On-board flow cytometric observation of picoplankton community structure in the East China Sea during the fall of different years

On-board flow cytometric determinations of picoplankton abundance (i.e. Synechococcus spp., Prochlorococcus spp., picoeukaryotes and also heterotrophic bacteria) were obtained in the East China Sea in fall of 2000 and 2003. The average abundances of Synechococcus, Prochlorococcus, picoeukaryotes and heterotrophic bacteria were 10(5), 10(5), 10(4) and 10(6) cells ml(-1), respectively. Synechococcus, picoeukaryotes and heterotrophic bacteria were abundant at all the stations and presented higher concentration in the inner shelf where influences from the Changjiang effluent plumes and the coastal upwelling were evident, while Prochlorococcus was absent from the near-shore stations and became the dominant picophytoplankton population in offshore waters, where its abundance was comparable to that for heterotrophic bacteria. All picoplankton groups showed a reduction in cell number with depth, and a positive correlation with water temperature were observed, which reflected the importance of light and temperature on picoplankton growth. A negative relationship with salinity was found for heterotrophic bacteria along two sections across the East China Sea Shelf, and distribution of picoplankton was dominated by different water masses. The fixation could lead to loss in Prochlorococcus cell numbers within one month, and all the picoplankton numbers decreased dramatically after three months.

Transmission dynamics of the Echinococcus granulosus sheep-dog strain (G1 genotype) in camels in Tunisia

Cystic echinococcosis, caused by Echinococcus granulosus, is highly endemic in North Africa and the Middle East. This paper examines the abundance and prevalence of infection of E. granulosus in camels in Tunisia. No cysts were found in 103 camels from Kébili, whilst 19 of 188 camels from Benguerden (10.1%) were infected. Of the cysts found 95% were considered fertile with the presence of protoscolices and 80% of protoscolices were considered viable by their ability to exclude aqueous eosin. Molecular techniques were used on cyst material from camels and this demonstrated that the study animals were infected with the G1 sheep strain of E. granulosus. Observed data were fitted to a mathematical model by maximum likelihood techniques to define the parameters and their confidence limits and the negative binomial distribution was used to define the error variance in the observed data. The infection pressure to camels was somewhat lower in comparison to sheep reported in an earlier study. However, because camels are much longer-lived animals, the results of the model fit suggested that older camels have a relatively high prevalence rate, reaching a most likely value of 32% at age 15 years. This could represent an important source of transmission to dogs and hence indirectly to man of this zonotic strain. In common with similar studies on other species, there was no evidence of parasite-induced immunity in camels.

Breastfeeding, amenorrhea and contraceptive practice among postpartum women in Zibo, China

This paper reports a hospital-based longitudinal study that was conducted in Zibo, China, in June 1996. The objective was to investigate the existing patterns of breastfeeding, amenorrhea and contraceptive use among postpartum women in urban areas of China. Information was obtained from 492 newly parturient women. Follow-up interviews were done at 42 days. 4 months and 1 year after delivery. The results showed that the full breastfeeding rate (including exclusive and almost exclusive breastfeeding) was 78% and 43% at 42 days and 4 months after delivery, respectively. The mean reported length of abstinence from sexual intercourse after delivery was 71 days. The mean reported time to menses resumption was 184 days. Ninety-three per cent of women had resumed sexual intercourse at 4 months after delivery. Seventy-three per cent of women were using contraceptive methods when they resumed sexual activity after delivery. After childbirth, the majority ofthe women interviewed used condoms within 3 months. Thereafter, most of them switched to intrauterine device (IUD)). Life table analysis shows that the continuation rates of full breastfeeding and amenorrhea at 4 months after delivery were 35% and 68%, respectively. This implies that if the full breastfeeding rate can be prolonged, it is feasible to use the lactational amenorrhea method (LAM) among Chinese postpartum women. The policy implications of this study are that quality care on contraceptive services and information for postpartum women in urban areas need to be improved further.

