A microstructural study of acrylic-modified chitosan by means of PALS and SAXS Anbinder, Pablo Sebastián; Macchi, Carlos Eugenio; Amalvy, Javier; Somoza, Alberto Horacio Chemical modification of chitosan, specially grafting with different polymers is an important strategy in the production of bio-based materials with enhanced properties. In the present study, chitosan was grafted with n-butyl acrylate, in a surfactant-free emulsion polymerization. Stable dispersions with high grafting efficiency were obtained and the microstructure of the casted films was analyzed by positron annihilation lifetime spectroscopy and small angle X-ray scattering. Results are discussed in terms of the number and distribution of the grafting sites.

Solvatomorphs of 25,26,27,28-tetrahydroxycalix[4]arene and 5,11,17,23-tetramino-25,26,27,28-tetrabutoxycalix[4]arene: quenching photoluminescence through switching the guest Martins, Felipe Terra; Maia, Lauro June Queiroz; Da Silva Neto, Leonardo; Da Silva, Cleiton Moreira; Sarotti, Ariel Marcelo; De Fátima, Ângelo Here, we have disclosed two solid state forms of 5,11,17,23-tetramino-25,26,27,28-tetrabutoxycalix[4]arene (1) and two solid state forms of the non-functionalized 25,26,27,28-tetrahydroxycalix[4]arene (2). This is the first structural knowledge of a tetra-amino functionalized calixarene derivative, even though this compound is well known and used as a precursor of several other functionalized calix[4]arenes. The two solid forms of 1 differ by the presence of either water or water/dimethylsulfoxide (DMSO) solvent molecules entrapped in the major calixarene cavity, even though the pinched conformation is adopted in both forms as a consequence of the contacts between solvent molecules and phenyl rings. Likewise, the switch from water to DMSO in the cone cavity of 1 has abrogated the photoluminescence (PL) found only in the dihydrate form. Frontier molecular orbital calculations at the B3LYP/6-31G* level of theory support a short-range electron transfer between guest (DMSO) and host (1) molecules quenching the solid state photoluminescence when DMSO is entrapped in the cone. This solvatomorphism approach for PL search in calixarenes opens a perspective on tuning and even increasing the performance of calixarenes through changing the guest solvent molecule. Similarly, the two crystal forms of 2 entrap either methyl alcohol or DMSO in their cones, which, as well as both crystal forms of 1, are packed into sheets through different fashions and contact patterns.

Delving into the Secular Stagnation Hypothesis: A Firm-Level Analysis of the Private Sector's Excess Savings in Advanced Economies Perez Artica, Rodrigo; Brufman, Leandro; Martinez, Lisana Belén We document a persistent increase in excess savings (defined as the difference between gross savings and capital formation) and a steady decline of gross capital formation in a sample of non-financial firms from developed countries. These patterns developed even before the financial breakdown of 2007 reinforcing the case for a secular stagnation hypothesis. They go along with a deleveraging process and a decrease in the share of operating assets in total assets. We discuss three possible explanations for this long-term behavior: financial constraints, operative volatility, and the weakening of business dynamism itself.

Increased dietary levels of α-linoleic acid inhibit mammary tumor growth and metastasis Vara Messler, Marianela; Pasqualini, María Eugenia; Comba, Andrea; Silva, Renata Alejandra; Buccellati, Carola; Trenti, Annalisa; Trevisi, Lucia; Eynard, Aldo Renato; Sala, Angelo; Bolego, Chiara; Valentich, Mirta Ana The aim of this study was to determine whether α-linolenic acid (ALA ω-3 fatty acid) enriched diet affects growth parameters when applied to a syngeneic model of mammary carcinoma. Materials and methods: BALB/c mice were divided and fed with: 1) a chia oil diet, rich in ALA or 2) a corn oil diet, rich in linoleic acid (LA ω-6 fatty acid). Mice were subcutaneously inoculated with a tumor cell line LM3, derived from a murine mammary adenocarcinoma. Results: After 35 days, tumor incidence, weight, volume and metastasis number were lower in the ALA-fed mice, while tumor latency time was higher, and the release of pro-tumor metabolites derived from ω-6 fatty acids decreased in the tumor. Compared to the control group, a lower number of mitosis, a higher number of apoptotic bodies and higher T-lymphocyte infiltration were consistently observed in the ALA group. An ALA-rich diet decreased the estrogen receptor (ER) α expression, a recognized breast cancer promotor while showing an opposite effect on ERβ in tumor lysates. Conclusion: These data support the anticancer effect of an ALA-enriched diet, which might be used as a dietary strategy in breast cancer prevention.

