Bioherbicidal potential of a strain of Xanthomonas spp. for control of common cocklebur (Xanthium strumarium)

Several isolates of a previously unreported bacterial pathogen were discovered on common cocklebur seedlings in Chicot County, AR and Washington County, MS. Diseased plants in nature exhibited angular-shaped leaf spotting symptoms on leaf margins and central leaf areas. The isolates were cultured from diseased leaf tissue and tentatively identified as Xanthomonas spp., and their virulence on common cocklebur seedlings compared. The most virulent isolate (LVA987) was used in studies to define disease progression on cocklebur seedlings and to carry out a host range evaluation on various weeds and crop plants. High virulence was found on common cocklebur > marestail (Conyza canadensis) > giant ragweed (Ambrosia trifida) ≥ and common ragweed (Ambrosia artemisifolia). These results suggest this pathogen may be useful for the biological control of these important species of weeds. This is also highly relevant since all of these weeds have evolved resistance to one or more synthetic herbicides and are thus becoming more difficult to control with conventional herbicides.     

土壤不同浓度铜对小飞蓬毒害及耐受性研究

通过对高Cu污染区(Ⅰ)、低Cu污染区(Ⅱ)和非污染区(Ⅲ)小飞蓬盆栽实验及生理生化指标分析,结果表明,生态型Ⅰ、Ⅱ、Ⅲ电导率均随着Cu浓度增加而增大,并且两者之间呈极显著正相关;叶绿素(a+b)含量随着Cu浓度增加呈极显著负相关;生态型Ⅰ的蛋白质和脯氨酸含量随着Cu浓度增加均先有所升高,然后又降低,而生态型Ⅱ、Ⅲ则一直呈现降低趋势.3种生态型小飞蓬体内SOD、POD、CAT酶活性在Cu胁迫下均有所提高,与对照相比,当Cu浓度为1200mg·kg^-1时,生态型Ⅰ的SOD、POD、CAT活性分别为194.1%、206.2%、1186%;Ⅱ的SOD、POD、CAT活性分别为170.1%、182.9%、1113%;Ⅲ的SOD、POD、CAT的活性分别为115.1%、155.4%、10.73%.对3种生态型小飞蓬的生理生化指标及酶活性分析表明,高Cu污染区小飞蓬的耐受性要强于低Cu污染区,两者又均强于非污染区小飞蓬,这3种生态型小飞蓬的耐受性呈现出了明显的种间差异.     

Biological Control of Black Rot (Xanthomonas campestris pv. campestris) of Cabbage in Tanzania with Bacillus strains

We evaluated the biocontrol efficacy of strains of Bacillus from Tanzania against the black rot pathogen, Xanthomonas campestris pv. campestris, in cabbage and the influence of the method of application under field conditions. The incidence and severity of black rot in the foliage, stems and heads of the highly susceptible cultivar, Copenhagen Market, were significantly reduced, especially when antagonists were applied through the roots as compared to application through the seeds or foliage (cotyledons). Promising antagonists included strains of B. cereus, B. lentimorbus and B. pumilus.     

Antimicrobial activities of Conyzolide and Conyzoflavone from Conyza canadensis

Antibacterial and antifungal activities of the two isolated compounds from Conyza canadensis have been reported in the current study. The two isolated compounds i.e. Conyzolide (1) and Conyzoflavone (2) were tested against six bacterial and five fungal strains, employing hole diffusion and macrodilution methods. Both the compounds showed significant activities against the tested pathogens with special reference to E. coli, P. aeruginosa, S. aureus, Trichophytom longifusus, C. albicans, and C. glaberata. Conyzolide revealed comparatively better antibacterial activity against E. coli (minimum inhibitory concentration (MIC): 25 µg/mL) in comparison to Conyzoflavone. However, in case of antifungal activities, Conyzoflavone exhibited superior antifungal activity against C. albicans (MIC: 10 µg/mL) as compared to Conyzolide.     

