Nitrogenase activity and vegetative regrowth of alfalfa grown alone and in mixture with grass after successive harvests

Foi conduzido um experimento de campo com o propósito de determinar o comportamento da atividade da nitrogenase e da massa nodular da alfafa (Medicago sativa L.) e a interação do efeito das gramíneas sobre a taxa de fixação de nitrogênio da leguminosa durante vários ciclos sucessivos de corte, quando ambos crescem em associação. Os resultados demonstraram que a atividade da nitogenase da alfafa não é afetada significativamente quando cultivada em associação com capim-timóteo (Phleum pratense L.) ou capim-bromo (Bromus inermis Leyss.). Foi concluído que a associação de alfafa com capim-timóteo ou capim-bromo não tem efeito sobre a fixação de N2 (redução do acetileno). O declínio inicial da atividade da nitrogenase em dois dias após o corte e a veloz recuperação da atividade nodular depois do corte associada com a manutenção dos nódulos sugere que as plantas de alfafa têm um mecanismo de adaptação ao estresse da remoção da parte aérea. Isto pode explicar por que a capacidade de fixação biológica de N2 pela alfafa é temporariamente enfraquecida com uma recuperação rápida, em comparação com outras leguminosas forrageiras.A field experiment was conducted with the purpose of establish the behavior of the nitrogenase activity and nodule mass of alfalfa plants and the effect that some grass species may have on the rate of legume N2-fixation during many successive harvest cycles, when both grown in mixed stands. The results have shown that nitrogenase activity of alfalfa (Medicago sativa L.) is not significantly affected when grown in association with timothy (Phleum pratense L.) or bromegrass (Bromus inermis Leyss.). It was concluded that mixed cultures of alfalfa with timothy or bromegrass have no effect on alfalfa N2-fixation (acetylene reduction). The initial decline in nitrogenase activity within two days of harvest, and subsequent fast recovery of nodule activity after harvest associated with the maintenance of the nodule weight of alfalfa suggest that the alfalfa plants have an adaptive mechanism to the stress of shoot removal. This may explain why the capacity of N2-fixation by alfalfa is only temporarily impaired with fast recovery rate in comparison to other forage legumes

Analyticity of The Ground State Energy For Massless Nelson Models

We show that the ground state energy of the translationally invariant Nelson model, describing a particle coupled to a relativistic field of massless bosons, is an analytic function of the coupling constant and the total momentum. We derive an explicit expression for the ground state energy which is used to determine the effective mass.Comment: 33 pages, 1 figure, added a section on the calculation of the effective mas

Multispecies virial expansions

We study the virial expansion of mixtures of countably many different types of particles. The main tool is the Lagrange–Good inversion formula, which has other applications such as counting coloured trees or studying probability generating functions in multi-type branching processes. We prove that the virial expansion converges absolutely in a domain of small densities. In addition, we establish that the virial coefficients can be expressed in terms of two-connected graphs

On the distribution of the Wigner time delay in one-dimensional disordered systems

We consider the scattering by a one-dimensional random potential and derive the probability distribution of the corresponding Wigner time delay. It is shown that the limiting distribution is the same for two different models and coincides with the one predicted by random matrix theory. It is also shown that the corresponding stochastic process is given by an exponential functional of the potential.Comment: 11 pages, four references adde

Resonant Inelastic X-Ray Scattering from Valence Excitations in Insulating Copper-Oxides

We report resonant inelastic x-ray measurements of insulating La$_2$CuO$_4$ and Sr$_2$CuO$_2$Cl$_2$ taken with the incident energy tuned near the Cu K absorption edge. We show that the spectra are well described in a shakeup picture in 3rd order perturbation theory which exhibits both incoming and outgoing resonances, and demonstrate how to extract a spectral function from the raw data. We conclude by showing {\bf q}-dependent measurements of the charge transfer gap.Comment: minor notational changes, discussion of anderson impurity model fixed, references added; accepted by PR

Universality of the Wigner time delay distribution for one-dimensional random potentials

We show that the distribution of the time delay for one-dimensional random potentials is universal in the high energy or weak disorder limit. Our analytical results are in excellent agreement with extensive numerical simulations carried out on samples whose sizes are large compared to the localisation length (localised regime). The case of small samples is also discussed (ballistic regime). We provide a physical argument which explains in a quantitative way the origin of the exponential divergence of the moments. The occurence of a log-normal tail for finite size systems is analysed. Finally, we present exact results in the low energy limit which clearly show a departure from the universal behaviour.Comment: 4 pages, 3 PostScript figure

Avaliação da transferência de nitrogênio da alfafa nodulada para as gramíneas associadas em condições de campo

