Especificidade hospedeira na simbiose com Rhizobium- Fejão e influência de diferente nutrientes

Four greenhouse experiments were carried out to study host plant specificity in beans (Phaseolus vulgaris L.) and the interference of several nutrients. In these experiments, four commercial bean varieties and several more or less efficient Rhizobium strains were used. The results of the experiments showed that the efficiency of the symbiosis was dependent on both, strains and varieties. Molybdenum was essential for optimal nitrogen fixation. However excess, molybdenum was more detrimental to nitrogen fixation and nodulation than to plant growth. Potash and magnesium seemed to reduce nodulation and nitrogen fixation whereas calcium had a stimulating effect. These elements interferred equally in both varieties. Nitrogenous fertilizer however had inhibiting effects on nodulation which varied with the varieties.Foram feitos quatro experimentos em casa de vegetação com a finalidade de estudar a especificidade hospedeira na simbiose de estirpes de Rhizobium phaseoli com variedades de Phaseolus vulgaris e a influência de vários nutrientes. Com os dados obtidos pudemos concluir que de fato existe um comportamento diferente na fixação de N das estirpes quando em simbiose com diferentes variedades. O molibdênio, que se mostrou indispensável na fixação do N, quando em excesso prejudicou mais o processo da simbiose do que o desenvolvimento das plantas. O K e o Mg foram prejudiciais para a simbiose e fixação do N, enquanto o Ca foi indispensável para um perfeito processamento da simbiose. Não houve diferença entre as variedades em relação à nutrição com estes elementos. O adubo nitrogenado entretanto agiu diferentemente na simbiose das variedades, inibindo a nodulação da variedade Rico 23 e não das outras

On Shape Transformations and Shape Fluctuations of Cellular Compartments and Vesicles

We discuss the shape formation and shape transitions of simple bilayer vesicles in context with their role in biology. In the first part several classes of shape changes of vesicles of one lipid component are described and it is shown that these can be explained in terms of the bending energy concept in particular augmented by the bilayer coupling hypothesis. In the second part shape changes and vesicle fission of vesicles composed of membranes of lipid mixtures are reported. These are explained in terms of coupling between local curvature and phase separation

Dynamic Phase Transitions in Cell Spreading

We monitored isotropic spreading of mouse embryonic fibroblasts on fibronectin-coated substrates. Cell adhesion area versus time was measured via total internal reflection fluorescence microscopy. Spreading proceeds in well-defined phases. We found a power-law area growth with distinct exponents a_i in three sequential phases, which we denote basal (a_1=0.4+-0.2), continous (a_2=1.6+-0.9) and contractile (a_3=0.3+-0.2) spreading. High resolution differential interference contrast microscopy was used to characterize local membrane dynamics at the spreading front. Fourier power spectra of membrane velocity reveal the sudden development of periodic membrane retractions at the transition from continous to contractile spreading. We propose that the classification of cell spreading into phases with distinct functional characteristics and protein activity patterns serves as a paradigm for a general program of a phase classification of cellular phenotype. Biological variability is drastically reduced when only the corresponding phases are used for comparison across species/different cell lines.Comment: 4 pages, 5 figure

Vesicle shape, molecular tilt, and the suppression of necks

Can the presence of molecular-tilt order significantly affect the shapes of lipid bilayer membranes, particularly membrane shapes with narrow necks? Motivated by the propensity for tilt order and the common occurrence of narrow necks in the intermediate stages of biological processes such as endocytosis and vesicle trafficking, we examine how tilt order inhibits the formation of necks in the equilibrium shapes of vesicles. For vesicles with a spherical topology, point defects in the molecular order with a total strength of $+2$ are required. We study axisymmetric shapes and suppose that there is a unit-strength defect at each pole of the vesicle. The model is further simplified by the assumption of tilt isotropy: invariance of the energy with respect to rotations of the molecules about the local membrane normal. This isotropy condition leads to a minimal coupling of tilt order and curvature, giving a high energetic cost to regions with Gaussian curvature and tilt order. Minimizing the elastic free energy with constraints of fixed area and fixed enclosed volume determines the allowed shapes. Using numerical calculations, we find several branches of solutions and identify them with the branches previously known for fluid membranes. We find that tilt order changes the relative energy of the branches, suppressing thin necks by making them costly, leading to elongated prolate vesicles as a generic family of tilt-ordered membrane shapes.Comment: 10 pages, 7 figures, submitted to Phy. Rew.

