Showing papers by "University of Buenos Aires published in 1989"
TL;DR: Results supported the overall hypothesis that grasses and shrubs in the Patagonian steppe use mainly different resources and led to questions about the role of nutrient recirculation, leaching, and nitrogen fixation in the steppe.
Abstract: Experiments were conducted in the Patagonian steppe in southern South America to test the following hypotheses: (a) grasses take up most of the water from the upper layers of the soil and utilize frequent and short-duration pulses of water availability; (b) shrubs, on the contrary, take up most of the water from the lower layers of the soil and utilize infrequent and long-duration pulses of water availability. Grasses and shrubs were removed selectively and the performance of plants and the availability of soil resources were monitored. Results supported the overall hypothesis that grasses and shrubs in the Patagonian steppe use mainly different resources. Removal of shrubs did not alter grass production but removal of grasses resulted in a small increase in shrub production which was mediated by an increase in deep soil water and in shrub leaf water potential. The efficiency of utilization of resources freed by grass removal was approximately 25%. Shrubs used water exclusively from lower soil layers. Grasses took up most of the water from upper layers but they were also capable of absorbing water from deep layers. This pattern of water partitioning along with the lack of response in leaf nitrogen to the removal treatments suggested that shrubs may be at a disadvantage to grasses with respect to nutrient capture and led to questions about the role of nutrient recirculation, leaching, and nitrogen fixation in the steppe.
364 citations
TL;DR: A vast region of upper Paleozoic to Middle Jurassic (300-150 Ma) silicic magmatic rocks that erupted inboard of the Gondwana margin is a possible Phanerozoic analogue to the extensive Middle Proterozoic (1500-1350 Ma) Silicic province that underlies much of the southern mid-continent of North America as mentioned in this paper.
Abstract: A vast region of upper Paleozoic to Middle Jurassic (300-150 Ma) silicic magmatic rocks that erupted inboard of the Gondwana margin is a possible Phanerozoic analogue to the extensive Middle Proterozoic (1500-1350 Ma) silicic magmatic province that underlies much of the southern mid-continent of North America. Like the North American rocks, the Gondwana silicic magmas appear to be melts of crust that formed about 200-300 m.y. earlier. In the North American case, this older crust formed and was accreted to the continent during a major period of crustal formation (1700-1900 Ma), whereas in the Gondwana case, the crust that melted consisted mainly of magmatic are terranes accreted to the continental margin during the Paleozoic. In both cases, basic to intermediate magmatic rocks are extremely rare and magmatism is less abundant in regions that contain older (and previously melted) crust. The similarities between the North American and Gondwana silicic rocks suggest that both suites formed in extensional settings where basaltic magmas, ponded at the base of the preheated crust, caused extensive crustal melting that inhibited upward passage of the basalts. In both cases, silicic volcanism occurred after major assembly of a supercontinent by subduction and accretion processes, and before breakup of the supercontinent. By analogy with the polar wander curves for Gondwana, the granite-rhyolite provinces may have formed during a period of very slow motion of the supercontinents relative to the poles.
354 citations
TL;DR: A significantly positive correlation between grain-yield and harvest index was found, and between these characters and the number of grains m −2 and grain number spike −1 were the yield components more affected by plant breeding.
159 citations
TL;DR: Sugar was not necessary for the antimicrobial activity of clove oil, but the concentrated sugar solution provided a good vehicle for obtaining an oil dispersion that is relatively stable for certain practical applications.
Abstract: Essential oil of clove, dispersed (0.4% v/v) in a concentrated sugar solution, had a marked germicidal effect against various bacteria and Candida albicans. Staphylococcus aureus (five strains), Klebsiella pneumoniae, Pseudomonas aeruginosa, Clostridium perfringens, and Escherichia coli inoculated at a level of 10(7) cfu/ml, and C. albicans (inoculum 4.0 x 10(5) cfu/ml) were killed (greater than 99.999%) after 2-7 min in a laboratory broth supplemented with 63% (v/w) of sugar, and containing 0.4% (v/w) of essential oil of clove. Added organic matter (i.e. human or bovine serum) did not impair its antimicrobial activity. Sugar was not necessary for the antimicrobial activity of clove oil, but the concentrated sugar solution provided a good vehicle for obtaining an oil dispersion that is relatively stable for certain practical applications.
