MtNramp1 mediates iron import in rhizobia-infected Medicago truncatula cells.

Symbiotic nitrogen fixation is a process that requires relatively high quantities of iron provided by the host legume. Using synchrotron-based X-ray fluorescence, we have determined that this iron is released from the vasculature into the apoplast of zone II of M. truncatula nodules. This overlaps with the distribution of MtNramp1, a plasma membrane iron importer. The importance of MtNramp1 in iron transport for nitrogen fixation is indicated by the 60% reduction of nitrogenase activity observed in knock-down lines, most likely due to deficient incorporation of this essential metal cofactor at the necessary levels.

Molecular physiology of nickel and cobalt homeostasis in Rhizobium leguminosarum.

Transition metals such as Fe, Cu, Mn, Ni, or Co are essential nutrients, as they are constitutive elements of a significant fraction of cell proteins. Such metals are present in the active site of many enzymes, and also participate as structural elements in different proteins. From a chemical point of view, metals have a defined order of affinity for binding, designated as the Irving-Williams series (Irving and Williams, 1948) Mg2+ menor que Mn2+ menor que Fe2+ menor que Co2+ menor que Ni2+ menor que Cu2+mayor queZn2+ Since cells contain a high number of different proteins harbouring different metal ions, a simplistic model in which proteins are synthesized and metals imported into a ?cytoplasmic soup? cannot explain the final product that we find in the cell. Instead we need to envisage a complex model in which specific ligands are present in definite amounts to leave the right amounts of available metals and protein binding sites, so specific pairs can bind appropriately. A critical control on the amount of ligands and metal present is exerted through specific metal-responsive regulators able to induce the synthesis of the right amount of ligands (essentially metal binding proteins), import and efflux proteins. These systems are adapted to establish the metal-protein equilibria compatible with the formation of the right metalloprotein complexes. Understanding this complex network of interactions is central to the understanding of metal metabolism for the synthesis of metalloenzymes, a key topic in the Rhizobium-legume symbiosis. In the case of the Rhizobium leguminosarum bv viciae (Rlv) UPM791 -Pisum sativum symbiotic system, the concentration of nickel in the plant nutrient solution is a limiting factor for hydrogenase expression, and provision of high amounts of this element to the plant nutrient solution is required to ensure optimal levels of enzyme synthesis (Brito et al., 1994).

Improving the compilation of prolog to C using type and determinism information: Preliminary results

We describe the current status of and provide preliminary performance results for a compiler of Prolog to C. The compiler is novel in that it is designed to accept different kinds of high-level information (typically obtained via an analysis of the initial Prolog program and expressed in a standardized language of assertions) and use this information to optimize the resulting C code, which is then further processed by an off-the-shelf C compiler. The basic translation process used essentially mimics an unfolding of a C-coded bytecode emúlator with respect to the particular bytecode corresponding to the Prolog program. Optimizations are then applied to this unfolded program. This is facilitated by a more flexible design of the bytecode instructions and their lower-level components. This approach allows reusing a sizable amount of the machinery of the bytecode emulator: ancillary pieces of C code, data definitions, memory management routines and áreas, etc., as well as mixing bytecode emulated code with natively compiled code in a relatively straightforward way We report on the performance of programs compiled by the current versión of the system, both with and without analysis information.

A language exchange program: sustainability innovation in language and culture engagement

Spanish Educational Laws have been promoting the widespread use of English; as a result, Spanish Uni versities are looking for ways to give students more international training in order to prepare them for a future that will increasingly involve global problems and partnerships. Therefore, the Polytechnic University of Madrid, Spain (UPM), and the University of British Columbia, Okanagan, Canada (UBCO) have come together to offer opportunities for international collaboration and learning, thus facilitating virtual encounters among Spanish and Canadian students. The Language Exchange Program between the UPM and UBCO acts as a model for sustainability innovation in language and culture engagement as the students can interact with native speakers in communication tasks. This interdisciplinary initiative supports the latest methodological principles observed in the Common European Framework for Languages, such as autonomous and life-long learning, self-assessment and peer-assessment as well as the incorporation of new technologies to the learning process. Additionally the ‘virtual’ mobility is provided at no extra cost. This article presents the preliminary results of two virtual exchange programs that have been offering varied forms of study which are venue-independent, and have clearly expanded the range of scenarios for the students on both sides by promoting collaborative work and cultural exchange.