Revisiting the Ring-opening Bulk Polymerization of ε -caprolactones using Commercial Lipases

The lipase-catalyzed ring-opening polymerization of ε-caprolactone ( ε-CL) and its derivatives was revisited using seven commercial enzymes. Lipases from Pseudomonas fluorescens (AK) and porcine pancreatic lipase (PPL) gave the best results, in both reaction conversion and degree of polymerization. Dependency on temperature and added concentration of enzyme was investigated, and there was a linear correlation between M n and the conversion ratio. The reaction proceeded rather slowly and the residual activity of these enzymes after prolonged incubation in ε-CL was studied. There was a negative correlation between the conversion ratio in the polymerization reaction and the tolerance of the enzymes for the solvent (monomer). Accordingly, a mechanism involving enzymatic ring-opening and non-enzymatic (but catalytic) polymerization was proposed.     

Responses of dune mosses to experimental burial by sand under natural and greenhouse conditions

Sand movement is a predominant feature of mobile coastal and lake-shoreline sand dunes. Plants growing in these environments are able to withstand and survive periods of burial by sand. Although mosses are important dune stabilizers in temperate dunes, there are few studies focused on their response to burial by sand. In this study we examined the effects of burial by sand on 11 moss species that grow naturally on Lake Huron sand dunes and occur in a gradient of habitats from the foredunes along the shore to forested areas. Artificial burial treatments (sand depth of 0, 1, 3, 5 and 7 cm) were imposed under greenhouse and field conditions. We measured final plant cover and calculated the speed of emergence and an interpretive index (tolerance index) to compare burial responses among species by calculating a burial ratio which standardized the initial size of each species. In the greenhouse, Ceratodon purpureus and Ditrichum flexicaule recorded the highest mean speeds of emergence and Dicranum scoparium, Plagiothecium laetum, Dicranum flagellare and Brachythecium sp. 1 the lowest. In the field the trends were similar although the speed of emergence was much slower. Three types of response to burial were evident in plant cover: neutral, inhibition and stimulation. Although all eleven studied species were able to emerge from the different depths of burial, we observed that species colonizing areas with high sand mobility and deposition (C. purpureus and D. flexicaule) were the most tolerant and emerged from depths of up to 35 times their height. Species growing inland, at the base of trees (Dicranum scoparium, Brachythecium sp. 2, Plagiomnium cuspidatum and Dicranum flagellare) showed the least tolerance of burial.     

长穗偃麦草基因组中与耐低磷营养胁迫有关的基因的染色体定位

以中国春－长穗偃麦草二体异附加系和二体异代换系为材料，对其耐低磷营养胁迫特性进行鉴定和遗传分析，结果表明（１）长穗偃麦草的４Ｅ一＾ 色体携有耐低营养胁迫的基因，且其效应远远超过背景亲本中国春。     

Class I MHC allochimeric presentation of composite immunogenic and self epitopes induces tolerance to genetically diverse rat strains

Functional topography of rat class I major histocompatibility complex (MHC) molecule was studied. The α₁-helical sequences that are shared by class I RT1.A^l and RT1.A^u were substituted in the RT1.A^a molecule to produce the composite -RT1.A^a MHC class I allochimeric molecule. Dominant immunogenic epitopes that induce accelerated rejection were identified within the hypervariable regions of the α₁ domain of RT1.A^a, RT1.A^l, and RT1.A^u. Peri-transplant portal venous delivery of MHC class I allochimeric proteins, that included composite α₁ helical immunodominant epitopes of RT1.A^u and RT1.A^l, induced donor-specific tolerance to RT1^u (Wistar Furth, WF) and RT1^l Lewis, LEW) disparate cardiac allografts in ACI (RT1^a) hosts. Allochimeric generated tolerance was characterized by absence of T cell deletion or anergy. Donor specific IgM allo-Abs was not detected, while IgG alloresponse was markedly attenuated in sera of tolerant hosts. Further, long-term allografts in allochimeric-conditioned hosts exhibited moderate B cell infiltration when compared to rejecting controls. Analysis of intragraft cytokines revealed selective upregulation of IL-10 and marked inhibition of IL-2, IFN-γ, and IL-4. Our findings indicate the emergence of a peripherally induced tolerant state, afforded by the novel approach of soluble class I allochimeric conditioning that presents donor immunogenic epitopes in the context of recipient class I determinants.     

Identification of Barley Varieties Tolerant to Cadmium Toxicity

Two successive hydroponic experiments were carried out to identify barley varieties tolerant to Cd toxicity via examining Soil–Plant Analyses Development (SPAD) value, plant height, leaves and tillers per plant, root number and volume, and biomass accumulation. The results showed that SPAD values (chlorophyll meter readings), plant height, leaf number, root number and volume, and biomass accumulation of shoot/root were significantly reduced in the plants grown in 20 μM Cd nutrient solution compared with control, and the uptake and translocation of Zn, Mn, and Cu was also strictly hindered. Furthermore, there was a highly significant difference in the reduction in these growth parameters among varieties, and varieties “Weisuobuzhi” and “Jipi 1” showed the least reduction both in the two experiments, suggesting their high tolerance to Cd toxicity, while “Dong 17” and “Suyinmai 2” with the greatest reduction and the toxicity symptoms appeared rapidly and severely, denoting as Cd-sensitive varieties. Significant variety difference in Cd concentration was also found, with Weisuobuzhi containing the highest and Jipi 1 the lowest Cd concentration in shoots.     

