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1.
Ernϕ H. Freundl E. A. Krogsgaard-Jerisen A. Rosendal S. 《Acta veterinaria Scandinavica》1972,13(2):263-265
The natural host-range of M. mycoides subsp. mycoides is generally believed to be restricted to cattle, although the production in experimental conditions of a generalized infection of sheep and goats has been reported on some occasions. 相似文献
2.
Summary The thecal ultrastructure ofScrippsiella faeroense (Paulsen) Balech and Oliveira Soares as seen in the electron microscope is described. Additional structural detail of the thecal plate surface, plate connections, and the apical pore, is revealed. 相似文献
3.
Rockwell NC Njuguna SL Roberts L Castillo E Parson VL Dwojak S Lagarias JC Spiller SC 《Biochemistry》2008,47(27):7304-7316
Phytochromes are widely occurring red/far-red photoreceptors that utilize a linear tetrapyrrole (bilin) chromophore covalently bound within a knotted PAS-GAF domain pair. Cyanobacteria also contain more distant relatives of phytochromes that lack this knot, such as the phytochrome-related cyanobacteriochromes implicated to function as blue/green switchable photoreceptors. In this study, we characterize the cyanobacteriochrome Tlr0924 from the thermophilic cyanobacterium Thermosynechococcus elongatus. Full-length Tlr0924 exhibits blue/green photoconversion across a broad range of temperatures, including physiologically relevant temperatures for this organism. Spectroscopic characterization of Tlr0924 demonstrates that its green-absorbing state is in equilibrium with a labile, spectrally distinct blue-absorbing species. The photochemically generated blue-absorbing state is in equilibrium with another species absorbing at longer wavelengths, giving a total of 4 states. Cys499 is essential for this behavior, because mutagenesis of this residue results in red-absorbing mutant biliproteins. Characterization of the C 499D mutant protein by absorbance and CD spectroscopy supports the conclusion that its bilin chromophore adopts a similar conformation to the red-light-absorbing P r form of phytochrome. We propose a model photocycle in which Z/ E photoisomerization of the 15/16 bond modulates formation of a reversible thioether linkage between Cys499 and C10 of the chromophore, providing the basis for the blue/green switching of cyanobacteriochromes. 相似文献
4.
5.
Water uptake by roots of maize and sunflower affects the radial transport of abscisic acid and its concentration in the xylem 总被引:13,自引:0,他引:13
The radial movement of cis-abscisic acid (ABA) has been investigated in young excised roots of Zea mays L. and Helianthus annuus L. which were grown hydroponically. In addition to the symplastic path, ABA was largely translocated across the root apoplast
by solvent drag with the water in the transpiration stream. On the apoplastic path ABA may even cross the endodermis. Depending
on the ABA concentration of the medium (range: 5–500 nM) and in the root apoplast, the solvent-drag component of the flow
of ABA counteracted the dilution of ABA in the xylem caused by transpirational water flow. Acidification of the rhizosphere
and of the root apoplast increased the apoplastic transport component. In sunflower, the apoplastic flow of ABA was significantly
weaker than in maize roots. This was also indicated by the larger apparent reflection coefficient (σABA) of sunflower roots for ABA (sunflower: σABA = 0.97 ± 0.02, n = 6 roots; maize: σABA = 0.68 ± 0.06, n = 6 roots; ±SD). For both species, σABA was smaller than unity. Root reflection coefficients were affected by factors such as pH, ABA concentration of the medium,
and by the suction force applied to excised root systems. Due to the complex composite structure of the permeation barrier
in the root, the reflection coefficient estimated from solvent drag is also complex. Since unstirred layers affected the absolute
value of the reflection coefficient, σABA has been termed `apparent'. It is concluded that the pH and ABA concentration of the soil solution as well as the transpiration
rate (suction force) modify the intensity of the root-to-shoot signal which is influenced by an apoplastic bypass flow of
ABA. The latter may be substantially affected by the existence of Casparian bands in the exodermis, which were lacking in
the roots studied in this paper.
Received: 25 February 1998 / Accepted: 16 July 1998 相似文献
6.
The toxic marine dinoflagellate Gonyaulax catenella Whedon & Kofoid was studied with scanning and transmission electron microscopy to describe the thecal morphology and to accurately define the taxonomic characters of the species. The closing platelet which lies in a U-shaped apical pore was revealed to be disassociable from a partly obscured apical platelet. Two previously unreported sulcal plates were charaterized and described. The entire complement of thecal plates numbered 33. 相似文献
7.
