Induction of DNA polymerase in mouse L cells

Two molecular species of DNA polymerase are found in mouse L cells. This study is concerned with the variation of these two species of enzyme with the rate of cell growth and DNA synthesis. The 3.4 S DNA polymerase, found in both nuclear and cytoplasmic fractions of mouse L cells, remains relatively constant during different stages of the growth curve. The heterogeneous 6 to 8 S DNA polymerase, found only in the cytoplasmic fractions, varies about 5 to 12-fold in correlation with DNA synthesis, as measured by [³H]thymidine incorporation.  

A comparison of the expression patterns of several senescence-associated genes in response to stress and hormone treatment

The expression of several Arabidopsis thaliana senescence-associated genes (SAGs) in attached and/or detached leaves was compared in response to age, dehydration, darkness, abscisic acid, cytokinin, and ethylene treatments. Most of the SAGs responded to most of the treatments in a similar fashion. Detachment in darkness and ethylene were the strongest inducers of both SAGs and visible yellowing. Detachment in light was also a strong inducer of SAGs, but not of visible yellowing. The other treatments varied more in their effects on individual SAGs. Responses were examined in both older and younger leaves, and generally were much stronger in the older ones. Individual SAGs differed from the norms in different ways, however, suggesting that their gene products play a role in overlapping but not identical circumstances. Some SAGs responded quickly to treatments, which may indicate a direct response. Others responded more slowly, which may indicate an indirect response via treatment-induced senescence. Four new SAGs were isolated as part of this work, one of which shows strong similarity to late embryogenesis-abundant (Lea) genes.  

Markers for hypersensitive response and senescence show distinct patterns of expression

Controlled cellular suicide is an important process that can be observed in various organs during plant development. From the generation of proper sexual organs in monoecious plants to the hypersensitive response (HR) that occurs during incompatible pathogen interactions, programmed cell death (PCD) can be readily observed. Although several biochemical and morphological parameters have been described for various types of cell death in plants, the relationships existing between those different types of PCD events remain unclear. In this work, we set out to examine if two early molecular markers of HR cell death (HIN1 and HSR203J) as well as a senescence marker (SAG12) are coordinately induced during these processes. Our result indicates that although there is evidence of some cross-talk between both cell death pathways, spatial and temporal characteristics of activation for these markers during hypersensitive response and senescence are distinct. These observations indicate that these markers are relatively specific for different cell death programs. Interestingly, they also revealed that a senescence-like process seems to be triggered at the periphery of the HR necrotic lesion. This suggests that cells committed to die during the HR might release a signal able to induce senescence in the neighboring cells. This phenomenon could correspond to the establishment of a second barrier against pathogens. Lastly, we used those cell death markers to better characterize cell death induced by copper and we showed that this abiotic induced cell death presents similarities with HR cell death.  

Allocation of extracellular enzymatic activity in relation to litter composition, N deposition, and mass loss

Decomposition of plant material is a complex process that requiresinteraction among a diversity of microorganisms whose presence and activity issubject to regulation by a wide range of environmental factors. Analysis ofextracellular enzyme activity (EEA) provides a way to relate the functionalorganization of microdecomposer communities to environmental variables. In thisstudy, we examined EEA in relation to litter composition and nitrogendeposition. Mesh bags containing senescent leaves of Quercusborealis (red oak), Acer rubrum (red maple) andCornus florida (flowering dogwood) were placed on forestfloor plots in southeastern New York. One-third of the plots were sprayedmonthly with distilled water. The other plots were sprayed monthly withNH₄NO₃ solution at dose rates equivalent to 2 or 8 g N m^–2 y^–1. Mass loss, litter composition, fungal mass, and the activities ofeight enzymes were measured on 13 dates for each litter type. Dogwood wasfollowed for one year, maple for two, oak for three. For each litter type andtreatment, enzymatic turnover activities were calculated from regressions of LN(%mass remaining) vs. cumulative activity. The decomposition of dogwood litterwas more efficient than that of maple and oak. Maple litter had the lowestfungal mass and required the most enzymatic work to decompose, even though itsmass loss rate was twice that of oak. Across litter types, N amendment reducedapparent enzymatic efficiencies and shifted EEA away from N acquisition andtoward P acquisition, and away from polyphenol oxidation and towardpolysaccharide hydrolysis. The effect of these shifts on decomposition ratevaried with litter composition: dogwood was stimulated, oak was inhibited andmaple showed mixed effects. The results show that relatively small shifts intheactivity of one or two critical enzymes can significantly alter decompositionrates.  

