Aspects of weed resistance to auxinic herbicides

Includes bibliographical references.2020 Summer.Synthetic auxins have been widely used for selective control of broadleaf weeds since the mid-1940s. After more than 70 years using synthetic auxin herbicides, there are 41 different resistant species reported. Weed resistance to auxin herbicides is poorly understood and in most reported cases, no studies have been done to investigate the mechanistic changes that occur in resistant populations. The mechanisms of herbicide resistance in weeds are classified as 1) target-site when mutations reduce the interaction of the herbicide molecule to its binding site and/or changes of gene expression of the targeted enzyme to compensate for herbicide inhibition; and as 2) non-target-site mechanisms, which include any genetic mutations that will prevent or reduce the herbicide reaching its site of action. In this present research, two 2,4-D resistant weed species were studied, and the mechanisms of resistance were elucidated, where one species evolved metabolic non-target-site resistance to 2,4-D and the second species evolved a novel mechanism of target side modification. In 2009, an Amaranthus tuberculatus (common waterhemp) population with ten-fold resistance to 2,4-D was found in Nebraska, USA. Using the same 2,4-D-resistant and a known susceptible A. tuberculatus population from Indiana, the mechanism of 2,4-D resistance was examined by conducting [14C] 2,4-D absorption, translocation and metabolism experiments. No differences were found in 2,4-D absorption, but resistant plants translocated more of the radioactive material than susceptible A. tuberculatus. Resistant plants metabolized [14C] 2,4-D more rapidly than susceptible plants. The main metabolites were purified and their structures were solved by NMR and HRMS. Susceptible plants conjugate 2,4-D to 2,4-D Aspartic Acid (2,4-D-Asp). Resistant plants showed a distinct metabolic profile where 2,4-D is hydroxylated into 5-OH-2,4-D, conjugated in a sugar metabolite (5-OH-2,4-D-Glucoside) and malonylated into 5-OH-2,4-D-(6-O-Malonyl)-Glucoside. Pre-treatment with the cytochrome P450 inhibitor malathion inhibited 2,4-D hydroxylation. Toxicological studies in waterhemp and Arabidopsis confirmed that the hydroxylated metabolite lost its auxinic action and toxicity. In contrast, the 2,4-D-Asp metabolite induced auxin inhibition to the plants tested. These results demonstrate that resistant A. tuberculatus evolved novel detoxification reactions that rapidly metabolize 2,4-D, potentially mediated by cytochrome P450. That novel mechanism is more efficient and produces metabolites with lower toxicity compared to the innate aspartic acid conjugation. Metabolism-based herbicide resistance poses a serious challenge for weed management due to the potential for cross-resistance to other herbicides. Sisymbrium orientale (Indian hedge mustard) is an important weed species in Australia reducing yields in crops and pastures. In 2005, a 2,4-D and MCPA resistant population was reported in the Port Broughton region in South Australia. Aux/IAAs are dynamic repressor proteins that regulate Auxin Response Factors (ARFs) to activate auxin related genes and are also co-receptors for auxins and synthetic auxin herbicides. The degradation of Aux/IAAs is done by the enzyme complex E3, called SCFTIR1/AFB, which, in the presence of auxin, performs ubiquitination on Aux/IAA making it a target of proteasome 26S, an enzyme responsible for proteolysis in eukaryotes. An RNAseq study showed that a 27 bp deletion in Aux/IAA2 (IAA2) degron tail was correlated to the resistant phenotype. The mutant allele was functionally validated to confer 2,4-D resistance by transforming Arabidopsis thaliana with the wild type SoIAA2 and SoIAA2Δ27 alleles. Performing binding analysis by surface plasmon resonance, the association of TIR1 in the presence of auxin (IAA, 2,4-D and dicamba) showed slower association and faster dissociation to the resistant IAA2 peptide compared to the susceptible IAA2 peptide. Our results suggest that the loss of 9 amino acids located in the degron tail may reduce the capacity of IAA2 to "embrace" TIR1 in the presence of auxin, reducing ubiquitination rate, resulting in higher stability to repress auxin response factors and ultimately conferring resistance to 2,4-D

