Redox changes during the cell cycle in the embryonic root meristem of Arabidopsis thaliana

Aims: The aim of this study was to characterize redox changes in the nuclei and cytosol occurring during the mitotic cell cycle in the embryonic roots of germinating Arabidopsis seedlings, and to determine how redox cycling was modified in mutants with a decreased capacity for ascorbate synthesis. Results: Using an in vivo reduction-oxidation (redox) reporter (roGFP2), we show that transient oxidation of the cytosol and the nuclei occurred at G1 in the synchronized dividing cells of the Arabidopsis root apical meristem, with reduction at G2 and mitosis. This redox cycle was absent from low ascorbate mutants in which nuclei were significantly more oxidized than controls. The cell cycle-dependent increase in nuclear size was impaired in the ascorbate-deficient mutants, which had fewer cells per unit area in the root proliferation zone. The transcript profile of the dry seeds and size of the imbibed seeds was strongly influenced by low ascorbate but germination, dormancy release and seed aging characteristics were unaffected. Innovation: These data demonstrate the presence of a redox cycle within the plant cell cycle and that the redox state of the nuclei is an important factor in cell cycle progression. Conclusions: Controlled oxidation is a key feature of the early stages of the plant cell cycle. However, sustained mild oxidation restricts nuclear functions and impairs progression through the cell cycle leading to fewer cells in the root apical meristem

Phenomenology of the Lense-Thirring effect in the Solar System

Recent years have seen increasing efforts to directly measure some aspects of the general relativistic gravitomagnetic interaction in several astronomical scenarios in the solar system. After briefly overviewing the concept of gravitomagnetism from a theoretical point of view, we review the performed or proposed attempts to detect the Lense-Thirring effect affecting the orbital motions of natural and artificial bodies in the gravitational fields of the Sun, Earth, Mars and Jupiter. In particular, we will focus on the evaluation of the impact of several sources of systematic uncertainties of dynamical origin to realistically elucidate the present and future perspectives in directly measuring such an elusive relativistic effect.Comment: LaTex, 51 pages, 14 figures, 22 tables. Invited review, to appear in Astrophysics and Space Science (ApSS). Some uncited references in the text now correctly quoted. One reference added. A footnote adde

Developmental trajectories of cerebral blood flow and oxidative metabolism at baseline and during working memory tasks

The neurobiological interpretation of developmental BOLD fMRI findings remains difficult due to the confounding issues of potentially varied baseline of brain function and varied strength of neurovascular coupling across age groups. The central theme of the present research is to study the development of brain function and neuronal activity through in vivo assessments of cerebral blood flow (CBF), oxygen extraction fraction (OEF) and cerebral metabolic rate of oxygen (CMRO2) both at baseline and during the performance of a working memory task in a cohort of typically developing children aged 7 to 18years. Using a suite of 4 emerging MRI technologies including MR blood oximetry, phase-contrast MRI, pseudo-continuous arterial spin labeling (pCASL) perfusion MRI and concurrent CBF/BOLD fMRI, we found: 1) At baseline, both global CBF and CMRO2 showed an age related decline while global OEF was stable across the age group; 2) During the working memory task, neither BOLD nor CBF responses showed significant variations with age in the activated fronto-parietal brain regions. Nevertheless, detailed voxel-wise analyses revealed sub-regions within the activated fronto-parietal regions that show significant decline of fractional CMRO2 responses with age. These findings suggest that the brain may become more "energy efficient" with age during development

Etnopedologia e transferência de conhecimento: diálogos entre os saberes indígena e técnico na Terra Indígena Malacacheta, Roraima Ethnopedology and knowledge transfer: dialogue between indians and soil scientists in the Malacacheta Indian Territory, Roraima, Amazon

