Kinetics of cell formation and growth stresses in the secondary xylem of Swietenia mahagoni (L.) Jacq. and Khaya ivorensis A. Chev. (Meliaceae)     

Oliver Dünisch  Otto Rühmann 《Wood Science and Technology》2006,40(1):49-62

The kinetics of xylem formation in four-year-old plants of Swietenia mahagoni (L.) Jacq. and Khaya ivorensis A. Chev. were studied by means of high resolution laser measurements (accuracy: ±2 μm) in a spatial resolution of 18.7 to 94.1 μm and a temporal resolution of 1 to 60 s. The radial enlargement of the xylem cells was completed within 0.36 to 8.85 hours in Swietenia and within 0.52 to 12.03 hours in Khaya, while secondary wall formation and lignification lasted days to weeks. Cell enlargement of vessels and ray parenchyma was significantly faster than radial enlargement of fibres and axial parenchyma. The processes of formation of the secondary cell wall and the lignification were slower in fibres than in vessels and parenchyma cells. In Swietenia new secondary cell formation was induced in distinct growth periods almost simultaneously in the whole shoot, while in Khaya new cell formation was restricted to parts of the shoot. Growth stresses in the shoot were studied in terms of released strain. Higher growth stresses were observed in the shoot of Khaya compared to Swietenia. The results indicate that the higher growth stresses in the xylem of Khaya compared to Swietenia originate in the different kinetics of cell development of different cell types in combination with the heterogenous sequence of cell formation within the shoot. Dedicated to Prof. Dr. Dr. h.c. mult. W. Liese on the occasion of his 80th birthday.  相似文献   

Veränderung von Humusform, -vorrat und -verteilung im Zuge von Waldumbau-Maßnahmen im Nordostdeutschen Tiefland     

Holger Fischer  Oliver Bens  Reinhard Hüttl 《European Journal of Forest Research》2002,121(6):322-334

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Longitudinal hardness and Young's modulus of spruce tracheid secondary walls using nanoindentation technique   总被引：6，自引：2，他引：6  

Dr. R. Wimmer  Dr. B. N. Lucas  W. C. Oliver  Dr. T. Y. Tsui 《Wood Science and Technology》1997,31(2):131-141

Summary Using a mechanical properties microprobe, measurements of hardness and elastic modulus of tracheid walls in the longitudinal direction of spruce wood were obtained by continuously measuring force and displacement as a diamond indenter impressed a cell wall. Maximum mechanical properties were found at the edges of the walls of angular shaped tracheids. Both the hardness and elastic modulus of latewood cell walls were higher than cell walls in the earlywood. The high spatial resolution of this new concept of mechanical testing allows a direct comparison with ultrastructural and microchemical parameters of lignified cells which opens a wider area of applications for the understanding of intrinsic wood properties.This work was conducted while the senior author was a Visiting Scientist at the Oak Ridge National Lab, Oak Ridge, TN 37831, USA partly with joint fundings from the Austrian Science Foundation (Schrödinger scholarship J799-BIO)  相似文献   

Genetic Diversity in Populations of Xanthomonas campestris pv. campestris in Cruciferous Weeds in Central Coastal California     

Ignatov A  Sechler A  Schuenzel EL  Agarkova I  Oliver B  Vidaver AK  Schaad NW 《Phytopathology》2007,97(7):803-812

ABSTRACT Xanthomonas campestris pv. campestris (X. campestris) infects a large number of cruciferous plants, including weeds. California has one of the largest and most diverse populations of wild cruciferous plants in the world. Although considerable information is available on the genetic diversity of X. campestris in commercial crop plants, nothing is known about the diversity in strains infecting weeds. To assess the genetic diversity among strains of X. campestris in weeds in noncultivated and cultivated areas, strains of the pathogen were isolated from populations of cruciferous weeds growing in coastal valley crop-production sites and from remote nonproduction sites along the California central coast. Results of fingerprinting over 68 strains using amplified fragment length polymorphism along with representative strains by sequence analysis showed the presence of seven genotypes. Genotypes A and B were limited to coastal sites; genotypes C, D, and E were from inland cultivated sites; and genotypes F and G were present in both coastal noncultivated and inland cultivated sites. Crop strains were grouped outside any weed strain group and were separated from the weed strains and other pathovars of X. campestris. These results revealed, for the first time, that strains of X. campestris present in noncultivated coastal weed populations generally were unique to a site and genetically distinct from strains present in populations of weeds in crop-production areas located nearby.  相似文献   