Lynch BA Matagne A Brännström A von Euler A Jansson M Hauzenberger E Söderhäll JA 《Biochemical and biophysical research communications》2008,375(4):491-495
The synaptic vesicle protein 2A (SV2A), the brain-binding site of the anti-epileptic drug levetiracetam (LEV), has been characterized by Protein Tomography™. We identified two major conformations of SV2A in mouse brain tissue: first, a compact, funnel-structure with a pore-like opening towards the cytoplasm; second, a more open, V-shaped structure with a cleft-like opening towards the intravesicular space. The large differences between these conformations suggest a high degree of flexibility and support a valve-like mechanism consistent with the postulated transporter role of SV2A. These two conformations are represented both in samples treated with LEV, and in saline-treated samples, which indicates that LEV binding does not cause a large-scale conformational change of SV2A, or lock a specific conformational state of the protein. This study provides the first direct structural data on SV2A, and supports a transporter function suggested by sequence homology to MFS class of transporter proteins. 相似文献
8.
The ultrastructure of resting state colonies of Botryococcus braunii Kützing from two localities is compared to active state colonies maintained in the laboratory. Qualitative hydrocarbon analyses confirmed the physiological status of each sample according to the precedent in the literature; resting state colonies contained botryococcenes, while active state colonies contained a predominance of straight-chain olefins. The ultrastructure of resting and active state colonies is fundamentally similar. The chloroplast of resting state cells contains fewer thylakoids and larger relative numbers of plastoglobuli than the chloroplast of active state cells maintained under favorable growth conditions. Previously undescribed phenomena include the cytochemical demonstration of polyphosphate bodies microbody-like organelles and ER-ribosomal-mitochondrial complexes. Attempts to elicit the transition of active to resting state colonies utilizing different light intensities and/or nitrogen deficient media were unsuccessful. Instead, these experiments induced the formation of yellow or whitish-brown senescent colonies which always contained a predominance of olefins. Senescent cells contain reduced, peripherally displaced organelles. Most of the cytoplasm is occupied by vacuoles and lipid (probably hydrocarbon) inclusions. Morphologically identifiable polyphosphate bodies are usually small or absent. Observations pertinent to the mechanism of hydrocarbon secretion were in basic agreement with previously published information. The outer cell wall, or trilamellar structure (TLS), was recently as the primary site of hydrocarbon accumulation and production. The role of the TLS in hydrocarbon biosynthesis, however, should be cautiously regarded without additional evidence. 相似文献
9.
Nancy W. Withers Elenor R. Cox Ronald Tomas Francis T. Haxo 《Journal of phycology》1977,13(4):354-358
An examination of the pigments of the binucleate dinoflagellate Peridinium balticum (Levander) Lemmerman revealed the presence of chlorophylls a, c1 and c2 and the carotenoids: fucoxanthin (most abundant), diadinoxanthin, diatoxanthin, an unidentified fucoxanthin-like xanthophyll, β-carotene, γ-carotene and astaxanthin. A comparison of the pigments of P. balticum and P. foliaceum (Stein) Biecheler, also a binucleate dinoflagellate, demonstrated similar compositions. However P. balticum lacked the β-carotene precursors (e.g. phytoene) which accumulated outside the chloroplast in P. foliaceum. This study indicates that P. balticum and P. foliaceum are closely related; each species is a heterotrophic dinoflagellate with a photosynthetic endosymbiont taxonomically affiliated with the Chrysophyta (Chrysophyceae or Bacillariophyceae). 相似文献
10.
Using scanning electron and light, microscopy, several hundred specimens of Campylostylus normanianus (Grev.) Gerloff, Licmophora abbreviata Agardh, L. gracilis var. anglica (Kütz) Per. et Per., and L. flabellata (Carm.) Agardh were examined to elucidate their valve morphology. These species were found to be heterovalvar with respect to the presence of the labiate process in the basal apices of the cell, although one was always present at the head pole of each valve. This form of heterovalvar may be one basis for partitioning the large and variable family Diatomaceae. Because of the similar valve morphologies exhibited by C. normanianus and Licmophora species examined, it is recommended that Campylostylus normanianus be placed in the older genus Licmophora, as L. normaniana (Grev.) Wahrer. 相似文献