Specific binding of atrial natriuretic factor to renal glomeruli in Doca- and Doca-salt-treated rats correlation with atrial and plasma levels

Since volume expansion and high blood pressure (BP) are known stimuli of atrial natriuretic factor (ANF) release, and since this peptide may be involved in mineralocorticoid escape, we investigated the effects of chronic deoxycorticosterone (DOCA) and DOCA-NaC1 treatment on renal glomerular ANF receptor density and affinity in relation to atrial and plasma ANF levels. An increase in plasma immunoreactive ANF (IR-ANF) was observed both after two and four weeks of treatment. IR-ANF concentrations were elevated in the left atrium only in four-week DOCA treated rats. Administration of the mineralocorticoid alone resulted in a decreased density of glomerular ANF receptors in both time periods investigated. DOCA-NaC1-treated animals presented an increased receptor density during the pre-hypertensive stage (2 weeks) and a reduced density in the later hypertensive period (4 weeks). Receptor affinity in both groups was identical to that in the controls after 2 weeks and was augmented after 4 weeks of treatment. Our data suggest that the down-regulation of renal glomerular ANF receptors during chronic DOCA-NaC1 administration may play a role in the maintenance of high BP in this model of volume-expanded hypertension.     

Identification of Algerian Field-Caught Phlebotomine Sand Fly Vectors by MALDI-TOF MS

Background

Phlebotomine sand flies are known to transmit Leishmania parasites, bacteria and viruses that affect humans and animals in many countries worldwide. Precise sand fly identification is essential to prevent phlebotomine-borne diseases. Over the past two decades, progress in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has emerged as an accurate tool for arthropod identification. The objective of the present study was to investigate the usefulness of MALDI-TOF MS as a tool for identifying field-caught phlebotomine.

Methodology/Principal Findings

Sand flies were captured in four sites in north Algeria. A subset was morphologically and genetically identified. Six species were found in these areas and a total of 28 stored frozen specimens were used for the creation of the reference spectrum database. The relevance of this original method for sand fly identification was validated by two successive blind tests including the morphological identification of 80 new specimens which were stored at -80°C, and 292 unknown specimens, including engorged specimens, which were preserved under different conditions. Intra-species reproducibility and inter-species specificity of the protein profiles were obtained, allowing us to distinguish specimens at the gender level. Querying of the sand fly database using the MS spectra from the blind test groups revealed concordant results between morphological and MALDI-TOF MS identification. However, MS identification results were less efficient for specimens which were engorged or stored in alcohol. Identification of 362 phlebotomine sand flies, captured at four Algerian sites, by MALDI-TOF MS, revealed that the subgenus Larroussius was predominant at all the study sites, except for in M’sila where P. (Phlebotomus) papatasi was the only sand fly species detected.

Conclusion

The present study highlights the application of MALDI-TOF MS for monitoring sand fly fauna captured in the field. The low cost, reliability and rapidity of MALDI-TOF MS analyses opens up new ways in the management of phlebotomine sand fly-borne diseases.     

A Computational Framework for 3D Mechanical Modeling of Plant Morphogenesis with Cellular Resolution

The link between genetic regulation and the definition of form and size during morphogenesis remains largely an open question in both plant and animal biology. This is partially due to the complexity of the process, involving extensive molecular networks, multiple feedbacks between different scales of organization and physical forces operating at multiple levels. Here we present a conceptual and modeling framework aimed at generating an integrated understanding of morphogenesis in plants. This framework is based on the biophysical properties of plant cells, which are under high internal turgor pressure, and are prevented from bursting because of the presence of a rigid cell wall. To control cell growth, the underlying molecular networks must interfere locally with the elastic and/or plastic extensibility of this cell wall. We present a model in the form of a three dimensional (3D) virtual tissue, where growth depends on the local modulation of wall mechanical properties and turgor pressure. The model shows how forces generated by turgor-pressure can act both cell autonomously and non-cell autonomously to drive growth in different directions. We use simulations to explore lateral organ formation at the shoot apical meristem. Although different scenarios lead to similar shape changes, they are not equivalent and lead to different, testable predictions regarding the mechanical and geometrical properties of the growing lateral organs. Using flower development as an example, we further show how a limited number of gene activities can explain the complex shape changes that accompany organ outgrowth.     

