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

The herbicide glyphosate inhibits the shikimate pathway of the synthesis of amino acids such as phenylalanine, tyrosine, andtryptophan. However, much uncertainty remains concerning precisely how glyphosate kills plants or affects cellular redoxhomeostasis and related processes in glyphosate-sensitive and glyphosate-resistant crop plants. To address this issue, weperformed an integrated study of photosynthesis, leaf proteomes, amino acid profiles, and redox profiles in the glyphosatesensitivesoybean (Glycine max) genotype PAN809 and glyphosate-resistant Roundup Ready Soybean (RRS). RRS leavesaccumulated 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/photorespiratorypathway proteins was observed together with oxidation of major redox pools. While treatment of a sensitive genotype withglyphosate rapidly inhibited photosynthesis and triggered the appearance of a nitrogen-rich amino acid profile, there was noevidence of oxidation of the redox pools. There was, however, an increase in starvation-associated and defense proteins. Weconclude that glyphosate-dependent inhibition of soybean leaf metabolism leads to the induction of defense proteins withoutsustained oxidation. Conversely, the accumulation of high levels of glyphosate in RRS enhances cellular oxidation, possiblythrough mechanisms involving stimulation of the photorespiratory pathway.