Showing papers by "University of Buenos Aires published in 1986"

Grazing effects upon plant community structure in subhumid grasslands of Argentina

Abstract: Changes in plant community structure are identified as a result of grazing in grasslands of the flooding pampa which evolved under supposedly light grazing conditions.; ; The effect of excluding grazing upon total leaf area index was an increase of 30%. The largest response was observed in the distribution of leaves in the canopy. In the grazed areas, most of the green material was concentrated in the 0?5 cm layer while in the ungrazed treatments the largest portion of the leaf area was in the 10?30 cm layer. Grazing exclusion resulted in a small change in total basal area but a larger change in its distribution, from many small tussocks to less numerous large ones.; ; The effect of grazing upon leaf area and basal area was accounted for by changes in vigor as well as by changes in species composition. The major effect of excluding grazing upon species composition was the disappearance of some native planophile species and most of the exotics. The species composition of grazed areas of both communities was very similar while there were large differences between the ungrazed areas and between the grazed and ungrazed areas of the same community. It is suggested that there is a group of species which responds to the coarse-grained i®signali¯ of grazing and its presence can cause dissimilar communities to converge under grazing conditions. The other group of species responded to the fine-grained i®signali¯ of the environmental conditions associated with topography.

Ray tracing formulas for monoaxial optical components: vectorial formulation.

Abstract: The formulas for ray tracing in monoaxial crystals for discontinuity surfaces of arbitrary shape are generalized. The formulas obtained are applied to the case of an achromatic calcite–calcite doublet.

Emergence and survival of bromus setifolius seedlings in different microsites of a patagonian arid steppe

Abstract: In a plant community of the arid steppe, structurally characterized by shrubs encircled by grasses and scattered tussocks with bare soil patches interspersed, the hypothesis of differential seedling survival in differentially protected microsites was tested. Seeds of Bromus setifolius were placed in the soil at two different depths and in two different microhabitats: leeward of a shrub and bare soil patch. No changes were recorded in the germination rate treatments. However, seadling survival under shrub protection was lower than in bare soil patches. Higher soil water potential in bare soil patches—probably due to smaller root biomass of established grasses—appeared to be the major determinant of the higher survival rate observed. A model based on seed density and seedling survival is proposed for seedling recruitment in relation to distance from the mother plant. The promotion of seedling establishment in the best suited microhabitats is visualized as a possible means of enhancing recovery of v...

Estudios cariologicos en compositae. I

Abstract: Meiotie and/or mitotic chromosome numbers were determined and observations on meiotic behavior were made in 104 accessions belonging to 75 species and 32 genera distributed in 10 tribes of the Asteraceae. One genus ( Picrosia ), 21 species and 2 varietes are investigated cytologically for the first time. These are as follows, tribe Mutisieae: Chaptalia graminifolia (Dus.) Cabrera and Ch. pilloselloides (Vahl.) Baker (2n = ca. 48); tribe Cichorieae: Picrosia longifolia Don (n = 7 II); tribe Astereae: Baccharis effusa Griseb. (n = 9 II), B. flabellata Hook. et Arn. (n = 9 II), B. flabellata var. argentina (Heer.) Ariza (n = 9 II), B. rhexioides H. B. K. (n = 9 II), B. tucumanensis Hook. et Arn. (n = 9 II), Grindelia buphthalmoides DC. (2n = 12); tribe Senecioneae: Senecio flagellisectus Griseb. (n = 20 II), S. grisebachii Baker var. grisebachii Baker (n = 20 II), S. l orentzii Griseb. (n = 20 II); tribe Heliantheae: Calea clematidea Baker (n = 19 II), Cosmos marginatus Klatt (n = 24 II), Spilanthes alpestris Griseb. (n = ca. 14 II), Tridax paraguayensis Kuntze (n = 18 II); tribe Eupatorieae: Eupatorium buniifolium Hook. et Arn. (2n = 20 + 2B), E. lorentzii Hieron. (n = ca. 17 II), E. grosidentatum Hieron. (n = 10 II), Ophryosporus macrodon Griseb. (n = 10 II), Pterocaulon lanatum O. K. (n = 11 II), Stevia aff. effusa Hieron. (n = 11 II) and S. maimarensis (Hieron.) Cabrera (n = 11 II). Different chromosome numbers to those reported previously in the literature were found for Aspilia montevidensis (Spreng.) Kuntze var. setosa (Griseb.) Cabrera (n = 11 II), Liabum polymnoides R. E. Fries (n = 15 II) and Eupatorium saltense Hieron. (n = ca. 26 II) The karyotypes of Hieracium tandilense Sleumer, Baccharis effusa Griseb., B. spicata (Lam.) Baillon, Eupatorium buniifolium Hook. et Arn. and Stevia satureaiefolia (Lam.) Sehultz-Bip. are described for the first time. The significance of some of the results in relation to taxonomical and evolutionary problems is discussed.

