Metabolism of environmental chemicals by plants - copolymerization into lignin

Abstract

Plants have frequently been found to incorporate xenobiotics into ill-defined ''insoluble'' metabolite fractions. Evidence for the lignin nature of such fractions and for the formation of ''insoluble'' metabolite fractions in sterile plant cell cultures is summarized. In several cases, total ''insoluble'' plant metabolite fractions of pesticides were found to be excreted undigested by rats and sheep. Conclusive evidence for covalent incorporation of chemicals into lignin has only recently been obtained. In the case of herbicide 2,4-dichlorophenoxyacetic acid and of the fungicide pentachlorophenol, the derived pesticide/lignin copolymers were characterized by gel permeation chromatography in dimethylformamide, spectral methods, and chemical degradation. In independent studies, artificial lignin was prepared from coniferyl alcohol with the aid of peroxidase/H/sub 2/O/sub 2/. Benzo(..cap alpha..)pyrene quinones and chlorinated anilines could be copolymerized, and the resulting copolymer species were characterized with regard to size distribution and spectral properties. Detailed /sup 1/H- and /sup 13/C-NMR spectroscopic studies showed that a major mechanism of copolymerization of the anilines consisted of a nucleophilic addition to the benzylic ..cap alpha..-carbon of lignol quinone-methide intermediates. In addition, covalent linkages involving the aromatic rings were also formed. 61 references, 3 figures, 4 tables.