Examination of bound (non-extractable) residues of MCPA and flamprop in wheat straw

The long term metabolism of [¹⁴C]MCPA and [¹⁴C]flamprop in wheat (Triticum aestivum) straw was found to involve incorporation of radioactivity as residues that were insoluble in acetone+water (1+1 by volume). A chemical and an enzymic solubilisation procedure were critically evaluated in attempts to release these residues for further examination. The chemical procedure resulted in complete solubilisation of all the radioactivity of both compounds in association with more than one cell wall fraction. However, routine quantitative analysis was found to be difficult for some fractions. Furthermore, the extracts did not appear to be suitable for investigation of the nature of the binding with the plant constituents. None of the enzymes employed in the enzymic procedures released significant amounts of the residues insoluble in the aqueous acetone. Despite these problems, the residues of MCPA that were insoluble in aqueous acetone were found to contain both the parent MCPA and its major metabolite 4-chloro-α-hydroxy-o-tolyloxyacetic acid.