Early cretaceous angiosperm leaves from southern South america.

Abstract: Early angiosperm leaves from the Aptian (113 to 119 million years ago) Baquero Formation of Patagonia have been found in a fossil flora dominated by more than 100 species of gymnosperms and pteridophytes. They may be the first early Cretaceous angiosperm leaves to be reported from southern South America and one of the few reported in the Southern Hemisphere. The leaves are large, lobate, craspedodromous, and dentate (A-1 teeth) and have ramified tertiary veins and random fourth-order venation. Several of these features have been found in coeval and younger strata elsewhere, but not in the same combination. They were probably a marginal component of the flora.

Maps between some different kinds of contraction function: The finite case

Abstract: In some recent papers, the authors and Peter Gardenfors have defined and studied two different kinds of formal operation, conceived as possible representations of the intuitive process of contracting a theory to eliminate a proposition. These are partial meet contraction (including as limiting cases full meet contraction and maxichoice contraction) and safe contraction. It is known, via the representation theorem for the former, that every safe contraction operation over a theory is a partial meet contraction over that theory. The purpose of the present paper is to study the relationship more finely, by seeking an explicit map between the component orderings involved in each of the two kinds of contraction. It is shown that at least in the finite case a suitable map exists, with the consequence that the relational, transitively relational, and antisymmetrically relational partial meet contraction functions form identifiable subclasses of the safe contraction functions, over any theory finite modulo logical equivalence. In the process of constructing the map, as the composition of four simple transformations, mediating notions of bottom and top contraction are introduced. The study of the infinite case remains open.

MATERIAL FUNGICO y GRANOS DE POLEN DE ANGIOSPERMAS DE LA FORMACION RIO TURBIO (EOCENO), PROVINCIA DE SANTA CRUZ, REPUBLICA ARGENTINA

Abstract: "Microplankton, spores of Pteridophyta, and pollen grains of Gymnosperms and Fagaceae have been already studied from this Formation. The purpose of this paper is to begin with the study of fungal remains and Angiosperm pollen (other than Nothofagidites Potonie). Eigtheen samples in the about 400 m deep w eH D-15 were analized. The fossils are described, measured and discussed. The most important taxa were: Plochmopeltinites masonii Cookson emend. Selkirk, germlings of Microthyriaceae, Pluricellaesporites psilatus Clarke, Lacrimasporonites sp, and a new species of Tulosporonites, among the Fungi, and Concopites leptos Fartridge, Gothanipollis bassensis Stover, Triatriopollenites latejlexus Archangelsky, Tricolpites gillii Cookson, Tricolpites reticulatus Cookson, Striatricolporites gamerroi Archangelsky and Ilexpollenites cliidenensis McIntyre among the Angiosperms. Problems of nomenclature and delimitation were found in Tricolpites Cookson ex Couper and Pluricellaesporites Van der Hammen emend. Sheffy and Drlcher. The taxa studied are varied though never dominant. Most species could be compared with a living genus or Iamily. The age indicated by the fossils is Eocene."

Partial characterization of an endogenous factor which modulates the effect of catecholamines on synaptosomal Na+, K+-ATPase

Abstract: We have previously presented evidence for the existence of a brain soluble factor which mediates the stimulation of synaptosomal ATPases by catecholamines. The stimulation of synaptosomal ATPases by dopamine plus brain soluble fraction was not modified if the soluble fraction was heated for 5 min at 95 degrees C. One day after preparation, the soluble factor inhibited the Na+, K+-ATPase, but not the Mg2+-ATPase activity, and subsequent addition of noradrenaline stimulated the ATPases activities. The inhibitory effect of a 24 h soluble fraction disappeared if the soluble fraction was dialyzed; in this case, noradrenaline did not activate the enzyme activities. Gel filtration in Sephadex G-50 permitted separating a subfraction which inhibited ATPase activity (peak II) from another which stimulated ATPase activity (peak I). Peak I stimulated both Na+, K+, and Mg2+ ATPases. Peak II inhibited only Na+, K+-ATPase, and when stored acidified, it mediated ATPases stimulation by noradrenaline.