Classical swine fever virus replicon particles lacking the Erns gene: a potential marker vaccine for intradermal application     

Frey CF  Bauhofer O  Ruggli N  Summerfield A  Hofmann MA  Tratschin JD 《Veterinary research》2006,37(5):655-670

Classical swine fever virus replicon particles (CSF-VRP) deficient for E(rns) were evaluated as a non-transmissible marker vaccine. A cDNA clone of CSFV strain Alfort/187 was used to obtain a replication-competent mutant genome (replicon) lacking the sequence encoding the 227 amino acids of the glycoprotein E(rns) (A187delE(rns)). For packaging of A187delE(rns) into virus particles, porcine kidney cell lines constitutively expressing E(rns) of CSFV were established. The rescued VRP were infectious in cell culture but did not yield infectious progeny virus. Single intradermal vaccination of two pigs with 10(7) TCID(50) of VRP A187delE(rns) elicited neutralizing antibodies, anti-E2 antibodies, and cellular immune responses determined by an increase of IFN-gamma producing cells. No anti-E(rns) antibodies were detected in the vaccinees confirming that this vaccine represents a negative marker vaccine allowing differentiation between infected and vaccinated animals. The two pigs were protected against lethal challenge with the highly virulent CSFV strain Eystrup. In contrast, oral immunization resulted in only partial protection, and neither CSFV-specific antibodies nor stimulated T-cells were found before challenge. These data represent a good basis for more extended vaccination/challenge trials including larger numbers of animals as well as more thorough analysis of virus shedding using sentinel animals to monitor horizontal spread of the challenge virus.  相似文献   

Field dissipation and environmental hazard assessment of clomazone, molinate, and thiobencarb in Australian rice culture     

Quayle WC  Oliver DP  Zrna S 《Journal of agricultural and food chemistry》2006,54(19):7213-7220

The fates of clomazone [2-(2-chlorophenyl)methyl-4,4-dimethyl-3-isoxazolidinone], molinate (S-ethyl hexahydro-1-H-azepine-1-carbothioate), and thiobencarb {S-[(4-chlorophenyl)methyl]diethylcarbamothioate} applied to rice were studied at two locations in New South Wales (Australia). Rates of dissipation (DT50) from floodwaters and soils were measured. Dissipation of the three herbicides from water and soil can be best explained by a first-order decay process. DT(50) values for clomazone, molinate, and thiobencarb were 7.2, 5.1, and 3.5 days, respectively, in water and 14.6, 23.9, and >46 days, respectively, in surface soil. Maximum measured concentrations of clomazone, molinate, and thiobencarb in floodwaters were 202, 1042, and 148 microg/L, respectively, taking 18.4, 26.4, and 21.4 days to dissipate to concentrations set to protect aquatic ecosystems. A hazard assessment identified clomazone as presenting a low environmental hazard while molinate and thiobencarb presented a medium environmental hazard when used at registered field rates.  相似文献   

Substrate-controlled succession of marine bacterioplankton populations induced by a phytoplankton bloom     

Teeling H  Fuchs BM  Becher D  Klockow C  Gardebrecht A  Bennke CM  Kassabgy M  Huang S  Mann AJ  Waldmann J  Weber M  Klindworth A  Otto A  Lange J  Bernhardt J  Reinsch C  Hecker M  Peplies J  Bockelmann FD  Callies U  Gerdts G  Wichels A  Wiltshire KH  Glöckner FO  Schweder T  Amann R 《Science (New York, N.Y.)》2012,336(6081):608-611

