Abstract
Glyphosate is the most widely used herbicide with a yearly increase in global application. Recent studies report glyphosate residues from diverse habitats globally where the effect on non-target plants are still to be explored. Glyphosate disrupts the shikimate pathway which is the basis for several plant metabolites. The central role of phytohormones in regulating plant growth and responses to abiotic and biotic environment has been ignored in studies examining the effects of glyphosate residues on plant performance and trophic interactions. We studied interactive effects of glyphosate-based herbicide (GBH) residues and phosphate fertilizer in soil on the content of main phytohormones, their precursors and metabolites, as well as on plant performance and herbivore damage, in three plant species, oat (Avena sativa), potato (Solanum tuberosum), and strawberry (Fragaria x ananassa). Plant hormonal responses to GBH residues were highly species-specific. Potato responded to GBH soil treatment with an increase in stress-related phytohormones abscisic acid (ABA), indole-3-acetic acid (IAA), and jasmonic acid (JA) but a decrease in cytokinin (CK) ribosides and cytokinin-O-glycosides. GBH residues in combination with phosphate in soil increased aboveground biomass of potato plants and the concentration of the auxin phenylacetic acid (PAA) but decreased phaseic acid and cytokinin ribosides (CKR) and O-glycosides. Chorismate-derived compounds [IAA, PAA and benzoic acid (BzA)] as well as herbivore damage decreased in oat, when growing in GBH-treated soil but concentrations of the cytokinin dihydrozeatin (DZ) and CKR increased. In strawberry plants, phosphate treatment was associated with an elevation of auxin (IAA) and the CK trans-zeatin (tZ), while decreasing concentrations of the auxin PAA and CK DZ was observed in the case of GBH treatment. Our results demonstrate that ubiquitous herbicide residues have multifaceted consequences by modulating the hormonal equilibrium of plants, which can have cascading effects on trophic interactions.
Highlights
Glyphosate-based herbicides (GBH) are the world’s most widely used pesticides due to their affordable price and efficiency in killing weeds (Myers et al, 2016)
aminomethylphosphonic acid (AMPA) concentrations in soils from G and phosphate + GBH (PG) treatments were 1.9 and 1.8 mg kg−1, respectively. Both glyphosate and AMPA concentrations were below quantification limit in soil samples collected from C and P treatments
The concentration of benzoic acid (BzA), an intermediate product of shikimate pathway involved in biosynthesis of many secondary metabolites, was suppressed by all treatments compared to control in oat (Figures 1, 2 and Supplementary Table 2)
Summary
Glyphosate-based herbicides (GBH) are the world’s most widely used pesticides due to their affordable price and efficiency in killing weeds (Myers et al, 2016). Glyphosate targets 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), the key enzyme in the shikimate pathway present in plants (Duke and Powles, 2008). By inactivating this enzyme, glyphosate interrupts the supply of chorismate which is the essential precursor for the biosynthesis of three aromatic amino acids tryptophan, phenylalanine and tyrosine (Maeda and Dudareva, 2012). Glyphosate interrupts the supply of chorismate which is the essential precursor for the biosynthesis of three aromatic amino acids tryptophan, phenylalanine and tyrosine (Maeda and Dudareva, 2012) Chorismate and these amino acids are key components of numerous primary and secondary compounds including the phytohormones indole-3-acetic acid (IAA) and salicylic acid (SA) which are involved in plant stress responses to many abiotic and biotic stressors (Kazan and Manners, 2009; Rekhter et al, 2019; Ding and Ding, 2020). Glyphosate residues may indirectly alter plant interactions by affecting core biochemical pathways (Fuchs et al, 2021)
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