Nontarget-site resistance due to rapid physiological response in 2,4-D resistant Conyza sumatrensis: reduced 2,4-D translocation and auxin-induced gene expression.

BACKGROUND: Resistance to 2,4-Dichlorophenoxyacetic acid (2,4-D) has been reported in several weed species since the 1950s; however, a biotype of Conyza sumatrensis showing a novel physiology of the rapid response minutes after herbicide application was reported in 2017. The objective of this research was to investigate the mechanisms of resistance and identify transcripts associated with the rapid physiological response of C. sumatrensis to 2,4-D herbicide. RESULTS: Differences were found in 2,4-D absorption between the resistant and susceptible biotypes. Herbicide translocation was reduced in the resistant biotype compared to the susceptible. In resistant plants 98.8% of [14 C] 2,4-D was found in the treated leaf, whereas ≈13% translocated to other plant parts in the susceptible biotype at 96 h after treatment. Resistant plants did not metabolize [14 C] 2,4-D and had only intact [14 C] 2,4-D at 96 h after application, whereas susceptible plants metabolized [14 C] 2,4-D into four detected metabolites, consistent with reversible conjugation metabolites found in other 2,4-D sensitive plant species. Pre-treatment with the cytochrome P450 inhibitor malathion did not enhance 2,4-D sensitivity in either biotype. Following treatment with 2,4-D, resistant plants showed increased expression of transcripts within plant defense response and hypersensitivity pathways, whereas both sensitive and resistant plants showed increased expression of auxin-response transcripts. CONCLUSION: Our results demonstrate that reduced 2,4-D translocation contributes to resistance in the C. sumatrensis biotype. The reduction in 2,4-D transport is likely to be a consequence of the rapid physiological response to 2,4-D in resistant C. sumatrensis. Resistant plants had increased expression of auxin-responsive transcripts, indicating that a target-site mechanism is unlikely. © 2023 Society of Chemical Industry.

Chromatographic determination of shikimate for identification of conventional soybean and glyphosate resistant soybean / Determinação cromatográfica de shikimato para identificação de soja convencional e soja resistente ao glifosato

A sensitive and reliable process was established using high-performance liquid chromatography (HPLC) to distinguish conventional varieties of glyphosate-resistant genetically modified crops via shikimate detection in soybean (Glycine max L. Merril) seeds. Glyphosate has a well-defined mechanism of action. It is the only herbicide that specifically inhibits 5-enolpiruvilshikimate-3-phosphate synthase (EPSPS E.C. 2.5.1.19), which catalyzes the condensation of shikimate with phosphoenolpyruvate. This study is based on the concept that shikimate significantly accumulates in soybean plant tissues after EPSPS inhibition by glyphosate. In plants not subjected to glyphosate, shikimate is not easily detected because it quickly metabolizes into shikimate 3-phosphate and subsequently into 5-enolpiruvilshikimate 3-phosphate through the action of EPSPS. Conversely, in non-genetically modified plants subjected to glyphosate, shikimate metabolism is impaired, resulting in its accumulation. This metabolite can be detected in extremely low quantities (in the microgram range), through HPLC. In this study, six different contrasts were analyzed, each being formed by a transgenic cultivation and its parental strain, subject or not subject to the treatment of soaking with a 0.6% glyphosate solution. Chromatographic analyses indicated shikimate accumulation only in conventional cultivars with seeds previously soaked in a 0.6% glyphosate solution. Thus, this shikimate detection method can be used as a rapid and accurate means to distinguish soybeans with glyphosate-resistant qualities.