Epidemiology and strain characteristics of Echinococcus granulosus in the Benghazi area of eastern Libya

The incidence of surgically confirmed cystic echinococcosis in eastern Libya was estimated to be at least 4.2 cases/100,000, with significantly more female cases than male. The prevalences of infection with Echinococcus granulosus among 1087 sheep, 881 goats, 428 camels and 614 cattle from the same region, determined postmortem in abattoirs, were 20%, 3.4%, 13.6% and 11%, respectively. Infection in the livestock was age-dependent and, generally, the female animals were more often infected than the male. The measurements of rostellar hooks on protoscoleces collected from sheep and cattle were similar but significantly different from the corresponding measurements of parasites of human or camel origin. However, when a portion of the cytochrome c-oxidase subunit I (cox1) gene from each of 30 protoscolex samples from Libya (12 from cattle, three from humans, five from camels and 10 from sheep) was sequenced, the sequences were all found to be identical to that published for the common sheep strain of E. granulosus.

Lymphotactin cotransfection enhances the therapeutic efficacy of dendritic cells genetically modified with melanoma antigen gp100

Lymphotactin (Lptn) is a C chemokine that attracts T cells and NK cells. Dendritic cells (DC) are highly efficient, specialized antigen-presenting cells and antigen-pulsed DC has been regarded as promising vaccines in cancer immunotherapy. The aim of our present study is to improve the therapeutic efficacy of DC-based tumor vaccine by increasing the preferential chemotaxis of DC to T cells. In this study, Lptn and/or melanoma-associated antigen gp100 were transfected into mouse bone marrow-derived DC, which were used as vaccines in B16 melanoma model. Immunization of C57BL/6 mice with DC adenovirally cotransfected with Lptn and gp100 (Lptn/gp100-DC) could enhance the cytotoxicities of CTL and NK cells, increase the production of IL-2 and interferon-gamma significantly, as compared with immunization with gp100-DC, Lptn-DC, LacZ-DC, DC or PBS counterparts. The Lptn/gp100-DC immunized mice exhibited resistance to tumor challenge most effectively. It was found that the tumor mass of mice vaccinated by Lptn/gp100-DC showed obvious necrosis and inflammatory cell infiltration. In vivo depletion analysis demonstrated that CD8(+) T cells are the predominant T cell subset responsible for the antitumor effect of Lptn/gp100-DC and CD4(+) T cells were necessary in the induction phase of tumor rejection, while NK cells were less important although they participated in the antitumor response either in the induction phase or in the effector phase. In the murine model with the pre-established subcutaneous B16 melanoma, immunization with Lptn/gp100-DC inhibited the tumor growth most significantly when compared with other counterparts. These findings provide a potential strategy to improve the efficacy of DC-based tumor vaccines.

Complete mitochondrial genomes confirm the distinctiveness of the horse-dog and sheep-dog strains of Echinococcus granulosus

Unlike other members of the genus, Echinococcus granulosus is known to exhibit considerable levels of variation in biology, physiology and molecular genetics. Indeed, some of the taxa regarded as 'genotypes' within E. granulosus might be sufficiently distinct as to merit specific status. Here, complete mitochondrial genomes are presented of 2 genotypes of E. granulosus (G1-sheep-dog strain: G4-horse-dog strain) and of another taeniid cestode, Taenia crassiceps. These genomes are characterized and compared with those of Echinococcus multilocularis and Hymenolepis diminuta. Genomes of all the species are very similar in structure, length and base-composition. Pairwise comparisons of concatenated protein-coding genes indicate that the G1 and G4 genotypes of E. granulosus are almost as distant from each other as each is from a distinct species, E. multilocularis. Sequences for the variable genes atp6 and nad3 were obtained from additional genotypes of E. granulosus, from E. vogeli and E. oligarthrus. Again, pairwise comparisons showed the distinctiveness of the G1 and G4 genotypes. Phylogenetic analyses of concatenated atp6, nad1 (partial) and cox1 (partial) genes from E. multilocularis, E. vogeli, E. oligarthrus, 5 genotypes of E. granulosus, and using T. crassiceps as an outgroup, yielded the same results. We conclude that the sheep-dog and horse-dog strains of E. granulosus should be regarded as distinct at the specific level.

