## 4 Discussion
Although not so explored as in target and resistant species, the influence of this herbicide on the redox status of non-target plants, including crops, willow and aquatic plants [30; 49; 51; 52; 54; 55; 56; 57; 58; 59; 90; 91] is starting to gain attention. Corroborating the results of the present work, several studies reported an increase in H\({}_{2}\)O\({}_{2}\) content and MDA levels in plants grown in GBH-contaminated solid substrate [65], or when GLY or GBH was supplied in nutrient solutions [50; 52; 55; 90], or applied as foliar spray [49; 51; 54]. However, according to [PERSON] et al. [91] and [PERSON] et al. [30], the exposure of soybean and tomato plants to GBH did not induce severe oxidative damage in leaves. In order to defend themselves from oxidative damage caused by ROS, plants developed protective mechanisms by synthetizing enzymatic and non-enzymatic antioxidants [22]. In the context of this work, TAC, TPC and Pro levels were measured to assess the involvement of the non-enzymatic component of the AOX system in limiting GLY-induced stress. The results showed an increase in TAC and Pro levels only at the highest a.i. concentration (40 mg kg\({}^{-1}\)). Since TAC gives a general idea regarding the cell's AOX status [92] and Pro acts as a strong AOX [22], the elevated TAC and Pro levels suggest that the AOX defense mechanisms were activated due to oxidative stress, but only at the highest concentrations of GLY. Thus, it can be hypothesized that _M. sativa_ plants boosted the accumulation of Pro, along with other non-enzymatic players, to counteract the induced oxidative stress by this herbicide; however, bearing in mind that LP remained higher at the two highest concentrations, this response was not enough to counteract the harmful effects observed. Moreover, phenolic compounds, which are known to chelate metals, scavenge ROS and inhibit LP [93], were negatively affected by the presence of the herbicide, since reduced levels of these specialized metabolites were found in treated plants. This effect probably arises as a consequence of GLY-induced impairment of the shikimate pathway, once phenolic compounds are formed through this biosynthetic process [94], and is in accordance with the results obtained for LP. Up to now, some studies were conducted in order to evaluate the AOX defense mechanisms of plant species exposed to both GLY and GBH [30; 52; 54; 65; 95]. These studies demonstrate that there is a dysregulation of the AOX defense system, with records of both increases and decreases in these mechanisms. Particularly, in the study of [PERSON] et al. [30], performed with GBH-contaminated soils, it was observed that this formulation stimulated the AOX defense mechanisms of tomato shoots, at concentrations of 20 and 30 mg kg\({}^{-1}\) of the a.i. This suggests that, like other environmental stresses, the response to herbicide application depends on several factors, such as the plant species, the concentration, and the mode of application. However, the results obtained in the present study are in line with those already published by other authors [30; 52; 54; 65] indicating that the increase in Pro levels seems to be the most consistent signal of the activation of the AOX defense against GLY-induced stress, suggesting that this amino acid can be used as a biomarker of exposure to GLY.