## 4 Discussion
Several studies were conducted in order to evaluate the phytotoxicity of GLY to non-target plants, such as: _Pisum sativum_ (GLY or GBH, applied directly to the seeds or supplemented to the nutrient solution) [55; 58]; _Hordeum vulgare_ (GBH supplemented to a mixture of perlite:vermiculite (1:2)) [65]; _Solanum lycopersicum_ (GLY applied by foliar spray) [54]; _Vigna radiata_ (seeds treated with a GBH) [66]; _Fagopryrum esculent_ (GLY isopropylamine salt supplemented to the nutrient solution) [67]; _Lemma minor_ (GBH supplemented to the nutrient solution) [68]; _Dimorphandra wilsonii_ (seeds treated with a GBH or analytical grade glyphosate) [12]. Even though the experimental conditions of the previously mentioned studies were not similar to the present study, they all recorded a decrease in plant growth, demonstrating the negative effect that both GLY and GBH have on biometric indicators. Concerning GBH-contaminated soils, a similar decrease was also observed in the work of [PERSON] et al. [30], in which tomato plants grew in an artificial soil contaminated by increasing a.i. concentrations (0, 10, 20 and 30 mg kg\({}^{-1}\)). Their results showed significant statistical differences even at 10 mg kg\({}^{-1}\), a concentration pretty much identical to the lowest dose tested in this study. Photosynthesis, one of the main biochemical processes occurring in photoautotrophic organisms, highly depends on light absorption by chlorophylls and carotenoids. The biosynthesis of these pigments, as well as fatty acids or amino acids, can be affected by GLY exposure [69]. As GLY is an EPSPS competitive inhibitor, it blocks the shikimate pathway, thus compromising the biosynthesis of secondary metabolites, such as quinones and photosynthetic pigments, all compounds involved in the photosynthetic metabolism [70]. Previous studies showed that GLY can impair plastoquinone synthesis, thereby contributing to a lower production of carotenoid precursors [50]. Regarding chlorophylls,both GLY and GBH can also directly inhibit its biosynthesis, by reducing \(\delta\)-aminolevulin acid (ALA) levels, or increase chlorophyll degradation, as reported by several authors [71; 72; 73; 50; 74; 55]. Based on these results, it was expected that we would observe a significant decrease in the levels of both chlorophylls and carotenoids. Indeed, even a previous work conducted with the same plant species but grown in perlite and quartz sand [75] reported that the foliar application of a GBH resulted in a reduction in the total photosynthetic pigments as the a.i. concentration increased. However, in the present study, the herbicide showed no effects on chlorophyll and carotenoid contents, despite the slightly lower contents observed when compared to the control group (except for 12 mg kg\({}^{-1}\)). Thus, these results suggest that, at the tested doses, this herbicide did not negatively affect the photosynthetic pigments as also demonstrated in the study performed by [PERSON] et al. [65] with a GLY concentration of 30 mg kg\({}^{-1}\), applied in the form of Roundup UltraMax(r) and using a mixture of perlite:vermiculite as substrate. As discussed by [PERSON] et al. [65], these results could be explained by the lack of (aminomethylphosphonic acid) AMPA production in the artificial medium. Indeed, AMPA, the main metabolite formed upon GLY degradation, is considered as a potent phytotoxin, capable of competing with glycine and consequently inhibiting chlorophyll biosynthesis [76; 77]. Thus, there are two hypotheses for the lack of negative effects due to GLY exposure on chlorophyll and carotenoid content: (i) the use of a standard artificial soil with low microbial activity, not allowing enough AMPA production to cause negative effects on biosynthesis of these pigments; (ii) the mode of application of GLY, which, in this study, was added to the soil contrasting to the majority of works which provided GLY as foliar spray.