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Iron (Fe) is an essential plant micronutrient, being a major limiting growth factor in calcareous soils. To increase Fe uptake, plants induce lateral roots growth, the expression of a Fe(III)-chelate reductase (FCR), a Fe(II)-transporter and a H+-ATPase and the secretion of flavins. Furthermore, auxin hormone family is involved in the Fe-deficiency responses but the action mechanism remains elusive. In this work, we evaluated the effect of the auxin-precursor indole-3-acetaldoxime (IAOx) on hydroponically grown Medicago truncatula plants under different Fe conditions. Upon 4-days of Fe starvation, the pH of the nutrient solution decreased, while both the FCR activity and the presence of flavins increased. Exogenous IAOx increased lateral roots growth contributing to superroot phenotype, decreased chlorosis, and delayed up to 3-days the pH-decrease, the FCR-activity increase, and the presence of flavins, compared to Fe-deficient plants. Gene expression levels were in concordance with the physiological responses.

The ornithine-urea cycle (urea cycle) makes a significant contribution to the metabolic responses of lower photosynthetic eukaryotes to episodes of high nitrogen availability. In this study, we compared the role of the plant urea cycle and its relationships to polyamine metabolism in ammonium-fed and nitrate-fed Medicago truncatula plants. High ammonium resulted in the accumulation of ammonium and pathway intermediates, particularly glutamine, arginine, ornithine, and putrescine. Arginine decarboxylase activity was decreased in roots, suggesting that the ornithine decarboxylase-dependent production of putrescine was important in situations of ammonium stress. The activity of copper amine oxidase, which releases ammonium from putrescine, was significantly decreased in both shoots and roots. In addition, physiological concentrations of ammonium inhibited copper amine oxidase activity in in vitro assays, supporting the conclusion that high ammonium accumulation favors putrescine synthesis. Moreover, early supplementation of plants with putrescine avoided ammonium toxicity. The levels of transcripts encoding urea-cycle-related proteins were increased and transcripts involved in polyamine catabolism were decreased under high ammonium concentrations. We conclude that the urea cycle and associated polyamine metabolism function as important protective mechanisms limiting ammonium toxicity in M. truncatula. These findings demonstrate the relevance of the urea cycle to polyamine metabolism in higher plants.

The ornithine-urea cycle (urea cycle) makes a significant contribution to the metabolic responses of lower photosynthetic eukaryotes to episodes of high nitrogen availability. In this study, we compared the role of the plant urea cycle and its relationships to polyamine metabolism in ammonium-fed and nitrate-fed Medicago truncatula plants. High ammonium resulted in the accumulation of ammonium and pathway intermediates, particularly glutamine, arginine, ornithine, and putrescine. Arginine decarboxylase activity was decreased in roots, suggesting that the ornithine decarboxylase-dependent production of putrescine was important in situations of ammonium stress. The activity of copper amine oxidase, which releases ammonium from putrescine, was significantly decreased in both shoots and roots. In addition, physiological concentrations of ammonium inhibited copper amine oxidase activity in in vitro assays, supporting the conclusion that high ammonium accumulation favors putrescine synthesis. Moreover, early supplementation of plants with putrescine avoided ammonium toxicity. The levels of transcripts encoding urea-cycle-related proteins were increased and transcripts involved in polyamine catabolism were decreased under high ammonium concentrations. We conclude that the urea cycle and associated polyamine metabolism function as important protective mechanisms limiting ammonium toxicity in M. truncatula. These findings demonstrate the relevance of the urea cycle to polyamine metabolism in higher plants.

The ornithine–urea cycle (urea cycle) makes a significant contribution to the metabolic responses of lower photosynthetic eukaryotes to episodes of high nitrogen availability. In this study, we compared the role of the plant urea cycle and its relationships to polyamine metabolism in ammonium-fed and nitrate-fed Medicago truncatula plants. High ammonium resulted in the accumulation of ammonium and pathway intermediates, particularly glutamine, arginine, ornithine, and putrescine. Arginine decarboxylase activity was decreased in roots, suggesting that the ornithine decarboxylase-dependent production of putrescine was important in situations of ammonium stress. The activity of copper amine oxidase, which releases ammonium from putrescine, was significantly decreased in both shoots and roots. In addition, physiological concentrations of ammonium inhibited copper amine oxidase activity in in vitro assays, supporting the conclusion that high ammonium accumulation favors putrescine synthesis. Moreover, early supplementation of plants with putrescine avoided ammonium toxicity. The levels of transcripts encoding urea-cycle-related proteins were increased and transcripts involved in polyamine catabolism were decreased under high ammonium concentrations. We conclude that the urea cycle and associated polyamine metabolism function as important protective mechanisms limiting ammonium toxicity in M. truncatula. These findings demonstrate the relevance of the urea cycle to polyamine metabolism in higher plants.

