Cluster explosion investigated by linearly chirped spectral scattering of an expanding plasma sphere

Femtosecond explosive processes of argon clusters irradiated by linearly chirped ultraintense laser pulses have been investigated by 90 degrees side spectral scattering. The spectral redshift and blueshift, which correlate with the cluster explosion processes have been measured for negatively and positively chirped driving laser pulses, respectively. The evolution of the heated-cluster polarizability indicates that the core of the cluster is shielded from the laser field in the beginning of the explosion and enhanced scattering occurs after the fast explosion initiates. Evidence of resonant heating is found from the coincidence of enhanced scattering with enhanced absorption measured using the transmitted spectra. Anomalously large-size clusters with very low gas density have been observed in this way and can be used as clean and important cluster targets.

Absorption characteristic and nonvolatile holographic recording in LiNbO3 : Cr : Cu crystals

The absorption characteristic of lithium niobate crystals doped with chromium and copper (Cr and Cu) is investigated. We find that there are two apparent absorption bands for LiNbO3:Cr:Cu crystal doped with 0.14 wt.% Cr2O3 and 0.011 wt.% CuO; one is around 480 nm, and the other is around 660 nm. With a decrease in the doping composition of Cr and an increase in the doping composition of Cu, no apparent absorption band in the shorter wavelength range exists. The higher the doping level of Cr, the larger the absorbance around 660 nm. Although a 633 nm red light is located in the absorption band around 660 nm, the absorption at 633 nm does not help the photorefractive process; i.e., unlike other doubly doped crystals, for example, LiNbO3:Fe:Mn crystal, a nonvolatile holographic recording can be realized by a 633 nm red light as the recording light and a 390 nm UV light as the sensitizing light. For LiNbO3:Cr:Cu crystals, by changing the recording light from a 633 nm red light to a 514 nm green light, sensitizing with a 390 nm UV light and a 488 nm blue light, respectively, a nonvolatile holographic recording can be realized. Doping the appropriate Cr (for example, N-Cr = 2.795 X 10(25)m(-3) and N-Cr/N-Cu = 1) benefits the improvement of holographic recording properties. (c) 2005 Optical Society of America.

Diode-pumped passively q-switched Nd : YAG ceramic laser with a Cr4+: YAG crystal-satiable absorber

Transparent polycrystalline Nd:YAG ceramics were fabricated by solid-state reactive sintering a mixture of commercial Al2O3,Y2O3, and Nd2O3 powders. The powders were mixed in ethanol and doped with 0.5 wt% tetraethoxysilane, dried, and pressed. Pressed samples were sintered at 1750 degrees C in vacuum. Transparent fully dense samples with average grain sizes of 10 mu m were obtained. The 1 at.% Nd:YAG ceramic was used to research passively Q-switched laser output with a Cr4+:YAG crystal as a saturable absorber. An average output power of 94 mW with a pulse width of 50 ns was obtained when the incident pump power was 750 mW. The slope efficiency was 13%. The pulse energy is 5 mu J, and the peak power is about 100 W.

Diode-pumped Yb : YAG ceramic laser

Transparent polycrystalline Yb:YAG ceramics were fabricated by solid-state reactive sintering a mixture of commercial Al2O3, Y2O3, and Yb2O3 powders. The powders were mixed in ethanol and doped with 0.5 wt% tetraethoxysilane, dried, and pressed. Pressed samples were sintered at 1730 degrees C in vacuum. Transparent fully dense samples with grain sizes of several micrometers were obtained. The phase from 1500 degrees to 1700 degrees C was important for the grain growth, in which the grains grew quickly and a mass of pores were eliminated from the body of the sample. Annealing was an important step to remove the vacancies of oxygen and transform Yb2+ to Yb3+. The 1 at.% Yb:YAG ceramic sample was pumped by a diode laser to study the laser properties. The maximum output power of 1.02 W was obtained with a slope efficiency of 25% at 1030 nm. The size of the lasering sample was 4 mm x 4 mm x 3 mm.