150 citations
136 citations
TL;DR: From behavioural evidence, it is concluded that T. infestans perceives the radiant heat of a warm source and can estimate its temperature at a distance, when seeking for food.
112 citations
97 citations
TL;DR: In the Sierras Pampeanas geomorphic province of central Argentina there are regions where exposed crystalline basement has had no sedimentary cover older than Neogene strata, and other areas where upper Paleozoic and Mesozoic strata overlie the basement.
96 citations
91 citations
01 Jan 1989
TL;DR: In the economy of nature there are a few privileged taxa sharing most of the richness in species, and a reduced middle class including a much lesser number, whereas the great majority of taxa is extremely poor.
Abstract: As well as in the economy of several countries the wealth is unevenly distributed among individual people, there is a notorious inequality in the distribution of richness in species among different taxa of organisms in nature. In the economy of nature there are a few privileged taxa sharing most of the richness in species, and a reduced middle class including a much lesser number, whereas the great majority of taxa is extremely poor.
87 citations
TL;DR: It is concluded that hyperthyroidism leads to hypermetabolism and oxidative stress in the brain, and the increased levels of oxygen and peroxyl radicals may contribute to premature ageing in these animals.
Abstract: Newborn Wistar rats were made hyperthyroid by injection of tri-iodothyronine and assayed for survival, brain oxygen uptake, brain chemiluminescence and activity of antioxidant enzymes. Brain chemiluminescence was measured (1) by removing the parietal bones or (2) through the translucid parietal bones. Control animals showed a brain chemiluminescence of 130 +/- 12 c.p.s./cm2 and 99 +/- 10 c.p.s./cm2 for procedures (1) and (2) respectively. Hyperthyroid rats showed increases in the spontaneous brain photoemission of 46 and 70% compared with controls, measured by procedures 1 and 2 respectively. The hyperthyroid state did not modify the oxygen-dependent chemiluminescence of brain homogenates. The hyperthyroid animals showed a 30% increase in the oxygen uptake of brain slices and a dramatic shortening of life-span to about 16 weeks. Superoxide dismutase (the Cu-Zn enzyme), catalase and Se-dependent glutathione peroxidase activities of brain homogenates were increased by 18, 36 and 30% respectively in the hyperthyroid animals. Isolated brain mitochondria produced 0.18-0.20 nmol of H2O2/min per mg of protein in state 4 in the presence of succinate as substrate. No difference was observed between control and hyperthyroid animals. It is concluded that hyperthyroidism leads to hypermetabolism and oxidative stress in the brain. The increased levels of oxygen and peroxyl radicals may contribute to premature ageing in these animals.
TL;DR: The presence of benzodiazepine (BZD)-like molecules as well as of other substances with affinity for the brain BZD-receptors was explored in eight non-flowering plants known to contain biflavonoids, three flowering plants used as sedatives in folkloric medicine and one plant extensively used in Argentina, Uruguay, Brazil and Paraguay as a tea substitute.
Journal Article•
TL;DR: A sequence of immunological events, concomitant with pathological changes of the testis, during the development of a severe EAO in Wistar rats is described.
Abstract: Wistar rats immunized with an homologous testicular homogenate (TH) and complete Freund's adjuvant, followed by i.v. injection of Bordetella pertussis, developed an autoimmune orchitis (EAO). Animals were studied at 7, 16, 30, 50, and 80 days (d) after the first immunization. An important lesion of the testis only appeared at 50 d, increasing in severity and incidence (77%) at 80 d. Lesions were characterized by a prevalent aspermatogenesis with tubular atrophy and mild interstitial mononuclear infiltrates. Delayed-type hypersensitivity response (DTH) against TH was detected early at 7 d and, except for 16 d, it increased with time, reaching a maximum at 80 d. A good temporal relationship between DTH and histopathology was found. Circulating antibodies to TH, detected by ELISA, were only present in 64% of the animals with testis lesion, while no deposits of IgG or C3 in the seminiferous tubules were seen. We describe a sequence of immunological events, concomitant with pathological changes of the testis, during the development of a severe EAO in Wistar rats.
