Naturally Occurring Regenerative Differentiation of Xylem Around Adventitious Roots in Luffa cylindrica Seedlings

Regeneration of xylem induced by adventitious root formationin the hypocotyl of Luff a cylindrica Roem. seedlings is described.This naturally occurring form of xylem regeneration involvesthe formation of a bypass of regenerated tracheary elementsaround a root without external severance of the vascular strands.The regeneration of xylem around an adventitious root is polarand is very similar in its developmental pattern to the well-knownxylem regeneration induced by wounding vascular strands. Adventitious root formation, Luffa cylindrica Roem, regenerated tracheary elements, vascular differentiation, xylem regeneration.     

Nucellar Tracheids in Ovules of Luffa cylindrica

In Luffa cylindrica a few cells around the archesporial cellsin the nucellus develop thick PAS-positive walls. At the globularembryo stage, they gradually differentiate into pitted tracheidswith reticulate thickenings. These cells cover the entire nucellusexcept the epidermis and extend right up to the ovular vascularsupply in a seed. The occurrence of such extensive nucellartracheids in the Cucurbitaceae is being reported here for thefirst time.     

Evidence for Naturally Occurring Inhibitors of Archegonial Differentiation in Lygodium japonicum

Archegonial differentiation in prothallia of Lygodium japonicum was inhibited when the filtrate of conditioned medium or the extracts of prothallia with organic solvents were added to the medium. By varying the timing of treatment with the methanol extract, archegonial differentiation was shown to start at least 4 days before microscopically detectable change. The inhibitory effect of methanol extract was nullified by transferring the treated plants to a fresh medium omitting the methanol extract, so that the archegonial formation became discernible 6 days after the transfer. The inhibitory activity was stable in both acidic and basic solutions at room temperature, and was partially lost by boiling at pH 3 or 11 for 30 min. The inhibitor, which could be retrieved from the filtrate and the methanol extract, was fractionated into the neutral ethyl acetate fraction, but was not found in the acidic ethyl acetate fraction and in the aqueous residue. At least two active zones were separated on thin layer chromatograms of the ethyl acetate extracts from the filtrate and the methanol extract, and the relative flow-rates of each active zone from these two sources were very similar. The evidence described above indicates that specific inhibitors of archegonial differentiation may be produced in the tissue of prothallia of Lygodium and eventually be secreted to the medium.     

多氯联苯促进毛白杨不定根分化的效应

多氯联苯是一种典型的持久性有机污染物。研究表明多氯联苯具有毒物兴奋效应, 但其影响植物生长发育的机制尚不清楚。以毛白杨(Populous tomentosa)组培苗为材料, 探讨3 mg·L^-1 Aroclor1254对不定根分化、植物激素水平、与生长素相关的P009g125900、P006g142600和P002g222700基因表达、与细胞分裂素相关的P005g2489和P005g2376基因表达的影响。结果显示, Aroclor1254可促进毛白杨组培苗不定根分化, 缩短不定根初根时间与分化率达100%的时间, 提高不定根数目; 在不定根诱导期, 用Aroclor1254单独诱导, IAA/(ZR+dhZR)比值与阳性对照无显著差异, P006g142600、P002g222700、P009g125900、P005g2489和P005g2376基因表达变化趋势与IBA单独诱导下各基因表达变化趋势一致。为验证Aroclor1254是否具有生长素效应, 以玉米(Zea mays)和转生长素报告基因DR5::GUS的拟南芥(Arabidopsis thaliana)为材料, 观察Aroclor1254对胚芽鞘生长及DR5::GUS基因表达的影响。结果显示, 一定浓度的Aroclor1254对胚芽鞘的生长无显著影响, 但可诱导生长素报告基因表达。以上结果表明, 多氯联苯类化合物Aroclor1254虽不属于植物生长调节剂, 但具有毒物兴奋效应, 在一定浓度下具有类似生长素的生物学活性。     