二脂酰甘油酰基转移酶基因(DGAT1)的沉默对烟草油脂合成的影响

二脂酰甘油酰基转移酶 (DGAT; EC 2.3.1.20) 是催化三脂酰甘油（TAG）合成的最后也是最关键步骤的酶。TAG是真核细胞中最重要的能量存储形式。在植物中，TAG主要在种子、花粉和许多物种的果实中积累。然而，DGAT1基因的转录本也存在于植物的其它器官中，这些器官包括根、茎、叶、花瓣、花粉囊、未成熟的角果、幼苗以及正在发芽的种子等。迄今为止，许多针对DGAT1基因的研究都集中于DGAT1基因的表达在对种子油脂的积累以及对种子中TAG的脂肪酸组成所起的作用上。在本研究中，我们通过构建烟草DGAT1基因带有内含子的发卡RNA（hpRNA）结构，使之在转基因烟草植株中表达双链RNA（dsRNA），利用RNAi原理达到使烟草内源DGAT1基因沉默的目的。转基因沉默烟草植株的获得将会为更好地研究DGAT1基因的功能奠定基础。本实验不仅研究分析了DGAT1基因的抑制对烟草种子油脂积累的影响，还对表现出沉默性状的转基因植株Sil7的不同器官中TAG的含量以及DGAT1的转录水平等进行了研究分析。此外，通过对转基因烟草不同株系种子中的主要贮藏物质——油脂、蛋白质和糖的含量测定，初步揭示出在烟草种子中三者生物合成代谢之间存在的相关性。主要研究结果如下： 采用烟草DGAT1基因的第615～1293碱基之间679bp的片段构建了能表达发卡RNA（hpRNA）结构的表达载体，并转化烟草（Nicotiana tabacum）Wisconsin 38。Northern杂交分析发现,与野生型对照烟草（WT）相比，在沉默植株的花和发育状态种子中DGAT1基因的转录水平有很大降低，这表明该发卡结构能够高效率地引起烟草DGAT1基因的沉默。此外，在对Sil1至Sil12共12株转基因烟草进行油脂含量分析的结果表明，其中有8株表现出油脂降低的性状，转基因沉默效率达到67％。这表明：利用RNAi的方法可对目标基因进行特异降解来研究基因的功能，因此是一个在研究基因的表达功能上十分有效的方法，而且已成为植物基因工程的有力工具。 为了研究DGAT1基因的沉默对转基因植株不同器官的影响，本实验分析了转基因植株Sil7的不同器官中TAG的含量和脂肪酸组成，并采用RT-PCR方法对野生型对照和转基因植株中DGAT1基因的转录水平进行了比较分析。研究发现，转基因植株不同器官中DGAT1基因转录水平的降低与各器官中TAG含量的减少呈正相关。由此看来，植物中DGAT1的表达水平与植物的各个器官内TAG的含量之间存在着一定的对应关系。此外，在转基因植株Sil7不同器官中依然能够产生TAG，这说明或者DGAT1酶活性丧失而由其它的酶（如DGAT2和PDAT）参与TAG的合成，或者DGAT1酶活性只是部分地受到影响。本实验还对Sil7的根、茎、叶、花瓣和种子中TAG的脂肪酸组成进行了分析，结果发现，与烟草野生型对照相比，在Sil7的这些器官中，除种子中TAG的脂肪酸组成无明显变化外，其余器官中TAG的18:3/18:2脂肪酸比例均有明显升高。 对其中8株转基因烟草种子进行油脂含量分析发现，在转基因烟草中由于DGAT1基因的沉默引起种子中TAG含量的减少，从而引起了种子平均千粒重的下降。而在TAG含量和种子平均千粒重下降的同时，种子中其它贮藏物质－蛋白质和糖类的含量却增加了。该实验结果表明：在烟草种子中TAG的生物合成与蛋白质和糖类物质的合成之间存在着负的相关性。

