DNA barcoding of Cymbidium by genome skimming: Call for next-generation nuclear barcodes

Cymbidium is an orchid genus that has undergone rapid radiation and has high ornamental, economic, ecological and cultural importance, but its classification based on morphology is controversial. The plastid genome (plastome), as an extension of plant standard DNA barcodes, has been widely used as a potential molecular marker for identifying recently diverged species or complicated plant groups. In this study, we newly generated 237 plastomes of 50 species (at least two individuals per species) by genome skimming, covering 71.4% of members of the genus Cymbidium. Sequence-based analyses (barcoding gaps and automatic barcode gap discovery) and tree-based analyses (maximum likelihood, Bayesian inference and multirate Poisson tree processes model) were conducted for species identification of Cymbidium. Our work provides a comprehensive DNA barcode reference library for Cymbidium species identification. The results show that compared with standard DNA barcodes (rbcL + matK) as well as the plastid trnH-psbA, the species identification rate of the plastome increased moderately from 58% to 68%. At the same time, we propose an optimized identification strategy for Cymbidium species. The plastome cannot completely resolve the species identification of Cymbidium, the main reasons being incomplete lineage sorting, artificial cultivation, natural hybridization and chloroplast capture. To further explore the potential use of nuclear data in identifying species, the Skmer method was adopted and the identification rate increased to 72%. It appears that nuclear genome data have a vital role in species identification and are expected to be used as next-generation nuclear barcodes.     

燕麦-绿豆间作效应及氮素转移特性

为探究燕麦(Avena sativa)-绿豆(Phaseolus radiatus)间作效应及氮素转移特性, 在不施氮肥的大田试验条件下, 设置3种种植模式(燕麦单作、绿豆单作和燕麦-绿豆间作), 采用传统挖根法和¹⁵N同位素标记法进行研究。结果表明, 间作系统中燕麦侵袭力强于绿豆, 绿豆生长受到抑制。整个生育期, 间作燕麦地上部干物质积累量比单作增加14.9%-33.1%, 2年成熟期间作燕麦的氮素积累量比单作分别提高53.1%和44.8%; 间作减少了开花结荚期绿豆氮素积累量和根瘤重量, 降低了绿豆的固氮效率, 绿豆的固氮效率2年平均降低23.7%, 生物固氮量平均减少11.66%。间作绿豆向燕麦的氮素转移率2年平均值达31.7%, 氮素转移量为212.16 kg∙hm^-2。燕麦-绿豆间作降低了开花结荚期绿豆的根瘤固氮酶活性和固氮效率, 但绿豆体内氮素转移增加了燕麦对氮素的吸收利用, 实现了地上部与地下部生长的相互调节和促进, 优化了农田生态系统的氮素管理。     

Evolutionary breakdown of distyly to homostyly is accompanied by reductions of floral scent in Primula oreodoxa

Reproductive traits that function in pollinator attraction may be reduced or lost during evolutionary transitions from outcrossing to selfing. Although floral scent plays an important role in attracting pollinators in outcrossing species, few studies have investigated associations between floral scent variation and intraspecific mating system transitions. The breakdown of distyly to homostyly represents a classic example of a shift from outcrossing to selfing and provides an opportunity to test whether floral fragrances have become reduced and/or changed in composition with increased selfing. Here, we evaluate this hypothesis by quantifying floral volatiles using gas chromatography-mass spectrometry in two distylous and four homostylous populations of Primula oreodoxa Franchet, a perennial herb from SW China. Our analysis revealed significant variation of volatile organic compounds (VOCs) among populations of P. oreodoxa. Although there was no difference in VOCs between floral morphs in distylous populations as predicted, we detected a substantial reduction in VOC emissions and the average number of scent compounds in homostylous compared with distylous populations. A total of 12 compounds, mainly monoterpenoids and sesquiterpenoids, distinguished homostylous and distylous morphs; of these, (E)-β-ocimene was the most important in contributing to the difference in volatiles, with significantly lower emissions in homostyles. Our findings support the hypothesis that the transition from outcrossing to selfing is accompanied by the loss of floral volatiles. The modification to floral fragrances in P. oreodoxa associated with mating system change might occur because high selfing rates in homostylous populations result in relaxed selection for floral attractiveness.     