[Study on the osteoblast and the growth factors of bone tissue engineering]

To build artificial bone with osteoblast and growth factors is one of popular studies on current bone tissue engineering. This paper has reviewed current studies on the function of the growth factors and the resource, isolation and culture of the osteoblast. It also introduces the interaction of the growth factors, and the development in the transgenosis of the relative growth factors.

Inhibition of cell cycle progression by the novel cyclophilin ligand sanglifehrin A is mediated through the NFkappa B-dependent activation of p53

Sanglifehrin A belongs to a novel family of immunophilin-binding ligands. Sanglifehrin A is similar to cyclosporin A in that it binds to cyclophilins. Unlike cyclosporin A, however, the cyclophilin-sanglifehrin A complex has no effect on the calcium-dependent protein phosphatase calcineurin. It has been previously shown that sanglifehrin A specifically blocks T cell proliferation in response to interleukin 2 by inhibiting the appearance of cell cycle kinase activity cyclinE-Cdk2. How sanglifehrin A treatment leads to the cell cycle blockade has remained unknown. We report that sanglifehrin A is capable of activating the tumor suppressor gene p53 at the transcription level, leading to up-regulation of p21 that then binds and inhibits the cylcinE-Cdk2 complex. Further analysis of different elements in the p53 promoter showed that sanglifehrin A activates p53 transcription primarily through the activation of the transcription factor NFkappaB by activating IkappaB kinase in a manner that is similar to several genotoxic agents. Unlike other genotoxic drugs, sanglifehrin A does not cause DNA damage, making it a unique natural product that is capable of activating the NFkappaB signaling pathway without affecting DNA.

Effects of extract F of red-rooted Salvia on mucosal lesions of gastric corpus and antrum induced by hemorrhagic shock-reperfusion in rats

AIM

To compare the effects of extract F of red-rooted Salvia (EFRRS) on mucosal lesions of gastric corpus and antrum induced by hemorrhagic shock and reperfusion in rats.

METHODS

The rats were subject to hemorrhagic shock and followed by reperfusion, and were divided randomly into two groups. Group 1 received saline, and group 2 received EFRRS intravenously. The index of gastric mucosal lesions (IGML) was expressed as the percentage of lesional area in the corpus or antrum. The degree of gastric mucosal lesions (DGML) was catalogued grade 0,1,2 and 3. The concentrations of prostaglandins (PGs) were measured by radioimmunoassay. The concentration of MDA was measured according to the procedures of Asakawa. The activity of SOD was measured by the biochemical way. The growth rates or inhibitory rates of above-mentioned parameters were calculated.

RESULTS

As compared with IGML (%), grade 3 damage (%) and MDA content (nmol/g tissue) of gastric antrum which were respectively 7.96 +/- 0.59, 34.86 +/- 4.96 and 156.98 +/- 16.12, those of gastric corpus which were respectively 23.18 +/- 6.82, 58.44 +/- 9.07 and 230.56 +/- 19.37 increased markedly (P <0.01), whereas the grade 0 damage, grade 1 damage, the concentrations of PGE(2) and PGI(2)(pg/mg tissue), the ratio of PGI(2)/TXA(2) and the activity of SOD (U/g tissue) of corpus which were respectively 3.01 +/- 1.01, 8.35 +/- 1.95, 540.48 +/- 182.78, 714.38 +/- 123.74, 17.38 +/- 5.93 and 134.29 +/- 13.35 were markedly lower than those of antrum which were respectively 13.92 +/- 2.25, 26.78 +/- 6.06, 2218.56 +/- 433.12, 2531.76 +/- 492.35, 43.46 +/- 8.51 and 187.45 +/- 17.67 (P<0.01) after hemorrhagic shock and reperfusion. After intravenous EFRRS, the growth rates (%) of grade 0 damage, grade 1 damage, the concentrations of PGE(2) and PGI(2), the ratio of PGI(2)/TXA(2) and the activity of SOD of corpus which were respectively 632.56, 308.62, 40.75, 74.75, 92.29 and 122.25 were higher than those in antrum which were respectively 104.89, 58.40, 11.12, 56.58, 30.65 and 82.64, whereas the inhibitory rates (%) of IGML, grade 3 damage and MDA content of gastric corpus were 82.93, 65.32 and 59.09, being higher than those of gastric antrum which were 76.64, 53.18 and 42.37.

