水杨酸和热锻炼诱导的高羊茅幼苗的耐热性与抗氧化的关系

研究了水杨酸（SA）处理和热锻炼（HH）对高羊茅（Festuca arundinacea Schred.)幼苗耐热性的影响和在耐热性诱导过程中植物体内可溶性蛋白含量与超氧化物歧化酶（SOD）,过氧化的酶（POD）和过氧化氢酶（CAT）等3种抗氧化酶的活性变化。结果表明：0.5mmol/L男SA预处理能显著提高高羊茅幼苗在42℃热胁迫（HS）后转至常温下恢复生长18d时的苗高,绿叶数和绿叶指数;在常温下SA提高高羊茅幼苗的CAT活性,降低POD活性,而对SOD的影响不显著;SA和HH均能降低高羊茅幼苗在HS下细胞外渗液电导率,提高可溶性蛋白的含量和SOD、CAT活性,但不能显著提高POD活性。因此,推测SA与HH提高耐热性上具有相似的机理。     

Studying cellular architecture in three dimensions with improved resolution: Ta replicas revisited

Metal replicas have been used for surface analysis of biological structures with a variety of spatial resolutions. Platinum (Pt) has been the metal of choice because it provides very stable replicas and images of high contrast. Some other metals, such as tantalum (Ta) have been reported to provide better resolution on isolated macromolecular complexes and cellular structures. Our goal is to study the gain in detail with Ta and to evaluate if it provides enough detail and resolution to assist in the study of complex volumes of intact cellular structures obtained by methods that reach molecular resolution. To this purpose Pt and Ta replicas of cellular structures and viruses have been studied by transmission electron microscopy (TEM). Replicas of Ta show new details on the surface of two types of isolated viral particles such as 100 nm bunyaviruses and large, > 300 nm, vaccinia virus (VV). Inside cells, the structural pieces that build VV immature particles are visualized only in Ta replicas. Looking for smaller intracellular complexes, new details are also seen in nuclear pores from Ta replicas. Additional masses, most likely representing the cargo during transport, are distinguished in some of the pores. Visualization of proteins in plasma membranes strongly suggests that detail and resolution of Ta replicas are similar to those estimated for 3D maps currently obtained by electron tomography of viruses and cells.     

Superficial photothermal laser ablation of ex vivo sheep esophagus using a cone‐shaped optical fiber tip

Superficial photothermal laser ablation (SPLA) may be useful as a therapeutic approach producing a depth of injury that is sufficient to eliminate mucosal lesion but not deep enough to induce thermal effects in deeper tissue layers. The purpose of this preliminary study is twofold: (a) to describe design steps of a fiber probe capable of delivering a tightly focused laser beam, including Monte‐Carlo‐based simulations, and (b) to complete the initial testing of the probe in a sheep esophagus model, ex vivo. The cone‐shaped (tapered) fiber tip was obtained by chemical etching of the optical fiber. A 1505 nm diode laser providing power up to 500 mW was operated in continuous wave. The successful SPLA of the sheep mucosa layer was demonstrated for various speed‐power combinations, including 300 mW laser power at a surface scanning rate of 0.5 mm/s and 450 mW laser power at a surface scanning rate of 2.0 mm/s. Upon further development, this probe may be useful for endoscopic photothermal laser ablation of the mucosa layer using relatively low laser power.     

Diversity in gas exchange and muscular activity patterns in insects studied by a respirometer-actograph

Different events in insect gas exchange and muscular activity are described by a new system of automatic respirometers, a differential electrolytic microrespirometer-actograph. This is very sensitive to volumetric changes caused by insect respiration and/or body movements. In this system, oxygen generation and its regulation are combined in the same current circuit. According to this principle, the oxygen consumed by the insect is continuously replaced by equal amounts of electrolytically produced oxygen. This simple laboratory-made apparatus records simultaneously metabolic rate, the cyclicity of external gas exchange, rhythms of muscular ventilating and the pattern of other body movements, including abdominal pulsations not observable with the naked eye. The respirometer-actograph described here is applicable also to the recording of the respiration of other terrestrial arthropods or other living organisms or tissues.     

