Combined use of 13C- and 19F-NMR to analyse the mode of action and the metabolism of the herbicide isoxaflutole

13C-Nuclear magnetic resonance was used to characterize the effects of the trifluoromethyl herbicide isoxaflutole on plant metabolism. A specific accumulation of tyrosine and phenylalanine in pea leaves was observed after treatment with this herbicide, consistent with an inhibition of 4-hydroxyphenylpyruvate dioxygenase (HPPD), an enzyme involved in plastoquinone and tocopherol synthesis and the known target of isoxaflutole. 19F-NMR permitted the analysis of the uptake and degradation of isoxaflutole, with detection limits around 1 μM in perchloric acid extracts. Isoxaflutole was incorporated and transformed to an active diketonitrile derivative, which further underwent degradation to an inactive benzoic acid derivative.