TL;DR: The evidence supports the hypothesis that, in stands formed by plants of similar size, the red:far-red ratio of the light that impinges laterally on the stems is among the earliest environmental cues that allow plants to detect local canopy density and adjust axis extension accordingly.
Abstract: A fiber optic probe inserted into plant tissues was used to investigate the effects of canopy density on the light environment in different organs. The red:far-red ratio inside the stem of Datura ferox L. seedlings and the estimated phytochrome photoequilibrium were strongly reduced by the presence of neighbors forming canopies too sparse to cause any mutual shading at the level of the leaves. In such canopies, changes in plant density had little effects on the light regime inside the leaves of the succulent Aeonium haworthii (S.D.) Webb et Berth., particularly when the lamina was kept nearly normal to the direct rays of the sun. In field experiments using D. ferox and Sinapis alba L. seedlings, the elongation of the internodes responded to various types of localized light-quality treatments that simulated different plant densities in sparse canopies. The responses were quantitatively similar to those elicited by changes in plant density. The evidence supports the hypothesis that, in stands formed by plants of similar size, the red:far-red ratio of the light that impinges laterally on the stems is among the earliest environmental cues that allow plants to detect local canopy density and adjust axis extension accordingly.
TL;DR: The aim of this study was to determine the viral agents associated with acute lower respiratory infections (ALRI) in young children, and histologic lesions were compatible with adenovirus infection, but this virus could be isolated from the lung in only one case.
Abstract: The aim of this study was to determine the viral agents associated with acute lower respiratory infections (ALRI) in young children During a 2-yr period, 204 nasopharyngeal aspirates (NPA) from children under 4 yr of age living in an orphanage and exhibiting febrile ALRI were studied by both indirect immunofluorescence (IIF) and isolation in four cell lines NPA cell smears as well as tissue culture cells exhibiting cytopathic effect (CPE) or hemadsorption were stained by IIF for respiratory syncytial virus (RSV), adenovirus, influenza A and B, and parainfluenza 1 and 3 Viral etiology was demonstrated in 212% of acute respiratory infection cases The most frequently detected virus was RSV (535% of viral positive diagnoses), followed by unidentified viruses (186%), adenovirus (139%), influenza A (7%), and parainfluenza 3 (47%) The most common clinical entities were: bronchitis, 461%; pneumonia, 24%; bronchiolitis, 22%; and multifocal pneumonia, 8% Malnourishment was found in 56% of children with ALRI, whereas 50% was found among total orphanage population The 3 to 8-month-old age group accounted for half of all ALRI cases Viral etiology was shown for 265% of patients with pneumonia, 22% with bronchitis, and 16% with bronchiolitis RSV and adenovirus occurred in fall and winter, while parainfluenza 3 was detected in early spring In the two fatal cases observed, histologic lesions were compatible with adenovirus infection, but this virus could be isolated from the lung in only one case
TL;DR: A restricted range of liminar values of magnetic TCS was obtained by defining the threshold for raising motor responses in complete muscle relaxation, indicating that magnetic pulses might represent a useful probe for testing the 'excitability' of the motor tracts.
TL;DR: Evaluated pupa developmental time as well as percentage of pupa mortality at different temperature regimes allowed to construct an efficiency index relating pupa survival and cocoon developmental time, which reached its maximal values in the range of temperatures selected by nurses.
