P. V. M. Da Silva

Response to inoculation and N fertilization for increased yield and biological nitrogen fixation of common bean (Phaseolus vulgaris L.)

Common bean (Phaseolus vulgaris L.) is able to fix 20–60 kg N ha−1 under tropical environments in Brazil, but these amounts are inadequate to meet the N requirement for economically attractive seed yields. When the plant is supplemented with N fertilizer, N2 fixation by Rhizobium can be suppressed even at low rates of N. Using the 15N enriched method, two field experiments were conducted to compare the effect of foliar and soil applications of N-urea on N2 fixation traits and seed yield. All treatments received a similar fertilization including 10 kg N ha−1 at sowing. Increasing rates of N (10, 30 and 50 kg N ha−1) were applied for both methods. Foliar application significantly enhanced nodulation, N2 fixation (acetylene reduction activity) and yield at low N level (10 kg N ha−1). Foliar nitrogen was less suppressive to nodulation, even at higher N levels, than soil N treatments. In the site where established Rhizobium was in low numbers, inoculation contributed substantially to increased N2 fixation traits and yield. Both foliar and soil methods inhibited nodulation at high N rates and did not significantly increase bean yield, when comparing low (10 kg N ha−1) and high (50 kg N ha−1) rates applied after emergence. In both experiments, up to 30 kg N ha−1 of biologically fixed N2 were obtained when low rates of N were applied onto the leaves.

Homology modeling and molecular interaction field studies of α-glucosidases as a guide to structure-based design of novel proposed anti-HIV inhibitors

SummaryFor AIDS therapy, there are currently a number of compounds available for multiple targets already approved by the FDA and in clinic, e.g. protease inhibitors, reverse transcriptase inhibitors (NRTI, NNRTI), fusion inhibitors, CCR4, CCR5 among others. Some pharmaceuticals act against the virus before the entrance of HIV into the host cells. One of these targets is the glucosidase protein. This novel fusion target has been recently explored because the synthesis of viral glycoproteins depends on the activity of enzymes, such as glucosidase and transferase, for the elaboration of the polysaccharides. In this work we have built an homology model of Saccharomyces cerevisiae glucosidase and superimposed all relevant glucosidase-like enzymes in complex with carbohydrates, and calculated as well molecular interaction fields in our S. cerevisiae active site model. Our results suggest that there are two saccharide binding sites which are the most important for the binding of inhibitors with this family of enzymes which supports the possibility of inhibitors containing only two sugar units. Based on these results, we have proposed a novel pseudo-dissacharide which is a potential pharmaceutical for AIDS treatment.

Variability in nitrogen fixation of common bean (Phaseolus vulgaris L.) intercropped with maize

Thirty one selected bean lines were evaluated in the field for ability to support N2 fixation when intercropped with maize which received 0, 30 and 60 kg N ha−1 as ammonium sulphate. The amount of fixed N2 was estimated using the natural variation of 15N and wheat as the standard non-fixing crop. Nitrogen as low as 15 kg N ha−1 at sowing suppressed nodule weight and activity (acetylene reduction activity) but not nodule number, suggesting that the main effect of mineral N was on nodule development and function. 15N data revealed a high potential of the bean genotypes to fix N2, with the most promising ones averaging between 50–60% of seed N coming from fixation. Bean lines CNF-480, Puebla-152, Mexico-309, Negro Argel, CNF-178, Venezuela-350 and WBR22-3, WBR22-50 and WBR22-55 were ranked as good fixers.

Growth and nutrient allocation in Phaseolus vulgaris L. colonized with endomycorrhizae or Rhizobium

Two cultivars of Phaseolus vulgaris L., one responsive to colonization with microsymbionts (Mexico 309) and one less-responsive (Rio Tibagi) were grown in Leonard jars containing sand/vermiculite under greenhouse conditions. Bean plants were either left non-inoculated (controls) or were inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus etunicatum or a strain of Rhizobium leguminosarum bv. phaseoli (UMR-1899). Plants from the Mexico 309 cultivar maintained a higher growth rate, supported proportionately more nodules and mycorrhizae, and assimilated relatively more N or P when colonized by Rhizobium or Glomus, respectively, than did plants of the Rio Tibagi cultivar. Estimated specific nodule activity for Mexico 309 beans was more than twice that of Rio Tibagi, whereas the specific phosphorus uptake rate (SPUR) was 35% greater in the non-inoculated roots of Rio Tibagi compared to Mexico 309. Colonization by G. etunicatum more than doubled the SPUR for each cultivar compared to control roots. New acid phosphatase isozymes appeared in VAM-colonized roots of both cultivars compared to controls. Acid and alkaline phosphatase activities were significantly higher in G. etunicatum-colonized Mexico 309 roots, but not in Rio Tibagi mycorrhizae, compared to uninfected roots. Polyphosphate hydrolase activity was elevated in mycorrhizae of both cultivars compared to control roots. These results indicate that the dependence of a host on a specific endophyte increases when there are limitations to the supply of a nutrient that the endophyte can provide. The greater the increase in absorption or utilization capacity following colonization by the microsymbiont, the greater the dependence by the host. More importantly, identification of enzymatic activities that influence these plant-microbe associations opens the possibility that the specific genes that code for these enzymes could be targeted for future manipulation.

A mobile data acquisition system

A mobile data aquisition (MobiDAQ) was developed for the ATLAS central hadronic calorimeter (TileCal). MobiDAQ has been designed in order to test the functionalities of the TileCal front-end electronics and to acquire calibration data before the final back-end electronics were built and tested. MobiDAQ was also used to record the first cosmic ray events acquired by an ATLAS subdetector in the underground experimental area.

Hydrogen uptake by Azolla-Anabaena

SummaryExperiments under laboratory conditions were carried out with the objective of studying hydrogen uptake in the Azolla-Anabaena system. Tritium was used as tracer and plants were incubated under different atmospheric composition: a) Air+3H2; b) Air+3H2+CO; c) Air+3H2+CO, d) Argon+3H2+CO2+CO and in presence and absence of light, to study hydrogen uptake via hydrogenase and nitrogenase activity.Azolla-Anabaena showed greater hydrogen uptake under argon atmosphere than under air. Carbon monoxide decrease hydrogen uptake as well as nitrogenase activity. Under dark conditions, nitrogenase activity was smaller under argon than air atmosphere. Carbon monoxide decreased hydrogen uptake. H2-uptake was not affected by light, as it occurs under dark conditions. There are evidences of recycling of the hydrogen evolved through nitrogenase.

Principal curves for identifying outsiders in experimental tests with calorimeters

Principal curves are used for particle discrimination. They are developed for application in calibration tests of the hadronic calorimeter (Tilecal) of the ATLAS detector. Defining principal curves for electrons, pions and muons, a discrimination efficiency better than 92.4% can be achieved, even when high particle contamination is observed in the experimental data sets.

A neural mapping for improving the performance of a high-energy calorimeter

For a scintillating calorimeter, which is being designed to perform energy measurements in a next-generation high-energy collider experiment, a neural mapping is established to improve the overall detector performance. Training a neural network with energy vectors formed by the energy deposited on each cell of this granular detector, the original energy scale of the experimental particle beam is reconstructed and the linearity is significantly improved. In practice, the neural mapping corrects the nonlinearities that arise from the calorimeter design, and it may replace classical methods that use energy dependent multiparameter functions.