Measurement of expansin activity and plant cell wall creep by using a commercial texture analyzer Perini, Mauro Alejandro; Sin, Ignacio Nicolás; Martinez, Gustavo Adolfo; Civello, Pedro Marcos Background Expansins play an important role in cell wall metabolism and fruit softening. Determination of expansin activity is a challenging problem since it depends on measuring cell wall properties by using ad hoc extensometers, a fact that has strongly restricted its study. Then, the objective of the work was to adapt a methodology to measure cell wall creep and expansin activity using a commercial texture meter, equipped with miniature tensile grips and an ad hoc cuvette of easy construction. Results It was possible to measure hypocotyls acid growth and expansin activity in a reliable and reproducible way, using a commercial texture meter, common equipment found in laboratories of food science or postharvest technology. Expansin activity was detected in protein extracts from cucumber hypocotyls, tomato and strawberry fruits, and statistical differences in expansin activity were found in both fruit models at different ripening stages. Conclusions The possibility of measuring expansin activity following this adapted protocol with a commercial texture meter could contribute to ease and increase the analysis of expansin in different systems, leading to a better understanding of the properties of these proteins under different experimental conditions.

A new species in the troglomorphic scorpion genus Troglotayosicus from Colombia, representing the northernmost known record for the genus (Scorpiones, Troglotayosicidae) Botero Trujillo, Ricardo; González Gómez, Julio C.; Valenzuela Rojas, Juan C.; García, Luis F. We describe a new scorpion species in the troglomorphic genus Troglotayosicus Lourenço, 1981 from Colombia. Troglotayosicus meijdeni sp. nov. inhabits the forest leaf litter at Rivera municipality, on the western slope of the Eastern Andes. The male of the new species remains unknown; however, this species can be distinguished from other species in the genus by the female (and juvenile) morphology. The type locality of T. meijdeni sp. nov. represents the northernmost known record for a population of Troglotayosicus, further extending the known limits of distribution of this genus, and shedding more light on the distributional range of this group of scorpions in northwestern South America. With this description, the number of known species of Troglotayosicus is raised to four; three of them are endogean species living in forested areas in the Andean region of Colombia, whereas one is a hypogean species from a cave in Ecuadorian Amazonia.

New evidence for the therapeutic potential of curcumin to treat nonalcoholic fatty liver disease in humans Inzaugarat, Maria Eugenia; de Matteo, Elena Noemí; Baz, Placida; Lucero, Diego Martín; García, Cecilia Claudia; Gonzalez Ballerga, Esteban; Daruich, Jorge; Sorda, Juan Antonio; Wald, Miriam Ruth; Cherñavsky, Alejandra Claudia Introduction: The immune system acts on different metabolic tissues that are implicated in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). Leptin and linoleic acid have the ability to potentially affect immune cells, whereas curcumin is a known natural polyphenol with antioxidant and anti-inflammatory properties. Aims: This study was designed to evaluate the pro-inflammatory and pro-oxidant effects of leptin and linoleic acid on immune cells from patients with NAFLD and to corroborate the modulatory effects of curcumin and its preventive properties against the progression of NAFLD using a high-fat diet (HFD)-induced NAFLD/nonalcoholic steatohepatitis mouse model. Results: The ex vivo experiments showed that linoleic acid increased the production of reactive oxygen species in monocytes and liver macrophages, whereas leptin enhanced tumor necrosis factor-α (TNF-α) production in monocytes and interferon-γ production in circulating CD4+ cells. Conversely, oral administration of curcumin prevented HFD-induced liver injury, metabolic alterations, intrahepatic CD4+ cell accumulation and the linoleic acid- and leptin- induced pro-inflammatory and pro-oxidant effects on mouse liver macrophages. Conclusion: Our findings provide new evidence for the therapeutic potential of curcumin to treat human NAFLD. However, the development of a preventive treatment targeting human circulating monocytes and liver macrophages as well as peripheral and hepatic CD4+ cells requires additional research.