LA EVOLUCIÓN POLÍTICO-CONSTITUCIONAL DE BRASIL

El presente artículo pretende analizar los aspectos singulares de la evolución político-constitucional del Brasil entre la década de sesenta y el período actual. Serán tratados temas como el sistema de gobierno, el poder judicial, los derechos fundamentales, los partidos políticos, los mecanismos de defensa de la Constitución y avances y amenazas a la democracia. Destacaremos la importancia de la Constitución Federal de 1988 al establecer que la República Federativa del Brasil se constituye en Estado Democrático de Derecho, inaugurando una nueva era en el constitucionalismo brasileño, quebrando el ciclo autoritario que dominó el país de 1964 hasta mediados de la década de 80. En suma, nuestro objetivo será demostrar cuáles son los principales aspectos y problemas del sistema político-constitucional brasileño

A INFLUÊNCIA DA DOUTRINA NAS CORTES CONSTITUCIONAIS

Trata-se de artigo produzido a propósito da conferência intitulada "L'Influenza Della Dottrina Nelle Decisioni Delle Corti Costituzionali" proferida em 13 de junho de 2014 na Università  Degli Studi Suor Orsola Benincasa - Facoltà Di Giurisprudenza, em que se discute o papel da doutrina como fundamentação das decisões das Cortes Constitucionais, percorrendo-se autores e casos de jurisprudência do Supremo Tribunal Federal em que determinadas teorias estrangeiras são acolhidas e referidas

Debt mutualisation in the eurozone

Mestrado em Economia Internacional e Estudos EuropeusO objectivo desta Dissertação prende-se com o estudo da mutualização da dívida na Zona Euro para resolução dos elevados níveis de endividamento, com os quais muitos Estados Membros se confrontam. Para a resolução da Grande Recessão, as instituições europeias criaram mecanismos de assistência financeira, os quais constituíram meramente uma resposta de curto prazo para a crise das dívidas soberanas. No entanto, a resolução de tal problema requer uma solução de longo prazo, que permita a gestão eficiente da dívida pública. Tendo em conta propostas apresentadas por outros autores, esta Dissertação propõe uma alternativa que permite aos governos lidarem com a disciplina orçamental, sem comprometer o crescimento económico.The objective of this Dissertation is to study debt mutualisation in the Eurozone as a means of dealing with the high levels of indebtedness that many Member States face. For the resolution of the Great Recession, the EU institutions created financial assistance mechanisms, which were merely a short-term answer to the sovereign debt crisis. However, the resolution of such problem requires a long-term solution that allows for the proper management of public debt. Bearing in mind proposals presented by other authors, this Dissertation provides an alternative way in which governments can deal with fiscal discipline without compromising economic growth

Um modelo multifásico para estruturas em concreto armado considerando a fissuração do concreto

Assessing the global behavior of reinforced materials from the individual properties of their components has been the subject of a considerable amount of experimental and theoretical works in the last years. The so-called multiphase model is an alternative generalization of the homogenization method and it relies upon the idea that, at the macroscopic scale, the reinforced concrete is a geometrical superposition of the matrix phase (concrete) and the reinforcing phase (steel bars). This technique was already successfully employed in several geotechnical structures. Considering the particular case of concrete structures, Figueiredo et al [1] analyzed the mechanical behavior of reinforced concrete flat slabs under prescribed loading using the multiphase model in elastoplasticity. The present contribution extents a previously numerical code to account for concrete cracking based on a smeared crack approach. Comparison with direct simulation results emphasizes the advantage of such multiphase model in terms of reduced computational cost.Determinar o comportamento global de materiais reforçados a partir das propriedades individuais de seus componentes vem sendo tema de um considerável número de trabalhos experimentais e teóricos nos últimos anos. A modelagem multifásica é uma generalização alternativa do método de homogeneização cujo princípio básico consiste em descrever o concreto armado como a superposição geométrica da fase matriz (concreto) e da fase reforço (barras de aço). Esta técnica foi empregada com sucesso em uma série de trabalhos envolvendo estruturas geotécnicas. No caso da estruturas de concreto, Figueiredo et al (2009) estuda o comportamento mecânico de placas de concreto armado sob a ação de carregamento prescrito com o uso da modelagem multifásica em elastoplasticidade. No presente trabalho é acrescentado ao modelo previamente desenvolvido o algoritmo que leva em conta a fissuração do concreto baseado no modelo de fissuras distribuídas apresentado por Hinton (1988). São realizadas comparações com simulações diretas clássicas visando salientar as vantagens do modelo como a redução significativa do custo computacional