Absorption, distribution, & metabolism of 2,2-dichloropropionic acid in relation to phytotoxicity. II. Distribution & metabolic fate of dalapon in plants.

P'atterns of absorption and initial translocation of ClI"'-and C'4-laheled 2,2-dichloropropionic acid (dalaponl) in both tolerant and susceptible species wrere dlescribe(d earlier (8). Of equal or perhaps more importance in understanding the physiological action of growth regulators are the long-term translocation, re-distribution, accumulation, and metabolic fate of the compound in association with plant tissues. The recent emphasis on pesticide residues in food and feed products has given the latter considerations an additional order of importance. Despite the foregoing, perhaps our greatest ignorance of herbicides todav concerns their ultimate fate in plants. The tendency of a herbicide to persist in an active form or to be detoxified rapidly is likely to be of primary importance, whatever the precise mechanism(s) of herbicidal action. Alll of a given herbicide that enters a plant, e.g. via the leaves, is not necessarily available for translocation and/or herbicidal action. Possible mechanisms accounting for the immobilizationi, inactivation, or disappearance of the compound are adsorption on colloidal surfaces, true accumulation by living cells, metabolic degradation followed by loss or incorporation of breakdown products, aln(d reduced movement due to phase distribution effects as on a chromatogram (6. 29, 30, 31). The direct loss of various substances fronm roots or other plant parts may also occur (4, 5, 8, 14, 16, 26). Considerable researchi has been conducted on the loss or persistence of 2,4-dichlorophenoxyacetic acid (2,4-D) in both active and (lormant tissues (17. 18. 19, 22, 29, 31). Several papers are summarized in a recent review (33). Radioactive 2,4-D is known to be metabolized to varying degrees in plant tissues, with the resultant incorporation of C'4-labeled compounds and the evolution of C140.. Strong evidence exists also for relatively long persistence of 2,4-D in plants, which leads to syniptonmatic expression in succeeding seasons (perennials) or succeeding generations (annuals) by transmission through dormant buds or seeds. This latter phenomenon has been observed following both foliar and root applications. 2.4-D is known to persist in plants for longer periods tlhaln exogenous indoleacetic acid.