杉木与楠木叶凋落物混合分解及其养分动态

采用网袋法研究了杉木和楠木叶凋落物以不同比例的混合分解及其养分动态,结果表明：杉木与楠木叶凋落物混合处理的分解速率和K释放率基本上均大于单独的纯杉木和纯楠木,而N和P释放率则介于单独的纯杉木和纯楠木之间;杉楠混合分解可加快了混合中杉木叶凋落物的分解速率和N、K两元素的释放率,并且随楠木叶比例的增加,促进作用越明显;混合分解对混合处理的分解速率和K元素释放有明显的促进作用,而对N、P元素的释放影响不明显。     

Environmental constraints in the study of flexible segments of proteins

The structural problem posed by ill-defined segments in protein structures is similar to those encountered in the study of most peptide hormones, with terminal tracts resembling linear peptides and loops resembling cyclic peptides. The conformational preferences of short linear peptides in solution can be influenced by the use of solvent mixtures of viscosity higher than that of pure water but comparable to that of cytoplasm. In order to check whether it is possible to use these media in the structural study of proteins, we undertook an exploratory study on BPTI in a mixture of dimethylsulfoxide and water. The complete assignment of BPTI in an 80:20 (by volume) DMSO-d ₆/water cryomixture at two temperatures showed that all resonances parallel those in water, hinting at the persistence of the correct protein architecture, which is also confirmed by NOESY experiments. In addition to the NOEs present in the aqueous solution it was possible to detect numerous new cross peaks, in particular from residues belonging to the less-defined regions. The new cross peaks do not originate from spin diffusion and are consistent with the best NMR structure and with the X-ray structures of BPTI.     

Mixed effects models with bivariate and univariate association parameters for longitudinal bivariate binary response data

When two binary responses are measured for each study subject across time, it may be of interest to model how the bivariate associations and marginal univariate risks involving the two responses change across time. To achieve such a goal, marginal models with bivariate log odds ratio and univariate logit components are extended to include random effects for all components. Specifically, separate normal random effects are specified on the log odds ratio scale for bivariate responses and on the logit scale for univariate responses. Assuming conditional independence given the random effects facilitates the modeling of bivariate associations across time with missing at random incomplete data. We fit the model to a dataset for which such structures are feasible: a longitudinal randomized trial of a cardiovascular educational program where the responses of interest are change in hypertension and hypercholestemia status. The proposed model is compared to a naive bivariate model that assumes independence between time points and univariate mixed effects logit models.     

Varietal mixtures: a viable strategy for sustainable productivity in subsistence agriculture

Remarkable parallels link the development of varietal mixtures across subsistence farming systems. Mixtures are grown and persist because they prolong harvest and income flow and provide diversity of diet. From our review of research on agronomic and disease aspects of mixtures in modern agriculture, it is also clear that improved stability and decreased disease severity are common features of mixtures relative to their components in monoculture. Such advantages are of value to both modern and subsistence agriculture. However, in the majority of cases, the yield advantage of mixtures is small. Overall, we conclude that varietal mixtures are presently a viable strategy for sustainable productivity in subsistence agriculture, have potential for improvement without sacrifice of diversity, are an important resource for future global food production and may have an expanding role in modern agriculture in situations where qualitative uniformity is not the guiding priority.     

Differential pulse polarography: a method for the direct study of biosorption of metal ions by live bacteria from mixed metal solutions