Evidence of a distribution difference between two gangliosides in bilayer membranes

Freeze-etch electron microscopy, a platinum shadowing technique, has been used to compare the lateral distribution of several gangliosides in bilayer model membranes by directly visualizing bound lectin molecules. In particular, GM₁ and GD_1a, major components of brain ganglioside, were studied in phase-separated mixtures of dipalmitoyl- and dielaidoylphosphatidylcholines exposed to Ricinus communis agglutinin and wheat germ agglutinin. The distribution of glycolipid showed evidence of microheterogeneity in that bound lectin tended to occur in clusters of several or more molecules. With GD_1a as receptor such clusters were small and very uniformly distributed over the membrane surface. Somewhat larger, irregularly spaced clusters of up to a dozen lectin particles were more typical of membranes bearing GM₁ and, in addition, there were occasional extensive patches of bound lectin coexisting with areas apparently devoid of glycolipid receptor in phase-separated mixtures of dipalmitoyl- and dielaidoylphosphatidylcholine. Gangliosides in the latter mixtures were not obviously influenced in their lateral distribution by the presence of coexisting fluid and rigid domains. These basic observations seem to extend to bilayer membranes containing mixtures of two gangliosides. The patterns of lectin binding were not grossly affected by incubation time or history of warming and cooling. This study was extended to bilayers of pure dipalmitoylphosphatidylcholine in expectation that the distinctive features characteristic of the P_β′ phase of this lipid might accentuate any behavioural differences between GM₁ and GD_1a.GM₁ was found to exist preferentially in the ‘trough’ regions between P_β′ ripples, while GD_1a showed no apparent preferential arrangement. Given that bound lectins adequately reflect glycolipid distribution in membranes, it would appear that structurally different glycolipids from the same host membrane can assume different distributions on the basis of interactions with defined lipid host matrices.     

Fast Proton Insertion in Layered H2W2O7 via Selective Etching of an Aurivillius Phase

H₂W₂O₇, a metastable material synthesized via selective etching of the Aurivillius-related Bi₂W₂O₉, is demonstrated as an electrode for high power proton-based energy storage. Comprehensive structural characterization is performed to obtain a high-fidelity crystal structure of H₂W₂O₇ using an iterative approach that combines X-ray diffraction, neutron pair distribution function, scanning transmission electron microscopy, Raman spectroscopy, and density functional theory modeling. Electrochemical characterization shows a capacity retention of ≈80% at 1000 mV s^–1 (1.5-s charge/discharge time) as compared to 1 mV s^–1 (≈16-min charge/discharge time) with cyclability for over 100 000 cycles. Energetics from density functional theory calculations indicate that proton storage occurs at the terminal oxygen sites within the hydrated interlayer. Last, optical micrographs collected during in situ Raman spectroscopy show reversible, multicolor electrochromism, with color changes from pale yellow to blue, purple, and last, orange as a function of proton content. These results highlight the use of selective etching of layered perovskites for the synthesis of metastable transition metal oxide materials and the use of H₂W₂O₇ as an anode material for proton-based energy storage or electrochromic applications.     

Single‐Step Preparation of Large Area TiO2 Photoelectrodes for Water Splitting

The fast, single‐step and easily scalable production by plasma electrolytic oxidation (PEO) of large area TiO₂ electrodes with excellent photoactivity in water splitting under simulated solar light is systematically investigated here. In particular, the effects that the cell voltage (100–180 V) and the processing time (0.5–15 min) have on the electrode properties are studied. The PEO‐produced oxide layers are porous, the predominant crystalline structure shifting from anatase, to an anatase‐rutile mixture, and finally to rutile by rising the cell voltage. The electrodes show a double‐layered structure, with a more compact layer at the interface with the titanium substrate and a thick porous layer on the external surface. The photocurrent density versus wavelength reflects the phase composition, with a maximum incident photon‐to‐current efficiency of 90% at 320 nm. The highest H₂ production rate is attained with the mixed anatase‐rutile electrode prepared by 300 s‐long PEO at 150 V.     

Surface Domains in the Pathogenic Protozoan Tritrichomonas foetus

ABSTRACT The quick-freezing and freeze-etching techniques were used to analyze surface domains of Tritrichomonas foetus . The surface of the protozoan body was not smooth, presenting surface projections, except on the flagellar surface. Images of the actual surface of the anterior flagella revealed the presence of intramembranous particles that form rosettes, as observed on the protoplasmic fracture face. They may represent integral transmembrane proteins exposed at the cell surface. Surface specializations were also observed at the flagella base and where the recurrent flagellum attaches to the cell body.