Abstract: 1) When a thermal gradient (20–40° C) was established along a laboratory nest, Camponotus mus nurse workers showed a photoperiodic circadian rhythm of temperature preferences for brood rearing. Two different temperatures were daily selected to translocate the brood, i.e. 30.8° C selected at the middle of the photophase, and 27.5° C selected during the scotophase, 8 h later. 2) The daily temperature response of nurse workers consisted of paired high and low-temperature translocations, with a 8 hs-interval in between: high-temperature translocation was shown to be entrained by the photophase length, whereas low-temperature translocation was shown to be dependent on the precedent one. 3) Prey deprivation to the colony modified the brood transport behaviors resulting in translocations of only cocoons and large (ripe) larvae, stages in which the pupation processes are triggered. Small larvae and eggs remained located at 27.5° C. 4) Evaluation of pupa developmental time as well as percentage of pupa mortality at different temperature regimes allowed to construct an efficiency index relating pupa survival and cocoon developmental time. In the range of temperatures selected by nurses, the index reached its maximal values. 5) The ecological significance of these results is discussed.
TL;DR: In this paper, a robust conditional location functional without requiring any moment condition is defined, and the nonparametric estimates of the regression function are obtained by using nearest neighbor weights or weights based on kernel methods under no assumptions whatsoever on the probability measure of the vector (X, Y ).
TL;DR: Crops of sunflower were grown in a coarse loam Typic Hapludoll to characterize the spatial and temporal development of the root systems, the relationships between root systems and leaf area, and their responses to plant population.
TL;DR: The structures of the rearranged genomic segment 11 of two spontaneous swine rotavirus strains were determined and it was shown that the two rearranged genes were transcribed into RNA molecules of the same length as their corresponding genomic segments.
Abstract: The structures of the rearranged genomic segment 11 of two spontaneous swine rotavirus strains were determined. We found that the rearrangements involved the duplication of normal segment 11 in a head-to-tail orientation, and partial deletions in both monomers. The open reading frame for VP11, the protein encoded by normal segment 11, was maintained. We also showed that the two rearranged genes were transcribed into RNA molecules of the same length as their corresponding genomic segments.
TL;DR: Weight gain of unsupplemented infants, the most important of the several criteria used to assess breast-feeding performance, was similar for the two contraceptive groups.
TL;DR: In this article, a quadrilateral 2D finite element for linear and nonlinear analysis of solids is presented, which is based on the technique of mixed interpolation of tensorial components.
Abstract: A quadrilateral 2‐D finite element for linear and non‐linear analysis of solids is presented. The element is based on the technique of mixed interpolation of tensorial components. It is shown that the new element is reliable and efficient, being apt, therefore, to be used in routine engineering applications.
TL;DR: Ceramography confirms the martensitic (displacive) nature of the transformation from high (cubic) to low (tetragonal) leucite upon cooling upon cooling, and identifies the crystalline phases in eight commercial dental porcelains in both powder (unfired) and sintered forms.
TL;DR: In this paper, the chiral enolates of glycolate imides 2a and 2b were alkylated in highly diastereoselective manner to give 2'-substituted products in good yield.
TL;DR: Human IgG or its F(ab')2 fragment purified from a pool of non-immune sera was passed through a Con A-Sepharose column and results indicate that partial asymmetric glycosylation is a general phenomenon that is not restricted exclusively to IgG molecules with known specificity.
TL;DR: It is concluded that ELISA using M. tuberculosis antigen 5 may be useful in those situations of high prevalence of disease when children suspected of tuberculosis are being evaluated and the difference in antibody titers between patient and control groups was found to be statistically significant.
Abstract: An enzyme-linked immunosorbent assay (ELISA) using Mycobacterium tuberculosis antigen 5 has been evaluated as a serodiagnostic test for active tuberculosis in children. Forty children of either sex, ages 1 to 14 yr, were studied, including 21 bacteriologically confirmed tuberculous patients and 19 control subjects who were evaluated for tuberculosis and found to be free of disease. At a 1:20 dilution, the test showed a sensitivity of 0.857 and a specificity of 1.000, with an accuracy value of 0.925, a positive predictive value of 1.000, and a negative predictive value of 0.864. The prevalence of disease calculated directly from the data of the study was found to be of 0.525. The geometric mean ELISA titer of the tuberculosis group was 1:58, and the difference in antibody titers between patient and control groups was found to be statistically significant (p less than 0.001). From our results, we conclude that ELISA using M. tuberculosis antigen 5 may be useful in those situations of high prevalence of disease when children suspected of tuberculosis are being evaluated.