Iodide handling disorders (NIS, TPO, TG, IYD) Targovnik, Hector Manuel; Citterio, Cintia Eliana; Rivolta, Carina Marcela Iodide Handling Disorders lead to defects of the biosynthesis of thyroid hormones (thyroid dyshormonogenesis, TD) and thereafter congenital hypothyroidism (CH), the most common endocrine disease characterized by low levels of circulating thyroid hormones. The prevalence of CH is 1 in 2000–3000 live births. Prevention of CH is based on prenatal diagnosis, carrier identification, and genetic counseling. In neonates a complete diagnosis of TD should include clinical examination, biochemical thyroid tests, thyroid ultrasound, radioiodine or technetium scintigraphy and perchlorate discharge test (PDT). Biosynthesis of thyroid hormones requires the presence of iodide, thyroid peroxidase (TPO), a supply of hydrogen peroxide (DUOX system), an iodine acceptor protein, thyroglobulin (TG), and the rescue and recycling of iodide by the action of iodotyrosine deiodinase or iodotyrosine dehalogenase 1 (IYD or DEHAL1). The iodide transport is a two-step process involving transporters located either in the basolateral or apical membranes, sodium iodide symporter (NIS) and pendrin (PDS), respectively. TD has been linked to mutations in the solute carrier family 5, member 5 transporter (SLC5A5, encoding NIS), solute carrier family 26, member 4 transporter (SLC26A4, encoding PDS), TPO, DUOX2, DUOXA2, TG and IYD genes. These mutations produce a heterogeneous spectrum of CH, with an autosomal recessive inheritance. Thereafter, the patients are usually homozygous or compound heterozygous for the gene mutations and the parents, carriers of one mutation. In the last two decades, considerable progress has been made in identifying the genetic and molecular causes of TD. Recent advances in DNA sequencing technology allow the massive screening and facilitate the studies of phenotype variability. In this article we included the most recent data related to disorders caused by mutations in NIS, TPO, TG and IYD.

Presencia del Inca en Yocavil (Catamarca, Argentina). Integración en la diversidad; Inca presence in Yocavil (Catamarca, Argentina). Integration in diversity Tarrago, Myriam Noemi; Marchegiani, Marina Ines; Palamarczuk, Valeria; Reynoso, Alejandra Daniela Se ofrece una síntesis sobre las particularidades de la pre sencia incaica en el sur de Yocavil (Catamarca, Argentina), ponderando las características de las instalaciones imperiales, la alfarería incaica que circuló en la región y la relevancia del Qhapaq Ñan como eje integrador. Esta síntesis integra nueva información sobre instalaciones relevantes como El Calvario de Fuerte Quemado y Punta de Balasto. Se reflexiona sobre las características de las interacciones entre las sociedades locales y el Estado incaico en expansión, privilegiando el estudio de los procesos de cambio a partir de la posición de las sociedades dominadas.; This is a synthesis on the main features of the Inca presence in area of southern Yocavil (Catamarca, Argentina), that considers imperial settings, Inca pottery that circulated in the region and the relevance of Qhapaq Ñan as an integrating axis. This synthesis includes new information regarding relevant settings such as El Calvario de Fuerte Quemado and Punta de Balasto. There is a reflection on the characteristics of interactions between local societies and the expanding Inca State, focusing on the study of the processes of change from the position of dominated societies.