Therapeutic effect of the antiviral agent ribavirin in Junín virus infection of primates.

Abstract: In order to assess the effect of the antiviral Ribavirin on the course of Junin virus infection in Callithrix jacchus, seven inoculated monkeys were treated with 15 mg of the drug, twice a day, starting 6 days after infection when all animals were viremic. The three untreated controls showed typical signs of Junin virus infection at 14 days pi and their mean time of death was 18 days. In contrast, no signs of illness were detected in Ribavirin-treated animals until 24 days pi, when marmosets showed signs of neurological involvement: 5 of these animals died (mean day of death: 36) but the two remaining treated monkeys improved and survived infection without sequelae. The comparison of survival rates (0% vs 28%) and the delay of the mean day of death observed indicates that the Ribavirin treatment used has therapeutic effect on Junin virus infection in vivo.

Spin-echo MR imaging of intracranial hemorrhage.

Abstract: This retrospective study was performed to describe the appearance of intracranial hemorrhagic lesions on magnetic resonance (MR) imaging at 0.35 tesla using the spin-echo technique, and define the present clinical role of MRI in this particular pathology. Forty-eight examinations of forty-three patients with forty-seven intracranial hemorrhagic lesions (39 true hematomas and 8 hemorrhagic lesions mixed with other tissues) were reviewed for this study. Comparative CT studies were available for all the patients. In our limited experience with acute hematomas (less than 3 days old), low or isointense signal was seen with a short TR (0.5 s), but a relative increase in signal intensity was observed with a long TR (2.0 s). This appearance of acute hematoma was not specific. Chronic hematomas (more than 3 days old) were imaged as foci of bright signal intensity on both short and long TR. This pattern was characteristic of chronic hematoma. With a short TR (0.5 s), two hemorrhagic lesions (5 and 7 days old) were displayed as an isointense signal surrounded by a rim of high intensity signal. This peripheral zone most likely represented liquefaction at the clot's periphery and the initial formation of methemoglobin. T1 and T2 relaxation times were found to be very long for acute hematomas (first two days). T1 values of chronic hematomas (more than 3 days old) were compaaatively short and in the same range as T1 of white matter. T2 values of chronic hematomas decreased also but remained very long.

Effects of sex and age on pancreatic secretion.

Abstract: The secretory response of the exocrine pancreas to an intravenous bolus of secretin (1.0 U/kg) was studied in healthy men and women below and above 45 years of age. We studied the secretory pattern, i.e., electrolyte and enzyme secretion in 8 sequential, 10-min collections and cumulative values for each parameter. Within the male group, no significant changes were observed, except for higher amylase and lipase secretions in the older subjects. On the other hand, females over 45 yr old had secretory patterns that showed a decline of flow and of bicarbonate concentration and output. No significant secretory differences were observed in the groups of younger males and females. When the over-45 groups of men and women were compared, the women exhibited a significant decrease in bicarbonate concentration and output. Moreover, this group of women had a cumulative 80-min output of bicarbonate and lipase significantly below these parameters in the men. Possible mechanisms are discussed.

An antiviral factor from Melia azedarach L. prevents Tacaribe virus encephalitis in mice

Abstract: Treatment of neonatal mice with an antiviral factor, (AVF), obtained from the leaves ofMelia azederach L. protected them against lethal encephalitis caused by Tacaribe virus inoculation. The degree of protection obtained varied from 66% to 100% depending on the virus dose. Similarly, administration of AVF to nursing mothers protected their offspring from developing virus encephalitis. AVF does not directly inactivate Tacaribe virus; it inhibits an early step (s) in the replication process in cell cultures.

Solid‐state 13C NMR study of drugs: Aspirin

Abstract: Natural abundance 13C NMR spectra of different crystal habits of pure aspirin and several aspirin tablets in the solid state have been measured by using the combined techniques of high-power decoupling, cross-polarization and magic angle spinning. Solid-state NMR of aspirin had excellent sensitivity compared with liquid-state NMR, and the carbon signals were assigned using a modified pulse sequence to detect non-protonated carbons. The solid-state 13C NMR spectra of two crystalline forms of aspirin were identical, suggesting that the origin of their difference is not polymorphic. The solid-state 13C NMR spectra of several commercial aspirin tablets, some of them containing buffer components, indicated that there were no interactions among the aspirin and the buffer components; only after dissolving the tablets and lyophilization did the 13C NMR spectra of the dry lyophilized powders show strong interactions between aspirin and the buffer components.

