pH do meio de cultivo e crescimento de plântulas de ginseng brasileiro cultivadas in vitro

O presente trabalho objetivou avaliar o efeito do pH do meio de cultivo sobre alguns parâmetros de crescimento da Pfaffia glomerata (Spreng.) Pedersen cultivada in vitro, bem como checar se o crescimento dos explantes altera o pH do meio ao longo do período de cultivo. Foram testados quatro tratamentos constituídos de distintos valores de pH (3,7; 5,0; 6,0 e 7,5) do meio de cultivo. O pH do meio de cultivo foi ajustado antes da inclusão do agar (6g L-1 - Merck) e da autoclavagem. Como fonte de explantes foram utilizadas segmentos nodais de plantas previamente estabelecidas in vitro em meio MS. Dos nove aos 15 dias após a inoculação (DAI) dos segmentos nodais, verificou-se maior número de raízes em pH 6,0 e o menor no pH 7,5. Aos 35 DAI, o comprimento da maior brotação e o número total de segmentos nodais por planta foram maiores em torno de pH 6,0. Aos 35 DAI, observou-se menor crescimento em biomassa de raízes em pH 3,7. Já a parte aérea apresentou menor biomassa em pH 7,5. Aos 35 DAI, a produção de matéria fresca e seca total da plântula foi maior em pH próximo a 6,0. Concluiu-se que valores de pH do meio de cultivo próximos a 6,0, ajustados antes da autoclavagem, são ideais para o crescimento da P. glomerata cultivada in vitro. Também se verificou que o crescimento da plântula modificou significativamente o pH do meio de cultivo.

Variabilidade espacial da textura de um Argissolo Vermelho Amarelo sob cultivo de pastagem e vegetação nativa

O conhecimento da variabilidade espacial dos atributos de um solo sob diferentes coberturas auxilia o estudo das alterações ocorridas em razão do manejo. O objetivo deste trabalho foi determinar, com uso da estatística clássica e geoestatística, a variabilidade espacial das frações texturais de um solo cultivado com pastagem e vegetação nativa. Amostras de solo foram coletadas na profundidade de 0-0,20m, nos pontos de cruzamento de uma malha, com intervalos regulares de 10m, totalizando 64 pontos em cada área. Na área de pastagem, as frações areia grossa e total apresentaram valores médios maiores em relação à vegetação nativa e correlações negativas com as altitudes dos pontos amostrais nas duas áreas. Todas as frações texturais apresentaram dependência espacial de moderada a alta nas duas áreas e com o patamar definido, com exceção da areia fina e do silte na pastagem. Grande parte dessa variabilidade ocorre em função da erosão hídrica.

Cultivo da microalga marinha Chaetoceros calcitrans (BACILLARIOPHYCEAE) utilizando diferentes tipos de água marinha artificial

The use of microalgae as live food to a wide variety of organisms is one of the most important aspects in aquaculture. Several commercial formulations have been available in the marine aquarium market in order to prepare artificial sea water (ASW). The present study accounted microalgae Chaetoceros calcitrans performance cultured using different ASW in comparison to natural seawater(NSW). it was carried out using red Sea, Coralife and oceanic, three different ASW brands and NSW as control. nonaerated cultures were grew in 400 mL with Conwy culture medium with five replicates each under defined conditions. All cultures began with an algal inoculum of 208.000 cells/mL. a 5-mL aliquot was removed daily from each culture for cells counts. data obtained using polynomial regression test demonstrated that all ASW brands reached higher algal density rates than the one with NSW, though the three ASW brands were significantly heterogeneous. C. calcitrans raised with oceanic and red Sea brands showed similar growth rates and both were higher than Coralife brand. the results suggest that all three ASW brands studied can be used in the culture of this microalgae specie.

Effect of alpha prime due to 475 degrees C aging on fracture behavior and corrosion resistance of DIN 1.4575 and MA 956 high performance ferritic stainless steels