The metabolism of exogenous hydroxyproline by gametophytes of Plagiochila arctica Bryhn et Kaal. (Hepaticae)

The metabolic fate of free 4-hydroxyproline (Hyp), dual-labeled in specific positions, supplied to axenically cultured gametophytes of Plagiochila arctica was found to be complex. It could enter into at least three pathways, and the one that predominated depended on the concentration supplied. At low concentrations (i.e., 1 M), free Hyp was mostly converted to proline (Pro) by a pathway in which pyrroline-5-carboxylate is the most probable intermediate. Lesser amounts entered a pathway(s) in which hydrogen was lost from the 3(2) carbon. And a small amount was directly incorporated into protein. At the higher concentrations that have been found to desuppress leaf and branch development in P. arctica the proportion of the labeled Hyp converted to Pro was markedly diminished and the proportion that was directly incorporated into peptide linkage was increased. This direct incorporation of Hyp into protein may be closely related to the ability of Hyp to relieve suppression of ventral leaves in leafy liverworts. the suppression-desuppression phenomenon is thought to involve cell surface and-or extracellular matrix proteins.Abbreviations Hyp 4-trans-hydroxyl-L-proline - Pro L-proline     

Isolation and expression analysis of low temperature-induced genes in white poplar (Populus alba)

Poplar is an important crop and a model system to understand molecular processes of growth, development and responses to environmental stimuli in trees. In this study, we analyzed gene expression in white poplar (Populus alba) plants subjected to chilling. Two forward suppression-subtractive-hybridization libraries were constructed from P. alba plants exposed to low non-freezing temperature for 6 or 48 h. Hundred and sixty-two cDNAs, 54 from the 6-h library and 108 from the 48-h library, were obtained. Isolated genes belonged to six categories of genes, specifically those that: (i) encode stress and defense proteins; (ii) are involved in signal transduction; (iii) are related to regulation of gene expression; (iv) encode proteins involved in cell cycle and DNA processing; (v) encode proteins involved in metabolism and energetic processes; and (vi) are involved in protein fate.Different expression patterns at 3, 6, 12, 24, 48 h at 4 °C and after a recovery of 24 h at 20 °C were observed for isolated genes, as expected according to the class in which the gene putatively belongs. Forty-four of 162 genes contained DRE/LTRE cis-elements in the 5′ proximal promoter of their orthologs in Populus trichocarpa, suggesting that they putatively belong to the CBF regulon. The results contribute new data to the list of possible candidate genes involved in cold response in poplar.     

Biological indices of toxicity in tropical legumes grown in oil-contaminated soil

This study evaluated the toxic effects of total petroleum hydrocarbons (TPH) on growth of the legumes Crotalaria incana L. and Leucaena leucocephala Lam., and on the development of nitrogen-fixing soil microorganisms, using biological toxicity indices and the toxicity potential index (TPI_c), which enable comparison of effects of exposure time and concentration. Growth and biomass accumulation in both plant species decreased with high pollutant concentrations. The EC₅₀ and the NOEC were not identified for either species. The Phytotoxicity Relative Index showed that root length was most strongly affected by the oil, and the Impact Index on Nitrogen Fixer Microorganisms indicated that, despite damage to the root system, L. leucocephala rhizosphere bacteria doubled at 10,000 mg kg⁻¹ TPH after of 240 days of exposure. Finally, the TPI_c revealed that C. incana was more sensitive than L. leucocephala to chronic TPH toxicity and might strongly depend on beneficial soil bacteria.     

两种肥力水平下水稻苗高QTL的比较分析

利用一个来源于粳／籼交组合的水稻重组自交系群体进行盆栽试验,设正常肥力(对照CK)和低肥力(不施肥)2个处理,分别在播种后25d(时期Ⅰ)和50d(时期Ⅱ)取样测定秧苗的苗高。结合一张含有198个标记的高密度分子遗传图谱,对性状进行复合区间作图。共检测到8个水稻苗高QTL,分别位于第1、3、5、6、8和10号染色体上,各QTL对性状的贡献率为4％～12％。通过对2种肥力水平下水稻苗高QTL的比较分析,发现大多数QTL只在1种肥力水平下表达,QTL与不同肥力水平之间存在着显著的互作。唯一一个在2种肥力水平下均能稳定起作用、而且加性效应的方向一致的QTL是qSH-3-2,该QTL位于3号染色体标记区间RM156-RM16,其加性效应值为正,增效基因来自于亲本Lemont。此外,有3个QTL(qSH-1、qSH-3-3和qSH-5)在2个抽样时期均起作用,且加性效应的方向一致。对利用分子标记辅助选择改良水稻品种的耐低肥特性的育种策略进行了讨论。     

MazF-induced Growth Inhibition and Persister Generation in Escherichia coli

Toxin-antitoxin systems are ubiquitous in nature and present on the chromosomes of both bacteria and archaea. MazEF is a type II toxin-antitoxin system present on the chromosome of Escherichia coli and other bacteria. Whether MazEF is involved in programmed cell death or reversible growth inhibition and bacterial persistence is a matter of debate. In the present work the role of MazF in bacterial physiology was studied by using an inactive, active-site mutant of MazF, E24A, to activate WT MazF expression from its own promoter. The ectopic expression of E24A MazF in a strain containing WT mazEF resulted in reversible growth arrest. Normal growth resumed on inhibiting the expression of E24A MazF. MazF-mediated growth arrest resulted in an increase in survival of bacterial cells during antibiotic stress. This was studied by activation of mazEF either by overexpression of an inactive, active-site mutant or pre-exposure to a sublethal dose of antibiotic. The MazF-mediated persistence phenotype was found to be independent of RecA and dependent on the presence of the ClpP and Lon proteases. This study confirms the role of MazEF in reversible growth inhibition and persistence.