Qualitative and comparative proteomic analysis of Xanthomonas campestris pv. campestris 17

The bacterium Xanthomonas campestris pathovar campestris (XCC) 17 is a local isolate that causes crucifer black rot disease in Taiwan. In this study, its proteome was separated using 2-DE and the well-resolved proteins were excised, trypsin digested, and analyzed by MS. Over 400 protein spots were analyzed and 281 proteins were identified by searching the MS or MS/MS spectra against the proteome database of the closely related XCC ATCC 33913. Functional categorization of the identified proteins matched 141 (50%) proteins to 81 metabolic pathways in the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. In addition, we performed a comparative proteome analysis of the pathogenic strain 17 and an avirulent strain 11A to reveal the virulence-related proteins. We detected 22 up-regulated proteins in strain 17 including the degrading enzymes EngXCA, HtrA, and PepA, which had been shown to have a role in pathogenesis in other bacteria, and an anti-host defense protein, Ohr. Thus, further functional studies of these up-regulated proteins with respect to their roles in XCC pathogenicity are suggested.     

小蓬草地上部分精油的活性组分

利用气质联用仪(GC-MS)对水蒸气蒸馏提取小蓬草(Conyza canadensis)地上部分精油的挥发性组分进行了分析,匹配度74以上的活性组分有柠檬烯、α-佛手柑油烯、顺式-β-麝子油烯等萜类化合物,反式-对-薄荷-2,8-二烯醇、顺式-对-薄荷-2,8-二烯-1-醇、香芹醇、反式香芹醇等醇类化合物,s-香芹酮等酮类化合物。通过纸上种子发芽的生物测定试验,结果表明小蓬草地上部分精油对受体植物油菜种子萌发具有抑制作用,且具有50%抑制作用的丙酮溶液的适宜浓度IC50为0.6 mg/mL。     

小蓬草的胚胎学研究

对小蓬草（Conyzacanadensis）大小孢子发生、雌雄配子体形成、受精、胚及胚乳发育过程进行了研究,主要结果如下：花药四室,药壁由表皮、药室内壁、中层和绒毡层组成。表皮退化;药室内壁宿存,细胞柱状伸长,纤维状加厚;中层细胞退化较早,在小孢子母细胞减数分裂开始时仅存残迹;绒毡层于小孢子母细胞减数第一次分裂前期开始原位变形退化,属于腺质型绒毡层;小孢子母细胞减数分裂为同时型,四分体的排列方式主要为四面体形和左右对称形;成熟花粉粒多为3-细胞花粉粒,偶见2-细胞花粉粒。子房下位,2心皮,1室,单胚珠,基生胎座;单珠被,薄珠心,倒生胚珠,具发达的珠被绒毡层。珠心表皮下分化出大孢子孢原细胞,孢原细胞直接发育为大孢子母细胞,大孢子母细胞减数分裂形成4个大孢子直线形排列,仅合点端的大孢子发育成功能大孢子母细胞,胚囊发育为蓼型。两个极核在受精前融合为次生核,珠孔受精。胚乳发育属于核型,胚胎发育为紫菀型;具胚乳吸器。     

十字花科黑腐病菌中一个与抗逆有关的小RNA的鉴定

十字花科黑腐病菌(Xanthomonas campestris pathovar campestris,Xcc),是引起十字花科植物黑腐病的病原菌。Xcc要经历寄生、腐生等多种环境变化,为适应这些环境变化,需要调控相应基因的表达。除蛋白外,小RNA在基因表达调控中也起到关键作用。本实验室前期实验从Xcc 8004中鉴定出数百个小RNA,但是绝大多数小RNA的功能仍然未知。本研究通过构建一个小RNA(sRNA3843)的过量表达株来研究其生物学功能。确定该小RNA过量表达后,对其过量表达株OE3843进行了一系列的表型检测。结果发现,s RNA3843过量表达株OE3843对金属离子Cu^2+、Zn^2+、Cd^2+及蛋白变性剂SDS的耐受能力明显下降,表明s RNA3843与Xcc的抗逆有关。本研究的实验结果为深入研究小RNA在Xcc抗逆中所起的作用及其作用机理打下基础。     