CONCLUSION

After hemorrhagic shock reperfusion, the gastric mucosal lesions in the corpus were more severe than those in the antrum, which were related not only to the different distribution of endogenous PGs in the mucosa, but also to the different ability of anti-oxidation of the mucosa. The protective effect of EFRRS on the gastric mucosa in the corpus was more evident than that in the antrum, which was related to higher growth degree of PGs contents and anti-oxitative ability in gastric corpus after administration of EFRRS.

Human ABCA1 BAC transgenic mice show increased high density lipoprotein cholesterol and ApoAI-dependent efflux stimulated by an internal promoter containing liver X receptor response elements in intron 1

By using BAC transgenic mice, we have shown that increased human ABCA1 protein expression results in a significant increase in cholesterol efflux in different tissues and marked elevation in high density lipoprotein (HDL)-cholesterol levels associated with increases in apoAI and apoAII. Three novel ABCA1 transcripts containing three different transcription initiation sites that utilize sequences in intron 1 have been identified. In BAC transgenic mice there is an increased expression of ABCA1 protein, but the distribution of the ABCA1 product in different cells remains similar to wild type mice. An internal promoter in human intron 1 containing liver X response elements is functional in vivo and directly contributes to regulation of the human ABCA1 gene in multiple tissues and to raised HDL cholesterol, apoAI, and apoAII levels. A highly significant relationship between raised protein levels, increased efflux, and level of HDL elevation is evident. These data provide proof of the principle that increased human ABCA1 efflux activity is associated with an increase in HDL levels in vivo.

Intrasplenic transplantation of IL-18 gene-modified hepatocytes: an effective approach to reverse hepatic fibrosis in schistosomiasis through induction of dominant Th1 response

Hepatic fibrosis is a common outcome of chronic liver diseases. In schistosomiasis, chronic parasite egg-induced granuloma formation can lead to fibrosis, which is immunologically characterized by the dominant Th2 response. Recently, it has been shown that gene therapy is an attractive approach for the treatment of hepatic fibrosis. To investigate the antifibrotic effects of IL-18 gene transfer, a normal murine liver cell line BNL.CL2 was transfected with recombinant adenovirus encoding mouse IL-18, and then intrasplenically transplanted into mice infected with Schistosoma japonicum (S. japonicum). Our data show that IL-18 gene-modified hepatocytes intrasplenically transplanted into mice can effectively express IL-18 in the liver and in peripheral blood. Intrasplenic transplantation of IL-18 gene-modified hepatocytes into S. japonicum-infected mice could result in a significantly increased IFN-gamma and IL-2 but decreased IL-4 and IL-10 concentration both in the liver and in the serum, suggesting that the dominant Th2 response in mice with schistosomiasis could be reversed by this intervention. Consistent with the changes in Th1 and Th2 cytokine production, mice intrasplenically transplanted with IL-18 gene-modified hepatocytes developed much less hepatic fibrosis at 20 weeks after infection, which was evaluated by liver content of hydroxyproline, collagens, and hepatic mRNA expression of procollagens. These data indicate that intrasplenic transplantation of IL-18 gene-modified hepatocytes can be a candidate for therapeutic intervention in hepatic fibrosis through induction of a dominant Th1 response.

Ion conductors derived from cholic acid and spermine: importance of facial hydrophilicity on NA(+) transport and membrane selectivity

A series of ion conductors have been synthesized in which the degree of facial hydrophilicity has been systematically varied. Specifically, conjugates have been prepared from cholic acid and spermine in which the hydrophilic face of each sterol bears methoxy (1), hydroxy (2), carbamate (3), or sulfate groups (4). The ability of these conjugates to promote the transport of Na(+) across phosphatidylcholine membranes of varying thickness has been investigated by (23)Na NMR spectroscopy. Examination of observed activities in three different phosphatidylcholine membranes has provided evidence for membrane-spanning dimers as the transport-active species. In the thinnest membranes investigated, made from 1,2-dimyristoleoyl-sn-glycero-3-phosphocholine (C14), Na(+)-transport activity was found to increase, substantially, with increasing facial hydrophilicity. In thicker membranes, made from 1,2-dioleoyl-sn-glycero-3-phosphocholine (C18), observed activities were found to decrease with increasing facial hydrophilicity; with a membrane of intermediate thickness, prepared from 1,2-dipalmitoleoyl-sn-glycero-3-phosphocholine (C16), ion-conducting activity increased and then decreased, with continuous increases in facial hydrophilicity. The possible origins for these variations in activity are briefly discussed.

