Phylogenetic diversity of Bradyrhizobium strains nodulating Calicotome spinosa in the Northeast of Algeria

Fifty-two slow-growing strains were isolated from root nodules of Calicotome spinosa grown in the Northeast of Algeria and grouped in 24 rep-PCR clusters. One representative strain for each profile was further phylogenetically characterized. The nearly complete 16S rRNA gene sequence indicated that all strains were affiliated to Bradyrhizobium. Multi-Locus Sequence Analysis (MLSA) of the atpD, glnII and recA genes and of the 16S-23S rRNA internal transcribed spacer (ITS) showed that these strains formed four divergent clusters: one close to Bradyrhizobium canariense and Bradyrhizobium lupini and three others separate from all the described species, representing three putative new Bradyrhizobium species. A phylogenetic analysis based on the nodC gene sequence affiliated the strains to either of the two symbiovars, genistearum or retamae.     

Application of remote sensing to site characterisation and environmental change analysis of North African coastal lagoons

This article describes the use of satellite imagery for identifying key environmental characteristics within three North African coastal lagoons (Merja Zerga, Morocco; Ghar El Melh, Tunisia and Lake Manzala, Egypt) and for detecting the major environmental changes within these environments. A combination of Landsat MSS, Landsat TM, Landsat ETM+ and ASTER imagery was acquired for the three sites for a period covering the last three decades (1972–2004). Following geometric correction and enhancement, the interpretation of the most recent image acquired for each of the three lagoons provides important insights into their current conditions. For Merja Zerga, these include the distribution of the largest channels which drain extensive inter-tidal mudflats and the two major depositional features associated with sources of freshwater. The distribution of marginal aquatic vegetation is highlighted as is the intensive use of the surrounding landscape for agriculture. Intensive agriculture around Ghar El Melh is also indicated. The influence of the Mejerda River, which was diverted away from the lagoon over 100 years ago, is shown to persist as a residual area of deltaic deposits in shallow water that has been eroded over time. Coastal processes including the direction of the alongshore sediment transport and the influence of engineering work associated with port construction can also be recognised. Within Lake Manzala, vegetated islands divide the lake into a series of sub-basins which can be clearly distinguished. The large influence of human activities within this lake can be identified and include reclamation for agriculture and the conversion of parts of the lake bed for fish farms. The historical images available for the three lagoons provide important insights into decadal scale changes, which have been greatest at Lake Manzala. Since the early 1970s large parts of the lake, in particular in the southwest where the shoreline has migrated northwards, have been reclaimed. Major engineering works, such as the El Salam Canal and road embankments, are shown to have resulted in significant lake change. The distribution of emergent vegetation within the lake has also changed. Classification of images for this lake into open water, vegetation and land enables the quantification of these changes. Between 1973 and 2003, the lake declined in area by approximately 50%. Changes at Merja Zerga over the last three decades include reconfiguration of the marine outlet and the expansion of the internal delta at the end of the Nador Canal. The images of this site clearly demonstrate the intensification of agriculture around the lagoon. The most marked changes evident within the images of Ghar El Melh concern the sand bars that separate the lagoon from the sea. Geomorphological processes operating within the coastal zone have resulted in the straightening of the bars with central sections migrating out towards the sea. Remote sensing is established as a promising application for detecting the quantitative surface cover changes in coastal lagoons and their near landscapes. Guest editors: J. R. Thompson & R. J. Flower Hydro-ecological Monitoring and Modelling of North African Coastal Lagoons     

Sediment distribution and accumulation in lagoons of the Southern Mediterranean Region (the MELMARINA Project) with special reference to environmental change and aquatic ecosystems