Use of agricultural wastes for xanthan production by Xanthomonas campestris

Four different acid-hydrolyzed wastes, from melon, watermelon, cucumber and tomato were compared for xanthan production. Growth of Xanthomonas campestris, xanthan biosynthesis, kinetics and chemical composition were investigated. Both growth and xanthan production were dependent on the acid hydrolysate concentrations and available nitrogen. Melon acid hydrolyzed waste was the best substrate for xanthan production. Exopolysaccharide obtained throughout this study was compared to commercial xanthan, showing a very similar chemical composition. Acid hydrolyzed wastes are proposed as a new carbon source for xanthan production. Received 16 July 1998/ Accepted in revised form 8 October 1998     

Mode of action of paraquat in leaves of paraquat-resistant Conyza canadensis (L.) Cronq

The mode of action of paraquat (1,1-dimethyl-4,4-bipyridinium) and the mechanism of resistance to it were studied in leaves of atrazine/paraquat co-resistant (R) and susceptible (S) biotypes of horseweed (Conyza canadensis) collected from Hungarian vineyards. The application of 0·5 mol m^?3 paraquat by spraying onto the surface of the leaves of intact plants in the light rapidly led to typical symptoms of paraquat action in the initial period in both biotypes, i.e. inhibition of CO₂ fixation, suppression of variable chlorophyll fluorescence (F_v), decrease of oxygen evolution and stimulation of ethane production. The inhibitory effect of paraquat in the S plants was irreversible, whereas it was transient in the R plants and those plants recovered gradually afterwards. The R plants recovered from the inhibitory effect of paraquat only in the light, and an increase in light intensity was found to have a pronounced effect on the recovery of F_v. The mechanism of resistance to paraquat in C. canadensis is discussed.     

野油菜黄单胞菌野油菜致病变种8004菌株wxcA基因与EPS的产量有关

在以前的工作中,采用转座子Tn5 gusA5对野油菜黄单胞菌野油菜致病变种(Xcc)8004菌株进行诱变,获得一批胞外多糖(EPS)合成减少的突变体,对这些突变体的Tn5 gusA5的插入位点进行分析后,发现有两株突变体是wxcA基因不同插入位点的突变体。以前认为wxcA基因与脂多糖(LPS)的O-抗原合成有关而与EPS的合成无关。为明确wxc4基因的功能,对8004菌株的wxcA基因进行缺失,获得的△wxcA突变体的EPS产量与野生型菌株相比,减少了50％,并且一段PCR合成的包含wxcA基因的DNA片段能反式互补△wxcA突变体,恢复突变体的EPS产量。这证实了8004菌株的wxcA基因与EPS的合成产量有关。     

Plant community diversity and invasibility by exotics: invasion of Mediterranean old fields by Conyza bonariensis and Conyza canadensis

A series of communities were established in situ to differentiate the effects of species richness, functional richness and functional group identity on invasibility of Mediterranean annual old fields. We monitored the demographic and vegetative parameters of two exotic annuals introduced as seedlings, Conyza bonariensis and C. canadensis . Community species richness and functional composition determined resistance to invasion by Conyza. Conyza bonariensis biomass decreased with increasing species richness. Legumes increased the biomass and consequently the net fecundity of both Conyza , while survival was favoured by Asteraceae . Communities with fewer Asteraceae and grasses increased the reproductive effort of C. bonariensis . A separate glasshouse experiment using the same species mixes revealed that establishment of Conyza decreased with increasing species richness or when grasses were present. Patterns of Conyza performance are interpreted in the light of measurements of ecosystem functional parameters, making it possible to formulate hypotheses about mechanisms limiting community invasibility.     

