Induction of abscisic acid is a common effect of auxin herbicides in susceptible plants

For more than forty years synthetic compounds possessing auxin activity have been among the most successful herbicides used in agriculture. However, in spite of extensive research a consensus on the biochemical basis of their phytotoxicity has yet to emerge. Comparing the effects of several representatives of the known chemical classes of auxin herbicides (e.g. dicamba, 2-methyl-4-chlorophenoxyacetic acid, picloram, quinclorac, quinmerac) and auxins (e.g. alpha-naphthaleneacetic acid, indole-3-acetic acid) in a variety of plant species, we demonstrate, to our knowledge for the first. time, that the induction of ABA is a common effect of auxin-type compounds, which appears to be implicated in their inhibition of growth in susceptible plants.