Terra-Sorb Foliar®, an amino acid based-biostimulant, mitigates the effects of glyphosate by triggering defence responses in glyphosate-resistant soybeans

The production of glyphosate-resistant (GR) soybeans continues to increase, as does the frequency of use of the herbicide glyphosate. Although largely resistant to glyphosate, GR soybean plants can still suffer adverse effects caused by the application of the herbicide particularly under stress conditions, risking limitations both on crop production and on the quality of the soybean crop. Glyphosate-induced effects on GR soybeans include decreased chlorophyll contents, lower photosynthesis and nitrogen fixation rates and also micronutrient deficiencies and increased susceptibility to diseases. Amino acid metabolism may be an important component of stress tolerance in plants, participating in processes such as osmotic adjustment and the detoxification of active oxygen species and xenobiotic compounds, as well as intracellular pH regulation. The application of the biostimulant Terra-Sorb Foliar to several grain crops in countries such as Argentina, England, Ukraine, Italy or Rumania increased photosynthetic activity and nutrient bioavailability and promoted rapid recovery from stress, traits that are likely to be related to the provision of an exogenous supply of L-free amino acids.The aim of the present study was to characterize the mechanism whereby Terra-Sorb Foliar modulates the plant response to glyphosate in commercial transgenic GR soybean lines using a combined physiological, proteomic and metabolite profiling approach. The levels of glyphosate accumulated in leaves of the transgenic plants were considerably higher than those observed in untransformed controls. Furthermore, when Terra-Sorb Foliar was applied together with glyphosate, leaf glyphosate accumulation was decreased, suggesting enhanced glyphosate degradation. The application of the biostimulant also protected photosynthesis against glyphosate-induced inhibition. Our data show that Terra-Sorb Foliar mitigates the effects of the herbicide by triggering defence responses in the plants that involve accumulation of heat-shock proteins, presumably with accelerated xenobiotic detoxification systems, and decreased oxidative stress.