bluuebunny/crossref_metadata_2025_split huggingface dataset:
VirE2, a Type IV secretion substrate, interacts with the VirD4 transfer protein at cell poles of Agrobacterium tumefaciens
Authors: Atmakuri Krishnamohan , Ding Zhiyong , Christie Peter J. 
Published: September 2003

Summary Agrobacterium tumefaciens transfers oncogenic DNA and effector proteins to plant cells during the course of infection. Substrate translocation across the bacterial cell envelope is mediated by a type IV secretion (TFS) system composed of the VirB proteins, as well as VirD4, a member of a large family of inner membrane proteins implicated in the coupling of DNA transfer intermediates to the secretion machine. In this study, we demonstrate with novel cytological screens – a two‐hybrid (C2H) assay and bimolecular fluorescence complementation (BiFC) – and by immunoprecipitation of chemically cross‐linked protein complexes that the VirE2 effector protein interacts directly with the VirD4 coupling protein at cell poles of A. tumefaciens. Analyses of truncation derivatives showed that VirE2 interacts via its C terminus with VirD4, and, further, an NH2‐terminal membrane‐spanning domain of VirD4 is dispensable for complex formation. VirE2 interacts with VirD4 independently of the virB‐encoded transfer machine and T pilus, the putative periplasmic chaperones AcvB and VirJ, and the T‐DNA transfer intermediate. Finally, VirE2 is recruited to polar‐localized VirD4 as a complex with its stabilizing secretion chaperone VirE1, yet the effector–coupling protein interaction is not dependent on chaperone binding. Together, our findings establish for the first time that a protein substrate of a type IV secretion system is recruited to a member of the coupling protein superfamily.
Genome‐based analysis of virulence genes in a non‐biofilm‐forming Staphylococcus epidermidis strain (ATCC 12228)
Authors: Zhang Yue‐Qing , Ren Shuang‐Xi , Li Hua‐Lin , Wang Yong‐Xiang , Fu Gang , Yang Jian , Qin Zhi‐Qiang , Miao You‐Gang , Wang Wen‐Yi , Chen Run‐Sheng , Shen Yan , Chen Zhu , Yuan Zheng‐Hong , Zhao Guo‐Ping , Qu Di , Danchin Antoine , Wen Yu‐Mei 
Published: September 2003

Summary Staphylococcus epidermidis strains are diverse in their pathogenicity; some are invasive and cause serious nosocomial infections, whereas others are non‐pathogenic commensal organisms. To analyse the implications of different virulence factors in Staphylococcus epidermidis infections, the complete genome of Staphylococcus epidermidis strain ATCC 12228, a non‐biofilm forming, non‐infection associated strain used for detection of residual antibiotics in food products, was sequenced. This strain showed low virulence by mouse and rat experimental infections. The genome consists of a single 2499 279 bp chromosome and six plasmids. The chromosomal G + C content is 32.1% and 2419 protein coding sequences (CDS) are predicted, among which 230 are putative novel genes. Compared to the virulence factors in Staphylococcus aureus, aside from δ‐haemolysin and β‐haemolysin, other toxin genes were not found. In contrast, the majority of adhesin genes are intact in ATCC 12228. Most strikingly, the ica operon coding for the enzymes synthesizing interbacterial cellular polysaccharide is missing in ATCC 12228 and rearrangements of adjacent genes are shown. No mec genes, IS256, IS257, were found in ATCC 12228. It is suggested that the absence of the ica operon is a genetic marker in commensal Staphylococcus epidermidis strains which are less likely to become invasive.
Influence of nitrogen source and concentration on nitrogen isotopic discrimination in two barley genotypes (Hordeum vulgareL.)
Authors: KOLB K. J. , EVANS R. D. 
Published: September 2003

