E.s.r. of spin-trapped radicals in aqueous solutions of peptides. Reactions of the hydroxyl radical.

The reactions of hydroxyl radicals with 30 dipeptides and several larger peptides were studied in aqueous solutions. The OH radicals were generated by U.V. photolysis of H2O2. The short-lived peptide radicals were spin-trapped using t-nitrosobutane and identified by e.s.r. For dipeptides containing the amino terminal residues glycine, alanine and phenylalanine, abstraction of the hydrogen from the carbon adjacent to the peptide nitrogen was the major process leading to the spin-adducts. Such radicals will be referred to as backbone radicals. Dipeptides with a carbonyl terminal serine residue and also glycylglutamic acid form both backbone and side-chain radicals, with the latter being formed in larger quantities. For dipeptides, side-chain radicals were detected on either the carboxyl or amino terminal residues of both. The effect of pD on the e.s.r. sectrum of the spin-adducts of glycylglycine was studied and the pK of the carboxyl group of this radical was determined to be 2.5. For (Ala)3 and (Ala)n, with an average value of n = 1800, backbone and minor side-chain radicals were observed. For ribonucleases-S-peptide, containing 20 amino acid residues, both backbone and side-chain radicals were detected.     

Using genetic variation to disentangle the complex relationship between food intake and health outcomes

Diet is considered as one of the most important modifiable factors influencing human health, but efforts to identify foods or dietary patterns associated with health outcomes often suffer from biases, confounding, and reverse causation. Applying Mendelian randomization in this context may provide evidence to strengthen causality in nutrition research. To this end, we first identified 283 genetic markers associated with dietary intake in 445,779 UK Biobank participants. We then converted these associations into direct genetic effects on food exposures by adjusting them for effects mediated via other traits. The SNPs which did not show evidence of mediation were then used for MR, assessing the association between genetically predicted food choices and other risk factors, health outcomes. We show that using all associated SNPs without omitting those which show evidence of mediation, leads to biases in downstream analyses (genetic correlations, causal inference), similar to those present in observational studies. However, MR analyses using SNPs which have only a direct effect on the exposure on food exposures provided unequivocal evidence of causal associations between specific eating patterns and obesity, blood lipid status, and several other risk factors and health outcomes.     

Effect of bioaccumulation of cadmium on biomass productivity,essential trace elements,chlorophyll biosynthesis,and macromolecules of wheat seedlings

Soil contamination with heavy metals has become a worldwide problem, leading to losses in agricultural yield and hazardous human health effects as they enter the food chain. The present investigation was undertaken to examine the influence of cadmium (Cd²⁺) on the wheat (Triticum aestivum L.) plant. Cd²⁺ accumulation and distribution in 3-wk-old seedlings grown in nutrient medium containing varying concentrations of Cd²⁺ (control, 0.25, 0.50, 1.0, 2.5, and 5.0 mg/L) was monitored. The effect of varying Cd²⁺ concentrations up to 21 d on biomass productivity, plant growth, photosynthetic pigments, protein, amino acids, starch, soluble sugars, and essential nutrients uptake was studied in detail to explore the level up to which the plant can withstand the stress of heavy metal. Plants treated with 0.5, 1.0, 2.5, and 5.0 mg/L Cd²⁺ showed symptoms of heavy-metal toxicity as observed by various morphological parameters which were recorded with the growth of plants. The root, shoot-leaf length and the root, shoot-leaf biomass progressively decreased with increasing Cd²⁺ concentration in the nutrient medium. Cd²⁺ uptake and accumulation was found to be maximum during the initial growth period. Cd²⁺ also interfered with the nutrients uptake, especially calcium (Ca²⁺), magnesium (Mg²⁺), potassium (K⁺), iron (Fe²⁺), zinc (Zn²⁺), and manganese (Mn²⁺) from the growth medium. Growth reduction and altered levels of major biochemical constituents such as chlorophyll, protein, free amino acids, starch, and soluble sugars that play a major role in plant metabolism were observed in response to varying concentrations of Cd²⁺ in the nutrient medium. In the present study, the effects of Cd²⁺ on growth, biomass productivity, mineral nutrients, chlorophyll biosynthesis, protein, free amino acid, starch, and soluble sugars in wheat plants was estimated to establish an overall picture of the Cd²⁺ toxicity at structural and functional levels.     

Assessment of genetic fidelity of micropropagated <Emphasis Type="Italic">Swertia chirayita</Emphasis> plantlets by ISSR marker assay

Inter simple sequence repeat (ISSR) marker assay was employed to validate the genetic fidelity of Swertia chirayita plantlets multiplied in vitro by axillary multiplication upto forty-two passages. Sixteen ISSR primers generated a total of 102 amplicons among the tissue-cultured plants. Forty-eight amplicons were amplified in the outlier (a Swertia species). The outlier (negative control) was employed to rule out the possibility that the invariant fingerprint was due to chance alone and that the ISSR technique employed was not discriminatory enough to detect the off-types. A homogenous amplification profile was observed for all the micropropagated plants. The results confirmed the clonal fidelity of the tissue culture-raised S. chirayita plantlets and corroborated the fact that axillary multiplication is the safest mode for multiplication of true to type plants.     

