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排序方式: 共有336条查询结果,搜索用时 234 毫秒
1.
A. Rulz i Altaba 《Developmental neurobiology》1993,24(10):1276-1304
In this review I summarize recent findings on the contributions of different cell groups to the formation of the basic plan of the nervous system of vertebrate embryos. Midline cells of the mesoderm—the organizer, notochord, and prechordal plate—and midline cells of the neural ectoderm—the notoplate and floor plate—appear to have a fundamental role in the induction and patterning of the neural plate. Vertical signals acting across tissue layers and planar signals acting through the neural epithelium have distinct roles and cooperate in induction and pattern formation. Whereas the prechordal plate and notochord have distinct vertical signaling properties, the initial anteroposterior (A-P) pattern of the neural plate may be induced by planar signals originating from the organizer region. Planar signals from the notoplate may also contribute to the mediolateral (M-L) patterning of the neural plate. These and other findings suggest a general view of neural induction and axial patterning. © 1993 John Wiley & Sons, Inc. 相似文献
2.
Dye-flow apparatus to measure the variation in axial xylem permeability over a stem cross-section 总被引:1,自引:1,他引:0
R. E. BOOKER 《Plant, cell & environment》1984,7(8):623-628
Abstract Equipment and methodology are described that allows the radial variation in axial xylem permeability (hydraulic conductivity) over a tree cross-section to be measured and the flow paths to be identified by the strictly controlled flow of dye through a specimen. The apparatus can be calibrated so that the point-to-point variation of absolute permeability over a xylem cross-section can be calculated from the dye-flow patterns, which otherwise show only relative variations in permeability. The effect of using different dyes and dye concentrations on the penetration time and the shape of the dye patterns was investigated. The penetration time through the wood of identical end-matched specimens is appreciably longer for fixing dyes than for non-fixing dyes, and for the fixing dyes it depends strongly on the dye concentration. However, the dye patterns of the end-matched specimens were indistinguishable with fixing and non-fixing dyes, and independent of dye concentration. The fixing dye toluidine blue at 0.25% to 0.5% (w/w) was found most suitable as it yields a clear permanent pattern. 相似文献
3.
Fröhlich S Lotz M Korte T Lübbert A Schügerl K Seekamp M 《Biotechnology and bioengineering》1991,37(10):910-917
Saccharomyces cerevisiae was cultivated in a 4-m(3) pilot plant airlift tower loop reactor with a draft tube in batch and continuous operations and for comparison in a laboratory airlift tower loop reactor of 0.08 m(3) volume. The reactors were characterized during and after the cultivation by measuring the distributions of the residence times of the gas phase with pseudostochastic tracer signals and mass spectrometer and by evaluating the mixing in the liquid phase with a pulse-shaped volatile tracer signal and mass spectrometer as a detector. The mean residence times and the intensities of the axial mixing in the riser and downcomer, the circulation times of the gas phase, and the fraction of the recirculated gas phase were evaluated and compared. 相似文献
4.
L. T. Furcht G. Wendelschafer-Crabb D. F. Mosher J. M. Foidart 《Journal of cellular biochemistry》1980,13(1):15-33
Fibronectin and collagens are major constituents of the cell matrix of fibroblasts. Fibronectin is a 220,000 dalton glycoprotein that mediates a variety of adhesive functions of cells examined in vitro. Fibronectin is secreted in a soluble form and interacts with collagen to form extracellular filaments. Fibronectin and procollage type I were localized using the peroxidase anti-peroxidase method. Under standard culture conditions, fibronectin and procollagen were localized to non-periodic 10 nm extracellular fibrils, the cell membrane and plasma membrane vesicles. Ascorbate treatment of cells leads to a new larger fibril with a diameter of approximately 40 nm. Antibodies to fibronectin and procollagen I react to these native collagen fibrils with an axial periodicity of approximately 70 nm. Fibronectin is clearly associated with native collagen fibrils produced by ascorbate treated cells and there is an asymetric distribution or segregation of fibronectin on these collagen fibrils with a 70 nm axial repeat. 相似文献
5.