ABSTRACTThe occurrence of nitrogen isotope discrimination with absorption and assimilation of nitrate (NO3–) and ammonium (NH4+) was investigated using two genotypes of barley,Hordeum vulgareL. cv. Steptoe and Az12 : Az70, the latter of which lacks the characterized nitrate reductase isozymes. Plants were grown under two situations: a closed system with limited nitrogen or an open system with unlimited nitrogen, to elucidate the conditions and processes that influence discrimination. There was no discrimination observed for Az12 : Az70 when supplied with limited nitrogen. Discrimination was observed for Steptoe seedlings at high external NO3–concentrations, but not with low NO3–when assimilation is probably rapid and complete. The same pattern was observed for Steptoe when NH4+was supplied; indicating that for both nitrogen forms discrimination is dependent upon the presence of the assimilatory enzyme and the external concentration. The implications of this study are that both internal (assimilatory enzyme distribution) and external (source concentration) factors may have a larger impact on tissueδ 15N than the form of nitrogen utilized. This suggests that tissueδ 15N may not always be a reliable indicator of a plant's integrated nitrogen nutrition.
Evaluation of models of leaf water 18O enrichment using measurements of spatial patterns of vein xylem water, leaf water and dry matter in maize leaves
Authors: GAN K. S. , WONG S. C. , YONG J. W. H. , FARQUHAR G. D. 
Published: September 2003

ABSTRACTThe effectiveness of several leaf water models (‘string‐of‐lakes’, ‘desert river’ and the Farquhar–Gan model) are evaluated in predicting the enrichment of leaf water along a maize leaf at different humidities. Progressive enrichment of both vein xylem water and leaf water was observed along the blade. At the tip, the maximum observed enrichment for the vein water was 17.6‰ at 50% relative humidity (RH) whereas that for the leaf water was 50‰ at 34% RH and 19‰ at 75% RH. The observed leaf water maximum was a fraction (0.5–0.6) of the theoretically possible maximum. The ‘string‐of‐lakes’ and ‘desert river’ models predict well the variation of leaf water enrichment pattern with humidity but overestimate the average enrichment of bulk leaf water. However, the Farquhar–Gan model gives good prediction for these two aspects of leaf water enrichment. Using the anatomical dimensions of vein xylem overestimates the effective longitudinal Péclet number (Pl). Possible explanations for this discrepancy between the effective and the xylem‐based estimate of Pl are discussed. The need to characterize the heterogeneity of transpiration rate over the leaf surface in studies of leaf water enrichment is emphasized. The possibility that past atmospheric humidity can be predicted from the slope of the Δ18O spatial variation of leaf macrofossils found in middens is proposed.
Molecular identification of proline‐rich protein genes induced during root formation in grape (Vitis vinifera L.) stem cuttings
Authors: THOMAS P. , LEE M. M. , SCHIEFELBEIN J. 
Published: September 2003

ABSTRACTVegetative reproduction relies on the initiation of new plant organs in response to environmental changes. The rapid formation of roots, and ultimately whole plants, from stem cuttings of grape (Vitis vinifera L.) provides a useful system to investigate the physiological and molecular basis of organ initiation during vegetative reproduction. In the present study the differential RNA display technique was employed to identify two genes, VvPRP1 and VvPRP2, that are induced in stem cuttings of grape during rooting. Each of these genes encodes a distinct type of proline‐rich protein that is related to different groups of putative cell wall proteins, and their expression is rapidly induced in stem segments within 6 h after severing. Further, each gene's transcript becomes most concentrated in the basal portion of the stem segment in the region of new root formation. Induction of these genes is not significantly enhanced by indole‐3‐acetic acid (IAA) treatment, and the expression of the VvPRP1 gene, but not the VvPRP2 gene, is wound‐inducible. These results suggest that these VvPRP genes play an important role in the initiation of new roots on grape stem cuttings, perhaps by altering the cell wall mechanical properties to enable root emergence.
Electrophysiological localization of blue light sensory sites in etiolated dicotyledon seedlings
Authors: BABOURINA O. K. , NEWMAN I. A. , SHABALA S. N. 
Published: September 2003

ABSTRACTChanges induced by blue light (BL) in ion fluxes and pH in etiolated seedlings of dicotyledons (Cucumis sativus L., Phaseolus lunatus L., Pisum sativum L.) were studied using a non‐invasive ion‐selective microelectrode technique (MIFE). BL induced significant Ca2+ uptake within the first 5 min after onset in upper parts of the whole cucumber seedling. To locate the sites of the BL perception, studies on excised segments were performed. The data obtained demonstrated that the observed Ca2+ uptake is associated with the very top of the hypocotyl hook of cucumber and butter bean, and with the whole epicotyl of pea, although the response was stronger for the upper parts of the epicotyl. Addition of Gd3+ and La3+ into the bathing solution completely prevented Ca2+ influx, implicating the involvement of Ca2+ channels in the regulation of Ca2+ transport during BL exposure. BL‐induced changes in H+ and Ca2+ fluxes were not likely to be linked to the one mechanism, as they were separated spatially and pharmacologically.
Transcriptomic analysis of metabolic changes by phosphorus stress in rice plant roots
Authors: WASAKI J. , YONETANI R. , KURODA S. , SHINANO T. , YAZAKI J. , FUJII F. , SHIMBO K. , YAMAMOTO K. , SAKATA K. , SASAKI T. , KISHIMOTO N. , KIKUCHI S. , YAMAGISHI M. , OSAKI M. 
Published: September 2003