O conhecimento indígena sobre a pedodiversidade é o objeto principal da etnopedologia. Nesse sentido, a tradição agrícola e cultural dos índios Uapixana, do tronco lingüístico Aruaque, em Roraima, constitui relevante acervo imaterial de valor etnocientífico, sendo valorizada pela Universidade Federal de Roraima em seus cursos superiores de Educação Indígena no Estado. Neste trabalho confrontou-se a experiência etnopedológica dos índios Uapixana com o Sistema Brasileiro de Classificação de Solos, durante o levantamento de solos da Terra Indígena (TI) Malacacheta. O sistema de classificação etnopedológica existente na comunidade indígena Uapixana da TI Malacacheta identifica e separa todos os principais compartimentos ambientais de ocorrência na área, permitindo relacionar aspectos de simples percepção e identificação (cor, textura, profundidade, vegetação) com aspectos cognoscíveis (uso, tipo de cultivo, vocação, etc.). Os índios Uapixana identificam e classificam oito tipos básicos de solos, que ocorrem individualmente ou formando associações: Imii Wyzda'u (Terra Amarelada), Imii Wyza'u (Terra Vermelha), Imii Pudiidiu (Terra Preta), Imii Pudiidiza'u (Terra Roxa), Katy Bara Pudiidiu (Barro Arenoso), Imii Kaxidia'u (Estopa Preta), Imii Katy Bara Pudiidiu Naik Baraka'u (Terra Arenosa Preta e Branca) e Imii Wyzadaza'u Rik Pudiidiu (Miscelânea de Terra Amarela, Roxa e afloramentos de rocha), abordando características morfológicas, físicas e químicas e as principais limitações quanto ao uso agrícola. Há relação evidente entre a dimensão do saber etnopedológico o saber etnoecológico, em sentido amplo. A experiência etnopedológica representa, assim, a extensão de uma abrangente cadeia de inter-relações homem-meio, dentro do princípio universal da ecologia humana da paisagem. O diálogo etnopedológico travado entre a comunidade indígena e os pedólogos trouxe contribuições muito relevantes e mutuamente benéficas: facilitou a transferência de conhecimento entre dois saberes, in loco, desvendando boa parte das relações etnopedológicas e etnoecológicas e refletindo sobre "como" e "por que" cada grupo identificava um dado tipo de solo. Permitiu ainda delinear o esboço da distribuição dos solos com base no saber indígena, utilizando a extrapolação cartográfica disponível ao pedólogo; esse fato facilitou o próprio mapeamento convencional, especialmente no reconhecimento de inclusões e associações de solos. De forma mais destacada, a experiência permitiu ainda uma real comunicação e aproximação entre os agentes do saber (indígenas e técnico), com base na troca e em descobertas mútuas de conhecimentos, gerando uma sinergia que aproxima o técnico e o indígena, com resultados práticos palpáveis, que extrapolam o próprio objetivo inicial do levantamento de solos da TI Malacacheta.<br>Ethnopedology deals mainly with indigenous knowledge on pedo-diversity. In this sense, the agricultural and cultural traditions of the Wapishana Indians in Roraima, of the Arawak linguistic background, constitute a relevant pool of ethno-scientific knowledge in Amazonia. The Federal University of Roraima has increasingly acknowledged their importance in the Indigenous Education undergraduate courses. In this study, the ethnopedological classifications of the Wapishana Indians were confronted with the Brazilian System of Soil Classification in a soil survey of the Malacacheta Indian Territory. The ethnopedological classification of Wapishana Indians identifies and separates all environmental segments of the area, relating easily recognizable aspects of the soilscape (color, texture, depth, vegetation) with observable aspects (land use, cultivation type, suitability). The Wapishana classify eight basic soil types, that occur either separately or in associations: Imii Wyzda'u (Yellowish earth), Imii Wyza'u (Red earth), Imii Pudiidiu (Black Earth), Imii Pudiidiza'u (Dusky-Red Earth), Katy Bara Pudiidiu (Sandy loam), Imii Kaxidia'u (Black spongy), Imii Katy Bara Pudiidiu Naik Baraka'u (Black and White Sandy Ground) and Imii Wyzadaza'u Rik Pudiidiu (Mixed Yellowish earth, Dusky-Red earth and Rock outcrops), based on morphological, physical and chemical attributes, as well as land use limitations. There are clear relationships between the ethnopedological knowledge and the ethno-ecological dimension of the Wapishana culture, in the broadest sense. The ethnopedological observations, thus, represent an expression of the interwoven network of man-environment relationships, seen in a framework of universal principles of human/landscape ecology. The intense ethnopedological dialogue between soil scientists and Indians resulted in enriching, mutually beneficial contributions: the proper knowledge transfer in loco between two different traditions, the clarification of great part of the ethnopedological perceptions of both groups, and the understanding on how and why each group identified a given soil. Moreover, a soil map based on indigenous knowledge was drawn up, in an extrapolation of the cartographical base available to pedologists; this supported the conventional soil mapping of the area as well, especially in the recognition of soil inclusions and associations. Particularly, the experience allowed effective communication and approach of the representatives of indigenous and technical knowledge, based on knowledge transfer and mutual discoveries of understanding, creating synergy effects with promising results, which outreached the original aim of soil mapping of the Malacacheta Indian Territory