丝瓜的三聚体G蛋白的初步研究

根据拟南芥（ａｒａｂｉｄｏｐｓｉｓｔｈａｈｌｉａｎａ）ＧＰＡ１的保守区段Ａ设计一对特异引物（５′ｃｔｇｇｇｇａａｔｃｔｇｇａａａａｔｃ３′,５′ｃａｃａｇｃｔｇｔａｃａｃｃｔｃａａａｃ３′）通过ＰＣＲ从丝瓜核基因组中扩增植物的三聚体Ｇ蛋白α亚基编码基因,获得了２个片段（ＬＦＧ１,ＬＦＧ２）,并已克隆和测序（已在ＥＭＢＬ数据库中登记,登记号为：ｙ１５２７０,ｙ１５２７１）．序列分析表明ＬＦＧ１和ＬＦＧ２分别由１５１５ｂｐ和７３２ｂｐ构成,都含有三聚体Ｇ蛋白α亚基编码基因的保守区段Ａ,但也都含有内含子．根据片段的大小及ＰＣＲ的特性,ＬＦＧ１可能是丝瓜三聚体Ｇ蛋白α亚基编码基因上的片段．     

The Physiology of Adventitious Roots

Adventitious roots are plant roots that form from any nonroot tissue and are produced both during normal development (crown roots on cereals and nodal roots on strawberry [Fragaria spp.]) and in response to stress conditions, such as flooding, nutrient deprivation, and wounding. They are important economically (for cuttings and food production), ecologically (environmental stress response), and for human existence (food production). To improve sustainable food production under environmentally extreme conditions, it is important to understand the adventitious root development of crops both in normal and stressed conditions. Therefore, understanding the regulation and physiology of adventitious root formation is critical for breeding programs. Recent work shows that different adventitious root types are regulated differently, and here, we propose clear definitions of these classes. We use three case studies to summarize the physiology of adventitious root development in response to flooding (case study 1), nutrient deficiency (case study 2), and wounding (case study 3).     

丝瓜肌球蛋白的电子显微学研究

从丝瓜 (Luffacylindrica (L .)Roem .)卷须中纯化得到分子量为 174kD的肌球蛋白 ,并对其进行了酶学与电子显微学的研究。这种肌球蛋白具有肌动蛋白激活的MgATPase活性 ,能够被抗动物肌肉的肌球蛋白的单克隆抗体识别。电子显微学研究表明 :它有两个头部 (大小和形状与动物肌肉的肌球蛋白相似 )和一条相对较短的尾部。还对丝瓜卷须的肌动蛋白进行了观测 ,偶尔发现一些尾部有球状结构的肌球蛋白。该肌球蛋白的免疫特性和超微结构证明了它由 2条重链组成 ,并与传统的肌球蛋白相似。然而 ,这种 174kD的肌球蛋白是否参与了丝瓜的接触卷曲有待于进一步研究。     

Naturally Occurring Penicillinase Plasmids in Staphylococcus aureus

A series of plasmids harbored by naturally occurring penicillin-resistant strains of Staphylococcus aureus were surveyed with a view toward exploring the variability in plasmid-linked marker patterns. Plasmids were transduced from their natural hosts to either of two plasmid-negative laboratory strains by selection for cadmium resistance, and the transductants were tested for all other markers previously found to be plasmid-linked. All of the strains that were able to serve as genetic donors to one of the two stock strains could donate cadmium and lead resistance as linked, plasmid-borne markers. Among the other plasmid markers, a wide variety of patterns was found, including four plasmids that did not carry the penicillinase determinant. Each of the 26 plasmids studied, including the latter 4, was found to belong to one of the two incompatibility sets of penicillinase plasmids previously identified. With the exception of the penicillinase-negative plasmids, which were found in both sets, all the plasmids of incompatibility set I directed the production of penicillinase type A; those belonging to set II directed either type A or type C. Those of set II without exception increased the sensitivity of their host strains to bismuth ion; those of set I carried determinants of bismuth resistance or did not affect the sensitivity of their host to this ion. No other perfect correlations between markers were encountered; in particular, there was no correlation between penicillinase serotype and the excretion of the enzyme. This finding allows the prediction that there is, in addition to all of the markers thus far identified, a plasmid-linked determinant of penicillinase excretion.     

丝瓜肌球蛋白的电子显微学研究

从丝瓜(Luffa cylindrica (L.) Roem.)卷须中纯化得到分子量为174kD的肌球蛋白,并对其进行了酶学与电子显微学的研究.这种肌球蛋白具有肌动蛋白激活的MgATPase活性,能够被抗动物肌肉的肌球蛋白的单克隆抗体识别.电子显微学研究表明:它有两个头部(大小和形状与动物肌肉的肌球蛋白相似)和一条相对较短的尾部.还对丝瓜卷须的肌动蛋白进行了观测,偶尔发现一些尾部有球状结构的肌球蛋白.该肌球蛋白的免疫特性和超微结构证明了它由2条重链组成,并与传统的肌球蛋白相似.然而,这种174 kD的肌球蛋白是否参与了丝瓜的接触卷曲有待于进一步研究.     

