Host plant resistance in Brachiaria grasses to the spittlebug Zulia colombiana

Twelve forage grass accessions including 11 accessions of Brachiaria Griseb, were evaluated in a glasshouse for host plant resistance to nymphs and tolerance to feeding damage caused by adults of Zulia colombiana (Lallemand) (Homoptera: Cercopidae). Resistance to nymphs was evaluated with a technique that provided uniform environmental conditions and abundant feeding sites. B. brizantha Stapf (cv. Marandú) was the most resistant of the accessions tested based on nymphal mortality, duration of nymphal stadia, and weight of adult females. Andropogon gayanus Kunth, resistant to spittlebug attack in the field, was susceptible under the conditions of this study. While growth habit and rooting characteristics may contribute to field resistance, other resistance factors are present within the genus Brachiaria, particularly in the case of B. brizantha cv. Marandú. The number of insect-days causing severe damage in the most tolerant species (B. dictyoneura Stapf and B. humidicola Schweick) was approximately six times greater than that necessary to cause the same level of damage to the most susceptible species (B. ruziziensis Germain & Evrard and B. decumbens Stapf). No difference was found in regrowth capacity between infested and noninfested plants within accessions. There was a significant positive correlation between number of insect-days causing severe damage (tolerance) and regrowth of infested plants.

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Résumé Brachiaria est une graminée fourragère prometteuse pour les sols tropicaux acides, saturés d'aluminium. Z. colombiana est un Cercopidae très répandu, limitant l'utilisation de Brachiaria en Amérique Latine. La résistance (antibiose et tolérance) à Z. colombiana, de Brachiaria d'origines diverses a été examinée. B. brizantha cv. Marandù s'est révélé le plus résistant d'après la forte mortalité larvaire, la prolongation du développement larvaire, et le poids réduit des femelles adultes de Z. colombiana. Andropogon gayanus, résistant dans la nature, s'est révélé sensible. Ces résultats suggèrent que cette résistance de A. gayanus dans la nature pourrait être due à la structure du végétal et à son mode de croissance. Dans le cas de B. brizantha cv. Marandù, des facteurs supplémentaires de résistance, mis en évidence à partir de différents modes de croissance, ont été éliminés, de façon à identifier les mécanismes de l'antibiose présents chez Brachiaria. Une grande gamme de résistance aux attaques alimentaires a été observée chez Brachiaria. Les plus résistants ont besoin de 6 fois plus de jours d'attaque par Z. colombiana pour provoquer les dégâts observés sur individus sensibles.

     

Compartmental analysis of 45Ca2+ efflux in perfused rat liver: effects of hormonal stimulation.

The kinetics of calcium movements in the isolated perfused rat liver were examined using compartmental analysis of the efflux profiles of 45Ca2+ from 45Ca(2+)-equilibrated livers under a variety of calcium concentrations and hormonal treatments. From the 45Ca2+ efflux profiles, we determined that a three compartment model was appropriate to describe the movements of calcium in the liver on the time scale of the experiments. Hormonal treatment with the alpha-adrenergic agonist, phenylephrine, or the vasoactive peptide, vasopressin, during the efflux period lowered significantly the rate of transfer of Ca2+ between the internal compartments at all of the calcium concentrations employed. Also, phenylephrine treatment leads to increased transfer of Ca2+ into the liver from the perfusate. The temporal characteristics of the phenylephrine and vasopressin sensitive Ca2+ pools were examined by pulsing livers, loaded for variable periods of time with 45Ca2+, with the two hormones during the efflux of 45Ca2+ to measure the kinetics of Ca2+ exchange in the hormone-sensitive pools. Results from these experiments indicate that the rate of unstimulated Ca2+ efflux, k2, for the phenylephrine and vasopressin sensitive Ca2+ pools, modeled as a one compartment system, are the same, 0.074 and 0.078 min-1 for phenylephrine and vasopressin respectively, corresponding to half times for turnover of the pool(s) of 9.3 and 8.9 min, respectively.     

Pentylenetetrazole inhibits glutamate dehydrogenase and aspartate aminotransferase, and stimulates GABA aminotransferase in homogenates from rat cerebral cortex

The mechanism by which pentylenetetrazole provokes convulsions in animals has been investigated by measuring its influence in vitro on the activities of several enzymes of glutamate metabolism in rat brain homogenates. Pentylenetetrazole does not affect the specific activities of glutamine synthetase, glutaminase, or glutamate decarboxylase; it inhibits those of glutamate dehydrogenase and aspartate aminotransferase, and stimulates that of gamma-aminobutyric acid (GABA) aminotransferase. The overall consequence of the action of pentylenetetrazole on the activities of these enzymes should be an increase in the concentration of glutamate and a decrease in that of GABA. This modulation of glutamate and GABA metabolism by pentylenetetrazole could contribute to the triggering of convulsions.     

Increasing the effectiveness of clinical supervision.