TL;DR: Results indicate that melatonin facilitates pre‐ and postsynaptic activities of y‐aminobutyric acid neurons, particularly in the hypothalamus, through an effect that displays a diurnal sensitivity compatible with the documented activity of the hormone on a number of physiological functions.
Abstract: The objective of the first series of experiments was to assess whether melatonin treatment modifies the activity of the y-aminobutyric acid synthesizing enzyme, glutamic acid decarboxylase, in the preoptic-medial basal hypotnalamic area, cerebral cortex and cerebellar cortex of rats receiving 25 to 300 mug of melatonin in the early morning and late evening in the diurnal cycle. A significant increase of apparent V(max) and K(m) of the enzyme was found in the hypothalamus of rats killed at the 12th h of the light phase (i.e. the time when lights were turned off) and receiving 25 to 300 mug/kg of melatonin 3 h earlier. In the early morning, only a 300 mug/kg dose of melatonin (injected in the 1st h of the light phase) was effective to increase V(max) and K(m) of hypothalamic glutamic acid decarboxylase 3 h later. In cerebral and cerebellar cortices, increases in V(max) and K(m) of enzyme activity were apparent only in the evening and with the highest melatonin dose employed (300 mug/kg). In a second series of experiments the activity of melatonin to modify in vitro(36)CI influx by 900 x g pellets of rat preoptic-medial basal hypothalamic area was studied at the 4th and 12th h of the light phase of daily photoperiod. Melatonin increased (36)CI(-) influx at a minimum concentration of 100 nM (in the morning) or 10 nM (in the evening). The effect of melatonin on (36)CI(-) influx was prevented by co-incubation with 100 muM picrotoxin. Addition of 10 to 100 muM of y-aminobutyric acid to the resuspended 900 x g pellets brought about a dose-dependent increase of (36)CI (-) influx. Preincubation with melatonin at threshold doses of 1 muM (in the morning) or 0.1 muM (in the evening) significantly augmented y-aminobutyric acid effect on (36)CI(-) uptake. These results indicate that melatonin facilitates pre- and postsynaptic activities of y-aminobutyric acid neurons, particularly in the hypothalamus, through an effect that displays a diurnal sensitivity compatible with the documented activity of the hormone on a number of physiological functions.
TL;DR: In this paper, a finite element for the analysis of thin-walled open section beam structures is presented, which is based on Vlasov's beam theory and does not require the use of numerical integration.
TL;DR: Molecular clock estimation calibrated by fossils showed that generic divergence within Akodontini started at least in the late Miocene and that divergence of Akodintini from Orizomyini occurred within the Miocene.
Abstract: Allozyme genetic distances were estimated for ten species of akodontine rodents, as compared with the Oryzomyini Oligoryzomys longicaudatus, which was used as an outgroup to assess plesiomorphic character-states. Twenty-six loci were analysed. Distribution patterns of allele frequencies were determined by both phenetic (UPGMA) and cladistic (PAUP') techniques. Allozyme analysis confirmed monophyly for the Akodontini, and among them, the distinctiveness of the genus Oxymycterus. Genetic divergence among the eight species of Akodon was small compared to most known species of rodents. Phenrtic and phylogenetic analysis between Bolonys obscurus and species of Akodon was m agreement with previous chromosomal work but in disagreement with the indications of morphology. The general lack of allozymic differentiation among members of the Akodontini suggests that in this group molecular divergence is unrelated to speciation. Molecular clock estimation calibrated by fossils showed that generic divergence within Akodontini started at least in the late Miocene and that divergence of Akodintini from Orizomyini occurred within the Miocene.