Quenching quorum-sensing-dependent bacterial infection by an N-acyl homoserine lactonase

Bacterial cells sense their population density through a sophisticated cell-cell communication system and trigger expression of particular genes when the density reaches a threshold. This type of gene regulation, which controls diverse biological functions including virulence, is known as quorum sensing. Quorum-sensing signals, such as acyl-homoserine lactones (AHLs), are the essential components of the communication system. AHLs regulate virulence gene expression in a range of plant and animal (including human) bacterial pathogens. AHL-producing tobacco restored the pathogenicity of an AHL-negative mutant of Erwinia carotovora. Different bacterial species may produce different AHLs, which vary in the length and substitution of the acyl chain but contain the same homoserine lactone moiety. Here we show that the acyl-homoserine lactonase (AHL-lactonase), a new enzyme from Bacillus sp., inactivates AHL activity by hydrolysing the lactone bond of AHLs. Plants expressing AHL-lactonase quenched pathogen quorum-sensing signalling and showed significantly enhanced resistance to E. carotovora infection. Our results highlight a promising potential to use quorum-sensing signals as molecular targets for disease control, thereby broadening current approaches for prevention of bacterial infections.

Molecular umbrella-assisted transport of glutathione across a phospholipid membrane

A di-walled molecular umbrella (1a) has been synthesized by acylation of the terminal amino groups of spermidine with cholic acid, followed by condensation with bis(3-O-[N-1,2,3-benzotriazin-4(3H)-one]yl)-5,5'-dithiobis-2-nitrobenzoate (BDTNB), and displacement with glutathione (gamma-Glu-Cys-Gly, GSH). Replacement of the sterol hydroxyls with sulfate groups, prior to displacement with GSH, afforded a hexasulfate analogue 1b. Both conjugates have been found to enter large unilamellar vesicles (200 nm diameter, extrusion) of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), and to react with entrapped GSH to form oxidized glutathione (GSSG). Evidence for vesicular entry has come from the formation of oxidized glutathione (GSSG) within the interior of the vesicle, the appearance of the thiol form of the umbrella (USH), and the absence of release of GSH into the external aqueous phase. Results that have been obtained from monolayer experiments, together with the fact that the heavily sulfated conjugate is able to cross the phospholipid bilayer, have yielded strong inferential evidence for an "umbrella-like" action of these molecules as they cross the lipid bilayer.

Sanglifehrin A, a novel cyclophilin-binding immunosuppressant, inhibits IL-2-dependent T cell proliferation at the G1 phase of the cell cycle

Sanglifehrin A (SFA) is a novel immunosuppressive natural product that binds to cyclophilin but is structurally distinct from cyclosporin A (CsA). We have investigated the cellular and molecular mechanisms of the action of SFA in T lymphocytes. We show that SFA inhibits T cell proliferation induced by IL-2 with an IC(50) of 200 nM. Distinct from CsA, which also binds to cyclophilin, SFA does not affect calcium-dependent IL-2 production, although SFA enhanced IL-2 gene transcription in the same cells. SFA blocks T cell proliferation induced by IL-2 in G(1) with no appreciable effect on IL-2 receptor expression in a manner similar to that of the immunosuppressant rapamycin. Unlike rapamycin, however, SFA has no effect on the phosphorylation or enzymatic activity of p70(s6k) kinase, distinguishing SFA from rapamycin in their mode of action. SFA inhibits hyperphosphorylation of Rb and the activity of cyclin E-cyclin-dependent kinase 2 on IL-2 signaling. These results suggest that SFA has a novel mode of action in comparison with CsA, FK506, and rapamycin, and that its use as a molecular probe may lead to the discovery of a novel target involved in T cell activation.