Fang Liu Kratika Singhal Rowan Matney Swati Acharya Cezmi A. Akdis Kari C. Nadeau Allis S. Chien Ryan D. Leib 《Proteomics》2020,20(11)
The analytical scale of most mass‐spectrometry‐based targeted proteomics assays is usually limited by assay performance and instrument utilization. A recently introduced method, called triggered by offset, multiplexed, accurate mass, high resolution, and absolute quantitation (TOMAHAQ), combines both peptide and sample multiplexing to simultaneously improve analytical scale and quantitative performance. In the present work, critical technical requirements and data analysis considerations for successful implementation of the TOMAHAQ technique based on the study of a total of 185 target peptides across over 200 clinical plasma samples are discussed. Importantly, it is observed that significant interference originate from the TMTzero reporter ion used for the synthetic trigger peptides. This interference is not expected because only TMT10plex reporter ions from the target peptides should be observed under typical TOMAHAQ conditions. In order to unlock the great promise of the technique for high throughput quantification, here a post‐acquisition data correction strategy to deconvolute the reporter ion superposition and recover reliable data is proposed. 相似文献
6.
Reiko Nishino Shohei Hamada Elghareeb E. Elboray Yoshihiro Ueda Takeo Kawabata Takumi Furuta 《Chirality》2020,32(5):588-593
Axial chirality in N,N-dimethylaminopyridines as well as N,N-dipropylaminopyridines bearing an internal carboxy group were evaluated based on their racemization barriers and circular dichroism spectra. The half-life of racemization of N,N-dipropylaminopyridine derivative 2 was estimated to be 19.7 days at 20°C. Its enantiomers isolated as optically active forms showed positive-negative and negative-positive Cotton effects for (+)- 2 and (−)- 2 , respectively, from 310 to 210 nm. Furthermore, (−)- 2 was applied as a chiral nucleophilic catalyst and exhibited asymmetric induction in acylative kinetic resolution of 1-(1-naphthyl)ethane-1-ol. 相似文献
7.
Trigonostemons G and H, two novel dimeric dinorditerpenoids, were isolated from the stem barks of Trigonostemon chinensis. Their planar structures and relative configurations were established by extensive analysis of spectroscopic data. Trigonostemons G and H possess a homodimeric biaryl skeleton obtained from two rearranged chiral nonracemic abietane-type dinorditerpenes through an axially chiral biaryl 11,11′-linkage. Torsional scan and computation of the transition states were carried out to estimate the rotational energy barrier, and the axial chirality (aS) was determined by time-dependent density functional theory (TDDFT) electronic circular dichroism (ECD) calculations. The positive n-π* ECD transitions of the isolated carbonyl chromophore above 300 nm could be used to determine the central chirality of trigonostemon G independently by ECD calculations of the diastereomers. 相似文献
8.
《Médecine Nucléaire》2020,44(4):231-249
The original thyroid scan (TS) was widely used to identify typical imaging patterns, suggesting the widely accepted main following clinical diagnoses: Grave's disease, Toxic adenoma, [hetero]-nodular goiters and thyroiditis. With the diffusion of sensitive TSH assays, considerable advances in the comprehension of the molecular mechanisms of hormonosynthesis, and new quantification possibilities especially using 123I, the TS is a textbook of molecular imaging. The image can be finely quantified with, not only as regards the Uptake (123IUp) and related parameters but also, the quantification of the spatial targeting leading to a Spatial Target Index (STI). Using this new molecular 123I-TS, TSH values, and when required, correlation to Multiparametric Ultrasounds (MPUS), we generated a basic classification system of hyperthyroidism, with well-defined indexed criteria (C11-1 to C17-3), that allows reporting 24 distinct etiologies. Selected criteria involve TS and contrast patterns, precocious 123IUp (p123IUp), maximal TSH-dependent physiological Uptake, lobar concentration, Uptake and concentration ratios, STI, 99mTc-MIBI TS and correlative MPUS. This approach allows to identify 4 subtypes of Graves’ disease, including hyperplastic, nodular and common GD variants entangled with Hashimoto's struma, 4 subtypes of Thyroid Functional Autonomy, including Disseminated Functional Autonomy, that cannot be diagnosed with other conventional procedures. Criteria C14-1 to C17-3 report on hyperthyroidism and iodine overload, factitia, main thyroiditis presentations and rare central or tumoral etiologies of hyperthyroidism. This classification, based on 123I-TS molecular imaging, leads to unprecedented diagnostic finesse and paves the way for a personalized theranostic approach in thyroid pathology. Further development towards artificial intelligence networks is under study. 相似文献
9.
