New Insights on Glyphosate Mode of Action in Nodular Metabolism:  Role of Shikimate Accumulation

Abstract

The short-term effects of the herbicide glyphosate (1.25-10 mM) on the growth, nitrogen fixation, carbohydrate metabolism, and shikimate pathway were investigated in leaves and nodules of nodulated lupine plants. All glyphosate treatments decreased nitrogenase activity rapidly (24 h) after application, even at the lowest and sublethal dose used (1.25 mM). This early effect on nitrogenase could not be related to either damage to nitrogenase components (I and II) or limitation of carbohydrates supplied by the host plant. In fact, further exposure to increasing glyphosate concentrations (5 mM) and greater time after exposure (5 days) decreased nodule starch content and sucrose synthase (SS; EC 2.4.1.13) activity but increased sucrose content within the nodule. These effects were accompanied by a great inhibition of the activity of phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31). There were remarkable and rapid effects on the increase of shikimic and protocatechuic (PCA) acids in nodules and leaves after herbicide application. On the basis of the role of shikimic acid and PCA in the regulation of PEPC, as potent competitive inhibitors, this additional effect provoked by glyphosate on 5-enolpyruvylshikimic-3-phosphate synthase enzyme (EPSPS; EC 2.5.1.19) inhibition would divert most PEP into the shikimate pathway, depriving energy substrates to bacteroids to maintain nitrogen fixation. These findings provide a new explanation for the effectiveness of glyphosate as a herbicide in other plant tissues, for the observed differences in tolerance among species or cultivars, and for the transitory effects on glyphosate-resistant transgenic crops under several environmental conditions.

Desempenho da soja roundup ready sob aplicação de glyphosate em diferentes estádios

“…Outra causa poderia ser um menor aporte de nitrogênio via fixação biológica, que pode ser afetado por aplicações com glyphosate (Zablotowicz & Reddy, 2004;María et al, 2006;Santos et al, 2007a,b;Dvoranen et al, 2008;Zobiole et al, 2010a).…”

Putative Porin of Bradyrhizobium sp. ( Lupinus ) Bacteroids Induced by Glyphosate

“…In addition, it was observed that not only was nitrogenase activity decreased rapidly in Bradyrhizobium sp. (Lupinus) bacteroids but also the amount of the two nitrogenase components (Mo-Fe protein and Fe protein) diminished after glyphosate application (10).…”

Inhibition of Shikimate Kinase and Type II Dehydroquinase for Antibiotic Discovery: Structure-Based Design and Simulation Studies

“…In addition, it has also been shown that the antimicrobial properties of glyphosate are not only due to EPSP inhibition, as mentioned previously, but also to the high concentrations of shikimic acid and protocatechuate that it causes [18,19]. These important features have encouraged diverse research groups to study in detail the substrate binding requirements of this enzyme [20][21][22][23][24][25].…”

“…The MD simulation studies carried out with (6R)-6-hydroxyshikimic acid (18) showed that this compound caused significant changes in the water network and caused an opening of the SB domain by nearly 6 Å. During the simulation the ligand also undergoes a conformational change to the thermodynamically more stable conformation, i.e., with C4 and C5 hydroxyl groups in the pseudo-equatorial conformation.…”