Bactérias diazotróficas em abacaxizeiros e bananeiras: técnicas de inoculação e monitoramento.

As bacterias diazotroficas tem sido isoladas de varias culturas, alem de leguminosas e gramineas, que tem importancia economica e social; deplantas de tuberculos como a mandioca foram isoladas bacterias do genero Burkholderia, entre outras(Balota, 1994); ja em plantas de batata-doce tem sido detectadas especies de Azospirillum(Hill et al.,1983) e Acetobacter diazophicus(Paula, 1992). Esta ultima especie também tem sido isolada de plantas de cafe(Jimenez-Salgado et al., 1998); na rizosfera de fruteiras tropicais tem sido isoladas especies de Azospirillum(Subba Rao, 1983; Ghai & Thomas, 1989). Especies deste genero e bacterias diazotroficas do tipo Herbaspirillum e Burkholderia foram tambem isoladas de raizes...bitstream/CNPAT-2010/4782/1/Dc-035.pd

Self-Consistent Thermal Accretion Disk Corona Models for Compact Objects: II. Application to Cygnus X-1

We apply our self-consistent accretion disk corona (ADC) model, with two different geometries, to the broad-band X-ray spectrum of the black hole candidate Cygnus X-1. As shown in a companion paper (Dove, Wilms, and Begelman), models where the Comptonizing medium is a slab surrounding the cold accretion disk cannot have a temperature higher than about 120 keV for optical depths greater than 0.2, resulting in spectra that are much softer than the observed 10-30 keV spectrum of Cyg X-1. In addition, the slab geometry models predict a substantial ``soft excess'' at low energies, a feature not observed for Cyg X-1, and Fe K\alpha fluorescence lines that are stronger than observed. Previous Comptonization models in the literature invoke a slab geometry with the optical depth \tau_T \gta 0.3 and the coronal temperature T_c \sim 150 keV, but they are not self-consistent. Therefore, ADC models with a slab geometry are not appropriate for explaining the X-ray spectrum of Cyg X-1. Models with a spherical corona and an exterior disk, however, predict much higher self-consistent coronal temperatures than the slab geometry models. The higher coronal temperatures are due to the lower amount of reprocessing of coronal radiation in the accretion disk, giving rise to a lower Compton cooling rate. Therefore, for the sphere+disk geometry, the predicted spectrum can be hard enough to describe the observed X-ray continuum of Cyg X-1 while predicting Fe fluorescence lines having an equivalent width of \sim 40 eV. Our best-fit parameter values for the sphere+disk geometry are \tau_T \approx 1.5 and T_c \approx 90 keV.Comment: 13 pages, Latex, 10 .eps figures, uses emulateapj.sty. To be published in ApJ, October 1, 1997, Vol. 48

Levantamento da nodulação de leguminosas florestais nativas na região sudeste do Brasil

A survey on nodulation of legume trees was perfomed in (1) Linhares-ES, Reserva Florestal da Companhia Vale do Rio Doce (2) Seropédica-RJ, Estação Florestal de Experimentação Eng°.-Agr°. Mário Xavier and (3) São Paulo, Instituto Florestal de São Paulo. In site (1) and (3) the observations were carried out in the field and with non-inoculated plants in nursery beds, and in place (2) only in nursery beds. The whole root system of young plants or roots attached to old plants were freed of soil, and the nodules assayed individually for nitrogenase activity (C2H2). After the nodule morphology had been observed, the nodules were dried and kept in CaCl2 for Rhizobium isolation. Thirty one out of 43 species of the sub-family Papilionoideae were nodulated, 19 of them reported for the first time. Seven out of 41 species of Caesalpinioideae were nodulated, 6 of them reported for the first time, and 30 out of 35 species of Mimosoideae were nodulated, 11 of them reported for the first time. All the species found with nodules showed nitrogenase activity. Within the new species found with nodules there were 5 genera not reported before: Bowdichia and Poecilanthe (Papilionoideae), Melanoxylon and Moldenhaurea (caesalpinioideae) and Pseudosamanea (Mimosoideae). Among the not nodulating species, 37 had not been reported as such, previously. The nitrogenase activity of individual nodules was variable with species and was in general lower in the species of the sub-family Mimosoideae than the other two sub-families.Foi realizado um levantamento da nodulação de leguminosas florestais na Reserva Florestal da Companhia Vale do Rio Doce, ES, Estação Florestal de Experimentação Eng°.-Agr°. Mário Xavier, Seropédica, RJ e no Instituto Florestal de São Paulo, SP. Após descrição da morfologia dos nódulos, estes foram testados individualmente quanto à atividade da nitrogenase (redução de acetileno), para posterior isolamento de Rhizobium dos nódulos mais ativos. Foram observadas 119 espécies de leguminosas, sendo 43, 41 e 35 das subfamílias Papilionoideae, Caesalpinioideae e Mimosoideae, respectivamente. Das 43 espécies Papilionoideae observadas, 31 apresentaram nódulos, sendo 19 descritos, pela primeira vez, como capazes de nodular. Das 41 espécies Caesalpinioideae, sete apresentaram nódulos, sendo seis em espécies ainda não observadas anteriormente. Das 35 espécies de Mimosoideae, 30 foram observadas com nódulos, sendo onze mencionadas, pela primeira vez, com nódulos. Foram observados também nódulos em cinco novos géneros: Melanoxylon, Moldenhaurea, Bowdichia, Poecilanthe e Pseudosamanea. Trinta e sete das espécies encontradas sem nódulos no tinham sido observadas antes como tal

