Efeito de herbicidas na atividade enzimática de milho e soja geneticamente modificados

Abstract

New soybean and corn cultivars are resistant to 2,4-D, glyphosate and ammonium glufosinate, and to haloxyfop-R in the case of maize. Knowing that the application of herbicides can induce accumulation of reactive oxygen species (ROS), which can generate oxidative stress even in resistant plants, the objective was to evaluate if the application of herbicides on soy and maize resistant cultivars affects negatively the activity of antioxidant enzymes and ALA-D. The experiments were conducted in a greenhouse at the Federal University of Southern Border, Erechim Campus in 2018. The experiment was a randomized complete block design with four replicates (two plants per replicate) using the soybean and corn transgenic cultivars Enlist ™ . The application of the herbicides was carried out in an isolated post-emergence or in tank mixtures at the doses recommended for the control of weeds. The treatments for the soybean experiment were: glyphosate (1080 g ha-1), 2,4-D (670 g ha-1), ammonium glufosinate (400 g ha-1), glyphosate + 2,4-D, glyphosate + ammonium glufosinate, ammonium glufosinate + 2,4-D and glyphosate + ammonium glufosinate + 2,4-D. The experiment with corn contained treatments: control, glyphosate, 2,4-D, ammonium glufosinate, haloxyfop-R (60 g ha-1), glyphosate + 2,4-D, glyphosate + ammonium glufosinate, glyphosate + haloxyfop-R, 2,4-D + ammonium glufosinate, 2,4-D + haloxyfop-R, ammonium glufosinate + haloxyfop-R, glyphosate + 2,4-D + ammonium glufosinate, glyphosate + 2,4- D + haloxyfop-R, glyphosate + ammonium glufosinate + haloxyfop-R and 2,4-D + ammonium glufosinate + haloxyfop-R, glyphosate + 2,4-D + ammonium glufosinate + haloxyfop-R. The applications occurred with soybean and maize at the phenological stage V1 and V2, respectively. At 7 days after application, the aerial part of the plants was collected, wrapped in foil, frozen and later macerated in liquid nitrogen. These samples were used to determine the activity of antioxidant enzymes such as catalase (CAT), ascorbate peroxidase (APX) and guaiacol peroxidase (GPX), lipid peroxidation levels and the activity of the enzyme delta-aminolevulinate dehydratase (ALA-D) submitted to herbicides. The results for soybean showed that there were no significant changes in lipid peroxidation and GPX activity due to no treatment, although APX and CAT activities were increased in glufosinate and glyphosate, 2,4-D and glyphosate + 2,4-D, respectively. There was also inhibition of the enzyme ALA-D. However, for maize, mainly in the mixtures there was lipid peroxidation and the activity of CAT and APX were activated. The GPX enzyme was inhibited and all treatments inhibited ALA-D. In conclusion, soybean and corn cultivars, especially mixtures, showed activation of important antioxidant enzymes in the antioxidant defense, such as CAT and APX. Even so, in the case of corn, lipids have been damaged. In addition, in both cultivars these treatments negatively affected ALA-D activity