Cytological studies on adventitious shoots and minitubers of a monoploid potato clone     

J. H. M. Hovenkamp-Hermelink  E. Jacobsen  L. P. Pijnacker  J. N. de Vries  B. Witholt  W. J. Feenstra 《Euphytica》1988,39(3):213-219

Summary A three step procedure for adventitious shoot regeneration on leaf explants of monoploid potato clone H7322 and a minituber induction procedure on stem segments have been described. Chromosome counts on 92 adventitious shoots showed that 85% of them had been polyploidized, i.e., 71% were diploid, 1% tetraploid, and 13% were mixoploid. Cytophotometric studies on nuclei of soil grown tubers of tetraploid cv Astarte, of 1x, 2x and 4x adventitious shoots of H7322, and of diploid H²578 showed in all cases polyploidization with prominent classes up to 8C and 16C. However, nuclei of pith cells of 5 weeks old minitubers which had developed on monoploid H7322 itself or on 1x adventitious shoots of H7322 showed predominantly 1C and 2C values. Pith cells of minitubers of monoploid H7322 were screened, after iodine staining, for the presence of variant cells containing reddish-brown staining (amylose-free) starch. In more than 75% of the investigated minitubers one or a few of such variant cells were found indicating that such a variation occurs in minitubers of monoploid potato and that this variant character is expressed in cells of vegetative storage organs like potato tubers.  相似文献   

Heterogeneity of bacterial populations and pesticide degradation potentials in the unsaturated zone of loamy and sandy soils     

Finn P. Vinther  Lars Elsgaard  Ole S. Jacobsen 《Biology and Fertility of Soils》2001,33(6):514-520

Soil microbial processes play an important role in relation to pesticide pollution of groundwater, and may be strongly influenced by hydrological and geochemical properties. The consequences of such heterogeneous environments on bacterial biomass, enzymatic activities, carbon utilisation patterns, and pesticide mineralisation potentials in the unsaturated zone of a sandy loam and a coarse sandy soil profile were studied. In sandy loam soil profiles the number of bacteria decreased from 10⁹ cells g^-1 in the surface layers to about 10⁷ cells g^-1 at 1.5-5 m depth. Simultaneously, the hydrolysis of fluorescein diacetate and arylsulfatase activity decreased to below the detection limit at about 1.5 m depth, and carbon utilisation patterns showed that bacterial populations from surface soil were significantly different from those from 4 m depth. Bacterial biomass and activity in macropore soil tended to be slightly higher than in matrix soil, and the carbon utilisation patterns of bacterial populations extracted from macropore soil and from matrix soil seemed to be different. Maximally 3% of ¹⁴C-labelled mecoprop and isoproturon was mineralised in soil from the 1-1.5 m depth, and less than 1.5% was mineralised in soil from the 3.5-4 m depth. The macropore soil tended to have a higher degradation potential than the matrix soil. The total number of bacteria in the coarse sandy soil profile decreased from about 10⁸ in the plough layer to 10⁷ cells g^-1 at 0.4-2 m. The enzymatic activities and the degradation potentials of ¹⁴C-labelled mecoprop and isoproturon were significantly correlated (r² >0.79) and showed a distinct decrease at about 0.4 m. In addition to the depth variability, a horizontal heterogeneity in this soil was observed as horizons or compartments that differed in colour, i.e. with different chemical composition and concentrations of Fe and organic matter. Counts of viable bacteria and measurements of fluorescein diacetate hydrolysis and arylsulfatase activity confirmed a high variability of microbial biomass and activity in the sandy soil profile.  相似文献   

Making sequential analysis of environmental monitoring data feasible by simplifying the covariance matrix structure     

Maria?SchipperEmail author  Evert?Meelis 《Journal of Agricultural, Biological & Environmental Statistics》2003,8(1):122-137