CREAM for high energy composition measurements

Ground-based indirect measurements have shown that the cosmic-ray all- particle spectrum extends many orders of magnitude beyond the energy thought possible for supernova acceleration. Our balloon-borne Cosmic Ray Energetics And Mass (CREAM) experiment is capable of extending direct measurements of cosmic-rays to the supernova energy scale of 1015 eV in a series of Ultra Long Duration Balloon (ULDB) flights. Identification of Z = 1 - 26 particles will be made with a timing-based charge detector and a pixelated silicon charge detector. Energy measurements will be made with a transition radiation detector and a tungsten/scintillating fiber calorimeter. The instrument has been tested with various particles in accelerated beams at the CERN SPS. The first flight is planned to be launched from Antarctica in December 2004

Oxidative stress response in sugarcane

Oxidative stress response in plants is still poorly understood in comparison with the correspondent phenomenon in bacteria, yeast and mammals. For instance, nitric oxide is assumed to play various roles in plants although no nitric oxide synthase gene has yet been isolated. This research reports the results of a search of the sugarcane expressed sequence tag (SUCEST) database for homologous sequences involved in the oxidative stress response. I have not found any gene similar to nitric oxide synthase in the SUCEST database although an alternative pathway for nitric oxide synthesis was proposed. I have also found several genes involved in antioxidant defense, e.g. metal chelators, low molecular weight compounds, antioxidant enzymes and repair systems. Ascorbate (vitamin C) is a key antioxidant in plants because it reaches high concentrations in cells and is a substrate for ascorbate peroxidase, an enzyme that I found in different isoforms in the SUCEST database. I also found many enzymes involved in the biosynthesis of low molecular weight antioxidants, which may be potential targets for genetic manipulation. The engineering of plants for increased vitamin C and E production may lead to improvements in the nutritional value and stress tolerance of sugarcane. The components of the antioxidant defense system interact and their synthesis is probably closely regulated. Transcription factors involved in regulation of the oxidative stress response in bacteria, yeast and mammals differ considerably among themselves and when I used them to search the SUCEST database only genes with weak similarities were found, suggesting that these transcription regulators are not very conserved. The involvement of reactive oxygen species and antioxidants in plant defense against pathogens is also discussed.<br>A resposta ao estresse oxidativo não é bem conhecida em plantas como em bactérias, leveduras e humanos. Por exemplo, assume-se que óxido nítrico tem várias funções em plantas apesar do gene que codificaria para óxido nítrico sintetase nunca ter sido isolado. Este trabalho descreve os resultados de uma busca no banco de dados de seqüências expressas de cana de açúcar (SUCEST) de genes envolvidos na resposta ao estresse oxidativo. Eu não encontrei genes similares a óxido nítrico no banco de dados do SUCEST, mas uma via alternativa para a produção deste radical livre pode ser proposta. Eu também encontrei vários genes envolvidos na defesa antioxidante, como quelantes de metais, antioxidantes de baixo peso molecular, enzimas antioxidantes e sistemas de reparo. Ascorbato (vitamina C) é um importante antioxidante em plantas porque é encontrado em altas concentrações em células vegetais e porque é substrato de ascorbato peroxidase, uma enzima que eu encontrei em diferentes isoformas no banco de dados do SUCEST. Eu também encontrei várias enzimas envolvidas na biossíntese de antioxidantes de baixo peso molecular que podem ser alvos para manipulação genética. A obtenção de plantas modificadas geneticamente que sintetizariam vitaminas C e E em altos níveis poderiam melhorar o valor nutricional e a tolerância a estresses de cana de açúcar. Os diversos componentes do sistema de defesa antioxidante interagem entre si e as suas sínteses devem ser muito bem reguladas. Fatores de transcrição envolvidos na regulação da resposta ao estresse oxidativo de bactérias, leveduras e de humanos diferem consideravelmente entre si e quando foram utilizados para buscas no banco de dados do SUCEST, somente genes com similaridades fracas foram encontrados, sugerindo que estas proteínas não são muito conservadas. O envolvimento de espécies reativas de oxigênio e nitrogênio na defesa de plantas contra patógenos também é discutido neste trabalho