外源乙酰胆碱在丝瓜卷须弯曲中起“神经递质”的作用

用乙酰胆碱（ＡＣｈ）或毒扁豆碱处理离体丝瓜卷须不仅能增强机械刺激引发的卷曲程度,甚至可以直接引发卷须的弯曲运动。用阿托品预处理卷须可以抑制由机械刺激引发的电化学波传递,减弱ＡＣｈ对卷须弯曲运动的效应;而Ｄ－管箭毒预处理卷须则无此效应。说明在丝瓜卷须中ＡＣｈ是通过毒蕈碱型受体传递电化波并引起原生质收缩和快速弯曲运动,这与动物神经－平滑肌突触传递兴奋的机制很相似。     

木质部细胞分化的程序

本文主要对近十几年来有关木质部细胞分化研究中使用的实验系统及用这些系统所取得的重要进展作了评述.并以作者实验室的研究成果为基础,结合国内外研究进展,提出木质部细胞分化程序由参与细胞编程死亡(PCD)和次生壁构建的全部基因综合编制而成.以PCD过程各阶段的划分标准来看,木质部细胞分化中从IAA诱导形成层细胞平周分裂到细胞扩大前为PCD的起始阶段,其间包括死亡信号的发生、接受和传导,以及启始caspase(半胱氨酰基天门冬氨酸蛋白酶)类似物(例如caspase-8类似物)的活化;木质部母细胞的径向扩大为PCD的效应阶段,而效应caspase类似物(例如caspase-3类似物)活化DNase、DNA的片段化及次生细胞壁的构建和各种细胞器的解体则为PCD的清除降解阶段.至今还无法将DNase活化及其引起的DNA断裂过程与次生细胞壁构建过程分开.     

普通丝瓜始雌花节位遗传分析

选用始雌花节位有差异的普通丝瓜品种配制‘五叶香丝瓜’ב短圆筒丝瓜’(L1×L2)和‘短圆筒丝瓜’ב蛇形丝瓜’(L2×L3)2套组合,通过调查P1、P2、F1、B1、B2和F2植株的始雌花节位,利用主基因 多基因混合遗传模型联合分离分析了始雌花节位遗传规律。结果显示:L1×L2始雌花节位遗传符合2对加性-显性-上位性主基因 加性-显性多基因遗传模型,L2×L3的遗传符合1对加性主基因 加性-显性多基因遗传模型;L1×L2组合的B1、B2和F2群体遗传率(主基因 多基因)分别为66.13%、51.29%和68.27%,L2×L3组合的B1、B2和F2群体遗传率(主基因 多基因)分别为82.02%、64.87%和65.62%;L1×L2组合B1、B2和F2群体的环境方差占总表型方差的比例分别是23.43%、48.69%和31.73%,L2×L3组合B1、B2和F2群体的环境方差占总表型方差的比例分别是34.27%、55.40%和34.38%。结果表明:普通丝瓜始雌花节位是由主基因和多基因控制的数量性状,早熟性(较低的始雌花节位)不太可能通过杂种优势来实现;始雌花节位遗传不稳定,易受环境因素的影响,但定向选择会有较好的效果。     

丝瓜籽中蛋白质生物合成抑制蛋白的分离、纯化及性质研究

丝瓜（Ｌｕｆｆａｃｙｌｉｎｄｒｉｃａ）种籽,经捣碎、抽提、硫酸铵分级沉淀,ＣＭ－５２离子交换层析,Ｓｅｐｈａｃｒｙ１Ｓ－１００分子筛,阳离子交换ＦＰＬＣ等步骤,分离到两种单链蛋白质生物合成抑制蛋白：Ｌｕｆｆｉｎ－Ａ和Ｌｕｆｆｉｎ－Ｂ。它们都是等电点接近１０的碱性蛋白,ＳＤＳ－ＰＡＧＥ测定分子量分别约为２７ｋｄ和２８ｋｄ,氨基酸组成分析表明两者具很大同源性,但免疫双扩散及ＥＬＩＳＡ检测证明两者的免疫原性有差异。Ｌｕｆｆｉｎｓ对兔网织红细胞裂解液的蛋白质生物合成有强烈的抑制作用,ＩＣ５０分别为１．４×１０－１１ｍｏｌ／Ｌ和２．０×１０－１１ｍｏｌ／Ｌ,比ＴＣＳ的２．９×１０－１０ｍｏｌ／Ｌ低得多。因而,Ｌｕｆｆｉｎｓ很有可能成为肿瘤导向药物的高效＂弹头＂。     

