Photosynthetic responses of three common mosses from continental Antarctica

Predicting the effects of climate change on Antarctic terrestrial vegetation requires a better knowledge of the ecophysiology of common moss species. In this paper we provide a comprehensive matrix for photosynthesis and major environmental parameters for three dominant Antarctic moss species (Bryum subrotundifolium, B. pseudotriquetrum and Ceratodon purpureus). Using locations in southern Victoria Land, (Granite Harbour, 77°S) and northern Victoria Land (Cape Hallett, 72°S) we determined the responses of net photosynthesis and dark respiration to thallus water content, thallus temperature, photosynthetic photon flux densities and CO2 concentration over several summer seasons. The studies also included microclimate recordings at all sites where the research was carried out in field laboratories. Plant temperature was influenced predominantly by the water regime at the site with dry mosses being warmer. Optimal temperatures for net photosynthesis were 13.7°C, 12.0°C and 6.6°C for B. subrotundifolium, B. pseudotriquetrum and C. purpureus, respectively and fall within the known range for Antarctic mosses. Maximal net photosynthesis at 10°C ranked as B. subrotundifolium > B. pseudotriquetrum > C. purpureus. Net photosynthesis was strongly depressed at subzero temperatures but was substantial at 0°C. Net photosynthesis of the mosses was not saturated by light at optimal water content and thallus temperature. Response of net photosynthesis to increase in water content was as expected for mosses although B. subrotundifolium showed a large depression (60%) at the highest hydrations. Net photosynthesis of both B. subrotundifolium and B. pseudotriquetrum showed a large response to increase in CO2 concentration and this rose with increase in temperature; saturation was not reached for B. pseudotriquetrum at 20°C. There was a high level of variability for species at the same sites in different years and between different locations. This was substantial enough to make prediction of the effects of climate change very difficult at the moment

Designing a light fabric metamaterial being highly macroscopically tough under directional extensio. First experimental evidence

In this paper, we study a metamaterial constructed with an isotropic material organized following a geometric structure which we call pantographic lattice. This relatively complex fabric was studied using a continuous model (which we call pantographic sheet) by Rivlin and Pipkin and includes two families of flexible fibers connected by internal pivots which are, in the reference configuration, orthogonal. A rectangular specimen having one side three times longer than the other is cut at 45° with respect to the fibers in reference configuration, and it is subjected to large-deformation plane-extension bias tests imposing a relative displacement of shorter sides. The continuum model used, the presented numerical models and the extraordinary advancements of the technology of 3D printing allowed for the design of some first experiments, whose preliminary results are shown and seem to be rather promising. Experimental evidence shows three distinct deformation regimes. In the first regime, the equilibrium total deformation energy depends quadratically on the relative displacement of terminal specimen sides: Applied resultant force depends linearly on relative displacement. In the second regime, the applied force varies nonlinearly on relative displacement, but the behavior remains elastic. In the third regime, damage phenomena start to occur until total failure, but the exerted resultant force continues to be increasing and reaches a value up to several times larger than the maximum shown in the linear regime before failure actually occurs. Moreover, the total energy needed to reach structural failure is larger than the maximum stored elastic energy. Finally, the volume occupied by the material in the fabric is a small fraction of the total volume, so that the ratio weight/resistance to extension is very advantageous. The results seem to require a refinement of the used theoretical and numerical methods to transform the presented concept into a promising technological prototype

The Southernmost bear: Pararctotherium (Carnivora, Ursidae, Tremarctinae) in the latest Pleistocene of Southern Patagonia, Chile

A second upper incisor belonging to the tremarctine bear Pararctotherium was recovered from latest Pleistocene deposits in Cueva de los Chingues, Magallanes, Chile (San Roman et al., 2000). This is the southernmost record of an ursid in the world and one of the youngest records of Pararctotherium. The paleoenvironment of southern Patagonia in the latest Pleistocene (ca. 11,000 yBP) was a cold grassland.Museo de La Plat

Manipulação de frutos da palmeira Syagrus romanzoffiana por vertebrados no sul do Brasil