The contribution of N2 . fixation to the nitrogen nutrition of alfafa (Medicaga sativa L.) and transference of N to associated grasses timothy (Phleum pratense L.) and bromegrass (Bromus inennis Leyss.) when grown in mixture, were estimated using the 15N isotope dilution technique. The percentage of alfafa N derived from atmosphere (% Ndfa) increased throughout the growing seasons ranging from 63 to 83%. The total amount of N2 fixed by alfafa has shown a pattern similar to % Ndfa with slight increases to the absolute amount of N2 fixed by alfalfa in mixed stands. N transfer from alfafa to an associated grass was evident, and contributed 26, 46 and 38% of the total annual N yield of grass and represented an absolute amount of about 5.0, 20.0 and 19.0 kg. ha-1 during the first, second and third year. The results showed that all grass species benefitted from N transfer from alfafa, although the early maturity species with greater competitive ability are slightly more responsive.Um experimento de campo foi conduzido para avaliar a contribuição da fixação biológica de N2 na nutrição nitrogenada da alfafa (Medicago sativa L.) e sobre a transferência de N para as gramíneas Phleum pratense L. e Bromus inermis Leyss., usando a técnica de diluição de isótopos (15N). A percentagem do N em alfafa derivado da atmosfera (% Ndfa) aumentou durante os cortes e variou de 63 a 83%. A quantidade total de N2 fixado apresentou um padrão similar a % Ndfa, com ligeiro incremento da quantidade absoluta de N2 fixado pela alfafa em associação. A transferência de N da alfafa para a gramínea foi evidente e contribuiu com 26, 46 e 38% do rendimento total de N das gramíneas, representando uma quantidade de 5,0, 20,0 e 19,0kg N.ha-1 no primeiro, segundo e terceiro ano, respectivamente. Os resultados mostraram que as gramíneas foram beneficiadas com a transferência de N, embora a espécie com maturidade precoce e maior habilidade de competição tenha sido ligeiramente mais responsiva

Growth cone-specific functions of XMAP215 in restricting microtubule dynamics and promoting axonal outgrowth

Background: Microtubule (MT) regulators play essential roles in multiple aspects of neural development. In vitro reconstitution assays have established that the XMAP215/Dis1/TOG family of MT regulators function as MT ‘plus-end-tracking proteins’ (+TIPs) that act as processive polymerases to drive MT growth in all eukaryotes, but few studies have examined their functions in vivo. In this study, we use quantitative analysis of high-resolution live imaging to examine the function of XMAP215 in embryonic Xenopus laevis neurons. Results: Here, we show that XMAP215 is required for persistent axon outgrowth in vivo and ex vivo by preventing actomyosin-mediated axon retraction. Moreover, we discover that the effect of XMAP215 function on MT behavior depends on cell type and context. While partial knockdown leads to slower MT plus-end velocities in most cell types, it results in a surprising increase in MT plus-end velocities selective to growth cones. We investigate this further by using MT speckle microscopy to determine that differences in overall MT translocation are a major contributor of the velocity change within the growth cone. We also find that growth cone MT trajectories in the XMAP215 knockdown (KD) lack the constrained co-linearity that normally results from MT-F-actin interactions. Conclusions: Collectively, our findings reveal unexpected functions for XMAP215 in axon outgrowth and growth cone MT dynamics. Not only does XMAP215 balance actomyosin-mediated axon retraction, but it also affects growth cone MT translocation rates and MT trajectory colinearity, all of which depend on regulated linkages to F-actin. Thus, our analysis suggests that XMAP215 functions as more than a simple MT polymerase, and that in both axon and growth cone, XMAP215 contributes to the coupling between MTs and F-actin. This indicates that the function and regulation of XMAP215 may be significantly more complicated than previously appreciated, and points to the importance of future investigations of XMAP215 function during MT and F-actin interactions

Fermented Camel (Camelus dromedarius) and Bovine Milk Attenuate Azoxymethane-induced Colonic Aberrant Crypt Foci in Fischer 344 Rats

Abstract: Background and Objective: Camel milk is a folk remedy that includes valuable nutrients and bioactive zoochemicals. However, the chemopreventive potential of camel milk against colon carcinogenesis is poorly understood. This study was conducted to investigate the chemopreventive potential of camel (Camelus dromedarius) and bovine milk as well as the impact of fermenting these milks with Lactobacillus acidophilus and Streptococcus thermophilus against early colon carcinogenesis as measured by the reduction of aberrant crypt foci (ACF) in azoxymethane (AOM)-treated Fischer 344 rats. Methodology: Each of 60 weanling male rats was assigned to one of 6 experimental diet groups: Fermented and unfermented camel milk with AOM, fermented and unfermented bovine milk with AOM and positive (PC, AOM only) and negative (NC, saline vehicle only) control groups. The animals were fed the corresponding diets for 3 weeks and then received two subcutaneous injections of AOM or vehicle for 2 consecutive weeks and they were then placed on the corresponding diets for 11 weeks. At termination, all rats were euthanized, colons were harvested and the ACF counts were determined for all tested groups. Immunohistochemical testing was then performed to examine cell proliferation and apoptosis in the camel milk groups. Results: Significant reductions (p<0.05) (48.4-62.1%) in the total ACF count were observed in the colons of the rats fed all milk diets compared with rats fed on PC. However, significant differences were not observed in the total ACF between the camel and bovine milk diets or between the fermented and unfermented milk diets. In addition, significant changes were not observed in the apoptotic index for the camel milk diet compared with the index values for PC and β-catenin was generally localized to the membrane in all examined specimens. Conclusion: By virtue of its bioactive components, camel milk exhibited a chemopreventive potential against early colon carcinogenesis, however, fermentation did not improve its chemopreventive potential