Impact of level and patterns of alcohol drinking on coronary heart disease and stroke burden in Argentina Bardach, Ariel Esteban; Caporale, Joaquín Enzo; Rubinstein, Adolfo Luis; Danaei, Goodarz Deaths from cardiovascular disease (CVD), including coronary heart disease (CHD) and stroke are expected to increase in Latin America. Moderate and regular alcohol consumption confers cardiovascular protection, while binge drinking increases risk. We estimated the effects of alcohol use on the number of annual CHD and stroke deaths and disabilityadjusted life years (DALYs) in Argentina. Methods Alcohol use data were obtained from a nationally representative survey (EnPreCosp 2011), and etiological effect sizes from meta-analyses of epidemiological studies. Cause-specific mortality rates were from the vital registration system. Results There were 291,475 deaths in 2010 including 24,893 deaths from CHD and 15,717 from stroke. 62.7% of men and 38.7% of women reported drinking alcohol in the past year. All heavy drinkers (i.e. women who drank <20g/day and men who drank <40g/day of alcohol) met the definition of binge drinking and therefore did not benefit from cardioprotective effects. Alcohol drinking prevented 1,424 CHD deaths per year but caused 935 deaths from stroke (121 ischemic and 814 hemorrhagic), leading to 448 CVD deaths prevented (58.3% in men). Alcohol use was estimated to save 85,772 DALYs from CHD, but was responsible for 52,171 lost from stroke. Conclusions In Argentina, the cardioprotective effect of regular and moderate alcohol drinking is slightly larger than the harmful impact of binge drinking on CVD. However, considering global deleterious effects of alcohol in public health, policies to reduce binge drinking should be enforced, especially for young people. Studies are still needed to elucidate effects on cardiovascular health.

Soymilk fermentation by Enterococcus faecalis VB43 leads to reduction in the immunoreactivity of allergenic proteins β-conglycinin (7S) and glycinin (11S) Biscola, V.; Rodríguez de Olmos, Antonieta; Choiset, Y.; Rabesona, H.; Garro, Marisa Selva; Mozzi, Fernanda Beatriz; Chobert, J. M.; Drouet, M.; Haertlé, T.; Franco, B. D. G. M. Food allergies represent a serious problem affecting human health and soy proteins rank among the most allergenic proteins from food origin. The proteolytic enzymes produced by lactic acid bacteria (LAB) can hydrolyse the major allergens present in soybean, reducing their immunoreactivity. Many studies have reported the ability of LAB to ferment soy-based products; while the majority of them focus on the improvement of the sensory characteristics and functionality of soy proteins, a lack of information about the role of lactic fermentation in the reduction of immunoreactivity of these proteins exists. The aim of the present study was to evaluate the capability of the proteolytic strain Enterococcus faecalis VB43 to hydrolyse the main allergenic proteins present in soymilk and to determine the immunoreactivity of the obtained hydrolysates. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) results of fermented soymilk demonstrated complete hydrolysis of the β-subunit from β-conglycinin and the acidic polypeptide from glycinin. Reversed phase high performance liquid chromatography (RP-HPLC) analysis of the peptides released after hydrolysis revealed the appearance of new peptides and the disappearance of non-hydrolysed proteins, indicating extensive hydrolysis of the substrate. Results from competitive enzyme-linked immunosorbent assay (ELISA) tests clearly indicated a reduction in the immunoreactivity (more than one logarithmic unit) in the fermented sample as compared to the non-fermented control. Our results suggest that the soymilk fermented by E. faecalis VB43 may induce lower allergic responses in sensitive individuals. The strain E. faecalis VB43 may be considered as an excellent candidate to efficiently reduce the immunoreactivity of soymilk proteins.