Kanika Narula Eman Elagamey Magdi A. E. Abdellatef Arunima Sinha Sudip Ghosh Niranjan Chakraborty Subhra Chakraborty 《The Plant journal : for cell and molecular biology》2020,103(2):561-583
Pathogen‐/microbe‐associated molecular patterns (PAMPs/MAMPs) initiate complex defense responses by reorganizing the biomolecular dynamics of the host cellular machinery. The extracellular matrix (ECM) acts as a physical scaffold that prevents recognition and entry of phytopathogens, while guard cells perceive and integrate signals metabolically. Although chitosan is a known MAMP implicated in plant defense, the precise mechanism of chitosan‐triggered immunity (CTI) remains unknown. Here, we show how chitosan imparts immunity against fungal disease. Morpho‐histological examination revealed stomatal closure accompanied by reductions in stomatal conductance and transpiration rate as early responses in chitosan‐treated seedlings upon vascular fusariosis. Electron microscopy and Raman spectroscopy showed ECM fortification leading to oligosaccharide signaling, as documented by increased galactose, pectin and associated secondary metabolites. Multiomics approach using quantitative ECM proteomics and metabolomics identified 325 chitosan‐triggered immune‐responsive proteins (CTIRPs), notably novel ECM structural proteins, LYM2 and receptor‐like kinases, and 65 chitosan‐triggered immune‐responsive metabolites (CTIRMs), including sugars, sugar alcohols, fatty alcohols, organic and amino acids. Identified proteins and metabolites are linked to reactive oxygen species (ROS) production, stomatal movement, root nodule development and root architecture coupled with oligosaccharide signaling that leads to Fusarium resistance. The cumulative data demonstrate that ROS, NO and eATP govern CTI, in addition to induction of PR proteins, CAZymes and PAL activities, besides accumulation of phenolic compounds downstream of CTI. The immune‐related correlation network identified functional hubs in the CTI pathway. Altogether, these shifts led to the discovery of chitosan‐responsive networks that cause significant ECM and guard cell remodeling, and translate ECM cues into cell fate decisions during fusariosis. 相似文献
10.
Carolina Mazo‐Molina Samantha Mainiero Benjamin J. Haefner Ryland Bednarek Jing Zhang Ari Feder Kai Shi Susan R. Strickler Gregory B. Martin 《The Plant journal : for cell and molecular biology》2020,103(4):1433-1445
The Ptr1 (Pseudomonas tomato race 1) locus in Solanum lycopersicoides confers resistance to strains of Pseudomonas syringae pv. tomato expressing AvrRpt2 and Ralstonia pseudosolanacearum expressing RipBN. Here we describe the identification and phylogenetic analysis of the Ptr1 gene. A single recombinant among 585 F2 plants segregating for the Ptr1 locus was discovered that narrowed the Ptr1 candidates to eight nucleotide‐binding leucine‐rich repeat protein (NLR)‐encoding genes. From analysis of the gene models in the S. lycopersicoides genome sequence and RNA‐Seq data, two of the eight genes emerged as the strongest candidates for Ptr1. One of these two candidates was found to encode Ptr1 based on its ability to mediate recognition of AvrRpt2 and RipBN when it was transiently expressed with these effectors in leaves of Nicotiana glutinosa. The ortholog of Ptr1 in tomato and in Solanum pennellii is a pseudogene. However, a functional Ptr1 ortholog exists in Nicotiana benthamiana and potato, and both mediate recognition of AvrRpt2 and RipBN. In apple and Arabidopsis, recognition of AvrRpt2 is mediated by the Mr5 and RPS2 proteins, respectively. Phylogenetic analysis places Ptr1 in a distinct clade compared with Mr5 and RPS2, and it therefore appears to have arisen by convergent evolution for recognition of AvrRpt2. 相似文献