烟草单半乳糖甘油二酯缺失对茉莉酸生物合成的影响

茉莉酸（JA）是由脂肪酸衍生而来的环戊酮化合物，广泛存在于自然界中，在植物逆境胁迫响应和生长发育调节过程中起重要作用。因此，JA被认为是一种新型植物激素。植物JA生物合成的最初底物是三烯脂肪酸（含有三个双键的十八碳和十六碳脂肪酸，18:3和16:3），这些脂肪酸经过脂氧合酶（LOX）、丙二烯氧化物合酶（AOS）和丙二烯氧化物环化酶（AOC）等一系列酶促反应，最终生成JA。JA生物合成所需要的三烯脂肪酸来自叶绿体膜脂。高等植物叶绿体类囊体膜含有四种极性甘油脂，它们是：单半乳糖甘油二酯(MGDG)、双半乳糖甘油二酯(DGDG)、硫代异鼠李糖甘油二酯(SQDG)和磷脂酰甘油(PG)。但是人们尚不清楚JA生物合成所需要的三烯脂肪酸主要来自哪一种膜脂。 最近，我们利用RNA干扰技术获得了烟草MGDG部分缺失的突变体。MGDG是质体中最重要的甘油脂，其含量高达50%，其中含有的三烯脂肪酸约占总脂中三烯脂肪酸含量的65%。本研究的目的是以烟草MGDG缺失的突变体（mgd1）为材料，通过研究MGDG缺失对茉莉酸生物合成的影响，阐明半乳糖脂与JA生物合成的关系。 首先我们对野生型烟草（WT）和mgd1的相关生物学特性进行了研究，包括甘油脂和脂肪酸组成。结果表明，mgd1烟草叶片中MGDG含量降低了57％，同时，其三烯脂肪酸相对含量也大幅度降低。其中十六碳三烯酸（16:3）降低了78%，亚麻酸（18:3）含量减少了28%。因此，由于MGDG缺失，类囊体中的三烯脂肪酸降低了27%。这一结果说明了JA生物合成的底物大幅度减少。 为了说明MGDG缺失导致的三烯脂肪酸含量的减少是否影响到JA的含量，我们利用GC-MS方法比较了WT和mgd1烟草中JA的含量。结果表明，mgd1叶片中的JA含量较WT降低了50%，说明了MGDG的缺失影响了JA的生物合成。 伤害可以诱导JA在短时间内大量合成。我们比较了机械损伤后JA在WT和mgd1叶片中积累的动态过程。伤害同时可以使WT和mgd1叶片中的JA含量增加，并且在1小时达到最大值。但是，JA在两种烟草叶片中增加的幅度不同，WT叶片受伤1小时后JA含量是未受伤时的5倍，而mgd1叶片受伤1小时后，其JA含量只增加了1倍。这些结果说明了MGDG缺失可以严重影响伤害诱导的 JA 的积累，MGDG是JA的生物合成底物的重要来源。 我们进一步研究了MGDG缺失对JA生物合成相关酶基因表达的影响。 LOX1和AOC编码JA生物合成途径中的关键酶LOX和AOC。RT-PCR分析表明mgd1叶片中这两个基因受伤害激活的程度比WT弱。进一步说明突变体中JA合成受到影响。 植物受到伤害时内源JA含量增加，并激活防御基因的表达。我们的结果显示，当植物受伤害后，mgd1叶片中与JA信号转导相关的防御基因HPL，PI-I和PI-II的表达量增加幅度明显低于WT。这说明突变体中JA信号转导途径受到了抑制。 JA在植物对昆虫侵害的防御反应中起重要作用，上述结果表明突变体对伤害响应受到削弱。昆虫饲喂实验显示，棉铃虫更趋向食用mgd1植株叶片，取食mgd1植株的棉铃虫的体重增加较多。这些结果与WT和mgd1在JA含量、防御相关基因表达方面的差异相一致。外源施加茉莉酸甲酯（MeJA）能够恢复mgd1的抗虫性和防御基因的表达，说明JA是恢复mgd1抗虫性所必须的。 上述结果表明MGDG缺失使JA生物合成受到影响，尤其是JA在植物受到伤害后的生物合成。对于这一现象的可能的解释是：MGDG是JA生物合成底物的主要来源，由于mgd1中缺少大量的MGDG，当植物受到伤害时，MGDG不能释放出足够三烯脂肪酸来合成JA，导致其含量降低，破坏了JA信号途径，最终使得植株表现出抗性降低等特性。我们的研究证明了MGDG可以作为JA生物合成的底物来源在JA信号途径中起重要作用。