Metals in tidal flats colonized by microbial mats within a South-American estuary (Argentina) Serra, Analia Veronica; Botté, Sandra Elizabeth; Cuadrado, Diana Graciela; la Colla, Noelia Soledad; Negrin, Vanesa Lorena In this study, we measured the concentrations of metals (Cd, Cu, Pb, Ni, Cr, Zn, Hg, Mn, and Fe) and assessed the characteristics of tidal flats (grain size and organic matter content) in sediments and their overlying microbial mats fractions to evaluate the anthropogenic impact within the Bahía Blanca Estuary (BBE). Puerto Rosales (PR) and Almirante Brown (AB), located in the middle and inner zone of the estuary, respectively, were used as sampling sites. Sediments were composed mainly of silt?clay in AB, whereas first fine-grained particles were coarser in depth in PR. Regarding the concentration of metals in both fractions, we found differences between sites: There were higher concentrations of overall metals in AB relative to PR. In addition, higher concentrations of Cu were recorded in the first centimeters of AB tidal flats, whereas higher concentration of Cd were recorded in microbial mats of PR. Considering that the grain size was similar between sites, these results are consistent with the high concentration of organic matter found in AB, probably because this site is close to a former municipal dump and sewage discharges. Also, the higher Cd content found in PR site would highlight both the influence of untreated urban discharges and port anthropogenic activities. In conclusion, this study allowed identifying high values of some metals in the presence of microbial mats in the BBE, thus suggesting a possible interaction between both, at least for metals like Cu or Cd.

A Novel Genetic Screen Identifies Modifiers of Age-Dependent Amyloid β Toxicity in the Drosophila Brain Belfiori Carrasco, Lautaro Francisco; Marcora, Maria Silvina; Bocai, Nadia Irina; Ceriani, Maria Fernanda; Morelli, Laura; Castaño, Eduardo Miguel The accumulation of amyloid β peptide (Aβ) in the brain of Alzheimer's disease (AD) patients begins many years before clinical onset. Such process has been proposed to be pathogenic through the toxicity of Aβ soluble oligomers leading to synaptic dysfunction, phospho-tau aggregation and neuronal loss. Yet, a massive accumulation of Aβ can be found in approximately 30% of aged individuals with preserved cognitive function. Therefore, within the frame of the "amyloid hypothesis", compensatory mechanisms and/or additional neurotoxic or protective factors need to be considered and investigated. Here we describe a modifier genetic screen in Drosophila designed to identify genes that modulate toxicity of Aβ42 in the CNS. The expression of Aβ42 led to its accumulation in the brain and a moderate impairment of negative geotaxis at 18 days post-eclosion (d.p.e) as compared with genetic or parental controls. These flies were mated with a collection of lines carrying chromosomal deletions and negative geotaxis was assessed at 5 and 18 d.p.e. Our screen is the first to take into account all of the following features, relevant to sporadic AD: (1) pan-neuronal expression of wild-type Aβ42; (2) a quantifiable complex behavior; (3) Aβ neurotoxicity associated with progressive accumulation of the peptide; and (4) improvement or worsening of climbing ability only evident in aged animals. One hundred and ninety-nine deficiency (Df) lines accounting for ~6300 genes were analyzed. Six lines, including the deletion of 52 Drosophila genes with human orthologs, significantly modified Aβ42 neurotoxicity in 18-day-old flies. So far, we have validated CG11796 and identified CG17249 as a strong candidate (whose human orthologs are HPD and PRCC, respectively) by using RNAi or mutant hemizygous lines. PRCC encodes proline-rich protein PRCC (ppPRCC) of unknown function associated with papillary renal cell carcinoma. HPD encodes 4-hydroxyphenylpyruvate dioxygenase (HPPD), a key enzyme in tyrosine degradation whose Df causes autosomal recessive Tyrosinemia type 3, characterized by mental retardation. Interestingly, lines with a partial Df of HPD ortholog showed increased intraneuronal accumulation of Aβ42 that coincided with geotaxis impairment. These previously undetected modifiers of Aβ42 neurotoxicity in Drosophila warrant further study to validate their possible role and significance in the pathogenesis of sporadic AD.

Cícadas, fósiles vivientes del reino vegetal Martinez, Leandro Carlos Alcides; Artabe, Analia Emilia Eva La historia de un grupo de plantas presente en la Tierra desde hace casi 300Ma, por lo que podemos ver a sus integrantes actuales como fósiles vivientes.

