Is soil contamination by a glyphosate commercial formulation truly harmless to non-target plants? - Evaluation of oxidative damage and antioxidant responses in tomato.

Using a realistic and environmental relevant approach, the present study aimed at understanding the biochemical and physiological basis of glyphosate (GLY)-induced stress in non-target plant species, using tomato (Solanum lycopersicum L.) as a model. For this purpose, plants were grown for 28 days under different concentrations of a commercial formulation of GLY (Roundup® UltraMax) - 0, 10, 20 and 30 mg kg-1 soil. The exposure of plants to increasing concentrations of GLY caused a severe inhibition of growth (root and shoot elongation and fresh weight), especially in the highest treatments. In what regards the levels of reactive oxygen species (ROS), both hydrogen peroxide (H2O2) and superoxide anion (O2.-) remained unchanged in shoots, but significantly increased in roots. Moreover, a concentration-dependent decrease in lipid peroxidation (LP) was found in shoots, though in roots differences were only found for the highest concentration of GLY. The evaluation of the antioxidant system showed that GLY interfered with several antioxidant metabolites (proline, ascorbate and glutathione) and enzyme activities (superoxide dismutase - SOD; catalase - CAT; ascorbate peroxidase - APX), generally inducing a positive response of the defense mechanisms. Overall, data obtained in this study unequivocally demonstrated that soil contamination by GLY, applied as part of its commercial formulation Roundup® UltraMax, impairs the growth and physiological performance of tomato plants, and likely of other non-target plant species, after 28 days of exposure by clearly affecting the normal redox homeostasis.