced crystallization of a-C:H films

The post-growth modification of diamond-like amorphous hydrogenated carbon a-C:H films by laser treatment has been studied by transmission electron microscopy and Raman spectroscopy. a-C:H films grown on Si substrates by benzene decomposition in a rf glow discharge were irradiated with 15 ns pulses of a KrF-excimer laser with fluences in the range of E=50–700 mJ/cm². At fluences below 100 mJ/cm² an increase in the number of graphitic clusters and in their ordering was evidenced from Raman spectra, while the film structure remained amorphous according to electron microscopy and electron diffraction observations. At higher fluences the appearance of diamond particles of 2–7 nm size, embedded into the lower crystallized graphitic matrix, was observed and simultaneously a progressive growth of graphite nanocrystals with dimensions from 2 nm to 4 nm was deduced from Raman measurements. The maximum thickness of the crystallized surface layer (400 nm) and the degree of laser annealing are limited by the film ablation which starts at E>250 mJ/cm². The laser-treated areas lose their chemical inertness. In particular, chemical etching in chromium acid becomes possible, which may be used for patterning the highly inert carbon films.     

Occurrence and ultrastructure of Albugo candida on a new host, Arabis alpina in Saudi Arabia

A population of Arabis alpina (Brassicaceae) growing in Saudi Arabia was observed to be infected for the first time by the Oomycete, Albugo candida. Both conventional chemical fixation and high pressure freezing followed by freeze substitution (HPF/FS) were used to prepare zoosporangia, intercellular hyphae, haustoria, invading host cells and host–parasite interface of A. candida for study with both scanning and transmission electron microscopy. Both fixations gave good preservation of ultrastructural details and data from the two sample types were highly complementary. Scanning electron microscopic observation revealed that mature zoosporangia of A. candida are spherical or ellipsoidal in shape and characterized by a smooth surface and faint terminal secession scar at each end. Transmission electron microscopic observation indicated that coenocytic intercellular hyphae are located in intercellular spaces of host leaf tissue forming haustoria in host mesophyll cell. Each haustorium is connected to intercellular hyphae by a narrow, slender neck which enclosed by a collar as a response of host cell to infection. The cytoplasm of the haustorium contains different organelles characteristic of the Oomycetes. No obvious responses are observed in host cell organelles following infection which may be due to the presence of a compatibility between the host and the Oomycete. Modifications of the host plasma membrane around the haustorium are detected. Many tubular elements were found to be continuous with the extrahaustorial membrane. This appears to be the first report of the presence of these tubular elements in case of A. candida haustoria. These tubular elements may increase membrane surface area and consequently increase the efficacy of nutrients uptake by haustoria from host cell.     

Morphological characterization of the antennal sensilla of the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), with reference to their probable functions

The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is one of the most significant economic pests of citrus worldwide. This insect vectors three phloem-restricted bacteria in the genus Candidatus Liberibacter that cause huanglongbing (citrus greening), the most severe disease limiting citrus production worldwide. We examined the external morphology of the antennal sensilla of male and female D. citri using scanning electron microscopy (SEM) and determined the putative functions of the identified sensilla using transmission electron microscopic (TEM) techniques. The filiform antennae of D. citri were of the conventional type comprised of a basal scape, pedicel and a long, thread-like flagellum, which is composed of eight flagellomeres. Eleven morphologically unique sensillar types were found and described on the antennae of male and female D. citri. Of those identified, the two apical setae, multiporous types I and II sensilla trichoidea, and the antennal rhinaria were porous and may be involved in perception of host- and mate-related volatile chemicals. However, the aporous types I, II and III sensilla trichoidea may have mechanosensory functions and the chaetica sensilla, cavity sensilla and unidentified uniporous sensilla may be involved in proprioception, thermo-hygroreception and cold detection, respectively. The shape, external morphology and array of sensilla on the antennae of male and female D. citri were similar. The only major difference observed was in the morphology of the short apical setae, whose tips were recessed inward in females but not so in males. The results are discussed in relation to plausible roles of the identified sensilla in mate and host location by this species.     

ZnO纳米线场效应管的制备及I-V特性研究

采用静电探针和原子力探针技术,将化学气相沉积工艺制备的,长度为30—200 μm,直径80—750 nm的单根半导体ZnO纳米线搭接在Au,Zn,Al不同功函的金属隔离沟道两端,构建出了最基本的ZnO纳米线绝缘栅场效应管. 研究了沟道类型、纳米线直径、退火温度和外加栅压对ZnO纳米线场效应管I-V特性的影响. 利用半导体与金属材料的肖特基接触、欧姆接触的产生机理及电子输运理论,对结果进行了分析和讨论. 关键词： ZnO纳米线 场效应管 I-V特性')" href="#">I-V特性