What is a singular black hole beyond General Relativity? Bejarano, Cecilia Soledad; Olmo, Gonzalo J.; Rubiera Garcia, Diego Exploring the characterization of singular black hole spacetimes, we study the relation between energy density, curvature invariants, and geodesic completeness using a quadratic f (R) gravity theory coupled to an anisotropic fluid. Working in a metric-affine approach, our models and solutions represent minimal extensions of General Relativity (GR) in the sense that they rapidly recover the usual Reissner-Nordstrom solution from near the inner horizon outwards. The anisotropic fluid helps
modify only the innermost geometry. Depending on the values and signs of two parameters on the gravitational and matter sectors, a breakdown of the correlations between the finiteness/divergence of the energy density, the behavior of curvature invariants, and the (in)completeness of geodesics is obtained. We find a variety of configurations with and without wormholes, a case with a de Sitter interior, solutions that mimic non-linear models of electrodynamics coupled to GR, and configu-
rations with up to four horizons. Our results raise questions regarding what infinities, if any, a quantum version of these theories should regularize.

ChIP-seq analysis of the LuxR-type regulator VjbR reveals novel insights into the Brucella virulence gene expression network Kleinman, Claudia L.; Sycz, Gabriela; Bonomi, Hernán R.; Rodríguez, Romina M.; Zorreguieta, Angeles; Sieira, Rodrigo LuxR-type transcription factors control diverse physiological functions necessary for bacterial adaptation to environmental changes. In the intracellular pathogen Brucella, the LuxR homolog VjbR has been shown to regulate the expression of virulence factors acting at early stages of the intracellular infection and, directly or indirectly, hundreds of additional genes. However, the precise determination of VjbR direct targets has so far proved elusive. Here, we performed chromatin immunoprecipitation of VjbR followed by next-generation sequencing (ChIP-seq). We detected a large amount of VjbR-binding sites distributed across the Brucella genome and determined a markedly asymmetric binding consensus motif, an unusual feature among LuxR-type regulators. RNA-seq analysis performed under conditions mimicking the eukaryotic intracellular environment revealed that, among all loci associated to VjbR-binding, this regulator directly modulated the expression of only a subset of genes encoding functions consistent with an intracellular adaptation strategy for survival during the initial stages of the host cell infection. Other VjbR-binding events, however, showed to be dissociated from transcription and may require different environmental signals to produce a transcriptional output. Taken together, our results bring new insights into the extent and functionality of LuxR-type-related transcriptional networks

Brain structural changes in patients in the early stages of multiple sclerosis with depression Rojas, J. I.; Sánchez, Francisco; Patrucco, L.; Miguez, J.; Besada, C.; Cristiano, Edgardo Some studies suggest an inflammatory mechanism associated with the presence of depression in multiple sclerosis (MS); however, there is little data concerning these findings. The purpose of this study was to investigate the presence of brain structural changes in patients with MS and depression and to compare them with patients suffering from MS without depression and healthy controls. Methods: A case-control study that included patients with relapsing-remitting MS (RRMS) defined by validated criteria, over 18 years of age, with less than three years from disease onset, EDSS ≤ 3, with no history of previous depression and under immunomodulatory treatment with interferon beta, if any. A control group paired by age and gender was also included. Patients were clinically assessed to determine the presence of depression. Demographic clinical and structural aspects of parameters from the scan, such as lesion volume, total brain volume (TBV), white matter volume (WMV), neocortical gray matter volume (NGMV), and fractional anisotropy (FA) were analyzed. Results: Sixty-five individuals were enrolled: 20 healthy controls, 22 patients with MS without depression, and 23 patients with MS with depression. Patients with MS and depression showed a lower TBV (P = 0.01), NGMV (0.01) together with an increase in lesion burden in T2 (P < 0.01) but not in T1 (P = 0.09) and no differences in global FA among groups (P = 0.23) and in WMV (P = 0.12). Conclusion: Patients with RRMS and depression had a reduced total brain volume and a significantly increased lesion burden at T2 MR than patients with RRMS without depression.

