Nepetalactone-rich essential oil mitigates BASTA-induced ammonium toxicity in Arabidopsis thaliana L. by maintaining glutamine synthetase activity

Abstract

Phosphinothricin, active ingredient of the commercial herbicide BASTA, acts as an inhibitor of glutamine synthetase (GS), a key enzyme in ammonium assimilation, which leads to the elevation of ammonium levels in plants and further to various physiological alternations, ammonium toxicity and lethality. Nepeta rtanjensis Diklić & Milojević essential oil (NrEO), rich in iridoid monoterpenoids nepetalactones, has been previously highlighted as a potential bioherbicide inducing oxidative stress in model plants. Interestingly, simultaneous foliar application of NrEO and BASTA, two agents showing differential mode of herbicidal action, suspends BASTA-induced toxicity in Arabidopsis thaliana plants by maintaining sub-toxic and/or sub-lethal ammonium concentration in tissues. NrEO effectively reduces BASTA efficacy, and the degree of antagonism between these agents escalates at increasing BASTA and NrEO levels. Regulation of GS activity, as influenced by BASTA, NrEO, and their joint action, partially occurs at transcriptional, posttranscriptional, and/or posttranslational levels, and is organ-specific. Furthermore, BASTA and NrEO interaction mitigates the effects of these agents, applied independently, on chlorophyll, soluble sugars and organic acids metabolism. Results suggest the existence of complex regulatory mechanisms determining antagonistic BASTA and NrEO interaction, and highlight the possible applications of the BASTA/NrEO mixture in agricultural practice. Furthermore, the possibility of using NrEO as a bioherbicide in BASTA-treated crop fields to mitigate the effect of BASTA residues in contaminated soils, is suggested here as a environment-friendly approach for weed control.