Local Approach of the Charpy Test at Low Temperature

Charpy V-notch impact testing is widely used in the toughness assessment of large forged components, e.g. the pressure vessel for pressurised water reactors (PWR). At low temperature, A508 Cl.3 nuclear pressure vessel steel fails by cleavage fracture. The results reported here are part of both an experimental program and numerical investigations which aim at the establishment of a non-empirical relationship between the lower shelf Charpy V-notch energy, CVN, and the fracture toughness, KIc, of this material. Here, the applicability of the Beremin cleavage fracture model to the Charpy specimen is demonstrated

Identification of Zantedeschia aethiopica Cat1 and Cat2 catalase genes and their expression analysis during spathe senescence and regreening

Plants encode catalase (CAT; EC 1.11.1.6) as multigene families, which may reflect the multiple and diverse roles played by this enzyme. Catalases from higher plants can be subdivided into three distinct types, according to their phylogenetic relationship. However, there is not a specific correlation of phylogeny and function within these groups, as catalases from the same type can play different specific roles. We report on the characterization of two monocot catalase genes from Zantedeschia aethiopica (a C_3-type Araceae) and its expression analysis during spathe senescence and regreening. Z. aethiopica CAT2 appears to play an exclusive role in scavenging photorespiratory H_2O_2, but is more phylogenetically related to the unspecific Zea mays CAT3 and Oryza sativa CATA than to the photorespiratory-related Zea mays CAT2 and Oryza sativa CATC. Z. aethiopica CAT1 is more phylogenetically related to Zea mays CAT1 and Oryza sativa CATB and appears to have a dual role in scavenging glyoxysomal and peroxisomal H_2O_2.Fundação para a Ciência e a Tecnologia (FCT) - PRAXIS XXI/BD/16280/98 , SFRH/BD/12081/2003

Differential Phosphorylation of Ribosomal Proteins in Arabidopsis thaliana Plants during Day and Night

Protein synthesis in plants is characterized by increase in the translation rates for numerous proteins and central metabolic enzymes during the day phase of the photoperiod. The detailed molecular mechanisms of this diurnal regulation are unknown, while eukaryotic protein translation is mainly controlled at the level of ribosomal initiation complexes, which also involves multiple events of protein phosphorylation. We characterized the extent of protein phosphorylation in cytosolic ribosomes isolated from leaves of the model plant Arabidopsis thaliana harvested during day or night. Proteomic analyses of preparations corresponding to both phases of the photoperiod detected phosphorylation at eight serine residues in the C-termini of six ribosomal proteins: S2-3, S6-1, S6-2, P0-2, P1 and L29-1. This included previously unknown phosphorylation of the 40S ribosomal protein S6 at Ser-231. Relative quantification of the phosphorylated peptides using stable isotope labeling and mass spectrometry revealed a 2.2 times increase in the day/night phosphorylation ratio at this site. Phosphorylation of the S6-1 and S6-2 variants of the same protein at Ser-240 increased by the factors of 4.2 and 1.8, respectively. The 1.6 increase in phosphorylation during the day was also found at Ser-58 of the 60S ribosomal protein L29-1. It is suggested that differential phosphorylation of the ribosomal proteins S6-1, S6-2 and L29-1 may contribute to modulation of the diurnal protein synthesis in plants

Charpy V-Notch Impact Testing and Brittle Fracture in an A508 CL.3 Bainitic Steel

Les essais charpy sont largement utilisés pour prévoir la ténacité de pièces forgées comme par exemple les viroles des cuves nucléaires des réacteurs à eau sous pression REP. Dans les aciers bainitiques de type A508 Cl 3 testés à basse température, il se produit une rupture instable par clivage. Les résulats d'un programme expérimental et de simulations numériques sont présentés ici dans le but d'établir une relation non empirique entre résilience KCV et ténacité KIC. Dans ce papier, le modèle de Beremin qui est basé sur un concept de contrainte critique et sur une statistique de type Weibull est appliqué aux seuls essais Charpy.Charpy V-notch impact testing is widely used in the toughness diagnostic of large forged components, e.g. the vessel of pressurized water reactors (PWR). In an A508 Cl.3 bainitic steel tested at low temperature, cleavage occurs at the initiation of unstable failure. The results reported here are part of both an experimental program and numerical investigations in order to establish a non-empirical relationship between Charpy V-notch energy CVN and fracture toughness KIC. The Beremin model which is based on a critical fracture stress concept and Weibull statistics, is only applied on CVN tests

Does oxidative stress metabolism play a role in Zantedeschia aethiopica spathe senescence?

Apresentação efectuada no Oxidative Stress and Cell Signalling IBMC Advanced Course, 27 a 29 Outubro 2004, Porto.Plant senescence is a natural regulated and programmed process that leads ultimately to cell death. Numerous studies in different plant species have suggested a role for reactive oxygen species (ROS) in the progress of senescence programs, which is frequently associated with the degradative aspects of senescence physiology. The general increase of ROS during leaf aging as well as their damage products are probably due to the induction of the generating systems of these oxidative species and/or to a decrease in the protective mechanisms against activated oxygen forms. In this work the development of the C3 monocot Zantedeschia aethiopica floral spathe has been used as a natural model for studying the physiological and biochemical features of senescence. This photosynthetic leaf-like organ undergoes senescence displaying the common features of leaf senescence, such as loss of protein, chlorophyll and a decline on photosynthetic ability. Fruiting inhibits the ongoing spathe senescence and the regreening of its abaxial parenchyma cells is observed. Previous studies have shown that during the time course of spathe development some dramatic changes occurs, namely in the ultraestructure of chloroplasts and peroxisomes. Some evidences suggest that during the spathe whitening peroxissomes differentiate into glyoxysomes and chloroplasts into amyloplasts. The regreening process is followed by the restructuration of chloroplasts and peroxisomes, resulting in the re-acquisition of photosynthetic and photorespiratory capacities. In order to clarify the role of oxidative stress metabolism in spathe senescence two cytosolic ascorbate-glutathione cycle enzymes (cytCuZn-SOD and csAPX), directly involved in the antioxidant cellular mechanism were studied. The corresponding expression analysis was correlated with H2O2 content and lipid peroxidation level during the time course of Z. aethiopica spathe development suggesting an initial burst of H2O2 in the cytosol that could serve as a signal for the progression of the senescence program during spathe whitening. An integrated approach involving EST analysis and multiparallel expression profiling by macroarray analysis of senescence associated genes and oxidative stress related genes was also undertaken. Expression profile of oxidative stress related genes seems to parallel the expression profile of senescence associated genes suggesting an involvement of ROS in signalling and in degradative processes during Z. aethiopica spathe senescence.Fundação para a Ciência e a Tecnologia (FCT) - grant ref. SFRH/BD/12081/2003