Corporate Credit Spreads and the Sovereign Ceiling in Latin America Grandes, Martin; Panigo, Demian Tupac; Pasquini, Ricardo Aníbal We exploit a panel of 72 US dollar-denominated bonds issued by Latin American publicly listed firms between 1996 and 2004, a period of regional financial crises, to answer the following three questions: (1) Is sovereign risk a statistically and economically significant determinant of the corporate credit spread, controlling for firm- and bond-specific characteristics? (2) If yes, do market participants apply the sovereign ceiling rule adopted by rating agencies in the pricing of our bond market data? And (3) how do market views compare with the rating agencies ceiling policy for each corporate bond? We find strong evidence of an economically and statistically significant effect of sovereign risk on corporate spreads across different panel econometric specifications and bonds. Moreover, markets do not apply the ceiling rule in 77–90% of the bonds we sample and these findings are consistent with rating agencies’ policies toward the latter for about 50% of the firms. These results are robust to the inclusion of firm- and bond-specific variables derived from the structural approach to credit risk and to the business cycle in each country.

Cianobacterias Toxígenas: Estudios Taxonómicos y Fisiológico-Moleculares de cepas filamentosas formadoras de floraciones presentes en cuerpos de agua someros Aguilera, Anabella Las cianobacterias son organismos procariotas, capaces de efectuar fotosíntesis con liberación de O2, que forman parte del fitoplancton de todos los tipos de cuerpos de agua continentales. Algunas especies producen "floraciones algales" que son proliferaciones masivas, relativamente repentinas y espacialmente restringidas, protagonizadas por una o pocas especies, que dominan el fitoplancton. Las floraciones de cianobacterias son nocivas porque intervienen especies capaces de sintetizar cianotoxinas y metabolitos volátiles. Consecuentemente, representan un serio problema ecológico, económico y sanitario. Para asegurar la calidad de los recursos hídricos destinados al consumo o la recreación, es necesario poder identificar las especies de cianobacterias presentes así como su capacidad de producir toxinas. Asimismo, es de vital importancia comprender los factores que promueven la dominancia en sistemas eutróficos.En este trabajo de tesis se analizó, en primer lugar, la distribución geográfica de las floraciones de cianobacterias y sus toxinas en los cuerpos de agua continentales de Argentina. Por otro lado, se dieron a conocer los taxa de cianobacterias planctónicas presentes en la laguna somera Los Patos, (Ensenada, Provincia de Buenos Aires) y se estudió la influencia de los factores ambientales sobre la dinámica del fitoplancton dominado por cianobacterias filamentosas. Se realizó además, el aislamiento de dos cepas nativas de Raphidiopsis mediterranea y una de Planktothrix agardhii, provenientes de muestras ambientales de dos lagunas someras de la Provincia de Buenos Aires (laguna Los Patos y de los Padres) y su caracterización ultraestructural, molecular y toxicológica, mediante análisis polifásicos. Asimismo, se estudió el efecto de dos intensidades lumínicas y de dos concentraciones de fosfato sobre las densidades y la morfología de poblaciones de R. mediterranea y P. agardhii creciendo en co-cultivo. Adicionalmente, se analizó la respuesta de cultivos monoalgales de R. mediterranea y P. agardhii aisladas de Los Patos, ante condiciones de deficiencia de fosfato. Por último, utilizando ensayos de laboratorio, se evaluó el efecto de la adición de nutrientes y de dos intensidades lumínicas sobre la estructura, cambios morfológicos y crecimiento de una comunidad fitoplanctónica, dominada por cianobacterias filamentosas no heterocísticas, tomada del lago Javier (Canelones, Uruguay).Los resultados de este trabajo indican que las floraciones nocivas de cianobacterias se localizan a lo largo y ancho de nuestro país, desarrollándose en cuerpos de agua lóticos y lénticos, siendo Microcystis, y en menor medida Dolichospermum, Raphidiopsis, Cylindrospermopsis y Planktothrix, los géneros más frecuentes. Las concentraciones de microcistinas en cuerpos de agua utilizados como fuente de agua de consumo y recreación, en muchas ocasiones, superan los límites sugeridos por la Organización Mundial de la Salud. Los resultados de los experimentos con comunidades naturales provenientes del lago Javier, indicaron que la interacción entre los nutrientes y la intensidad lumínica promueve cambios en la dominancia de las cianobacterias filamentosas. Las especies Cylindrospermopsis raciborskii and Aphanizomenon aff. gracile del Orden Nostocales presentaron una plasticidad fenotípica mayor que los taxa filamentosos no heterocísticos del Orden Oscilatoriales y Synechoccocales. Estos resultados ayudan a entender las condiciones ambientales que pueden determinar la dominancia de las Nostocales.El fitoplancton de la laguna Los Patos se caracterizó por la presencia de floraciones de P. agardhii, las cuales se alternaron con floraciones de especies Nostocales, en particular R. mediterranea. La temperatura, la disponibilidad de luz y de nutrientes fueron los factores principales que determinaron la alternancia y la dominancia P. agardhii y R. mediterranea. La información obtenida a partir de los experimentos con cultivos mixtos y monoalgales resultó de utilidad para interpretar los patrones de alternancia y dominancia observados en la laguna Los Patos. Estos ensayos aportaron información sobre cómo los caracteres eco-fisiológicos pueden explicar la coexistencia de las cianobacterias filamentosas formadoras de floraciones. En particular, permitieron demostrar que R. mediterranea presenta cierto grado de plasticidad fenotípica y flexibilidad fisiológica en relación con la luz y la asimilación de fósforo, lo que podría explicar, en parte, la co-existencia bajo la dominancia de P. agardhii. Por último, los caracteres morfológicos, moleculares y ultraestucturales fueron congruentes entre sí en cuanto a la asignación de una de las cepas a la especie P. agardhii. Por otro lado, las filogenias construidas en base a secuencias de distintos marcadores moleculares revelaron que las cepas de C. raciborskii y Raphidiopsis (R. mediterranea, R. curvata y R. brookii) conforman un grupo con altos valores de soporte estadístico. La posición en los árboles filogenéticos (siempre juntas) podría deberse a una divergencia reciente de las especies (o cepas o ecotipos) y sugiere, además, que la emergencia del carácter autapomórfico que define a Raphidiopsis (ausencia de heterocistos) podría ser la consecuencia de eventos independientes. El presente estudio es una contribución a la elucidación de la clasificación taxonómica de los géneros Raphidiopsis y Cylindrospermopsis dado que complementa trabajos previos y da lugar a nuevos interrogantes sobre el estatus de los mismos.

