Absorption, distribution, & metabolism of 2,2-dichloropropionic acid in relation to phytotoxicity. I. Penetration & translocation of Cl36- and C14-labeled dalapon

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Abstract
That dalapon enters and moves readily through leaves and roots of cotton (a tolerant species) and sorghum (a susceptible species), remaining essentially nonmetabolized, was confirmed by radioautography and counting. Some foliar sorption occurred almost immediately in both species. Acute toxicity at the point of foliar application, whether due to excess H ions, herbicide, or toxic surfactant, reduced or prevented systemic distribution. With no acute toxicity, absorption and trans-location out of the treated region were protracted (2 weeks). Transport occurred via the transpiration stream (following uptake by roots, severed vein, or severed petiole), in the phloem (associated with and dependent upon the movement of photosynthates), and laterally in phloem-xylem interchange. In both species, re-translocation and accumulation occurred in response to shifts in loci of high metabolic activity. Some leakage of foliar-applied dalapon occurred, from roots of cotton especially, and also from sorghum under certain conditions, and slight radioactivity was detected in the guttate from hydathodes of sorghum. Despite its ready mobility, some dalapon was retained in transport. Restriction of dalapon movement was especially noticeable in the basal sections of young sorghum leaves. Probable factors are accumulation by living cells and weak adsorption on colloidal surfaces. Neither penetrability nor metabolic inactivation appeared to play a major role in determining species specificity. Furthermore, differences in translocation observed among species would tend to minimize or refute the importance of such differences in determining herbicidal selectivity.