Oxygen Requirement and Inhibition of C4 Photosynthesis1 : An Analysis of C4 Plants Deficient in the C3 and C4 Cycles

The basis for O2 sensitivity of C4 photosynthesis was evaluated using a C4-cycle-limited mutant of Amaranthus edulis (a phosphoenolpyruvate carboxylase-deficient mutant), and a C3-cycle-limited transformant of Flaveria bidentis (an antisense ribulose-1,5-bisphosphate carboxylase/oxygenase [Rubisco] small subunit transformant). Data obtained with the C4-cycle-limited mutant showed that atmospheric levels of O2 (20 kPa) caused increased inhibition of photosynthesis as a result of higher levels of photorespiration. The optimal O2 partial pressure for photosynthesis was reduced from approximately 5 kPa O2 to 1 to 2 kPa O2, becoming similar to that of C3 plants. Therefore, the higher O2 requirement for optimal C4 photosynthesis is specifically associated with the C4 function. With the Rubisco-limited F. bidentis, there was less inhibition of photosynthesis by supraoptimal levels of O2 than in the wild type. When CO2 fixation by Rubisco is limited, an increase in the CO2 concentration in bundle-sheath cells via the C4 cycle may further reduce the oxygenase activity of Rubisco and decrease the inhibition of photosynthesis by high partial pressures of O2 while increasing CO2 leakage and overcycling of the C4 pathway. These results indicate that in C4 plants the investment in the C3 and C4 cycles must be balanced for maximum efficiency.

Regulation of Leaf Senescence by Cytokinin, Sugars, and Light : Effects on NADH-Dependent Hydroxypyruvate Reductase

The aim of this study was to investigate the interactions between cytokinin, sugar repression, and light in the senescence-related decline in photosynthetic enzymes of leaves. In transgenic tobacco (Nicotiana tabacum) plants that induce the production of cytokinin in senescing tissue, the age-dependent decline in NADH-dependent hydroxypyruvate reductase (HPR), ribulose-1,5-bisphosphate carboxylase/oxygenase, and other enzymes involved in photosynthetic metabolism was delayed but not prevented. Glucose (Glc) and fructose contents increased with leaf age in wild-type tobacco and, to a greater extent, in transgenic tobacco. To study whether sugar accumulation in senescing leaves can counteract the effect of cytokinin on senescence, discs of wild-type leaves were incubated with Glc and cytokinin solutions. The photorespiratory enzyme HPR declined rapidly in the presence of 20 mm Glc, especially at very low photon flux density. Although HPR protein was increased in the presence of cytokinin, cytokinin did not prevent the Glc-dependent decline. Illumination at moderate photon flux density resulted in the rapid synthesis of HPR and partially prevented the negative effect of Glc. Similar results were obtained for the photosynthetic enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase. It is concluded that sugars, cytokinin, and light interact during senescence by influencing the decline in proteins involved in photosynthetic metabolism.

Sistema de creación de tutoriales interactivos para el aprendizaje de lenguajes de programación

En estos últimos años la curiosidad por el sector informático, y más específicamente en la programación, ha producido una gran demanda por los interesados en estas áreas. Esto ha provocado que el número de tutoriales y entrenadores haya aumentado de una forma considerable. Debido a esta gran demanda, ha surgido la idea de desarrollar una herramienta con la que poder gestionar tutoriales de programación con una aplicación de escritorio. La finalidad de este proyecto es poder crear tutoriales interactivos que permitan a los alumnos adquirir conocimientos de una forma sencilla y atractiva. Esto se consigue mediante la posibilidad de enriquecer el formato del texto al mostrar las explicaciones o los enunciados de las preguntas y añadir imágenes. Para evitar que sea un tutorial de sólo lectura, que resulta poco atractivo y no permite al estudiante evaluar los conocimientos adquiridos, con esta herramienta se podrán intercalar preguntas entre la teoría para enganchar más al alumno, y conseguir que el aprendizaje sea muy incremental, para no tener una cantidad abrumadora de información en poco tiempo. Con estos tutoriales el alumno podrá comprobar los conocimientos adquiridos gracias al seguimiento continuo. El estudiante, según lea la teoría y realice los ejercicios con grado de dificultad creciente, tendrá más capacidad para resolver ejercicios nuevos y prepararse para continuar el tutorial. El resultado de este proyecto ha sido una herramienta multiplataforma y con licencia abierta MIT, que puede ser descargada de https://github.com/Kherdu/TFG.