Surface sediments and sediment cores were collected from coastal lagoons and lakes located in the Southern Mediterranean Region (SMR) as part of the MELMARINA Project which involved integrated eco-hydrological monitoring and modelling. This study uses surface sediments and sediment cores to infer spatial characteristics and temporal changes at the MELMARINA primary sites, Merja Zerga in Morocco, Ghar El Melh in Tunisia and Lake Manzala in Egypt. In addition, surface sediment sampling was undertaken at Egyptian Lake Bardawil and sediment cores were collected from the Lagune de Nador (Morocco). Sediment distribution patterns are investigated using GIS with georeferenced sample locations to facilitate display and resurvey. Major variations in sedimentary organic matter and, particularly, carbonate content, occur within and between sites. Local landscapes combined with hydrological and biogeochemical processes influence the distributions of sediment bulk components (carbonates, organic material and clastic matter) and molluscan shells and shell debris are an important source of sedimentary carbonate at all three primary sites. Sediment cores were dated using natural (²¹⁰Pb) and artificial (¹³⁷Cs) radionuclides, and sediment accumulation rate changes indicate that sources of sediment supply varied markedly through the twentieth century but have generally diminished after the mid-1960s. Sedimentary siliceous microfossils (diatoms) were generally poorly preserved, but mollusc shell remains were well represented. Sediment chronologies and sediment bulk composition allow discussion of some recent changes in bulk, minerogenic and biogenic sediment accumulation patterns in the SMR lagoons. Sediment accumulation rates also varied between sites and multiple cores from Lake Manzala indicated that rates showed considerable spatial variability. Low-level sediment contamination by fossil fuel combustion particulates and trace metals was demonstrated for Ghar El Melh and Lagune de Nador where Pb and Zn accumulation rates were highest in twentieth century sediment. It is emphasized that sediment quality and quantity have strong influences on lagoon ecosystem function and sedimentation is relevant to hydromorphology and to concepts of ecological quality. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Guest editors: J. R. Thompson & R. J. Flower Hydro-ecological Monitoring and Modelling of North African Coastal Lagoons     

Effects of removal of dietary polyunsaturated fatty acids on plasma extravasation and mechanical allodynia in a trigeminal neuropathic pain model

Background

Catechol-O-methyltransferase (COMT), an enzyme that metabolizes catecholamines, has recently been implicated in the modulation of pain. Specifically, low COMT activity is associated with heightened pain perception and development of musculoskeletal pain in humans as well as increased experimental pain sensitivity in rodents.

Results

We report that the proinflammatory cytokine tumor necrosis factor α (TNFα) downregulates COMT mRNA and protein in astrocytes. Examination of the distal COMT promoter (P2-COMT) reveals a putative binding site for nuclear factor κB (NF-κB), the pivotal regulator of inflammation and the target of TNFα. Cell culture assays and functional deletion analyses of the cloned P2-COMT promoter demonstrate that TNFα inhibits P2-COMT activity in astrocytes by inducing NF-κB complex recruitment to the specific κB binding site.

Conclusion

Collectively, our findings provide the first evidence for NF-κB-mediated inhibition of COMT expression in the central nervous system, suggesting that COMT contributes to the pathogenesis of inflammatory pain states.     

Biochemical and Immunocytological Characterizations of Arabidopsis Pollen Tube Cell Wall