Este estudo estabelece um processo, sensível e confiável, com aplicação de cromatografia líquida de alta eficiência (HPLC) para distinguir variedades de soja convencionais de geneticamente modificadas, resistentes ao glifosato, por detecção de chiquimato nas sementes. O mecanismo de ação doglifosato é bem definido. É o único herbicida que inibe especificamente a enzima 5-enolpiruvilchiquimato-3-fosfato sintase (EPSPS, E.C. 2.5.1.19), que catalisa a condensação do chiquimato com fosfoenolpiruvato. O trabalho está baseado na concepção do chiquimato se acumular significativamente nos tecidos vegetais de soja convencional, após a inibição da EPSP sintase pelo glifosato. Em plantas não submetidas ao glifosato, o chiquimato não é facilmente detectado, pois rapidamente é metabolizado a chiquimato 3-fosfato e, a seguir, em 5-enolpiruvilchiquimato 3-fosfato, pela ação da EPSPS. Por outro lado, em plantas não geneticamente modificadas submetidas ao glifosato, a metabolização do chiquimato é prejudicada, resultando em seu acúmulo. Este metabólito pode ser detectado em quantidades extremamente baixas (na faixa de µg), por HPLC. Neste trabalho foram analisados seis contrastes diferentes, sendo cada contraste formado por uma cultivar transgênica e sua respectiva cultivar parental convencional, submetidas ou não a embebição com solução de glifosato 0,6%. As análises cromatográficas indicaram o acúmulo de chiquimato apenas em cultivares convencionais, nas quais as sementes foram previamente embebidas em solução de glifosato 0,6%. Os resultados demonstraram que adetecção de chiquimato pode ser utilizada como um método rápido e preciso na diferenciação de soja resistente ao glifosato de soja convencional.

Sunflower micronutrient uptake curves / Curva de absorção de micronutrientes na cultura do girassol

Most studies in the literature regarding the uptake of micronutrients [zinc (Zn), manganese (Mn), iron (Fe), copper (Cu) and boron (B) accumulation] by sunflower are old. For this reason, this work is aimed to establish curves of sunflower micronutrient accumulation in tropical edaphoclimatic conditions. The experiment was conducted in field on Rhodic Eutrudox, located at the experimental farm of Embrapa Soja in Londrina-PR, using the commercial hybrid BRS 191. The experimental design was completely randomized, with four replicates. The experimental units consisted of 14 lines with a spacing of 0.70 meter between lines and 25.0 meters in length, with final density of 42,858 plants per hectare. Plants samples were collected every 14 days after emergence. After each collection, plants were divided into petiole, leaf, stem, capitulum and achenes. They were dried until reaching constant weight. Then, dry matter was weighed and the concentrations of Zn, Mn, Fe, Cu, and B were determined in the vegetal tissue. Micronutrient uptake occurred faster in the phase initiated 42 days after emergence (DAE). Iron was the most absorbed micronutrient, accumulating higher amounts in the achenes as well as in relation to the total absorbed. Fe, Mn, Zn, B and Cu concentrations were 38.06, 19.68, 9.20, 8,62 and 4.27 mg plant-1, respectively.

Devido ao fato de a maioria dos trabalhos encontrados na literatura a respeito do acúmulo dos micronutrientes [zinco (Zn), manganês (Mn), ferro (Fe), cobre (Cu) e boro (B)] no girassol serem antigos, objetiva-se, com este trabalho estabelecer curvas de acúmulo de micronutrientes em um híbrido de girassol na condição edafoclimática dos trópicos. O experimento foi instalado no campo sobre Latossolo Vermelho distroférrico de textura argilosa, localizado na fazenda experimental da Embrapa Soja, em Londrina-PR, utilizando o híbrido comercial BRS 191. O delineamento experimental utilizado foi o inteiramente casualizado, com quatro repetições. As unidades experimentais foram constituídas de 14 linhas, com espaçamento de 0,70 m entre linhas e 25 m de comprimento, com densidade final de 42.858 plantas ha-1. As amostras das plantas foram coletadas em intervalos de 14 dias após a emergência. Após cada coleta, dividiram-se as plantas em pecíolo, folha, caule, capítulo e aquênios, sendo que as mesmas foram secas até peso constante, quando foram tomados os pesos da matéria seca e determinados os teores de Zn, Mn, Fe, Cu e B no tecido vegetal. A absorção de micronutrientes ocorreu em maior velocidade a partir dos 42 dias após a emergência (DAE). O Fe foi o micronutriente mais absorvido, acumulando maior quantidade tanto nos aquênios como em relação ao total absorvido. O acúmulo total de Fe, Mn, Zn, B e Cu foram 38,06, 19,68, 9,20, 8,62 e 4,27 mg planta-1, respectivamente.