小蓬草精油的分离组分比较分析

通过薄层色谱分析和柱色谱分离结合气相色谱-质谱分析小蓬草精油的分离组分,结果表明其不同分离组分组成有差异,可以分离得到以香芹酮(18.33%)为特征成分,含有cis-香芹醇(3.79%),cis-香芹酮氧化物(1.74%),trans-香芹醇(1.62%),橙花叔醇(1.13%),石竹烯氧化物(0.38%),对甲基苯乙酮(0.64%)或者是以cis-香芹醇为特征成分,含有cis-马鞭草烯酮的分离组分。香芹酮、cis-香芹醇、橙花叔醇、对甲基苯乙酮、cis-马鞭草烯酮等是具有香气的化合物。     

野油菜黄单胞菌野油菜致病变种中一个与EPS合成有关的新基因的鉴定

用转座子Tn5gusA5对野油菜黄单胞菌野油菜致病变种(Xanthomonas campestris pv.campestris,简称Xcc)野生型菌株8004进行诱变,分离到一批胞外多糖(EPS)合成减少的突变体。采用TAIL-PCR(thermal asymmetric interlaced PCR)分析突变体的Tn5gusA5插入位点,发现其中一株编号为151D09的突变体的插入位点位于Xcc 8004菌株的基因组编号为XC3695的ORF内,该ORF功能尚未见报道。序列分析表明,该ORF演绎的编码产物与Serratia marcescens的kdtX基因和Klebsiella pneumoniae的waaE基因演绎的编码产物分别具有52%和50%的相似性,并具有第2家族糖基转移酶的功能域, 因此暂将该ORF命名为waxE基因。用同源双交换方法构建了waxE基因的缺失突变体,并采用PCR和Southern杂交的方法对突变体进行了验证。waxE基因缺失突变体在营养丰富培养基的生长繁殖不受影响,但其EPS产量与野生型菌株8004相比,降低35%左右,并且一段PCR合成的包含waxE基因的DNA片段能反式互补waxE基因缺失突变体,恢复缺失突变体的EPS产量,表明Xcc waxE基因与EPS的生物合成有关。     

Defence-related enzymatic response in cabbage to Xanthomonas campestris pv. campestris

Black rot of cabbage caused by Xanthomonas campestris pv. campestris is one of the most important diseases of crucifers worldwide. Expression of defence-related enzymes in cabbage in response to X. campestris pv. campestris was investigated in the current experiment. Among the defence-related enzymes (phynylalanine ammonia lyase, peroxidase, polyphenol oxidase, superoxide dismutase [SOD] and chitinase) and quantity of phenolic compounds studied in the present investigation, phenylalanine ammonia lyase (PAL), the key enzyme in the phenylpropanoid pathway was the first enzyme suppressed at three days after inoculation in X. campestris pv. campestris-cabbage system. Correlation analysis indicated that PAL and phenolic compounds are the two most important compounds determining the susceptibility of cabbage to X. campestris pv. campestris. Induction of peroxidase isoform-1 (Rf value: 0.059) and SOD isoform-1 (Rf value: 0.179) three days after pathogen inoculation implicated the role of these isozymes in susceptible cabbage – X. campestris pv. campestris interaction. This study demonstrates the susceptibility of cabbage to X. campestris pv. campestris is a result of declination of PAL and phenolic contents at biochemical level as a manifestation of increase in bacterial population at the cellular level within the host tissues.     

超声波提取加拿大蓬总黄酮的研究

目的:研究加拿大蓬中总黄酮提取方法及最佳工艺.方法:采用超声提取法,通过单因素试验和正交试验筛选最佳工艺条件.结果:最佳提取条件为60%乙醇、料液比1:20、60 kW下超声45 min.得率为31.076 mg/g.结论:该方法提取提取总黄酮快速、简便,可适用于生产中加拿大蓬总黄酮类物质的检测.该方法是提取加拿大蓬总...     

