Herbicides that inhibit
branched chain amino acid biosynthesis induce aerobic fermentation. The role of fermentation in the mode of action of these
herbicides is not known, nor is the importance of this physiological response in the growth inhibition and the lethality caused by them. Metabolic profiling was used to compare the effects of the
herbicide imazethapyr (IM) on pea plants with two other treatments that also induce fermentation:
hypoxia and the exogenous supply
pyruvate for seven days. While hypoxic roots did not show internal
anoxia, feeding
pyruvate or applying IM to the roots led to internal
anoxia, probably related to the respiratory burst detected. The three treatments induced
ethanol fermentation, but fermentation induced following
herbicide treatment was earlier than that following
pyruvate supply and was not associated with a decrease in the energy status. No striking changes were detected in the metabolic profiling of hypoxic roots, indicating that metabolism was only slightly impaired. Feeding
pyruvate resulted in marked
succinate accumulation and a general
amino acid accumulation. IM-treated roots showed a general accumulation of glycolytic metabolites upstream of
pyruvate, a decrease in some TCA intermediates and an increase in the free
amino acid pool sizes. All treatments caused
GABA and
putrescine accumulation. Our results indicate that IM supply impairs
carbon/
nitrogen metabolism and this impaired metabolism is likely to be related to the growth arrest detected. As growth is arrested,
carbohydrates and glycolytic intermediates accumulate and energy becomes more available.