ABSTRACTAs most soil phosphates exist as insoluble inorganic phosphate and organic phosphates, higher plants have developed several strategies for adaptation to low phosphorus (P). These include the secretion of acid phosphatase and organic acids, induction of the inorganic phosphate (Pi) transporter and the substitution of some enzyme activities as alternative pathways to increase P utilization efficiency. It has been proposed that plants also have a ‘pho regulon’ system, as observed in yeast and Escherichia coli; however, the detail of the regulation system for gene expression on P status is still unclear in plants. To investigate the alteration of gene expression of rice roots grown under P‐deficient conditions, a transcriptomic analysis was conducted using a cDNA microarray on rice. Based on the changes of gene expression under a –P treatment, the up‐regulation of some genes due to P deficiency was confirmed . Some new important metabolic changes are suggested, namely: (1) acceleration of carbon supply for organic acid synthesis through glycolysis; (2) alteration of lipid metabolism; (3) rearrangement of compounds for cell wall; and (4) changes of gene expression related to the response for metallic elements such as Al, Fe and Zn.
Influence of elevated CO2 and nitrogen nutrition on photosynthesis and nitrate photo‐assimilation in maize (Zea mays L.)
Authors: COUSINS A. B. , BLOOM A. J. 
Published: September 2003

ABSTRACTMeasurements of CO2 and O2 gas exchange and chlorophyll a fluorescence were used to test the hypothesis that elevated atmospheric CO2 inhibits nitrate (NO3–) photo‐assimilation in the C4 plant, maize (Zea mays L.). The assimilatory quotient (AQ), the ratio of net CO2 assimilation to net O2 evolution, decreases as NO3– photo‐assimilation increases so that the difference in AQ between the ammonium‐ and nitrate‐fed plants (ΔAQ) provided an in planta estimate of NO3– photo‐assimilation. In fully expanded maize leaves, NO3– photo‐assimilation was detectable only under high light and was not affected by CO2 treatments. Furthermore, CO2 assimilation and O2 evolution were higher under NO3– than ammonia (NH4+) regardless of CO2 levels. In conclusion, NO3– photo‐assimilation in maize primarily occurred at high light when reducing equivalents were presumably not limiting. Nitrate photo‐assimilation enhanced C4 photosynthesis, and in contrast to C3 plants, elevated CO2 did not inhibit foliar NO3– photo‐assimilation.
Reactive oxygen species stimulate homologous recombination in plants
Authors: KOVALCHUK I. , FILKOWSKI J. , SMITH K. , KOVALCHUK O. 
Published: September 2003

ABSTRACTCoping with the continuous production of free radicals is a daily routine of the cell. Despite their toxicity, the reactive oxygen species (ROS) are involved in dual physiological action – signal transduction and immune response. We analysed the influence of oxidative stress‐generating compounds, rose Bengal (RB), paraquat (PQ) and amino‐triazole (ATZ) on the genome stability of Arabidopsis using transgenic recombination‐monitoring plants. Homologous recombination frequencies in plants were increased upon the treatment with RB and PQ but not ATZ. Application of the N‐acetyl‐L‐cysteine (NAC), radicals scavenging compound, decreased the DNA damage caused by RB. Interestingly, the incubation of plants with very low concentration of RB (less than 0.2 µM) led to the subsequent increase in plant tolerance to methyl methane sulfonate (MMS): stronger plants with a lower increase of homologous recombination frequency. In contrast, the incubation of plants with 0.5 µM of RB resulted in the potentiation of the MMS effect: the weaker plants with higher frequency of recombination. The data of the present study suggest the existence of a dual concentration‐dependent role of ROS in plants.
Signal transduction downstream of salicylic and jasmonic acid in herbivory‐induced parasitoid attraction by Arabidopsis is independent of JAR1 and NPR1
Authors: VAN POECKE R. M. P. , DICKE M. 
Published: September 2003