La llegada de los smartphones junto con Internet ha supuesto una revolución tecnológica, haciendo posible la comunicación de manera casi instantánea entre varias personas sin importar la distancia. Son numerosos los elementos cotidianos que se han aprovechado de este hecho: la forma de relacionarnos, comprar, entretenernos, etc, han cambiado gracias a esto, y la medicina no iba a ser menos. Es por ello que en los últimos años, y más desde que comenzó el Covid-19, los servicios de salud han tratado de adaptarse con el objetivo de acercarse al paciente de forma telemática, haciendo que las consultas puedan estar más despejadas. Otro de los elementos que ha hecho posible el surgimiento de grandes cantidades de aplicaciones que nos ayudan con nuestro día a dia es la aparición de marcos de desarrollo multiplataforma, que nos permiten un desarrollo más sencillo y rápido sin tener que preocuparnos de las características de los sistemas finales en los que se ejecuta la aplicación. En este documento se analiza y utiliza una de estas herramientas, React Native, con el fin de crear una aplicación para la autogestión de los pacientes con enfermedades de coagulación.

Monolithic polymers functionalised with BOX-Cu moieties can be applied for the cyclopropanation reaction under batch and flow conditions using either conventional or supercritical solvents.

The mechanism of the ruthenium(II)-catalyzed cyclopropanation reaction of olefins with diazo compounds has been extensively investigated for a medium-sized reaction model by means of DFT calculations. The starting ethylene complex of the dichloro[(E)-2-(methylimino)-N-(1E,2E)-2-(methyliminoethylidene)ethanamine]ruthenium(II) catalyst undergoes a ligand exchange with methyl diazoacetate to yield a reaction intermediate, which subsequently undergoes nitrogen extrusion to generate a ruthenium−carbene complex. The cyclopropanation step takes place through a direct carbene addition of the ruthenium carbene species to the olefin double bond to yield a catalyst-product complex, which can finally regenerate the starting complex. Stereochemical considerations on a “real-world” systemthe cyclopropanation reaction of styrene with methyl diazoacetate, catalyzed by a chiral pybox−ruthenium complexhave been investigated by means of full quantum-mechanical calculations on this reaction. The theoretical results show excellent agreement with the experimental observations and allow a mechanistic explanation to be advanced concerning the origin of the stereoselectivities observed. The explanation is based on the intermolecular steric interaction between the alkene and one of the isopropyl groups of the chiral ligand in the disfavored approaches. The model developed also provides an explanation for some particular stereoelectronic behavior of pybox ligands, such as the remote stereoelectronic effects and the good enantioselectivities described with C1-pybox ligands.

[EN] A simple, versatile and efficient methodology for the immobilization of chiral pybox systems has been developed by formation of a covalent bond between the pyridine ring and the insoluble support using copolymerization (polystyrene-pybox) or grafting (silica gel-pybox). The results indicated that the polymerised pybox offers a behaviour close to that of a homogeneous catalyst. This new route opens the way for the preparation of a range of different supported pybox-based catalysts for a wide variety of enantioselective reactions., [FR] Une méthodologie simple, polyvalente et efficace a été développée pour l’immobilisation de systèmes pybox chiraux au travers de la formation d’une liaison covalente entre l’anneau de pyridine et le support insoluble, en utilisant la copolymérisation (polystyrène-pybox) ou le greffage (silice-pybox). Les résultats indiquent que le comportement de la pybox polymérisée est très semblable à celui du catalyseur homogène. Cette nouvelle procédure ouvre la voie à la préparation d’un groupe de catalyseurs à base de pybox destinés à un large éventail de réactions énantiosélectives.

Chiral pyridinebis(oxazoline) (pybox) ligands can be efficiently immobilized onto silica through position 4 of the pyridine ring. The crucial intermediate in this strategy is 4-chloropybox, which is prepared in good yield from chelidamic acid. 4-Chloropybox reacts with p-hydroxybenzaldehyde and p-aminophenol to give two intermediates (pybox-CHO and pybox-NH2) that allow to introduce the formyl and amino groups able to link to spacers with triethoxysilylgroups. The modified ligands and their ruthenium complexes are immobilized by grafting onto pre-formed silicas or, alternatively, the support is created by sol-gel synthesis using the functionalizedchiral ligand as a silica monomer. In this way it is possible to create a library where the variation involves the support rather than the catalyst. The aim of this approach is to study the influence of different parameters, such as the textural properties of the support and the immobilization method, on the functionalization and catalytic performance. Some of the immobilized complexes are compared as heterogeneous catalysts in the cyclopropanation reaction of styrene with ethyl diazoacetate.

The clay surface plays a role in the enantioselectivity of the cyclopropanation reaction, in the case of copper catalysts immobilized on laponite by electrostatic interactions. The effect is different depending on the type of chiral ligand, bis(oxazoline) or pyridineoxazoline. In the first case the clay promotes a reversal of the stereochemical course of the reaction. The pyridineoxazoline-copper complexes lead to very low enantioselectivity in homogeneous phase. However, the asymmetric induction increases when the complexes are immobilized on laponite, showing that it is possible to design good chiral ligands specific for the use in immobilized catalysts. © 2002 Elsevier Science B.V. All rights reserved.

A chiral pyridine-bis(oxazoline) ligand, functionalized with a vinyl group in the pyridine ring, can be polymerized with styrene and divinylbenzene to obtain supported chiral ligands. As proof of the usefulness of this supported ligands, the corresponding ruthenium complexes are catalysts for the cyclopropanation reaction of styrene with ethyl diazoacetate with up to 85% ee.