The 475 degrees C embrittlement in stainless steels is a well-known phenomenon associated to alpha prime (alpha`) formed by precipitation or spinodal decomposition. Many doubts still remain on the mechanism of alpha` formation and its consequence on deformation and fracture mechanisms and corrosion resistance. In this investigation, the fracture behavior and corrosion resistance of two high performance ferritic stainless steels were investigated: a superferritic DIN 1.4575 and MA 956 superalloy were evaluated. Samples of both stainless steels (SS) were aged at 475 degrees C for periods varying from 1 to 1,080 h. Their fracture surfaces were observed using scanning electron microscopy (SEM) and the cleavage planes were determined by electron backscattering diffraction (EBSD). Some samples were tested for corrosion resistance using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. Brittle and ductile fractures were observed in both ferritic stainless steels after aging at 475 degrees C. For aging periods longer than 500 h, the ductile fracture regions completely disappeared. The cleavage plane in the DIN 1.4575 samples aged at 475 degrees C for 1,080 h was mainly {110}, however the {102}, {314}, and {131} families of planes were also detected. The pitting corrosion resistance decreased with aging at 475 degrees C. The effect of alpha prime on the corrosion resistance was more significant in the DIN 1.4575 SS comparatively to the Incoloy MA 956.

Columbia revisited: Paleomagnetic results from the 1790 Ma colider volcanics (SW Amazonian Craton, Brazil)

In an attempt to improve our understanding of the Paleoproterozoic geodynamic evolution, a paleomagnetic study was performed on 10 sites of acid volcanic rocks of the Colider Suite, southwestern Amazonian Craton. These rocks have a well-dated zircon U-Pb mean age of 1789 +/- 7 Ma. Alternating field and thermal demagnetization revealed northern (southern) directions with moderate to high upward (downward) inclinations. Rock magnetism experiments and magnetic mineralogy show that this characteristic magnetization is carried by Ti-poor magnetite or by hematite that replaces magnetite by late-magmatic cleuteric alteration. Both magnetite and hematite carry the same characteristic component. The mean direction (Dm = 183.0 degrees, Im = 53.5 degrees, N = 10, alpha(95) = 9.8 degrees, K = 25.2) yielded a paleomagnetic pole located at 298.8 degrees E, 63.3 degrees S (alpha(95) = 10.2 degrees, K = 23.6), which is classified with a quality factor Q = 5. Paleogeographic reconstructions using this pole and other reliable Paleoproterozoic poles suggest that Laurentia, Baltica, North China Craton and Amazonian Craton were located in laterally contiguous positions forming a large continental mass at 1790 Ma ago. This is reinforced by geological evidence which support the existence of the supercontinent Columbia in Paleoproterozoic times. (C) 2008 Elsevier B.V. All rights reserved.

Isotopic evidence for the late Brasiliano (500-550 Ma) ore-forming mineralization of the Araes gold deposit, Brazil

The Araes gold deposit, located in eastern Mato Grosso State, central Brazil, is hosted in Neoproterozoic volcanosedimentary rocks of the Paraguay belt, which formed during collision of the Amazonian craton and the Rio Apa block. Ar-40/Ar-39 geochronology and Pb and S isotopic analyses constrain the timing and sources of mineralization. Three biotite flakes from two samples of metavolcanic host rock yield Ar-40/Ar-39 plateau ages between 5941 and 531 Ma, interpreted as cooling ages following regional metamorphism. Clay minerals from a hydrothermal alteration zone yield an Ar-40/Ar-39 integrated age of 503 +/- 3 Ma. Galena grains from ore-bearing veins yield values of Pb-206/(204)pb from 17.952 to 18.383, Pb-207/Pb-204 from 15.156 to 15.811, and Pb-208/Pb-204 from 38.072 to 39.681. Pyrite grains from ore-bearing veins yield values of Pb-206/Pb-204 from 18.037 to 18.202, Pb-207/Pb-204 from 15.744 to 15.901., and Pb-208/(204)pb from 38.338 to 38.800. Pb isotope variations may be explained in terms of mixing a less radiogenic lead component (mu similar to 8.4) from mafic and ultramafic basement host-rocks (Nova Xavantina metavolcanosedimentary rocks) and a more radiogenic lead component (mu similar to 9.2) probably derived from supracrustal rocks (Cuiaba sedimentary groups). Sulfur isotope compositions are homogeneous, with delta S-34 values ranging from -1.1 parts per thousand to 0.9 parts per thousand (galena) and -0.7 parts per thousand to 0.9 parts per thousand (pyrite), suggesting a mantle-derived reservoir for the mineralizing solutions. Based on the Ar, Pb, and S isotope data, we suggest that the precious metals were remobilized from metavolcanic host rocks by hydrothermal solutions during Brasilide-Panafrican regional metamorphism. The Arabs gold deposit probably formed during a late stage of the orogeny, coeval with other mineralization events in the Paraguay Belt.