ABSTRACTPlants can defend themselves indirectly against herbivores by emitting a volatile blend upon herbivory that attracts the natural enemies of these herbivores, either predators or parasitoids. Although signal transduction in plants from herbivory to induced volatile production depends on jasmonic acid (JA) and salicylic acid (SA), the pathways downstream of JA and SA are unknown. Use of Arabidopsis provides a unique possibility to study signal transduction by use of signalling mutants, which so far has not been exploited in studies on indirect plant defence. In the present study it was demonstrated that jar1‐1 and npr1‐1 mutants are not affected in caterpillar (Pieris rapae)‐induced attraction of the parasitoid Cotesia rubecula. Both JAR1 and NPR1 (also known as NIM1) are involved in signalling downstream of JA in induced defence against pathogens such as induced systemic resistance (ISR). NPR1 is also involved in signalling downstream of SA in defence against pathogens such as systemic acquired resistance (SAR). These results demonstrate that signalling downstream of JA and SA differs between induced indirect defence against herbivores and defence against pathogens such as SAR and ISR. Furthermore, it was demonstrated that herbivore‐derived elicitors are involved in induced attraction of the parasitoid Cotesia rubecula
Regulation of nitrogen uptake by Fagus sylvatica on a whole plant level – interactions between cytokinins and soluble N compounds
Authors: COLLIER M. D. , FOTELLI M. N. , NAHM M. , KOPRIVA S. , RENNENBERG H. , HANKE D. E. , GEßLER A. 
Published: September 2003

ABSTRACTPedospheric nitrate uptake is a strongly regulated process adapted to the N demand of the whole plant. Pre‐requisites for an integrating regulatory system are signal substances communicating the N demand of the shoot to the roots. In the current study it was shown that an additional atmospheric N source results in activation of cytokinins in the shoot as indicated by an increase in the trans‐hydroxylation ratio, and in increased shoot‐to‐root transport of cytokinins in the phloem. Phloem mobility and basipetal transport of cytokinins were also demonstrated by feeding zeatin riboside into the phloem. The resulting enrichment of cytokinins in the roots caused an increased expression of a high‐affinity nitrate transporter, the enrichment of amino compounds (Glu, Val, Phe, Lys) in the fine roots and a significant decrease in nitrate net uptake. Significant enrichment in amino acids – accompanied by decreased nitrate net uptake but not by increased expression of the high‐affinity nitrate transporter – was also observed when Gln the major long‐distance transport form of nitrogen in beech was fed into the phloem. These results provide experimental evidence that, in addition to amino compounds, cytokinins that are known to cycle within the plant are also communicating changes in N metabolism from the shoot to the roots. Apparently increased cytokinin contents in the root can transiently increase nitrate uptake, but this up‐regulation may be overridden by transcriptional and post‐transcriptional down‐regulation mediated by amino compounds.
Scaling phloem transport: water potential equilibrium and osmoregulatory flow
Authors: THOMPSON M. V. , HOLBROOK N. M. 
Published: September 2003

ABSTRACTIn this work, the common assumption that phloem sap is in water potential equilibrium with the surrounding apoplast was examined. With a dimensionless model of phloem translocation that scales with just two dimensionless parameters (R̂and F̂), a ‘map’ of phloem behaviour as a function of these parameters was produced, which shows that the water potential equilibrium assumption (R̂F̂ >> 1) is valid for essentially all realistic values of the relevant scales. When in water potential equilibrium, a further parameter reduction is possible that limits model dependence to a single parameter (F̂), which describes the ratio of the solution's osmotic strength to its axial pressure drop. Due to the locally autonomous nature of individual sieve element/companion cell complexes, it is argued that long‐distance integrative control is most efficient when F̂ is large (that is, when the pressure drop is relatively small), permitting the sieve tube to regulate solute loading in response to global changes in turgor. This mode of transport has been called ‘osmoregulatory flow.’ Limitations on the pressure drop within the transport phloem could require that sieve tubes be shorter than the long axis of the plant, and thus arranged in series and hydraulically isolated from one another.
Regulation of T Helper Cell Differentiation In Vivo by GP43 from Paracoccidioides brasiliensis Provided by Different Antigen‐Presenting Cells
Authors: Ferreira K. S. , Lopes J. D. , Almeida S. R. 
Published: September 2003