EFFECTS OF HELPER PROTEINS ENCODED BY p19 AND orf1-orf2 GENES ON Cyt1Aa PROTEIN EXPRESSION IN ACRYSTALLIFEROUS STRAIN OF BACILLUS THURINGIENSIS

A series of plasmids were constructed to examine the effects of p19 and orf1‐orf2 genes from Bacillus thuringiensis on Cyt1Aa synthesis and inclusion formation. The plasmids expressed the cyt1Aa gene along with either p19 or orf1‐orf2, or each of them coordinatively with p20 in the acrystalliferous strain of B. thuringiensis subsp. israelensis 4Q7. No effect on the expression of Cyt1Aa protein was found when P19 or Orf1‐Orf2 co‐expressed with Cyt1Aa. However, when including p20 gene, the constructs with p19 or orf1‐orf2 gene produced lower yield of Cyt1Aa proteins than without p19 or orf1‐orf2 gene. Electron microscopy observation and bioassay showed that P19 and Orf1‐Orf2 have no influence on the crystal size and toxicity of Cyt1Aa protein. It is presumed that P19 and Orf1‐Orf2 might have negative effects on Cyt1Aa synthesis in B. thuringiensis.     

Incorporating an Asymptotic Parameter into the Weibull Model to Describe Plant Disease Progress

The Weibull model is a flexible growth model that describes both general population growth and plant disease progress. However, lack of an asymptotic parameter has limited its wider application. In the present study, an asymptotic parameter K was introduced into the original Weibull model, written as; y = K {1 − exp [− ( t − a ) ^c ]}, in which a , b , c and K are location, scale, shape, and asymptotic parameters, respectively, y is the proportion of disease and t is time. A wide range of simulated disease progress data sets were generated using logistic, Gompertz and monomolecular models by specifying different parameter values, and fitted to both original and modified Weibull models. The modified model provided statistically better fits for all data than the original model. The modified model can thus improve the curve-fitting ability of the original model which often failed to converge, especially when the asymptote is less than 1.0. Actual disease progress data on wheat leaf rust and tomato root rot with different asymptotic values were also used to compare the original and modified Weibull models. The modified model provided a statistically better fit than the original model, and model estimates of asymptotic parameter K were nearly identical to the actual disease maxima reflecting the characteristics of the host-pathosystem. Comparison of logistic, Gompertz, and Weibull models including parameter K by fitting to the observed data on wheat leaf rust and tomato root rot revealed the applicability of the modified Weibull model, which in a majority of cases provided a statistically superior fit.     

清栓酶治疗脑梗塞疗效与血浆血栓素A2及前列环素之间的关系

应用清栓酶治疗不同病期脑梗塞３８例,总有效率８６．７％,发病后治疗时间越早,疗效越好。治疗前病人均有不同程度的ＴＸＡ２升高,ＰＧＩ２下降,急性期更为明显,治疗后ＴＸＡ２下降,ＰＧＩ２上升,使失调的ＰＧＩ２－ＴＸＡ２平衡得以恢复     

光谱技术研究固氮酶铁硫簇的理化特性

Ｎ－甲基甲酰胺碱度是提取高质量固氮酶铁钼辅基的关键因素之一。过量的亚甲蓝能氧化并分解铁铜铺基为含双相铁硫簇和铁硫簇固氮酶铁钼辅基和在紫外可见光谱区中均无特征吸收峰,而在３２０ｎｍ处却呈弱吸收峰,棕色固氮菌固氮酶和该菌的突变菌侏ＵＷ４５固氮酶（缺铁钼辅基）中的非含钼的铁硫簇在紫外可见光谱区３２０ｎｍ和４０５ｎｍ处均含有特征吸收峰．     

油麻藤凝集素的荧光光谱研究

用化学修饰、内源荧光和荧光淬灭等方法研究了油麻藤凝集素（ＭＳＬ）的溶液构象变化和微环境的构象特征。研究发现ＭＳＬ分子中总共有９个色氨酸（Ｔｒｐ）残基,它们的荧光能被丙烯酰胺淬灭,但不易为ＫＩ接近而淬灭,ＭＳＬ经Ｎ－溴代琥珀酰亚胺（ＮＢＳ）修饰后,其内源性荧光发射谱发生相应变化,结果表明ＭＳＬ分子中部分Ｔｒｐ残基埋藏于分子内部,而位于分子表面的Ｔｒｐ残基可能处于分子的疏水袋中。