During plant sexual reproduction, pollen germination and tube growth require development under tight spatial and temporal control for the proper delivery of the sperm cells to the ovules. Pollen tubes are fast growing tip-polarized cells able to perceive multiple guiding signals emitted by the female organ. Adhesion of pollen tubes via cell wall molecules may be part of the battery of signals. In order to study these processes, we investigated the cell wall characteristics of in vitro-grown Arabidopsis (Arabidopsis thaliana) pollen tubes using a combination of immunocytochemical and biochemical techniques. Results showed a well-defined localization of cell wall epitopes. Low esterified homogalacturonan epitopes were found mostly in the pollen tube wall back from the tip. Xyloglucan and arabinan from rhamnogalacturonan I epitopes were detected along the entire tube within the two wall layers and the outer wall layer, respectively. In contrast, highly esterified homogalacturonan and arabinogalactan protein epitopes were found associated predominantly with the tip region. Chemical analysis of the pollen tube cell wall revealed an important content of arabinosyl residues (43%) originating mostly from (1→5)-α-l-arabinan, the side chains of rhamnogalacturonan I. Finally, matrix-assisted laser desorption ionization time-of-flight mass spectrometry analysis of endo-glucanase-sensitive xyloglucan showed mass spectra with two dominant oligosaccharides (XLXG/XXLG and XXFG), both being mono O-acetylated, and accounting for over 68% of the total ion signals. These findings demonstrate that the Arabidopsis pollen tube wall has its own characteristics compared with other cell types in the Arabidopsis sporophyte. These structural features are discussed in terms of pollen tube cell wall biosynthesis and growth dynamics.Fertilization of flowering plants requires the delivery of the two sperm cells, carried by a fast growing tip-polarized pollen tube, to the egg cell. In plants with dry stigma and solid style such as Arabidopsis (Arabidopsis thaliana), this process begins with the deposition and specific adhesion of the pollen grains on the stigmatic tissue, subsequent hydration of the pollen grains, and germination of pollen tubes (Palanivelu and Preuss, 2000). Pollen tubes invade the papillae cell wall of the stigma, enter the short style, and grow through the apoplast of the specialized transmitting tract (TT) that is filled with a nutrient-rich extracellular matrix (Kandasamy et al., 1994; Lennon et al., 1998). During this invasive growth, pollen tubes are guided to the ovules via signals that need to pass through the cell wall to reach their membrane-associated or intracellular targets (Lord and Russell, 2002; Kim et al., 2003; Boavida et al., 2005; McCormick and Yang, 2005; Johnson and Lord, 2006). In plant species with wet stigma and hollow style such as lily (Lilium longiflorum), adhesion between the pollen tube wall and the TT epidermis extracellular matrix is important for the growth of the pollen tubes toward the ovules (Mollet et al., 2000, 2007; Park et al., 2000; Chae et al., 2007). In addition to being the interface between the tube cells and the surroundings (female sporophyte or culture medium), the pollen tube wall also controls the cell shape, protects the generative cells, and allows resistance against turgor pressure (Geitmann and Steer, 2006; Geitmann, 2010).Most of our knowledge on cell wall polymers of higher plants comes from investigations on vegetative organs in which cells have diffuse growth. The cell wall is mainly composed of polysaccharides (cellulose, hemicellulose, pectin, and occasionally callose, depending on the tissue) and proteoglycans (e.g. extensin and arabinogalactan proteins [AGPs]) forming a complex network with processing enzymes.Pectins are complex wall macromolecules with uncertain supramolecular organization (Vincken et al., 2003) consisting of homogalacturonan (HG) that can be methylesterified and acetylesterified, rhamnogalacturonan I (RG-I), rhamnogalacturonan II (RG-II), and xylogalacturonan (Carpita and McCann, 2000). HG is a polymer of repeated units of (1→4)-α-d-GalUA that can be cross-linked with calcium upon block-wise action of pectin methylesterases (PMEs) on methylesterified HG (Micheli, 2001). RG-II has the same homopolymer backbone as HG but is substituted with four different oligosaccharides composed of unusual sugars, such as apiose, aceric acid, and 3-deoxy-d-manno-2-octulosonic acid, of unknown function (for review, see Caffall and Mohnen, 2009). RG-I consists of the repeating disaccharide (1→4)-α-d-GalUA-(1→2)-α-l-Rha, with a wide variety of side chains attached to the rhamnosyl residues, ranging from monomers to large oligosaccharides such as (1→4)-β-d-galactan, (1→5)-α-l-arabinan, and/or type I arabinogalactan (Caffall and Mohnen, 2009).Xyloglucan (XyG) is the major hemicellulosic polysaccharide of the primary wall of flowering plants. Classic XyG consists of a (1→4)-β-d-glucan backbone substituted with Xyl, Gal-Xyl, or Fuc-Gal-Xyl motifs, which correspond, according to the one-letter code proposed by Fry et al. (1993), to X, L, and F, respectively, G being the unsubstituted glucosyl residue of the glucan backbone. The main XyG fragments released after endo-glucanase treatment of the cell wall from wild-type Arabidopsis vegetative organs are generally XXXG, XXLG/XLXG, XXFG, and XLFG (Zablackis et al., 1995; Lerouxel et al., 2002; Nguema-Ona et al., 2006; Obel et al., 2009). In addition, O-acetylation of XyG can occur, most generally on the galactosyl residues, but its biological function is unknown (Cavalier et al., 2008). In the primary wall, XyG interacts with cellulose microfibrils via hydrogen bonds and participates in the control of cell expansion (Cosgrove, 1999).AGPs and extensin belong to the Hyp-rich glycoproteins superfamily with very high levels of type II arabinogalactan glycosylation (Nothnagel, 1997; Showalter, 2001). These proteoglycans have been implicated in many aspects of plant development, including cell expansion, cell signaling and communication, embryogenesis, wound response, and pollen tube guidance (Wu et al., 1995; Nothnagel, 1997; Seifert and Roberts, 2007; Driouich and Baskin, 2008).Despite the importance of pollen tubes for the delivery of the sperm cells to the egg, little is known about the underlying molecular mechanisms that regulate the mechanical interaction of pollen tubes with female floral tissues. There are very scarce data concerning the different components of the pollen tube cell wall. Past approaches to characterize the pollen tube cell wall are limited to a few plant genera, including Camellia (Nakamura and Suzuki, 1981), Lilium (Jauh and Lord, 1996; Mollet et al., 2002), Nicotiana (Rae et al.,1985; Li et al., 1995; Ferguson et al., 1998; Qin et al., 2007), Pinus (Derksen et al., 1999), and Zea (Rubinstein et al., 1995), and are mostly based on immunocytochemistry. These studies revealed that, depending on the species, the pollen tube cell wall contains epitopes that are found in the polymers described above, including HGs with varying levels of methylesterification, AGPs, extensin-like proteins, and low amounts of cellulose. Unlike most other plant cells, callose, a (1→3)-β-glucan, is predominant and is deposited in the wall back from the tip. Moreover, it is deposited at regular intervals to form callose plugs that maintain the tube cell in the apical expanding region of the tube and separate the viable from the degenerating region of the tube (for review, see Geitmann and Steer, 2006). Only a few reports have investigated the pollen tube of the model plant Arabidopsis. They have focused either on in vivo-grown or on in vitro-grown pollen tubes using monoclonal antibodies (MAbs) directed against a subset of cell wall epitopes present in HG, XyG, and AGPs (Lennon and Lord, 2000; Freshour et al., 2003; Pereira et al., 2006), but quantitative chemical analyses are lacking. This lack of information is most likely due to the fact that substantial amounts of pollen tube material are needed for chemical analysis, and a reproducible and efficient method for liquid culture of Arabidopsis pollen tubes had not been established until recently (Boavida and McCormick, 2007; Bou Daher et al., 2009).Here, we report the composition and localization of different cell wall polymers of in vitro-grown wild-type Arabidopsis pollen tubes based on biochemical analyses coupled to immunocytochemical investigations both at light and transmission electron microscopy (TEM) levels using recently developed MAbs. Our results show distinct patterns of labeling (tip, whole tube, and shank of the tube) depending on the recognized epitope. The most striking observations are (1) the abundance of (1→5)-α-l-arabinan in the tube wall (greater than 40 mol % of Ara), mostly localized, with LM6 and LM13, in the outer wall layer of the tube and (2) an atypical XyG matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) profile with over 68% of the oligosaccharide fragments being O-acetylated.     