In vivo analysis of local wall stiffness at the shoot apical meristem in Arabidopsis using atomic force microscopy

Whereas the morphogenesis of developing organisms is relatively well understood at the molecular level, the contribution of the mechanical properties of the cells to shape changes remains largely unknown, mainly because of the lack of quantified biophysical parameters at cellular or subcellular resolution. Here we designed an atomic force microscopy approach to investigate the elastic modulus of the outer cell wall in living shoot apical meristems (SAMs). SAMs are highly organized structures that contain the plant stem cells, and generate all of the aerial organs of the plant. Building on modeling and experimental data, we designed a protocol that is able to measure very local properties, i.e. within 40-100 nm deep into the wall of living meristematic cells. We identified three levels of complexity at the meristem surface, with significant heterogeneity in stiffness at regional, cellular and even subcellular levels. Strikingly, we found that the outer cell wall was much stiffer at the tip of the meristem (5 ± 2 MPa on average), covering the stem cell pool, than on the flanks of the meristem (1.5 ± 0.7 MPa on average). Altogether, these results demonstrate the existence of a multiscale spatialization of the mechanical properties of the meristem surface, in addition to the previously established molecular and cytological zonation of the SAM, correlating with regional growth rate distribution.     

Contributions of turgor pressure, the contractile ring, and septum assembly to forces in cytokinesis in fission yeast

A paradigm of cytokinesis in animal cells is that the actomyosin contractile ring provides the primary force to divide the cell [1]. In the fission yeast Schizosaccharomyces pombe, cytokinesis also involves a conserved cytokinetic ring, which has been generally assumed to provide the force for cleavage [2-4] (see also [5]). However, in contrast to animal cells, cytokinesis in yeast cells also requires the assembly of a cell wall septum [6], which grows centripetally inward as the ring closes. Fission yeast, like other walled cells, also possess high (MPa) turgor pressure [7-9]. Here, we show that turgor pressure is an important factor in the mechanics of cytokinesis. Decreasing effective turgor pressure leads to an increase in cleavage rate, suggesting that the inward force generated by the division apparatus opposes turgor pressure. The contractile ring, which is predicted to provide only a tiny fraction of the mechanical stress required to overcome turgor, is largely dispensable for ingression; once septation has started, cleavage can continue in the absence of the contractile ring. Scaling arguments and modeling suggest that the large forces for cytokinesis are not produced by the contractile ring but are driven by the assembly of cell wall polymers in the growing septum.     

Cardiovascular adaptations to parabolic flight in rats: a radio-telemetry feasibility study

This experiment was a feasibility study which consisted in investigating arterial blood pressure and heart rate to transient and repeated exposure to microgravity in eight unrestrained rats previously implanted with radio-telemetry transmitter. The aim was to perform such recordings throughout all the phases of a parabola during parabolic flights. This study revealed that it was possible to collect the radio-signal without any interference with electronic or magnetic environment. We observed in microgravity a significant reduction in heart rate (6%) and a significant increase in arterial blood pressure (7%). In conclusion, such a study seems to be feasible during longer exposure to microgravity (space flight) in order to study the cardiovascular adaptation in rat.     

The impact of mechanical compression on cortical microtubules in Arabidopsis: a quantitative pipeline

Exogenous mechanical perturbations on living tissues are commonly used to investigate whether cell effectors can respond to mechanical cues. However, in most of these experiments, the applied mechanical stress and/or the biological response are described only qualitatively. We developed a quantitative pipeline based on microindentation and image analysis to investigate the impact of a controlled and prolonged compression on microtubule behaviour in the Arabidopsis shoot apical meristem, using microtubule fluorescent marker lines. We found that a compressive stress, in the order of magnitude of turgor pressure, induced apparent microtubule bundling. Importantly, that response could be reversed several hours after the release of compression. Next, we tested the contribution of microtubule severing to compression‐induced bundling: microtubule bundling seemed less pronounced in the katanin mutant, in which microtubule severing is dramatically reduced. Conversely, some microtubule bundles could still be observed 16 h after the release of compression in the spiral2 mutant, in which severing rate is instead increased. To quantify the impact of mechanical stress on anisotropy and orientation of microtubule arrays, we used the nematic tensor based FibrilTool ImageJ/Fiji plugin. To assess the degree of apparent bundling of the network, we developed several methods, some of which were borrowed from geostatistics. The final microtubule bundling response could notably be related to tissue growth velocity that was recorded by the indenter during compression. Because both input and output are quantified, this pipeline is an initial step towards correlating more precisely the cytoskeleton response to mechanical stress in living tissues.     