As environmental monitoring data are collected successively in time, the data are suitable for sequential analysis. An earlier article proposed a refined sequential probability ratio test (SPRT) to test against a minimal relevanttrend, assuming no serial correlations and without modeling the spatial covariance matrix. As the model parameters are unknown in advance, a minimal number of observations(n _min) is required for estimation prior to analysis. Leaving the spatial covariance matrix unstructured, n _min increases if the number of sampling locations increases. Therefore, assumptions on the spatial covariance matrix are proposed, thereby reducing the number of nuisance parameters, thus reducingn _min. This article studies. three simple types of spatial covariance matrix structures and derives an adjusted SPRT for each of these types. Furthermore, we examine the robustness against deviations from the assumed spatial covariance matrix structure. Simulation studies show that adjusted SPRTs can be derived rather easily and that they are in general robust against deviations from the assumed type of spatial covariance matrix. Sequential analysis of simulated data, which are based on monitoring data of bats in the Netherlands, illustrates the use of one of the derived SPRTs.  相似文献   

Small interfering RNA-induced transcriptional gene silencing in human cells   总被引：1，自引：0，他引：1  

Morris KV  Chan SW  Jacobsen SE  Looney DJ 《Science (New York, N.Y.)》2004,305(5688):1289-1292

  相似文献   

Generation of spatially coherent light at extreme ultraviolet wavelengths     

Bartels RA  Paul A  Green H  Kapteyn HC  Murnane MM  Backus S  Christov IP  Liu Y  Attwood D  Jacobsen C 《Science (New York, N.Y.)》2002,297(5580):376-378

We present spatial coherence measurements of extreme ultraviolet (EUV) light generated through the process of high-harmonic up-conversion of a femtosecond laser. With a phase-matched hollow-fiber geometry, the generated beam was found to exhibit essentially full spatial coherence. The coherence of this laser-like EUV source was shown by recording Gabor holograms of small objects. This work demonstrates the capability to perform EUV holography with a tabletop experimental setup. Such an EUV source, with low divergence and high spatial coherence, can be used for experiments involving high-precision metrology, inspection of optical components for EUV lithography, and microscopy and holography with nanometer resolution. Furthermore, the short time duration of the EUV radiation (a few femtoseconds) will enable EUV microscopy and holography to be performed with ultrahigh time resolution.  相似文献   

High-Resolution Imaging by Fourier Transform X-ray Holography     

McNulty I  Kirz J  Jacobsen C  Anderson EH  Howells MR  Kern DP 《Science (New York, N.Y.)》1992,256(5059):1009-1012

Fourier transform x-ray holography has been used to image gold test objects with submicrometer structure, resolving features as small as 60 nanometers. The hologram-recording instrument uses coherent 3.4-nanometer radiation from the soft x-ray undulator beamline X1A at the National Synchrotron Light Source. The specimen to be imaged is placed near the first-order focal spot produced by a Fresnel zone plate; the other orders, chiefly the zeroth, illuminate the specimen. The wave scattered by the specimen interferes with the spherical reference wave from the focal spot, forming a hologram with fringes of low spatial frequency. The hologram is recorded in digital form by a charge-coupled device camera, and the specimen image is obtained by numerical reconstruction.  相似文献   

One-way control of FWA imprinting in Arabidopsis endosperm by DNA methylation   总被引：1，自引：0，他引：1  

Kinoshita T  Miura A  Choi Y  Kinoshita Y  Cao X  Jacobsen SE  Fischer RL  Kakutani T 《Science (New York, N.Y.)》2004,303(5657):521-523

  相似文献   

A maximum in the strength of nanocrystalline copper     

Schiøtz J  Jacobsen KW 《Science (New York, N.Y.)》2003,301(5638):1357-1359

We used molecular dynamics simulations with system sizes up to 100 million atoms to simulate plastic deformation of nanocrystalline copper. By varying the grain size between 5 and 50 nanometers, we show that the flow stress and thus the strength exhibit a maximum at a grain size of 10 to 15 nanometers. This maximum is because of a shift in the microscopic deformation mechanism from dislocation-mediated plasticity in the coarse-grained material to grain boundary sliding in the nanocrystalline region. The simulations allow us to observe the mechanisms behind the grain-size dependence of the strength of polycrystalline metals.  相似文献   

Cancer risk and salmon intake     

Lund E  Engeset D  Alsaker E  Skeie G  Hjårtaker A  Lundebye AK  Niebor E 《Science (New York, N.Y.)》2004,305(5683):477-8; author reply 477-8

  相似文献   

RNA silencing genes control de novo DNA methylation   总被引：1，自引：0，他引：1  

Chan SW  Zilberman D  Xie Z  Johansen LK  Carrington JC  Jacobsen SE 《Science (New York, N.Y.)》2004,303(5662):1336

  相似文献