印度北部Pali Gad流域资源利用模式研究

喜马拉雅西部独特、丰富的自然资源对当地居民生计及生态服务等方面起着重要的作用。由于长期以来当地居民与山地生态系统的相互作用,特别是农业生产、畜牧业放牧、薪柴采集以及其他多种多样的资源利用方式,形成了一种特殊的山区文化景观。本文以印度北部的山地小流域PaliGad（共有25个村子）为例,主要研究当地的资源利用状况,利用卫星遥感数据对该地区可利用自然资源进行评估分析,通过从户到户的社会经济调查,对其提供的生态服务功能以及受威胁的程度进行估计,研究分析了村民对资源需求及获取的时空变化情况。结果显示,平均每人每天的薪柴采集量为1．12k,平均每人每天通过修剪枝叶获得饲料采集量为3．69kg,平均每人每天从森林中采集草料的量为3．25kgo对生态系统服务功能进行估测的结果显示,森林可提供更多的临时调节功能,而农业更多的是支撑服务功能,河流,水体给当地人提供了文化服务功能。以山区典型的人-地生态系统为例,这类生态系统中的自然资源破碎化程度很高。研究发现,该区域贫瘠土地上的自然资源需求还在不断增加。因此,从长远来看,人对资源的无止境获取将不利于整个流域的可持续发展。     

Analysis of fluorescence decay kinetics measured in the frequency domain using distributions of decay times

We describe the theoretical and practical aspects of analyzing complex fluorescence decay kinetics using continuous distributions of decay times. Our analysis uses frequency-domain data, provides for global analysis of multiple data sets and includes the possibility of excited-state processes. Simulated data were used to estimate the types of distributions which can be reasonably recovered from the measurements. Additionally, we describe a variety of distributions recovered from experimental data. For mixtures of one, two or three exponentially decaying fluorophores we recovered narrow lifetime distributions, which are essentially identical to a multiexponential decay. Similarly, a two-state excited-state reaction also yielded a narrow distribution with negative preexponential factors. The presence of time-dependent spectral relaxation of labeled lipids results in a wide distribution of decay times, which becomes narrower for faster relaxation rates at higher temperatures. Hence, the decay-time distributions appear to be sensitive to the dynamics of the environment surrounding the fluorophore. Additionally, distributions of decay times were observed to result from transient effects in collisional quenching, from energy transfer in the presence of a range of donor-to-acceptor distances, and for several single-tryptophan proteins.     

Mechanism of copper resistance in a copper mine isolate Pseudomonas putida strain S4

The mechanism of copper resistance in a multiple-metal-resistant natural isolate Pseudomonas putida strain S4 is based on inducible efflux. Active extrusion of copper ions occurs from the cytoplasm during the exponential phase of growth. Involvement of ATPase in the efflux of copper ions has been demonstrated by employing specific inhibitors. The effluxed copper is not thrown out of the cell, but remains in a bound form (to a protein) in the periplasm. Thus, a balance between the intracellular level, to fulfill the metabolic requirements, and the periplasmic sequestration, to evade toxicity, is maintained by this isolate.     

An integrative approach to the identification of Arabidopsis and rice genes involved in xylan and secondary wall development

Xylans constitute the major non-cellulosic component of plant biomass. Xylan biosynthesis is particularly pronounced in cells with secondary walls, implying that the synthesis network consists of a set of highly expressed genes in such cells. To improve the understanding of xylan biosynthesis, we performed a comparative analysis of co-expression networks between Arabidopsis and rice as reference species with different wall types. Many co-expressed genes were represented by orthologs in both species, which implies common biological features, while some gene families were only found in one of the species, and therefore likely to be related to differences in their cell walls. To predict the subcellular location of the identified proteins, we developed a new method, PFANTOM (plant protein family information-based predictor for endomembrane), which was shown to perform better for proteins in the endomembrane system than other available prediction methods. Based on the combined approach of co-expression and predicted cellular localization, we propose a model for Arabidopsis and rice xylan synthesis in the Golgi apparatus and signaling from plasma membrane to nucleus for secondary cell wall differentiation. As an experimental validation of the model, we show that an Arabidopsis mutant in the PGSIP1 gene encoding one of the Golgi localized candidate proteins has a highly decreased content of glucuronic acid in secondary cell walls and substantially reduced xylan glucuronosyltransferase activity.     

Homochiral Selectivity in RNA Synthesis: Montmorillonite-catalyzed Quaternary Reactions of D,L-Purine with D,L- Pyrimidine Nucleotides

Selective adsorption of D, L-ImpA with D, L-ImpU on the platelets of montmorillonite demonstrates an important reaction pathway for the origin of homochirality in RNA synthesis. Our earlier studies have shown that the individual reactions of D, L-ImpA or D, L-ImpU on montmorillonite catalyst produced oligomers which were only partially inhibited by the incorporation of both D- and L-enantiomers. Homochirality in these reactions was largely due to the formation of cyclic dimers that cannot elongate. We investigated the quaternary reactions of D, L-ImpA with D, L-ImpU on montmorillonite. The chain length of these oligomers increased from 9-mer to 11-mer as observed by HPLC, with a concominant increase in the yield of linear dimers and higher oligomers in the reactions involving D, L-ImpA with D, L-ImpU as compared to the similar reactions carried out with D-enantiomers only. The formation of cyclic dimers of U was completely inhibited in the quaternary reactions. The yield of cyclic dimers of A was reduced from 60% to 10% within the dimer fraction. 12 linear dimers and 3 cyclic dimers were isolated and characterized from the quaternary reaction. The homochirality and regioselectivity of dimers were 64.1% and 71.7%, respectively. Their sequence selectivity was shown by the formation of purine-pyrimidine (54–59%) linkages, followed by purine-purine (29–32%) linkages and pyrimidine-pyrimidine (9–13%) linkages. Of the 16 trimers detected, 10 were homochiral with an overall homochirality of 73–76%. In view of the greater homochirality, sequence- and regio- selectivity, the quaternary reactions on montmorillonite demonstrate an unexpectedly favorable route for the prebiotic synthesis of homochiral RNA compared with the separate reactions of enantiomeric activated mononucleotides.