Isolation of yeast with killer activity and its breeding with an industrial baking strain by protoplast fusion

Abstract: “Wild” strains of Saccharomyces cerevisiae were isolated from dairy products, bakery goods, fresh fruit and vegetables, and tested for killer activity. Four isolates out of 238 strains possessed killer activity. The best of these was converted to the petite form and hybridized with an industrial strain of Saccharomyces cerevisiae by protoplast fusion. Thirty-eight out of 104 isolates had killer activity, and some of these had good dough-raising activity as well.

Immunodetection of involucrin in lesions of the oral mucosa.

Abstract: The immunoperoxidase method for involucrin detection was applied to the study of the maturation of epithelial lesions of the oral mucosa that included specimens of leukoplakia, lichen planus, verrucous carcinoma, carcinoma in situ and invasive carcinoma. Areas of orthokeratinized, parakeratinized, and non-keratinized normal mucosa were also studied. Normal orthokeratinized epithelia showed intracytoplasmic or pericellular staining in the suprabasal epithelial layers in a pattern similar to that of the normal epidermis. Parakeratinized and non-keratinized epithelia were less stained. Intense staining was observed in leukoplakia, whereas the staining of lichen planus was less intense but exhibited a more homogeneous pericellular staining pattern than leukoplakia. Verrucous carcinoma was markedly and very irregularly stained. Carcinomas in situ and invasive carcinoma exhibited a slightly positive and patchy reaction. The distribution patterns of involucrin in the lesions correlated very well with the degree of epithelial differentiation. In addition, irregular patchy distribution correlated with the degree of atypia, and was especially evident in carcinomas.

Dynamics of transmission of Trypanosoma cruzi in a rural area of Argentina. I The dog reservoir: an epidemiological profile

Abstract: Levou-se a cabo numa area rural da Argentina uma pesquisa epidemiologica dos caes associados ao domicilio, com vistas a caracterizar sua dinâmica populacional as infeccoes naturais pelo T. cruzi empregando tecnicas sorologicas e xenodiagnostico. A estrutura de idades da populacao mostrou que os individuos participam no ciclo domestico da transmissao uma media de 4 anos; a proporcao de sexos por grupos etarios sugeriu uma mortalidade diferencial para as femeas, especialmente nas cadelas. Achou-se uma prevalencia geral de infeccao de 84%, crescendo desde 69% em caes 1 ano ate 100% nos maiores de 3 anos, indicando alta eficiencia de transmissao do T. cruzi aos caes na qual a infeccao congenita ou pelo leite pode estar implicada. A sorologia mostrou concordância de 98% com os xenodiagnosticos positivos. A parasitemia nao diminuiu com a idade em caes seropositives < 10 anos. Ao menos os 50% dos reservatorios achavam-se estreitamente associados as moradas da gente. A estreita associacao trdfica entre os caes e T. infestans; a persistencia da parasitemia nos reservatorios; a alta eficiencia de transmissao do parasito a este; padroes de exposicao do hospedeiro adequados; e altas taxas de recrutamento de individuos suscetiveis qualificam o cao como hospedeiro amplificador da doenca de Chagas nas areas rurais do centro e norte da Argentina. Os programas rurais de atencao primaria da saude vieram estimular a introducao de medidas dirigidas a diminuir o contacto cao-barbeiro para ser executadas em conexao a luta quimica contra os vetores na Argentina.

Conformational analysis of DL‐, L‐ and D‐methionine by solid‐state 13C NMR spectroscopy

Abstract: The conformational analysis of DL-, L- and D-methionine was studied by solid-state 13C NMR with the help of cross-polarization and magic-angle spinning techniques. The spectrum of commercial crystalline DL-methionine showed two chemical shifts (18.7 and 15.8 ppm) for the methyl carbon. Crystallization from water or water-ethanol (95 : 5) allowed the separation of two crystalline forms (α and β), of which one had δ (CH3) 18.7 ppm and the other δ (CH3) 15.8 ppm. Therefore, each crystalline form of DL-methionine consists of a single conformer, a result in agreement with x-ray diffraction data. This conformational difference of the two crystalline forms was also reflected in the carbon resonances of C-β and C-γ. When L- and D-methionine were crystallized from water-ethanol (3 : 2), the solid-state 13C NMR spectra showed that each isomer displayed two methyl carbon peaks at 18.1 and 16.2 ppm of equal intensities, while the α-carbon resonances showed a broad peak due to two unresolved doublets. These results suggest that the L- or D-methionine crystal contains two different conformers in one unit cell, a conclusion that is also supported by the x-ray data.