Abstract
The herbicides glyphosate and imazamox inhibit the biosynthetic pathway of aromatic amino acids (AAA) and branched-chain amino acids (BCAA), respectively. Both herbicides share several physiological effects in the processes triggered in plants after herbicide application that kills the plant, and mixtures of both herbicides are being used. The aim of this study was to evaluate the physiological effects in the mixture of glyphosate and imazamox in glyphosate-sensitive (GS) and -resistant (GR) populations of the troublesome weed Amaranthus palmeri. The changes detected in the physiological parameters after herbicide mixtures application were similar and even less to the changes detected after individual treatments. This pattern was detected in shikimate, amino acid and carbohydrate content, and it was independent of the EPSPS copy number, as it was detected in both populations. In the case of the transcriptional pattern of the AAA pathway after glyphosate, interesting and contrary interactions with imazamox treatment were detected for both populations; enhancement of the effect in the GS population and alleviation in the GR population. At the transcriptional level, no cross regulation between AAA and BCAA inhibitors was confirmed. This study suggests that mixtures are equally or less toxic than herbicides alone, and would implicate careful considerations when applying the herbicide mixtures.
Highlights
The herbicides glyphosate and imazamox inhibit the biosynthetic pathway of aromatic amino acids (AAA) and branched-chain amino acids (BCAA), respectively
Due to its relevance in the BCAA biosynthesis pathway, acid synthase (AHAS) has been widely used as target point for herbicides[7]
They target different enzymes located in different pathways, these common physiological effects suggest that these herbicides kill plants by similar mechanisms
Summary
The herbicides glyphosate and imazamox inhibit the biosynthetic pathway of aromatic amino acids (AAA) and branched-chain amino acids (BCAA), respectively. Previous findings showed that both AHAS and EPSPS inhibitors cause growth arrest followed by a slow plant death of the herbicide-treated plants[9,10] Both types of herbicides provoke an accumulation of free amino acids[11,12,13,14,15], a decrease in the soluble protein content[12,16,17] and accumulation of carbohydrates[11,12,15,18]. They target different enzymes located in different pathways, these common physiological effects suggest that these herbicides kill plants by similar mechanisms. Some specific interactions between AHAS-inhibitors involved in Leu synthesis and the levels of Tyr and Phe have been described[23]
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