Effect of organic amendment on soil fertility and plant nutrients in a post-fire Mediterranean ecosystem

Backgrounds and aims

In Mediterranean frequently burnt areas, the decrease of soil fertility leads to regressive vegetation dynamics. Organic amendments could help to accelerate post-fire ecosystem resilience, by improving soil properties and plant nutrition. This study was conducted to assess the potential of a composted biosolid to restore an early post-fire shrubland.

Methods

About 50 Mg.ha^?1 of fresh co-composted sewage sludge and green wastes were surface applied 7 months after fire on a silty-clayey soil. We monitored over a 2-year period organic matter and nutrient transfers to soil, nutrient responses of dominant plant species, and ecosystem contamination by potentially toxic trace elements.

Results

Over the experimental survey, compost rapidly and durably improved soil P₂O₅, MgO and K₂O content, and temporarily increased N-(NO₃ ^? + NO₂ ^?) content. Plant nutrition was improved more or less durably depending species. The most positive compost effect was on plant and soil phosphorus content. Plant nutrient storage was not improved 2 years after amendment, suggesting luxury consumption. No contamination by trace elements was detected in soil and plant.

Conclusions

The use of compost after fire could help for rapidly restoring soil fertility and improving plant nutrition. The increase of soil nutrient pools after amendment emphazised the diversity of plant nutritional traits. Eutrophication risk could occur from high compost and soil P₂O₅ content.     

Inter-population variability of leaf morpho-anatomical and terpenoid patterns of Pistacia atlantica Desf. ssp. atlantica growing along an aridity gradient in Algeria

Three Algerian populations of female Pistacia atlantica shrubs were investigated in order to check whether their terpenoid contents and morpho-anatomical parameters may characterize the infraspecific variability. The populations were sampled along a gradient of increasing aridity from the Atlas mountains into the northwestern Central Sahara.As evidenced by Scanning Electron Microscopy, tufted hairs could be found only on seedling leaves from the low aridity site as a population-specific trait preserved also in culture. Under common garden cultivation seedlings of the high aridity site showed a three times higher density of glandular trichomes compared to the low aridity site. Increased aridity resulted also in reduction of leaf sizes while their thickness increased. Palisade parenchyma thickness also increases with aridity, being the best variable that discriminates the three populations of P. atlantica.Analysis of terpenoids from the leaves carried out by GC-MS reveals the presence of 65 compounds. The major compounds identified were spathulenol (23 μg g⁻¹ dw), α-pinene (10 μg g⁻¹ dw), verbenone (7 μg g⁻¹ dw) and β-pinene (6 μg g⁻¹ dw) in leaves from the low aridity site; spathulenol (73 μg g⁻¹ dw), α-pinene (25 μg g⁻¹ dw), β-pinene (18 μg g⁻¹ dw) and γ-amorphene (16 μg g⁻¹ dw) in those from medium aridity and spathulenol (114 μg g⁻¹ dw), α-pinene (49 μg g⁻¹ dw), germacrene D (29 μg g⁻¹ dw) and camphene (23 μg g⁻¹ dw) in leaves from the high aridity site. Terpene concentrations increased with the degree of aridity: the highest mean concentration of monoterpenes (136 μg g⁻¹ dw), sesquiterpenes (290 μg g⁻¹ dw) and total terpenes (427 μg g⁻¹ dw) were observed in the highest arid site and are, respectively, 3-, 5- and 4-fold higher compared to the lower arid site. Spathulenol and α-pinene can be taken as chemical markers of aridity. Drought discriminating compounds in low, but detectable concentrations are δ-cadinene and β-copaene. The functional roles of the terpenoids found in P. atlantica leaves and principles of their biosynthesis are discussed with emphasis on the mechanisms of plant resistance to drought conditions.