Global and regional financial safety nets: lessons from Europe and Asia. Bruegel Working Paper 2013/06 [07?], November 2013

The Asian financial crisis (1997) and the European crisis (2009) have both contributed to the development and deepening of regional safety net arrangements. This paper analyses the relationships between global and regional financial safety nets, and uncovers the potential tensions and operational challenges associated with the involvement of several institutional players with potentially different interests, analytical biases and governance. The G20 has acknowledged the importance of these new players for the international monetary system, but the principles for cooperation between the IMF and regional financing arrangements are far too broad and ad hoc to contribute to a coherent and effective architecture. This paper tries to establish some lessons learned from the Asian financial crisis in 1997 and the current European crisis in order to enhance the effectiveness, efficiency, equity and governance of these arrangements. In particular, it proposes changes to the IMF articles of agreement to allow for lending or guarantees to regional arrangements directly and it establishes some key desirable features and practices of regional mechanisms that should be adopted everywhere to ensure some global consistency, particularly in the field of macroeconomic surveillance, programme design and conditionality.

Der Knallfall; Knalldruckmessungen in der Forensik

Beim Gebrauch von Schusswaffen, welche im Rahmen von Straftaten und Delikten ihre Verwendung finden, kommt es, wie der vorliegende Fall zeigt, neben der Gefährdung durch das Geschoss oder den Gasstrahl (Schreckschusswaffen) selbst, zu einer akustischen Belastung, durch die das Gehör irreversibel geschädigt werden kann. Im Rahmen eines versuchten Brandanschlags mit nachfolgender Flucht vor der Polizei, kam es bei der Stellung des Tatverdächtigen zum Gebrauch einer Schreckschusswaffe vom Modell Colt Government 1911 im Kaliber 9 mm PA Knall, welche von diesem, nach der Aufforderung durch die Polizei sich auszuweisen, in einer Distanz von höchstens einem Meter zu einem der Polizeibeamten abgefeuert wurde. Neben den von der zuständigen Staatsanwaltschaft gestellten Fragen zum Gefahrenpotenzial des Gasstrahls dieser Waffe beim Abfeuern, wurde die Frage nach der Möglichkeit der Entstehung eines Gehörschadens infolge des lauten Knalls selbst gestellt.

Protein Hydrolysis and Nitrogen Remobilisation in Plant Life and Senescence

In plant cells, as in all other cells, proteins are submitted to permanent turnover, and the intracellular content of a given protein depends on its rate of both synthesis and degradation. The life time of most proteins is shorter than that of the cell. Thus, in young leaves of Lemna minor, the average half-life of protein was estimated to be 7 days, and it was shorter under stress conditions (Davies 1982). Such observations mean that nitrogen and amino acid fluxes are both cylic and permanent. Although protein turnover may appear wasteful, in terms of energy, numerous studies have shown that proteolysis provides multiple functions in cell physiology, and is an essential regulatory mechanism of cell metabolism and development.

Stable oxygen isotope and Mg/Ca ratios of planktonic foraminifera from the Caribbean and North Atlantic

Variations in the strength of the North Atlantic Ocean thermohaline circulation have been linked to rapid climate changes during the last glacial cycle through oscillations in North Atlantic Deep Water formation and northward oceanic heat flux. The strength of the thermohaline circulation depends on the supply of warm, salty water to the North Atlantic, which, after losing heat to the atmosphere, produces the dense water masses that sink to great depths and circulate back south. Here we analyse two Caribbean Sea sediment cores, combining Mg/Ca palaeothermometry with measurements of oxygen isotopes in foraminiferal calcite in order to reconstruct tropical Atlantic surface salinity during the last glacial cycle. We find that Caribbean salinity oscillated between saltier conditions during the cold oxygen isotope stages 2, 4 and 6, and lower salinities during the warm stages 3 and 5, covarying with the strength of North Atlantic Deep Water formation. At the initiation of the Bølling/Allerød warm interval, Caribbean surface salinity decreased abruptly, suggesting that the advection of salty tropical waters into the North Atlantic amplified thermohaline circulation and contributed to high-latitude warming.

Geochemistry of Globigerinoides ruber from ODP Hole 130-806B

A sea surface temperature (SST) record based on planktonic foraminiferal magnesium/calcium ratios from a site in the western equatorial Pacific warm pool reveals that glacial-interglacial oscillations in SST shifted from a period of 41,000 to 100,000 years at the mid-Pleistocene transition, 950,000 years before the present. SST changes at both periodicities were synchronous with eastern Pacific cold-tongue SSTs but preceded changes in continental ice volume. The timing and nature of tropical Pacific SST changes over the mid-Pleistocene transition implicate a shift in the periodicity of radiative forcing by atmospheric carbon dioxide as the cause of the switch in climate periodicities at this time.