Resistance Mechanisms of Oxalis Pes-Oaprae (Soursob) to 2,4-Dichlorophenoxyacetic Acid

Abstract

The uptake, translocation, and metabolism by O. pes-capl'ae plants of carboxyl-and methyl-labelled [14C]-2,4-dichlorophenoxyacetic acid (2,4-D) were studied by chromatographic, radioautographic, and scintillation-counting tech-niques. In young O. pes-caprae plants some translocation of 14C out of the treated leaves occurred while in older plants it was severely restricted. Qualitative and quantitative chromatography of the acidic fructions of methanolic extracts soluble in ethel' or ethyl acetate or both revealed the presence of at least 12 radioactive compounds, often within 1 day from treatment. The bulk of the activity (90-95%), was present in a spot chromatographically identical with 2,4.D regardless of the region of the plant or the position of 14C in the molecule. Evidence was obtained that about half of the "presumed" uptake was not accounted for even after 14002 evolution, leakage from roots, and residual activity in extracted material are taken into account. The observed instability of the various radioactive products upon .rechromatography underlines the caution that must be exercised in interpreting the physiological significance of interconversions. It is concluded that restricted trans-location and metabolic attack of the 2,4.D molecule, with the formation of unstable intermediates, some of which may be volatile, are contributing factors in the high resistance of O. pes·caprae to the herbicidal action of 2,4-D.