Effective use of preceptors in the clinical training and supervision of residents involves four essential steps: careful screening of the preceptor''s practice to ensure it reflects the goals of the residency program and teaching the preceptor about the goals; setting a realistic contract for learning between resident and preceptor; teaching the preceptor to use constructive feedback techniques in the day-to-day supervision of residents; and developing the preceptor''s skills in the reliable and valid evaluation of the resident''s performance. Clinical preceptors must be trained to become effective teachers and evaluators in residency programs.     

Kinetics of carrier-mediated ion transport in two new types of solvent-free lipid bilayers.

In contrast with the usual glyceryl-monooleate/decane (GMO-D) bilayer lipid membranes, new membranes, formed from a mixture of GMO in squalene (GMO-S) or from a mixture of GMO in triolein (GMO-T), seem to be almost solvent free. Our results from voltage-jump relaxation studies, using these "solvent-free" membranes with the homologue carriers, nonactin, monactin, dinactin, trinactin, and tetranactin, are compared with the corresponding ones for GMO-D membranes. With all homologues, solvent-free membranes show an increase of the free carrier translocation rate, ks, by a factor of 2.5, a decrease in the dissociation rate constant of the complex, kDi, by a factor of 1.5 and no significant change in its formation rate constant, kRi. However, the principal effect of the absence of solvent in these membranes is an increase by a factor of approximately 10 of the translocation rate constant for moving the complex across the membrane, kis. This increase varies regularly from a factor of 7-15 with decreasing carrier size, and is always larger for GMO-T than for GMO-S membranes. These solvent-free effects are interpreted in terms of modifications of electrostatic and hydrophobic energy profiles in the membrane.     

Elucidation of the complete Azorhizobium nicotinate catabolism pathway.

A complete pathway for Azorhizobium caulinodans nicotinate catabolism has been determined from mutant phenotype analyses, isolation of metabolic intermediates, and structural studies. Nicotinate serves as a respiratory electron donor to O2 via a membrane-bound hydroxylase and a specific c-type cytochrome oxidase. The resulting oxidized product, 6-hydroxynicotinate, is next reduced to 1,4,5,6-tetrahydro-6-oxonicotinate. Hydrolytic ring breakage follows, with release of pyridine N as ammonium. Decarboxylation then releases the nicotinate C-7 carboxyl group as CO2, and the remaining C skeleton is then oxidized to yield glutarate. Transthioesterification with succinyl coenzyme A (succinyl-CoA) yields glutaryl-CoA, which is then oxidatively decarboxylated to yield crotonyl-CoA. As with general acyl beta oxidation, L-beta-hydroxybutyryl-CoA, acetoacetyl-CoA, and finally two molecules of acetyl-CoA are produced. In sum, nicotinate is catabolized to yield two CO2 molecules, two acetyl-CoA molecules, and ammonium. Nicotinate catabolism stimulates Azorhizobium N2 fixation rates in culture. Nicotinate catabolism mutants still able to liberate pyridine N as ammonium retain this capability, whereas mutants so blocked do not. From, mutant analyses and additional physiological tests, N2 fixation stimulation is indirect. In N-limited culture, nicotinate catabolism augments anabolic N pools and, as a consequence, yields N2-fixing cells with higher dinitrogenase content.     

Nitrosoguanidine-induced attenuated Clostridium perfringens type A mutant in gas gangrene]

A fully virulent classical type A strain of Clostridium perfringens was treated during its logarithmic growth phase with 100 mug/ml of N-méthyl-N'-nitro-N-nitrosoguanidine, the bacteria being exposed to the mutagen for 30 min at 37 degrees C in a phosphate buffer adjusted to pH 6.2; after treatment the suspension was streaked on sheep blood agar plates, and colonies that showed an alteration in the theta-hemolysis pattern were selected for isolation. The virulence of two mutants, thus altered in their theta-hemolysis, was studied. One, designated LNG 5, was still capable of killing most of the inoculated guinea pigs in less than 24 h with all the clinical, macroscopic, and bacteriological signs of gas gangrene; however, histological sections showed that tissue damage was not as marked as with the wild strain. On the contrary, the second mutant, labelled LNG 11, was completely avirulent as far as gas gangrene was concerned; indeed, the injection of fluid cultures containing 1 times 10(8) - 10(9)/ml viable bacteria, was not followed by any clinical, bacteriological, or histological signs of gas gangrene. However, strain LNG 11 did give rise to a firm swelling of the inoculated thigh with a corresponding acute inflammatory response of the connective tissue, although the muscle fiber was unaltered. Eventually, this local reaction was followed by necrosis of the skin accompanied by an acute or subacute inflammation with fibroblastic proliferation. These superficial lesions healed spontaneously. They could not be reproduced with crude filtrate alone or with washed bacilli. Strain LNG 11 was therefore considered to be soletly an attenuated strain since, although avirulent as far as gas gangrene is concerned. it is still capable of producing low levels of toxic material. This appears to be the first time that such a strain of C. perfringens type A has been obtained by nitrosoguanidine treatment.