Intratumoral IL-18 gene transfer improves therapeutic efficacy of antibody-targeted superantigen in established murine melanoma

Antibody-targeted superantigen C215Fab-SEA is a fusion protein of staphylococcal enterotoxin A (SEA) and the Fab region of the tumor-reactive C215 mAb. It can trigger CTL against C215 antigen-positive tumor cells and induce tumor-suppressive cytokines. However, the antitumor effect of C215Fab-SEA is not satisfactory because of suboptimal production of Th1 cytokines after repeated administration. Interleukin 18 (IL-18) is a novel cytokine with profound effects on Th1 cellular response. In this study, we showed that adenovirus-mediated intratumoral IL-18 gene transfer strongly improved the therapeutic efficacy of C215Fab-SEA in the pre-established C215 antigen-expressing B16 melanoma murine model. More significant tumor inhibition and prolonged survival time were observed in tumor-bearing mice received combined therapy of C215Fab-SEA and Ad IL-18 than those of mice treated with C215Fab-SEA or AdIL-18 alone. Combination therapy augmented NK and CTL activities of tumor-bearing mice more markedly. The production of IL-2 and IFN-gamma also increased more significantly. More potent antitumor effect of combined therapy was observed in IL-10 KO mice with enhanced Th1 response. Our data demonstrated that the antitumor effect of C215Fab-SEA immunotherapy could be potentiated significantly by combination with intratumoral IL-18 gene transfer through more efficient activation of Th1 immune responses.

Hybrid characteristics of oligonucleotides consisting of isonucleoside 2',5'-anhydro-3'-deoxy-3'-(thymin-1-yl)-D-mannitol with different linkage modes

Oligonucleotides consisting of the isonucleoside repeating unit 2',5'-anhydro-3'-deoxy-3'-(thymin-1-yl)-D-mannitol (4) were synthesized with the monomeric unit 4 incorporated into oligonucleotides as 1'-->4' linkage 4a (oligomer I) or 6'-->4' linkage 4b (oligomer II). The hybrid properties of the two oligonucleotides I and II with their complementary strands were investigated by thermal denaturation and CD spectra. Oligonucleotide I (4a) formed a stable duplex with d(A)(14) with a slightly reduced T(m) value of 36.6 degrees C, relative to 38.2 degrees C for the control duplex d(T)(14)/d(A)(14), but oligomer II (4b) failed to hybridize with a DNA complementary single strand. The spectrum of the duplex oligomer I/d(A)(14) showed a positive CD band at 217 nm and a negative CD band at 248 nm attributable to a B-like conformation. Molecular modeling showed that in the case of oligomer I: the C6' hydroxy group of each unit could be located in the groove area when hybridized to the DNA single strand, which might contribute additional hydrogen bonding to the stability of duplex formation.

[Meiosis-like reduction in the culture system for somatic embryogenesis of Arabidopsis thaliana]

The somatic meiosis-like reduction was observed in some cells in the embryogenic calli of Arabidopsis thaliana. One type was somatic chromosome reductional grouping, in which the chromosomes in a cell either separated into two groups, or separated into more than two groups at prophase or metaphase. The chromosomes separated directly, the morphology of the chromosomes did not show any role of the spindle fibers. Chromosome reductional grouping happened more frequently in polyploid cells. The other type was somatic meiossi which was analogous to that existed in the process of gametogenesis, and characterized by the pairing and synapsis of homologues chromosomes. In the embryogenic calli cultured on dedifferentiation medium, about 3% of the observed cells contained haploid number of chromosomes, while the tetrad cells occurred at a frequency of about 4%. The somatic meiosis-like reduction could result in the recombination of chromosomes in the cells generated by these processes. The roles of somatic meiosis-like reduction in the somatic embryogenesis and somaclonal variations were discussed.

[Experimental study of inhibitory effect of kangxian recipe on TGF-beta 1 induced hepatocyte apoptosis]

OBJECTIVE

To study the inhibitory effect of Kangxian Recipe (KXR) on TGF-beta 1 induced hepatocyte apoptosis.