Production of transgenic soybean lines expressing the bean pod mottle virus coat protein precursor gene

Soybean (Glycine max. Merrill. cv. Fayette) cotyledonary nodes were transformed with bean pod mottle virus (BPMV) coat protein precursor (CP-P) gene via Agrobacterium-mediated transformation. The transformation rate was low, and only five primary transformants derived from five different cotyledons were obtained from 400 original cotyledons. Southern blot hybridization verified the integration of the BPMV CP-P gene. Inheritance and expression of this gene in R₁ plants were also demonstrated. About 30% of R₂ plants derived from one transgenic line showed complete resistance to BPMV infection, as assessed by symptomatology and ELISA, suggesting that homozygous, but not hemizygous, plants exhibit the resistant phenotype.Abbreviations BAP 6-benzyladenine phosphate - BPMV bean pod mottle virus - CP-P coat protein-precursor - CTAB hexadecyltrimethylammonium bromide - DAS-ELISA double antibody sandwich-enzyme-linked immunosorbent assay - IBA indole-butyric acid - kbp kilobase pairs - MES 2-(N-Morpholino)ethanesulfonic acid - NOS nopaline synthase - NPTII neomycin phosphotransferase II - NTP nucleoside triphosphate - PBS phosphate-buffered saline - PCR polymerase chain reaction - PVP polyvinyl pyrrolidone - VPg viral genome-linked protein  

CXCR4–SDF-1 Signalling, Locomotion, Chemotaxis and Adhesion

Chemokines, small pro-inflammatory chemoattractant cytokines, that bind to specific G-protein-coupled seven-span transmembrane receptors present on plasma membranes of target cells are the major regulators of cell trafficking. In addition some chemokines have been reported to modulate cell survival and growth. Moreover, compelling evidence is accumulating that cancer cells may employ several mechanisms involving chemokine-chemokine receptor axes during their metastasis that also regulate the trafficking of normal cells. Of all the chemokines, stromal-derived factor-1 (SDF-1), an alpha-chemokine that binds to G-protein-coupled CXCR4, plays an important and unique role in the regulation of stem/progenitor cell trafficking. First, SDF-1 regulates the trafficking of CXCR4+ haemato/lymphopoietic cells, their homing/retention in major haemato/lymphopoietic organs and accumulation of CXCR4+ immune cells in tissues affected by inflammation. Second, CXCR4 plays an essential role in the trafficking of other tissue/organ specific stem/progenitor cells expressing CXCR4 on their surface, e.g., during embryo/organogenesis and tissue/organ regeneration. Third, since CXCR4 is expressed on several tumour cells, these CXCR4 positive tumour cells may metastasize to the organs that secrete/express SDF-1 (e.g., bones, lymph nodes, lung and liver). SDF-1 exerts pleiotropic effects regulating processes essential to tumour metastasis such as locomotion of malignant cells, their chemoattraction and adhesion, as well as plays an important role in tumour vascularization. This implies that new therapeutic strategies aimed at blocking the SDF-1-CXCR4 axis could have important applications in the clinic by modulating the trafficking of haemato/lymphopoietic cells and inhibiting the metastatic behaviour of tumour cells as well. In this review, we focus on a role of the SDF-1-CXCR4 axis in regulating the metastatic behaviour of tumour cells and discuss the molecular mechanisms that are essential to this process.  

Variation in the Structure and Response to Flooding of Root Aerenchyma in some Wetland Plants

The structure and response to flooding of root cortical aerenchyma(air space tissue) in a variety of wetland (flood-tolerant)species was investigated and compared with some flood-intolerantspecies. In some species aerenchyma consisted of enlarged schizogenousintercellular spaces and in others aerenchyma formation involvedlysigeny. Two types of lysigenous aerenchyma were distinguished.In the first the diaphragms between lacunae were arranged radiallyand consisted of both collapsed and intact cells. In the secondtype, which was confined to the Cyperaceae, the radial diaphragmscontained intact cells, and stretched between them were tangentially-arrangeddiaphragms of collapsed cells. Flooding in sand culture generally increased root porosity (airspace content) although there were exceptions. The flood-intolerantspecies Senecio jacobaea produced aerenchyma but did not survivelong-term flooding. Among the flood-tolerant species, Filipendulaulmaria did not produce extensive aerenchyma even when flooded.Eriophorum angustifolium and E. vaginatum produced extensiveaerenchyma under drained conditions which was not increasedby flooding. In Nardus stricta root porosity was increased bylow nutrient levels as well as by flooding. Aerenchyma, root cortex, wetland plants, waterlogging, flooding-tolerance, Ammophila arenaria, Brachypodium sylvalicum, Caltha palustris, Carex curia, Eriophorum vaginatum, Filipendula ulmaria, Glyceria maxima, Hieracium pilosella, Juncus effusus, Myosotis scorpioides, Nardus stricta, Narthecium ossifragum, Phalaris arundinacea, Senecio jacobaea, Trichophorum cespitosum