Perturbations of Amino Acid Metabolism Associated with Glyphosate-Dependent Inhibition of Shikimic Acid Metabolism Affect Cellular Redox Homeostasis and Alter the Abundance of Proteins Involved in Photosynthesis and Photorespiration    

Abstract

The herbicide glyphosate inhibits the shikimate pathway of the synthesis of amino acids such as phenylalanine, tyrosine, and tryptophan. However, much uncertainty remains concerning precisely how glyphosate kills plants or affects cellular redox homeostasis and related processes in glyphosate-sensitive and glyphosate-resistant crop plants. To address this issue, we performed an integrated study of photosynthesis, leaf proteomes, amino acid profiles, and redox profiles in the glyphosate-sensitive soybean (Glycine max) genotype PAN809 and glyphosate-resistant Roundup Ready Soybean (RRS). RRS leaves accumulated much more glyphosate than the sensitive line but showed relatively few changes in amino acid metabolism. Photosynthesis was unaffected by glyphosate in RRS leaves, but decreased abundance of photosynthesis/photorespiratory pathway proteins was observed together with oxidation of major redox pools. While treatment of a sensitive genotype with glyphosate rapidly inhibited photosynthesis and triggered the appearance of a nitrogen-rich amino acid profile, there was no evidence of oxidation of the redox pools. There was, however, an increase in starvation-associated and defense proteins. We conclude that glyphosate-dependent inhibition of soybean leaf metabolism leads to the induction of defense proteins without sustained oxidation. Conversely, the accumulation of high levels of glyphosate in RRS enhances cellular oxidation, possibly through mechanisms involving stimulation of the photorespiratory pathway.

Physiological changes and in the carbohydrate content of sunflower plants submitted to sub-doses of glyphosate and trinexapac-ethyl

“…When the energy from light is not efficiently used in the photochemical step, reactive oxygen species (ROS) that are responsible for the loss of activity of PSII and the degradation of D 1 protein might be produced. Moreover, according Vivancos et al (2011), glyphosate can inhibit protein synthesis D 1 hurting the repair of PSII. There are 2 possible paths to this end: the first is that the herbicide, after inhibiting EPSP S , reduces the synthesis of aromatic amino acids, thus harming the amino acid pool.…”

<i>In-Silico</i> Analysis & <i>In-Vivo</i> Results Concur on Glutathione Depletion in Glyphosate Resistant GMO Soy, Advancing a Systems Biology Framework for Safety Assessment of GMOs

“…Resistant plants displayed relatively less change in amino acid metabolism and photosynthesis, although there was increased oxidation of redox pools accompanied by a decrease in the ratios of GSH/ GSSG. The authors infer that the accumulation of higher levels of glyphosate in resistant plants enhanced cellular oxidation, possibly by stimulation of photorespiration [28].…”

“…The authors suggest that it is possible that the insensitivity of EPSPS to glyphosate in the resistant genotype decreases the ability of the plant to trigger glyphosate detoxification pathways. Thus, the herbicide accumulates to a level that triggers oxidative stress [28].…”

“…Vivancos et al specifically provides in vivo experimental data on GSH/GSSG ratios in RRS and Organic Soy in controlled-environment chambers until the fourth leaf stage, at day/night temperatures of 24˚C/19˚C with a 12-h-day/12-hnight cycle and were watered twice a day. For the glyphosate treatments, 20 mL of Clinic Ace (41.5% glyphosate plus 8.1% Tallow alkylamine ethoxylate; Nufarm) was used in a total 900 mL of water solution [28].…”

“…The literature search for in vivo experimental studies measuring the GSH/GSSG ratio in RRS yielded several reports that analyzed the effect of genetic modification on GSH/GSSG ratios [19] [20] [28] [29]. Vivancos et al specifically provides in vivo experimental data on GSH/GSSG ratios in RRS and Organic Soy in controlled-environment chambers until the fourth leaf stage, at day/night temperatures of 24˚C/19˚C with a 12-h-day/12-hnight cycle and were watered twice a day.…”