Coupled Growth and Division of Model Protocell Membranes

The generation of synthetic forms of cellular life requires solutions to the problem of how biological processes such as cyclic growth and division could emerge from purely physical and chemical systems. Small unilamellar fatty acid vesicles grow when fed with fatty acid micelles and can be forced to divide by extrusion, but this artificial division process results in significant loss of protocell contents during each division cycle. Here we describe a simple and efficient pathway for model protocell membrane growth and division. The growth of large multilamellar fatty acid vesicles fed with fatty acid micelles, in a solution where solute permeation across the membranes is slow, results in the transformation of initially spherical vesicles into long thread-like vesicles, a process driven by the transient imbalance between surface area and volume growth. Modest shear forces are then sufficient to cause the thread-like vesicles to divide into multiple daughter vesicles without loss of internal contents. In an environment of gentle shear, protocell growth and division are thus coupled processes. We show that model protocells can proceed through multiple cycles of reproduction. Encapsulated RNA molecules, representing a primitive genome, are distributed to the daughter vesicles. Our observations bring us closer to the laboratory synthesis of a complete protocell consisting of a self-replicating genome and a self-replicating membrane compartment. In addition, the robustness and simplicity of this pathway suggests that similar processes might have occurred under the prebiotic conditions of the early Earth.Exobiology Program (U.S.) (Grant EXB02- 0031-0018)United States. National Aeronautics and Space Administration (Exobiology Program) (Grant EXB02-0031-0018)Howard Hughes Medical Institute (Investigator

Bistability in the actin cortex

Multi-color fluorescence imaging experiments of wave forming Dictyostelium cells have revealed that actin waves separate two domains of the cell cortex that differ in their actin structure and phosphoinositide composition. We propose a bistable model of actin dynamics to account for these experimental observation. The model is based on the simplifying assumption that the actin cytoskeleton is composed of two distinct network types, a dendritic and a bundled network. The two structurally different states that were observed in experiments correspond to the stable fixed points in the bistable regime of this model. Each fixed point is dominated by one of the two network types. The experimentally observed actin waves can be considered as trigger waves that propagate transitions between the two stable fixed points

Cell–Matrix De-Adhesion Dynamics Reflect Contractile Mechanics

Measurement of the mechanical properties of single cells is of increasing interest both from a fundamental cell biological perspective and in the context of disease diagnostics. In this study, we show that tracking cell shape dynamics during trypsin-induced de-adhesion can serve as a simple but extremely useful tool for probing the contractility of adherent cells. When treated with trypsin, both SW13−/− epithelial cells and U373 MG glioma cells exhibit a brief lag period followed by a concerted retraction to a rounded shape. The time–response of the normalized cell area can be fit to a sigmoidal curve with two characteristic time constants that rise and fall when cells are treated with blebbistatin and nocodazole, respectively. These differences can be attributed to actomyosin-based cytoskeletal remodeling, as evidenced by the prominent buildup of stress fibers in nocodazole-treated SW13−/− cells, which are also two-fold stiffer than untreated cells. Similar results observed in U373 MG cells highlights the direct association between cell stiffness and the de-adhesion response. Faster de-adhesion is obtained with higher trypsin concentration, with nocodazole treatment further expediting the process and blebbistatin treatment blunting the response. A simple finite element model confirms that faster contraction is achieved with increased stiffness

An Adhesion-Dependent Switch between Mechanisms That Determine Motile Cell Shape

Keratocytes are fast-moving cells in which adhesion dynamics are tightly coupled to the actin polymerization motor that drives migration, resulting in highly coordinated cell movement. We have found that modifying the adhesive properties of the underlying substrate has a dramatic effect on keratocyte morphology. Cells crawling at intermediate adhesion strengths resembled stereotypical keratocytes, characterized by a broad, fan-shaped lamellipodium, clearly defined leading and trailing edges, and persistent rates of protrusion and retraction. Cells at low adhesion strength were small and round with highly variable protrusion and retraction rates, and cells at high adhesion strength were large and asymmetrical and, strikingly, exhibited traveling waves of protrusion. To elucidate the mechanisms by which adhesion strength determines cell behavior, we examined the organization of adhesions, myosin II, and the actin network in keratocytes migrating on substrates with different adhesion strengths. On the whole, our results are consistent with a quantitative physical model in which keratocyte shape and migratory behavior emerge from the self-organization of actin, adhesions, and myosin, and quantitative changes in either adhesion strength or myosin contraction can switch keratocytes among qualitatively distinct migration regimes