A year-long study was carried out in a deciduous forest to examine the vertebrate manipulation on fruits of Syagrus romanzoffiana in southern Brazil. Eleven 50x50 cm-track traps (each one baited with ten ripe fruits) were placed monthly around 11 adult palm trees, totalling a sampling effort of 935 traps. The fruits removed (absent) or chewed (left in situ) by a given vertebrate species were counted for each trap. Three species of mammals and one bird were monitored. The coati (Nasua nasua) removed more fruits (N = 250; 50 %) than chewed (N = 130; 26 %), leaving intact 120 fruits (24 %). The dusky-legged guan (Penelope obscura) also removed more fruits (N = 107; 43 %) than chewed (N = 44; 18 %), leaving intact 96 (39 %). On the other hand, the opossum (Didelphis albiventris) removed 127 (13 %), but chewed 622 (63 %), leaving intact 236 (24 %). Similarly, the agouti (Dasyprocta azarae) removed 16 (12 %), and chewed 64 (49 %), leaving intact 51 fruits (39 %). Results are discussed in light of the roles of these vertebrate species in seed dispersal of S. romanzoffiana. Key words: Atlantic forest, Dasyprocta azarae, Didelphis albiventris, Nasua nasua, palm tree, Penelope obscura, seed dispersal, fruit removal.Este estudo teve a duração de um ano e avaliou a manipulação por vertebrados (três espécies de mamíferos e uma de ave) nos frutos da palmeira Syagrus romanzoffiana no sul do Brasil. Onze armadilhas de pegada de 50x50 cm (cada uma iscada com 10 frutos maduros) foram colocadas próximas a onze palmeiras adultas, totalizando um esforço amostral de 935 armadilhas. Os frutos removidos (ausentes) ou mastigados (deixados in situ) pelas espécies de vertebrados foram contabilizadas para cada armadilha. Três espécies de mamíferos e uma de ave foram monitoradas. O coati (Nasua nasua) removeu 250 frutos (50%), mastigou 130 (26%) e deixou intactos 120 frutos (24%). O jacu (Penelope obscura) também removeu mais frutos (N = 107; 43%) do que mastigou (N = 44; 18%), deixando intactos 96 frutos (39%). O gambá (Didelphis albiventris) removeu 127 (13%), e mastigou 622 (63%), deixando intactos 236 (24%). Similarmente, a cutia (Dasyprota azarae) removeu 16 (12%), mastigou 64 (49%), deixando intactos 51 frutos (39%). Os resultados são discutidos relacionando o papel das espécies de vertebrados na dispersão de sementes de S. romanzoffiana. Palavras-chave: Floresta Atlântica, Dasyprocta azarae, Didelphis albiventris, Nasua nasua, palmeira, Penelope obscura, dispersão de sementes, remoção de frutos

Effect of gelled inner aqueous phase rheology on the colour degradation of muitle aqueous extracts incorporated into water-in-oil-in-water double emulsions

The aim of this work was to study different W1/O/W2 double emulsions in preserving color muitle aqueous extract (MAE), for which the work was divided into two fold, formulation and analysis of primary emulsion W1/O and W1/O/W2 double emulsions. Sodium alginate (SA), xanthan gum, guar gum, locust bean gum were used as gelling agents of MAE, and it was found that SA produced inner aqueous phase with enhanced viscoelastic properties, resulting in a W1/O primary emulsion with more uniform mean droplet size and distribution than when using the other gelling agents or ungelled MAE. Subsequently W1/O/W2 double emulsions were produced containing MAE gelled with SA or ungelled in the inner aqueous phase stabilized using pure gum Arabic (GA) or a blend of GA-mesquite gum (MG) in a 70:30 ratio in the outer aqueous phase. The double emulsion formulated with gelled MAE and 70:30 GA-MG blend exhibited more uniform mean inner water and outer oil droplet sizes, and protected best the anthocyanins contained in MAE to preserve its color when exposed to 8 h sunlight, providing a half-time life (t1/2) of 55.23 h. The double emulsion formulated with ungelled MAE and stabilized with pure GA displayed a t1/2 of 7.40 h. Keywords: double emulsions, muitle aqueous extract, gelling agents, viscoelastic properties, droplet size, half-time life

Thermodynamic study of the effect of ions on the interaction between dengue virus NS3 helicase and single stranded RNA

Dengue virus nonstructural protein 3 (NS3) fulfills multiple essential functions during the viral replication and constitutes a prominent drug target. NS3 is composed by a superfamily-2 RNA helicase domain joined to a serine protease domain. Quantitative fluorescence titrations employing a fluorescein-tagged RNA oligonucleotide were used to investigate the effect of salts on the interaction between NS3 and single stranded RNA (ssRNA). We found a strong dependence of the observed equilibrium binding constant, Kobs, with the salt concentration, decreasing at least 7-fold for a 1-fold increase on cation concentration. As a result of the effective neutralization of ~10 phosphate groups, binding of helicase domain of NS3 to ssRNA is accompanied by the release of 5 or 7 monovalent cations from an oligonucleotide or a polynucleotide, respectively and of 3 divalent cations from the same oligonucleotide. Such estimates are not affected by the type of cation, either monovalent (KCl, NaCl and RbCl) or divalent (MgCl2 and CaCl2), nor by the presence of the protease domain or the fluorescein label. Combined effect of mono and divalent cations was well described by a simple equilibrium binding model which allows to predict the values of Kobs at any concentration of cations.Fil: Cababie, Leila Alejandra. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Departamento de Química Biológica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Química y Físico-Química Biológicas "Prof. Alejandro C. Paladini". Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Físico-Química Biológicas; ArgentinaFil: Incicco, Juan Jeremías. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Departamento de Química Biológica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Química y Físico-Química Biológicas "Prof. Alejandro C. Paladini". Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Físico-Química Biológicas; ArgentinaFil: Gonzalez-Lebrero, Rodolfo Martin. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Departamento de Química Biológica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Química y Físico-Química Biológicas "Prof. Alejandro C. Paladini". Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Físico-Química Biológicas; ArgentinaFil: Roman, Ernesto Andres. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Departamento de Química Biológica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Química y Físico-Química Biológicas "Prof. Alejandro C. Paladini". Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Físico-Química Biológicas; ArgentinaFil: Gebhard, Leopoldo German. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Gamarnik, Andrea Vanesa. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Kaufman, Sergio Benjamín. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Departamento de Química Biológica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Química y Físico-Química Biológicas "Prof. Alejandro C. Paladini". Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Físico-Química Biológicas; Argentin