1 research outputs found
New Insights on Glyphosate Mode of Action in Nodular Metabolism: Role of Shikimate Accumulation
8 pages, figures, and tables statistics.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.We thank M. C. de Mesa and M. I. Menendez for technical
assistance.Peer reviewe