AbstractParacoccidioidomycosis, endemic in Latin America, is a progressive systemic mycosis caused by Paracoccidioides brasiliensis. The infection can evolve into different clinical forms that are associated with various degrees of suppressed cell‐mediated immunity. Assuming that the effector immune response is a consequence of the preferential activation of either Th1 or Th2 subsets, in the present work we evaluated whether the nature of antigen‐presenting cells (APCs) can influence the Th1/Th2 balance in vivo. It was observed that the injection of mature dendritic cells (DCs), macrophages and B cells primed the mice and induced a proliferation of T cells in vitro. It was seen that DCs from resistant mice stimulated predominantly interleukin‐2 (IL‐2) and interferon‐γ (IFN‐γ), whereas macrophages activated IL‐10, IL‐4 and IFN‐γ‐secreting T cells and B cells IL‐4 and IL‐10 only. Results presented here clearly demonstrate that DC drives the development of cells secreting Th1‐derived cytokines, whereas B cells induce the differentiation of a Th2 phenotype in vivo.
Generation of Antibodies to the Urokinase Receptor (uPAR) by DNA Immunization of uPAR Knockout Mice: Membrane‐Bound uPAR is Not Required for an Antibody Response
Authors: Pass J. , Gårdsvoll H. , Lund L. R. , Danø K. , Høyer‐Hansen G. 
Published: September 2003

AbstractThe urokinase receptor (uPAR) is a glycolipid‐anchored cell surface glycoprotein that plays a central role in extracellular proteolysis during tissue remodeling processes including cancer invasion. Furthermore, uPAR is found on the surface of both dendritic cells (DCs) and T cells, and has been proposed to play a role in DC‐induced T‐cell activation and, therefore, in the induction of an immune response. In order to investigate the possibility of using DNA immunization for the generation of poly‐ and monoclonal antibodies to uPAR, we injected wild‐type mice and mice deficient in uPAR (uPAR knockouts) intramuscularly with plasmid DNA encoding a carboxy‐terminal truncated soluble form of the human uPAR. Multiple injections of 100 µg of DNA resulted in a strong and specific antibody response in all mice irrespective of genotype. Antisera with a maximum titre of 32,000 were obtained, comparable with that obtained after immunization with recombinant uPAR. The subclass distribution of uPAR‐specific antibodies in the sera demonstrated the induction of a mixed TH1/TH2 response, irrespective of the genotype of the mice. Our results demonstrate the possibility of generating high titre antibodies to uPAR by DNA immunization of wild‐type as well as uPAR knockout mice, and that cell surface uPAR is not indispensable for the generation of a humoral immune response.
The Stimulus‐Dependent Release of Eosinophil Cationic Protein and Eosinophil Protein X Increases in Apoptotic Eosinophils
Authors: Seton K. , Håkansson L. , Karawajczyk M. , Venge P. 
Published: September 2003

AbstractApoptotic cells are regarded as inert bodies that turn off intracellular processes and functional abilities. To study the changes in the ability of eosinophils to release their granule proteins while undergoing apoptosis. Eosinophils were cultured for up to 72 h. Living cells were separated from the apoptotic cells and their release of eosinophil cationic protein (ECP) and eosinophil protein X (EPX) was measured in response to serum‐opsonized sephadex particles and phorbol 12‐myristate 12‐acetate (PMA). Changes in cell structure were examined by electron microscopy, and surface receptor expression of β1‐ and β2‐integrins was investigated by flow cytometry. Stimulus‐dependent release of the granule proteins ECP and EPX was found to increase in apoptotic eosinophils, whereas surface expression of β1‐ and β2‐integrins was downregulated. Ultrastructural examination revealed that the granules of apoptotic eosinophils were translocated to the periphery of the cell, just beneath the plasma membrane. Apoptotic eosinophils are able to release their toxic granule proteins, which is probably because of the rearrangement of the cytoskeleton and spontaneous translocation of granules to the membrane. Our results suggest that apoptotic eosinophils are potentially harmful cells that have retained their ability to react to certain extracellular stimuli. The findings point to unexpected consequences of eosinophil apoptosis.