Probing the mechanism of drug/lipid membrane interactions using Biacore

Assay conditions were established to screen a panel of drugs for binding to liposome surfaces using a surface plasmon resonance (SPR) biosensor. Drugs were found to bind negligibly or reversibly or were retained on the liposome surface. Cationic amphiphilic drugs fell into the last class and correlated with drugs that induce phospholipidosis in vivo. To a first approximation, a single-site model yielded apparent binding affinities that adequately described a drug's dose-dependent binding to liposome surfaces. Affinities ranged at least 1000-fold within the drug panel. A liposome's drug-binding capacity and affinity depended on both the lipid headgroup and the drug's structure. Although a drug's charge state generally dominated whether or not it remained bound to the liposome, subtle structural differences between members of certain drug families led to them having widely differing binding affinities. A comparison between the dissociation of drugs from liposome surfaces by Biacore and the lipid retention measurements determined by a parallel artificial membrane permeability assay was drawn. The results from this study demonstrate the potential of using SPR-based assays to characterize drug/liposome-binding interactions.     

The Rho-associated protein kinase p160ROCK is required for centrosome positioning

The p160-Rho-associated coiled-coil-containing protein kinase (ROCK) is identified as a new centrosomal component. Using immunofluorescence with a variety of p160ROCK antibodies, immuno EM, and depletion with RNA interference, p160ROCK is principally bound to the mother centriole (MC) and an intercentriolar linker. Inhibition of p160ROCK provoked centrosome splitting in G1 with the MC, which is normally positioned at the cell center and shows little motion during G1, displaying wide excursions around the cell periphery, similar to its migration toward the midbody during cytokinesis. p160ROCK inhibition late after anaphase in mitosis triggered MC migration to the midbody followed by completion of cell division. Thus, p160ROCK is required for centrosome positioning and centrosome-dependent exit from mitosis.