Phylogenomic study of the subfamily Caprinae by cross-species chromosome painting with Chinese muntjac paints

Chromosomal homologies have been established between the Chinese muntjac (Muntiacus reevesi, MRE, 2n = 46) and five ovine species: wild goat (Capra aegagrus, CAE, 2n = 60), argall (Ovis ammon, OAM, 2n = 56), snow sheep (Ovis nivicola, ONI, 2n = 52), red goral (Naemorhedus cranbrooki, NCR, 2n = 56) and Sumatra serow (Capricornis sumatraensis, CSU, 2n = 48) by chromosome painting with a set of chromosome-specific probes of the Chinese muntjac. In total, twenty-two Chinese muntjac autosomal painting probes detected thirty-five homologous segments in the genome of each species. The chromosome X probe hybridized to the whole X chromosomes of all ovine species while the chromosome Y probe gave no signal. Our results demonstrate that almost all homologous segments defined by comparative painting show a high degree of conservation in G-banding patterns and that each speciation event is accompanied by specific chromosomal rearrangements. The combined analysis of our results and previous cytogenetic and molecular systematic results enables us to map the chromosomal rearrangements onto a phylogenetic tree, thus providing new insights into the karyotypic evolution of these species.

High-density comparative BAC mapping in the black muntjac (Muntiacus crinifrons): Molecular cytogenetic dissection of the origin of MCR 1p+4 in the X1X2Y1Y2Y3 sex chromosome system

The black muntjac (Muntiacus crinifrons, 2n = 8 female/9 male) is a critically endangered mammalian species that is confined to a narrow region of southeastern China. Male black muntjacs have an astonishing X1X2Y1Y2Y3 sex chromosome system, unparalleled i

Comparative genome maps of the pangolin, hedgehog, sloth, anteater and human revealed by cross-species chromosome painting: further insight into the ancestral karyotype and genome evolution of eutherian mammals

To better understand the evolution of genome organization of eutherian mammals, comparative maps based on chromosome painting have been constructed between human and representative species of three eutherian orders: Xenarthra, Pholidota, and Eulipotyphla,

Cross-species chromosome painting unveils cytogenetic signatures for the Eulipotyphla and evidence for the polyphyly of Insectivora

Insectivore-like animals are traditionally believed among the first eutherian mammals that have appeared on the earth. The modern insectivores are thus crucial for understanding the systematics and phylogeny of eutherian mammals as a whole. Here cross-spe

Chromosome painting between human and lorisiform prosimians: Evidence for the HSA 7/16 Synteny in the primate ancestral karyotype

Multidirectional chromosome painting with probes derived from flow-sorted chromosomes of humans (Homo sapiens, HSA, 2n = 46) and galagos (Galago moholi, GMO, 2n = 38) allowed us to map evolutionarily conserved chromosomal segments among humans, galagos, a

Karyotype evolution in Rhinolophus bats (Rhinolophidae, Chiroptera) illuminated by cross-species chromosome painting and G-banding comparison

Rhinolophus (Rhinolophidae) is the second most speciose genus in Chiroptera and has extensively diversified diploid chromosome numbers (from 2n=28 to 62). In spite of many attempts to explore the karyotypic evolution of this genus, most studies have been

Karyotypic evolution and phylogenetic relationships in the order Chiroptera as revealed by G-banding comparison and chromosome painting

Bats are a unique but enigmatic group of mammals and have a world-wide distribution. The phylogenetic relationships of extant bats are far from being resolved. Here, we investigated the karyotypic relationships of representative species from four families