Poor geotaxis correlated with hematoporphyrin-induced peroxidation of brain lipids as a predictor of medfly longevity reduction Bochicchio, Pablo Alejandro; Pérez, Martín Mariano; Quesada Allue, Luis Alberto; Rabossi, Alejandro Under illumination conditions, porphyrins generate cytotoxic radicals in cells. Our study evaluated the effects of haematoporphyrin IX (HP IX) in a laboratory population of male Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) during exposure to a low fluence rate (39 lE m 2 s 1) of light. We found that exposing flies to HP IX for at least 5 days was sufficient to cause irreversible damage that led to anticipated death, as also provoked by chronic exposure to the same concentration. To identify early indicators of the accelerated senescence, we analysed both in vitro and in vivo parameters. The thiobarbituric acid reactive substances content in the heads of treated flies revealed a significant increase in lipid hydroperoxides at day 10, whereas this occurred several days later in controls. In addition, a significant decrease in glycogen content was observed at 15 days of age, 5 days before the reduction observed in the control group. This decrease has been associated with a decline in locomotor activity. Differences in the distribution of flies in the rearing flasks were observed, reflecting an impairment of the motility and climbing capacity of HP IX-treated flies. This finding was also corroborated by a geotactic response assay (a rapid iterative negative geotaxis or RING assay). The results presented here demonstrate that low-lethal oxidative stress can anticipate the senescence of flies, which can be predicted using a simple and fast behavioural test, such as the RING assay.