“Cara inchada” (doença peridentária) em bezerros mantidos em pastos de Panicum maximum

Six, 4 to 5 months old calves affected by periodontal lesions were kept on a Guinea grass (Panicum maximum Jacq.) pasture cleared of weeds for 5 months. Another group of eight of about 1 year old calves and also affected by "cara inchada" were kept grazing on such a clean pasture for 7 months. The experiments were conducted on two farms where the disease has been observed to be present, in the region of Rondonópolis, Mato Grosso. When the animals were reexamined two or three times within 2 to 6 months, it was found that the periodontal lesions had persisted or worsened in almost all of them. A number of 67 cows were introduced onto the clean P. maximum pasture of one of the two forms together with their 3 week old calves. Up until the calves reached the age of 9 months, periodontal lesions had been found in 52.2% of them. It was concluded by these experiments that the alimentary factor responsible for "cara inchada" seems to be present in the P. maximum pastures of farms where the periodontal disease occurs.Um lote de seis bezerros mestiços zebu com 4 a 5 meses de idade e outro de oito bezerros Nelore com aproximadamente 1 ano de idade, todos afetados por lesões peridentárias da "cara inchada", foram mantidos, durante 5 e 7 meses respectivamente, em pastos de capim-colonião (Panicum maximum Jacq.) limpos de outros vegetais de baixo porte, em duas fazendas de ocorrência da doença na região de Rondonópolis, Mato Grosso. Através de dois ou três reexames, após 2 a 6 meses, verificou-se persistência e agravamento das lesões peridentárias em quase todos os animais. Num desses pastos "limpos" também foram introduzidas 67 vacas com bezerros de 3 semanas de idade, posteriormente examinados para verificação da incidência de lesões da "cara inchada" até terem alcançado 9 meses de idade. Observou-se incidência de lesões peridentárias em 52,2% destes bezerros. Concluiu-se que o fator alimentar responsável pela ocorrência da "cara inchada" dos bovinos existe em pastos formados exclusivamente de P. maximum em fazendas positivas para a doença

Efeito da temperatura do solo na simbiose da soja anual

In three greenhouse experiments the effects of high soil temperature on nodulation and nitrogen fixation were studied on four soybean varieties. Daily maximal temperatures above 33°C reduced nodule initiation and nodule efficiency while nodule growth was less affected. Rhizobium strains occurring naturally in the soil seemed more tolerant to excessive soil temperature than selected strains. Soybean varieties and Rhizobium strains varied in their tolerance to excessive soil temperatures.Foram feitos 3 experimentos em casa de vegetação para pesquisar efeitos de temperaturas excessivamente altas do solo na nodulação e fixação de nitrogênio atmosférico através da simbiose Rhizobium japonicum - Glycine max L. Merril. Temperaturas máximas diurnas acima de 33°C prejudicaram a iniciação dos nódulos e sua eficiência, observando-se efeitos menos pronunciados no desenvolvimento dos nódulos uma vez iniciados e na eficácia da simbiose proveniente da nodulação natural. Houve diferenças entre variedades de soja e estirpes de Rhizobium na tolerância à temperatura alta do solo

Tilt Texture Domains on a Membrane and Chirality induced Budding

We study the equilibrium conformations of a lipid domain on a planar fluid membrane where the domain is decorated by a vector field representing the tilt of the stiff fatty acid chains of the lipid molecules, while the surrounding membrane is fluid and structureless. The inclusion of chirality in the bulk of the domain induces a novel budding of the membrane, which preempts the budding induced by a decrease in interfacial tension.Comment: 5 pages, 3 figure

Phase ordering and shape deformation of two-phase membranes

Within a coupled-field Ginzburg-Landau model we study analytically phase separation and accompanying shape deformation on a two-phase elastic membrane in simple geometries such as cylinders, spheres and tori. Using an exact periodic domain wall solution we solve for the shape and phase ordering field, and estimate the degree of deformation of the membrane. The results are pertinent to a preferential phase separation in regions of differing curvature on a variety of vesicles.Comment: 4 pages, submitted to PR