METHODS

The in vitro model of hepatocyte apoptosis was established by cell biologic methods, utilizing the characteristics of TGF-beta 1 to observe the inhibitory effect of KXR on hepatocyte apoptosis.

RESULTS

TGF-beta 1 induced apoptosis of hepatocyte in a dose-dependent manner. The apoptosis rate of 2.2.15 cells was 63% when 500 ng/L TGF-beta 1 was used, while for HepG2 cell, it was merely 44%. After treatment of 20 ng/L KXR, the apoptosis rate of the two kinds of cell lines lowered to 33% and 24% respectively. The inhibition rate of both groups was about 50%.

CONCLUSION

KXR had strong inhibitory effect on hepatocyte apoptosis induced by TGF-beta 1.

Superheating of confined Pb thin films

In this work we report, for the first time, an experimental observation of a superheating phenomenon in metal thin films. By means of cold rolling, Pb thin films of about 20 nm thick were sandwiched by Al layers, and between them semicoherent epitaxial Pb/Al interfaces were formed. In situ x-ray diffraction analysis indicated that the confined Pb thin films could be superheated for at least 6 degrees C. Thermodynamic analysis indicated that such a substantial superheating in the confined two-dimensional thin films may originate from suppression of growth of the molten droplets by the epitaxial Al/Pb/Al confinement, instead of suppression of melt nucleation for the confined particle superheating.

AiiA, an enzyme that inactivates the acylhomoserine lactone quorum-sensing signal and attenuates the virulence of Erwinia carotovora

N-acylhomoserine lactones, known as autoinducers (AIs), are widely conserved signal molecules present in quorum-sensing systems of many gram-negative bacteria. AIs are involved in the regulation of diverse biological functions, including expression of pathogenic genes in the plant pathogens Pseudomonas solanacearum, several Erwinia species, and the human pathogen Pseudomonas aeruginosa. A bacterial isolate, Bacillus sp. 240B1, is capable of enzymatic inactivation of AIs. The gene (aiiA) for AI inactivation from Bacillus sp. 240B1 has been cloned and shown to encode a protein of 250 amino acids. Sequence alignment indicates that AiiA contains a "HXHXDH" zinc-binding motif that is conserved in several groups of metallohydrolases. Site-directed mutagenesis showed that conserved aspartate and most histidine residues are required for AiiA activity. Expression of aiiA in transformed Erwinia carotovora strain SCG1 significantly reduces the release of AI, decreases extracellular pectolytic enzyme activities, and attenuates pathogenicity on potato, eggplant, Chinese cabbage, carrot, celery, cauliflower, and tobacco. Our results indicate that the AI-inactivation approach represents a promising strategy for prevention of diseases in which virulence is regulated by AIs.

[Studies on transgenic oilseed rape (Brassica napus) plants transformed with beta-1,3-glucanase and chitinase genes and its resistance to Sclerotinia sclerotiorium]

By Agrobacterium-mediated method, the cotyledonary petiole of good quality rape variety H165 was transformed with plant expression vector pBLGC which constitutively express beta-1,3-glucanase and chitinase genes. We obtained some Kanamycin(Kan)-resistant regenerational green shoots, with these shoots, PCR identification was conducted. Results showed that 30% green shoots which grew in medium of Kan 15 mg/L and 53% green shoots in Kan 25 mg/L had positive reaction. We also made dot blot analysis with those green shoots, some of them gave positive signal, indicating that the foreign genes had integrated into rape genome. Fungal challenge of these transgenic plants showed that some plants were much more resistant to Sclerotinia sclerotiorium than non-transgenic control plants.

[Studies of transgenic tobacco plants expressing beta-1,3-glucanase and chitinase genes and their potential for fungal resistance]

Plant bivalent expression vector pBLGC for basic tobacco beta-1, 3-glucanase and bean chitinase genes were constructed, and the tobacco tissue was transformed. Transgenic tobacco plants were carried out for analysis by PCR, PCR-Southern blot, Dot blot, Western blot, etc., and the results showed that some transgenic plants gave strong positive signal, it suggested that foreign genes have been integrated into tobacco genome, and expressed correctly. Fungal challenge with Alternaria alternata showed that transgenic plants were much more resistant to this pathogenic fungus.