The Metabolic Fate of Phenoxyacetic Acids in Higher Plants

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Abstract
The metabolism of phenoxyacetie acid (POA) was followed over short periods in segments of Auena and Pisum using a vacuum infiltration technique. Both species form 4-hydroxyphenoxy-acetic acid (4-OH-POA) and its phenolic glucoside (OGlu-POA) but Pisum incorporates much of the substrate into an insoluble wall component. This insoluble material appears to be formed from 4-OH-POA. Preliminary kinetic experiments show that the overall conversion of POA is linearly related to concentration up to 2μmol POA g-1 fresh tissue and can be completed in a few hours. The method provides a very useful means of preparing sufficient quantities of 14C-labelled 4 OH POA and O-Glu-POA in a pure form for subsequent use as substrates for the enzymes involved in glucosylation and formation of the insoluble material. Although light has relatively little effect on hydroxylation, the capacity formation of both the glucoside and the insoluble material is increased by continuous fluorescent, red, and far red light. The results so far obtained suggest that phytochromeis involved in the transformations. The chlorinated derivatives of phenoxyacetic acid with high herbicidal activity e.g. 2, 4-dichlorophenoxyacetic acid (2, 4-D) are also metabolized by analogous reactions and the formation of hydroxylated and glycosylated derivatives may contribute to the detoxification of such herbicides in resistant species.

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