Alterações morfológicas, fisiológicas e metabólicas induzidas por glifosato em Vigna unguiculata (L.) Walp

Abstract

Glyphosate (N-(phosphonomethyl)glycine) is one of the most widely used herbicides in agriculture worldwide. It acts systemically in the plant, inhibiting the enzyme 5-enolpyruvylshikimate-3-phosphate synthase, an important enzyme in the shikimate pathway. It is known that glyphosate blocks the synthesis of aromatic amino acids and secondary metabolites, which are important for plant defense. However, little is known about how other metabolic pathways are affected by this herbicide. In addition, non-transgenic crops that are not resistant to glyphosate, such as cowpeas, may be accidentally exposed to this herbicide, mainly through spray drift. In this sense, this study aimed to analyze the effects of glyphosate exposure on morphological, physiological, and metabolic parameters of cowpeas. To this end, three experiments were conducted, the first with different doses of glyphosate (0.0, 62.5, 125, 250, 500, and 1000 mg L-1) to assess oxidative stress and metabolic profile. The results showed that only doses above 125 mg L-1 induced oxidative stress, evidenced by an increase in malondialdehyde (MDA) concentration. Based on this experiment, two others were conducted with a dosage of 125 mg L-1 of glyphosate, in which analyses of metabolic profile, oxidative stress, morphology, and physiology of the plants were performed. The application of 125 mg L-1 of glyphosate had virtually no effect on gas exchange and the photochemical apparatus, even with occasional differences in Y(NA) and ETR(I). However, 7 days after application, plants exposed to glyphosate showed lower dry biomass accumulation. In metabolism, when analyzing different concentrations of the herbicide, it was possible to verify a significant change in metabolites such as malate, citrate, glycerate, and glutamate, suggesting that glyphosate alters metabolites associated with photorespiration and the citric acid (TCA) and glutamine synthetase-glutamate synthase (GS-GOGAT) cycles. At a dose of 125 mg L-1, accumulation of shikimate and urea was observed, along with changes in amino acids and carbohydrates. In addition to confirming that glyphosate alters the shikimic acid pathway, our results reveal that the application of this herbicide also alters the level of metabolites in carbon and nitrogen metabolism, possibly as a secondary effect and/or a direct action of the herbicide on enzymes in the TCA and/or GS-GOGAT cycles.