RESUMEN
Convolvulus arvensis is a troublesome weed that is naturally tolerant to glyphosate. This weed tolerates glyphosate at a rate 5.1 times higher than that of glyphosate-susceptible Calystegia hederacea. Glyphosate-treated C. arvensis plants accumulated less shikimic acid than C. hederacea plants. The overexpression of EPSPS genes from the two species in transgenic Arabidopsis thaliana resulted in similar glyphosate tolerance levels. qPCR of genomic DNA revealed that the EPSPS copy number in C. arvensis was approximately 2 times higher than that in C. hederacea. Moreover, glyphosate treatment caused a marked increase in EPSPS mRNA in C. arvensis compared to C. hederacea. GUS activity analysis showed that the promoter of CaEPSPS (CaEPSPS-P) highly improved GUS expression after glyphosate treatment, while no obvious differential GUS expression was observed in ChEPSPS-P transgenic A. thaliana in the presence or absence of glyphosate. Based on the obtained results, two coexisting mechanisms may explain the natural glyphosate tolerance in C. arvensis: (i) high EPSPS copy number and (ii) specific promoter-mediated overexpression of EPSPS after glyphosate treatment.
Asunto(s)
3-Fosfoshikimato 1-Carboxiviniltransferasa/genética , Arabidopsis/efectos de los fármacos , Calystegia/efectos de los fármacos , Convolvulus/efectos de los fármacos , Regulación de la Expresión Génica de las Plantas , Glicina/análogos & derivados , 3-Fosfoshikimato 1-Carboxiviniltransferasa/biosíntesis , Arabidopsis/enzimología , Bioensayo , Calystegia/enzimología , Convolvulus/enzimología , Bases de Datos Genéticas , Relación Dosis-Respuesta a Droga , Tolerancia a Medicamentos , Glicina/química , Resistencia a los Herbicidas/genética , Herbicidas/química , Plantas Modificadas Genéticamente , Reacción en Cadena de la Polimerasa , Polvos , Regiones Promotoras Genéticas , Ácido Shikímico/metabolismo , GlifosatoRESUMEN
Hexavalent chromium is a contaminant highly mobile in the environment that is toxic for plants at low concentrations. In this work, the physiological response of Convolvulus arvensis and Medicago truncatula plants to Cr(VI) treatments was compared. C. arvensis is a potential Cr hyperaccumulator well adapted to semiarid conditions that biotransform Cr(VI) to the less toxic Cr(III). M. truncatula is a model plant well adapted to semiarid conditions with a well studied genetic response to heavy metal stress. The results demonstrated that C. arvensis is more tolerant to Cr toxicity and has a higher Cr translocation to the leaves. The inductively coupled plasma optical emission spectroscopy results showed that C. arvensis plants treated with 10 mg Cr(VI) L(-1) accumulated 1512, 210, and 131 mg Cr kg(-1) in roots, stems, and leaves, respectively. While M. truncatula plants treated with the same Cr(VI) concentration accumulated 1081, 331, and 44 (mg Cr kg(-1)) in roots, stems, and leaves, respectively. Enzymatic assays demonstrated that Cr(VI) decreased ascorbate peroxidase activity and increased catalase activity in M. truncatula, while an opposite response was found in C. arvensis. The x-ray absorption spectroscopy studies showed that both plant species reduced Cr(VI) to the less toxic Cr(III).
Asunto(s)
Cromo/farmacocinética , Convolvulus/metabolismo , Medicago truncatula/metabolismo , Absorción , Ascorbato Peroxidasas/metabolismo , Biodegradación Ambiental , Catalasa/metabolismo , Cromo/toxicidad , Convolvulus/enzimología , Convolvulus/crecimiento & desarrollo , Medicago truncatula/enzimología , Medicago truncatula/crecimiento & desarrollo , Oxidación-Reducción , Estrés Oxidativo , Hojas de la Planta/enzimología , Hojas de la Planta/crecimiento & desarrollo , Hojas de la Planta/metabolismo , Raíces de Plantas/enzimología , Raíces de Plantas/crecimiento & desarrollo , Raíces de Plantas/metabolismo , Tallos de la Planta/enzimología , Tallos de la Planta/crecimiento & desarrollo , Tallos de la Planta/metabolismo , Plantones/enzimología , Plantones/crecimiento & desarrollo , Plantones/metabolismo , Contaminantes del Suelo/farmacocinética , Contaminantes del Suelo/toxicidad , Espectroscopía de Absorción de Rayos XRESUMEN
The objective of the present study was to determine the oxidative stress caused by hexavalent chromium (Cr[VI]), the chromium (Cr) uptake, and the Cr speciation in Convolvulus arvensis L. plants grown in hydroponics media containing either Cr(VI) or Cr(III). The results demonstrated that C. arvensis plants exposed to Cr(VI) concentrations ranging from 0 to 40 mg/L expressed higher ascorbate peroxidase specific activity in roots than in shoots. On the other hand, catalase activity monitored in plants exposed to 2 mg/L of Cr(VI) for 24 h increased in roots after a few hours of exposure. However, catalase activity in shoots revealed a decrement almost immediately after treatment was initiated. The results from x-ray absorption spectroscopic studies indicated that the oxidation state of the supplied Cr(III) remained the same in plant tissues. The supplied Cr(VI), however, was reduced to the trivalent form in plant tissues. The results of inductively coupled plasma/optical emission spectroscopy demonstrated that after 5 d, the roots of plants exposed to 40 mg/L of Cr(III) or Cr(VI) accumulated approximately 25,000 and 3,500 mg/kg dry weight of Cr, respectively. Nevertheless, shoots concentrated 1,500 and 2,000 mg/kg dry weight of Cr from Cr(III) and Cr(VI), respectively, which indicated that Cr moved faster into C. arvensis plants when supplied as Cr(VI).