Phytoplankton blooms characterize temperate ocean margin zones in spring. We investigated the bacterioplankton response to a diatom bloom in the North Sea and observed a dynamic succession of populations at genus-level resolution. Taxonomically distinct expressions of carbohydrate-active enzymes (transporters; in particular, TonB-dependent transporters) and phosphate acquisition strategies were found, indicating that distinct populations of Bacteroidetes, Gammaproteobacteria, and Alphaproteobacteria are specialized for successive decomposition of algal-derived organic matter. Our results suggest that algal substrate availability provided a series of ecological niches in which specialized populations could bloom. This reveals how planktonic species, despite their seemingly homogeneous habitat, can evade extinction by direct competition.  相似文献   

A fine-scale chimpanzee genetic map from population sequencing     

Auton A  Fledel-Alon A  Pfeifer S  Venn O  Ségurel L  Street T  Leffler EM  Bowden R  Aneas I  Broxholme J  Humburg P  Iqbal Z  Lunter G  Maller J  Hernandez RD  Melton C  Venkat A  Nobrega MA  Bontrop R  Myers S  Donnelly P  Przeworski M  McVean G 《Science (New York, N.Y.)》2012,336(6078):193-198

To study the evolution of recombination rates in apes, we developed methodology to construct a fine-scale genetic map from high-throughput sequence data from 10 Western chimpanzees, Pan troglodytes verus. Compared to the human genetic map, broad-scale recombination rates tend to be conserved, but with exceptions, particularly in regions of chromosomal rearrangements and around the site of ancestral fusion in human chromosome 2. At fine scales, chimpanzee recombination is dominated by hotspots, which show no overlap with those of humans even though rates are similarly elevated around CpG islands and decreased within genes. The hotspot-specifying protein PRDM9 shows extensive variation among Western chimpanzees, and there is little evidence that any sequence motifs are enriched in hotspots. The contrasting locations of hotspots provide a natural experiment, which demonstrates the impact of recombination on base composition.  相似文献   

Bright coherent ultrahigh harmonics in the keV x-ray regime from mid-infrared femtosecond lasers     

Popmintchev T  Chen MC  Popmintchev D  Arpin P  Brown S  Alisauskas S  Andriukaitis G  Balciunas T  Mücke OD  Pugzlys A  Baltuska A  Shim B  Schrauth SE  Gaeta A  Hernández-García C  Plaja L  Becker A  Jaron-Becker A  Murnane MM  Kapteyn HC 《Science (New York, N.Y.)》2012,336(6086):1287-1291

High-harmonic generation (HHG) traditionally combines ~100 near-infrared laser photons to generate bright, phase-matched, extreme ultraviolet beams when the emission from many atoms adds constructively. Here, we show that by guiding a mid-infrared femtosecond laser in a high-pressure gas, ultrahigh harmonics can be generated, up to orders greater than 5000, that emerge as a bright supercontinuum that spans the entire electromagnetic spectrum from the ultraviolet to more than 1.6 kilo-electron volts, allowing, in principle, the generation of pulses as short as 2.5 attoseconds. The multiatmosphere gas pressures required for bright, phase-matched emission also support laser beam self-confinement, further enhancing the x-ray yield. Finally, the x-ray beam exhibits high spatial coherence, even though at high gas density the recolliding electrons responsible for HHG encounter other atoms during the emission process.  相似文献   

MMS19 assembles iron-sulfur proteins required for DNA metabolism and genomic integrity     

Stehling O  Vashisht AA  Mascarenhas J  Jonsson ZO  Sharma T  Netz DJ  Pierik AJ  Wohlschlegel JA  Lill R 《Science (New York, N.Y.)》2012,337(6091):195-199

Instability of the nuclear genome is a hallmark of cancer and aging. MMS19 protein has been linked to maintenance of genomic integrity, but the molecular basis of this connection is unknown. Here, we identify MMS19 as a member of the cytosolic iron-sulfur protein assembly (CIA) machinery. MMS19 functions as part of the CIA targeting complex that specifically interacts with and facilitates iron-sulfur cluster insertion into apoproteins involved in methionine biosynthesis, DNA replication, DNA repair, and telomere maintenance. MMS19 thus serves as an adapter between early-acting CIA components and a subset of cellular iron-sulfur proteins. The function of MMS19 in the maturation of crucial components of DNA metabolism may explain the sensitivity of MMS19 mutants to DNA damage and the presence of extended telomeres.  相似文献