The technique of differential pulse polarography is shown here to be applicable to the monitoring directly the biosorption of metal ions from solution by live bacteria from mixed metal solutions. Biosorption of Cd(II), Zn(II) and Ni(II) by P. cepacia was followed using data obtained at the potential which is characteristic of the metal ion in the absence and presence of cells. Hepes buffer (pH 7.4, 50 mM) was used as a supporting electrolyte in the polarographic chamber and metal ion peaks in the presence of cells of lower amplitude were obtained due to metal-binding by the cells. Well defined polarographic peaks were obtained in experiments involving mixtures of metal ions of Cd(II)-Zn(II), Cu(II)-Zn(II), Cu(II)-Cd(II) and Cd(II)-Ni(II). Biosorption of Cd(II), Zn(II) increased with solution pH. The method was also tested as a rapid technique for assessing removal of metal ions by live bacteria and the ability of the polarographic technique in measuring biosorption of metal ions from mixed metal solutions is demonstrated. Cu(II) was preferentially bound and removal of metals was in the order Cu(II) > Ni(II) > Zn(II), Cd(II) by intact cells of P. cepacia. This revised version was published online in August 2006 with corrections to the Cover Date.     

DNA aptamers for as analytical tools for the quantitative analysis of DNA-dealkylating enzymes

The AlkB family of oxygenases catalyze the removal of alkyl groups from nucleic acid substrates in an iron and 2-oxoglutarate-dependent manner and have roles including in DNA repair. To understand the biological functions of these DNA-dealkylating enzymes it is desirable to measure their expression levels in vitro and in vivo in complex biological matrixes. Quantitative analyses of the enzymes require affinity probes capable of binding AlkB family members selectively and with high affinity. Here we report that DNA aptamers can serve as efficient affinity probes for quantitative detection of such enzymes in vitro. Nonequilibrium capillary electrophoresis of equilibrium mixtures (NECEEM) was applied as a general tool for: (i) selection of DNA aptamers, (ii) characterization of binding parameters for the aptamers, and (iii) quantitative detection of the target in an aptamer-based affinity analysis. The selected aptamers have a range of K_d values between 20 and 240 nM. The aptamers enabled accurate quantitative analysis of AlkB even in the presence of the Escherichia coli cell lysate. Aptamers can likely be developed for other nucleic acid repair enzymes. They may also be developed for use in in vitro and potentially in vivo studies of known nucleic acid-modifying enzymes including for functional analysis.     

The Effect of Glycerol on Molecular Mobility in Amorphous Sucrose Detected by Phosphorescence of Erythrosin B

Luminescence from the triplet probe erythrosin B provides spectroscopic characteristics such as emission energy and lifetime that are sensitive to molecular mobility of the local solvent environment. This study investigated how variation in glycerol content influences the properties of an amorphous sucrose matrix by monitoring phosphorescence of erythrosin B over the temperature range from 5 to 100°C. Emission energy, lifetime, and red-edge excitation data revealed that glycerol affected the mobility of amorphous sucrose matrix primarily through plasticization when the mole ratio of glycerol/sucrose was above 0.27, resulting in a decrease in emission energy (ν _p), lifetime (τ) and energy difference (Δν _P) with excitation at the absorption peak and red edge and an increase in the nonradiative, collisional quenching rate k _TS0. At mole ratios ≤0.27 and at temperatures below the matrix T _g, glycerol exhibited an “antiplasticization” effect, as indicated by higher values of emission energy, lifetime, and energy difference and lower values of the matrix collisional quenching rate. Changes in the distribution of emission energy (emission bandwidth) and lifetime, and variation in the emission lifetime vs wavelength showed that glycerol reduced the spectral heterogeneity. These data illustrate the complex effect of a hydrogen bonding solute on the mobility of an amorphous, hydrogen bonded sugar matrix.     

Deployment of diversity for enhanced crop function

Mixtures of genotypes are the norm in natural and seminatural ecosystems and subsistence agriculture but have been replaced by pure genotypes in modern agriculture to maximise profitability in high-input systems. However, crop function with respect to the stability of yield and quality in particular tends to be lost in this process. Diversity can be reintroduced into cropping systems as a trait not only to confer stability but also to exploit synergies between component genotypes, compensating for potential performance losses against the best performing genotype in any given season or location. Quality need not be compromised, and research has demonstrated practical development and deployment approaches, which challenge the assumed benefits of current approaches to agronomy and achieve enhanced crop function.