Identity and Activity of 2,4-Dichlorophenoxyacetic Acid Metabolites in Wild Radish (Raphanus raphanistrum)

Synthetic
auxin herbicides, such as 2,4-dichlorophenoxyacetic acid
(2,4-D), are widely used for selective control of broadleaf weeds
in cereals and transgenic crops. Although the troublesome weed wild
radish (Raphanus raphanistrum) has
developed resistance to 2,4-D, no populations have yet displayed an
enhanced capacity for metabolic detoxification of the herbicide, with
both susceptible and resistant wild radish plants readily metabolizing
2,4-D. Using mass spectrometry and nuclear magnetic resonance, the
major 2,4-D metabolite was identified as the glucose ester, and its
structure was confirmed by synthesis. As expected, both the endogenous
and synthetic compounds retained auxin activity in a bioassay. The
lack of detectable 2,4-D hydroxylation in wild radish and the lability
of the glucose ester suggest that metabolic 2,4-D resistance is unlikely
to develop in this species.