Surplus Photosynthetic Antennae Complexes Underlie Diagnostics of Iron Limitation in a Cyanobacterium

Chlorophyll fluorescence from phytoplankton provides a tool to assess iron limitation in the oceans, but the physiological mechanism underlying the fluorescence response is not understood. We examined fluorescence properties of the model cyanobacterium Synechocystis PCC6803 and a ΔisiA knock-out mutant of the same species grown under three culture conditions which simulate nutrient conditions found in the open ocean: (1) nitrate and iron replete, (2) limiting-iron and high-nitrate, representative of natural high-nitrate, low-chlorophyll regions, and (3) iron and nitrogen co-limiting. We show that low variable fluorescence, a key diagnostic of iron limitation, results from synthesis of antennae complexes far in excess of what can be accommodated by the iron-restricted pool of photosynthetic reaction centers. Under iron and nitrogen co-limiting conditions, there are no excess antennae complexes and variable fluorescence is high. These results help to explain the well-established fluorescence characteristics of phytoplankton in high-nutrient, low-chlorophyll ocean regions, while also accounting for the lack of these properties in low-iron, low-nitrogen regions. Importantly, our results complete the link between unique molecular consequences of iron stress in phytoplankton and global detection of iron stress in natural populations from space

Estructural-funcionalismo: un análisis crítico de su estructura y función

Área de Política y Gestión Públic

Elaboración de un "Peletizado" flotante para Tilapia con 30% de proteína

32 p.La extrusión es un proceso donde una mezcla de materiales crudos son calentados y cocinados por medio de altas temperaturas y un choque de posición. En los países en vías de desarrollo, la mayoría del alimento concentrado utilizado para la alimentación de tilapia es pulverizado, lo que presenta desventajas por las altas pérdidas durante el transporte, precipitación de nutrientes, deriva y contaminación del agua. En la Planta de procesamiento de Granos de Zamorano se evaluaron tres velocidades de alimentación (1.8, 2.5 y 3,2 kg/min) y tres flujos de agua (0.6, 0,8 y 1 1/min) añadidos al proceso para obtener un "pellet" flotante para tilapia, empleando una maquina "peletizadora" marca Insta-Pro. Se evaluaron las características físicas del producto (densidad, resistencia física y flotabilidad) y se compararon los tratamientos usando la prueba Tukey de medias. Al aumentar la velocidad de alimentación del extrusor, el "pellet" tendió a ser más, denso y a perder resistencia física, mientras que al aumentar el flujo de agua, el volumen y la resistencia física del "pellet" aumentaron. EI tratamiento con un flujo de agua de 0,8 1/min y una velocidad de alimentación de 3,2 kg/min produjo un "pellet" con valores aceptables de densidad aparente (45 kg/HI) y resistencia al manipuleo (19.5% de finos). Ningún "pellet" flotó en el agua. La no flotabilidad de los "pellets" se debió, probablemente, a la falta de eficiente presión de agua inyectada al extrusor.1. índice de cuadros 2. Índice de figuras 3. Índice de anexos 4. Introducción 5. Revisión de literatura 6. Materiales y métodos 7. Conclusiones 8. Recomendaciones 9. Bibliografía 10. Anexo

Colômbia: mais insegurança humana, menos segurança regional Colombia: more human insecurity, less regional security

No contexto da grave crise que atravessa a região andina em seu conjunto, o exemplo da Colômbia é o mais dramático e serve potencialmente de modelo de intervenção externa nos assuntos internos de um país do hemisfério. Nesse sentido, analisa-se o tipo de guerra que vive a Colômbia, assim como o chamado novo intervencionismo e as possíveis saídas para o conflito armado no referido país. Trata-se de uma situação complexa e instável em que se misturam e confundem guerra política, violência criminal, demolição do Estado, violação dos direitos humanos e expansão do poderio estadunidense na região. Como decorrência do aumento dos confrontos internos, da persistência da "guerra contra as drogas" e do começo da "guerra contra o terrorismo", a ingerência dos Estados Unidos é cada vez mais eloqüente e preocupante. Enquanto isso, uma América do Sul passiva não parece querer comprometer-se com uma saída viável para um conflito expansivo no coração dos Andes.<br>The Colombian predicament, characterized by foreign intervention in the domestic issues of a country in the Southern hemisphere, can be considered the most dramatic crisis amongst the various crises in the Andes region. The author analyzes the kind of war that exists in Colombia, as well as the so-called new interventionism and the possible solutions of the conflict in that country. It is a very complex and unstable situation in which political war, criminal violence, the destruction of the state, violation of human rights and the expansion of US power are all mixed. The intervention of the US in Colombia as a consequence of growing domestic conflicts, the continuation of the "war against drugs" and the beginning of "the war against terrorism," is increasingly evident and worrying. Meanwhile, a passive South America does not seem to be willing to engage itself in the search for a viable solution to an expanding conflict in the heart of the Andes

Regional contribution of CO₂ and CH₄ fluxes from the fluvial network in a lowland boreal landscape of Québec

Boreal rivers and streams are known as hot spots of CO2 emissions, yet their contribution to CH4 emissions has traditionally been assumed to be negligible, due to the spatially fragmented data and lack of regional studies addressing both gases simultaneously. Here we explore the regional patterns in river CO2 and CH4 concentrations (pCO2 and pCH4), gas exchange coefficient (k), and the resulting emissions in a lowland boreal region of Northern Québec. Rivers and streams were systematically supersaturated in both gases, with both pCO2 and pCH4 declining along the river continuum. The k was on average low and increased with stream order, consistent with the hydrology of this flat landscape. The smallest streams (order 1), which represent < 20% of the total river surface, contributed over 35% of the total fluvial greenhouse gas (GHG) emissions. The end of winter and the spring thaw periods, which are rarely included in annual emission budgets, contributed on average 21% of the annual GHG emissions. As a whole, the fluvial network acted as significant source of both CO2 and CH4, releasing on average 1.5 tons of C (CO2 eq) yr−1 km−2 of landscape, of which CH4 emissions contributed approximately 34%. We estimate that fluvial CH4 emissions represent 41% of the regional aquatic (lakes, reservoirs, and rivers) CH4 emissions, despite the relatively small riverine surface (4.3% of the total aquatic surface). We conclude that these fluvial networks in boreal lowlands play a disproportionately large role as hot spots for CO2 and more unexpectedly for CH4 emissions