Expression of a subcloned alpha-amylase gene under the control of a Xanthomonas campestris promoter

Abstract Using the promoter probe pKK232-8 a 0.6-kb fragment containing an active promoter sequence from Xanthomonas campestris pv campestris was cloned. Two new plasmids were constructed: (a) pAP2, which contains the amy gene from Bacillus subtilis cloned between the Eco RI and Hin dIII sites in the pMFY40 plasmid, and (b) pAP2X, obtained after introduction of the cloned X. campestris promoter upstream from the amy gene. These plasmids were introduced into amylolytic and non-amylolytic strains of X. campestris pv campestris and pv manihotis , respectively. Quantification of alpha-amylase specific activity in liquid culture showed that the introduction of a Xanthomonas promoter doubled the expression of amy gene when the host strain was the pathovar campestris but had little effect on the strain from pathovar manihotis . This difference in the promoter activity might indicate that the cloned promoter is specific and could be involved in pathovar differentiation or plant-pathogen interaction.     

Genetic and Proteomic Analyses of a Xanthomonas campestris pv. campestris purC Mutant Deficient in Purine Biosynthesis and Virulence

Bacterial proliferation in hosts requires activation of a number of housekeeping pathways, including purine de novo biosynthesis. Although inactivation of purine biosynthesis genes can attenuate virulence, it is unclear which biochemical or virulence factors are associated with the purine biosynthesis pathway in vivo. We report that inactivation of purC, a gene encoding phosphoribosylaminoimidazole-succinocarboxamide synthase, caused complete loss of virulence in Xanthomonas campestris pv. cam- pestris, the causal agent of black rot disease of cruciferous plants. The purC mutant was a purine auxotroph; it could not grow on minimal medium, whereas addition of purine derivatives, such as hypoxanthine or adenine plus guanine, restored growth of the mutant. The purC mutation also significantly enhanced the production of an unknown purine synthesis associated pigment and extracellular polysaccharides by the bacterium. In addition, comparative proteomic analyses of bacteria grown on rich and minimal media revealed that the purC mutation affected the expression levels of diverse proteins involved in purine and pyrimidine synthesis, carbon and energy metabolisms, iron uptake, proteolysis, protein secretion, and signal transduction. These results provided clues to understanding the contributions of purine synthesis to bacterial virulence and interactions with host immune systems.     

Sensitive and specific detection of Xanthomonas campestris pv campestris by PCR using species-specific primers based on hrpF gene sequences

A sensitive and specific assay was developed to detect bacterial black rot of crucifers caused by Xanthomonas campestris pv. campestris (X. c. pv. campestris), in cabbage seed and plant. Primers XCF and XCR from hrpF homologous to nolX, host recognition protein, were used to amplify a 525 bp DNA fragment. PCR technique was applied to detect the pathogen in naturally infected seed and plant of cabbage. The PCR product was only produced from X. c. pv. campestris among 40 isolates of Xanthomonas strains, Escherichia coli (O157:H7), Pectobacterium carotovorum subsp. carotovorum, and other reference bacteria.     

Comprehensive analysis of the extracellular proteins from Xanthomonas campestris pv. campestris B100

The extracellular proteome of Xanthomonas campestris pv. campestris (Xcc) cultivated in minimal medium was isolated from the cell-free culture supernatant and separated by two-dimensional gel electrophoresis. This technique resolved 97 clearly visible protein spots, which were excised, digested with trypsin and identified on the basis of their peptide mass fingerprints generated by matrix assisted laser desorption/ionisation-time of flight-mass spectrometry. Using this approach 87 different proteins could be distinguished. The Signal P software predicted putative signal peptides for 53% of the extracellular proteins. These proteins are probably transported over the inner membrane and are localized in the periplasm, the outer membrane or secreted into the extracellular space. Among the secreted proteins are 11 degradative enzymes, which are involved in pathogenesis of Xcc. The proteins without obvious secretion signals are known to serve functions in the cytosol. How the cytosolic proteins are delivered to the extracellular space remains unclear.