Detecting Selective Sweeps in Naturally Occurring Escherichia Coli

The nucleotide sequences of the gapA and pabB genes (separated by approximately 32.5 kb) were determined in 12 natural isolates of Escherichia coli. Three analyses were performed on the data. First, the levels of polymorphism at the loci were compared within and between E. coli and Salmonella strains relative to their degrees of constraint. Second, the gapA and pabB loci were analyzed by the Hudson-Kreitman-Aguade (HKA) test for selective neutrality. Four additional dispersed genes (crr, putP, trp and gnd) were added to the analysis to provide the necessary frame of reference. Finally, the gene genealogies of gapA and pabB were examined for topological consistency within and between the loci. These lines of evidence indicate that some evolutionary event has recently purged the variability in the region surrounding the gapA and pabB loci in E. coli. This can best be explained by the spread of a selected allele through the global E. coli population by directional selection and the resulting loss in variability in the surrounding regions due to genetic hitchhiking.     

Forecasting Seizures in Dogs with Naturally Occurring Epilepsy

Seizure forecasting has the potential to create new therapeutic strategies for epilepsy, such as providing patient warnings and delivering preemptive therapy. Progress on seizure forecasting, however, has been hindered by lack of sufficient data to rigorously evaluate the hypothesis that seizures are preceded by physiological changes, and are not simply random events. We investigated seizure forecasting in three dogs with naturally occurring focal epilepsy implanted with a device recording continuous intracranial EEG (iEEG). The iEEG spectral power in six frequency bands: delta (0.1–4 Hz), theta (4–8 Hz), alpha (8–12 Hz), beta (12–30 Hz), low-gamma (30–70 Hz), and high-gamma (70–180 Hz), were used as features. Logistic regression classifiers were trained to discriminate labeled pre-ictal and inter-ictal data segments using combinations of the band spectral power features. Performance was assessed on separate test data sets via 10-fold cross-validation. A total of 125 spontaneous seizures were detected in continuous iEEG recordings spanning 6.5 to 15 months from 3 dogs. When considering all seizures, the seizure forecasting algorithm performed significantly better than a Poisson-model chance predictor constrained to have the same time in warning for all 3 dogs over a range of total warning times. Seizure clusters were observed in all 3 dogs, and when the effect of seizure clusters was decreased by considering the subset of seizures separated by at least 4 hours, the forecasting performance remained better than chance for a subset of algorithm parameters. These results demonstrate that seizures in canine epilepsy are not randomly occurring events, and highlight the feasibility of long-term seizure forecasting using iEEG monitoring.     

Thermoradiation Inactivation of Naturally Occurring Bacterial Spores in Soil

Samples of soil collected from the Kennedy Space Center near the spacecraft assembly facilities were found to contain microorganisms very resistant to conventional sterilzation techniques. The inactivation kinetics of the naturally occurring spores in soil were investigated by using dry heat and ionizing radiation, first separately and then simultaneously. Dry-heat inactivation kinetics of spores was determined at 105 and 125 C; radiation inactivation kinetics was determined for dose rates of 660 and 76 krads/h at 25 C. Simultaneous combinations of heat and radiation were then investigated at 105, 110, 115, 120, and 125 C, with a dose rate of 76 krads/h. Combined treatment was found to be highly synergistic, requiring greatly reduced radiation doses to accomplish sterilization of the population.     

Syntheses of Naturally Occurring Terphenyls and Related Compounds

Naturally occurring terphenyls and related compounds such as terferol and its corresponding quinone and phlebiarubrone were synthesized from 2,5-diphenyl-1,4-benzoquinone. According to the proposed biosynthetic pathway, chemical conversion of phlebiarubrone to ustalic acid, a toxic compound isolated from the poisonous mushroom, Tricholoma ustale, was examined to find a low-yield conversion to the ustalic acid dimethyl ester.