Studies on translocation of herbicides in skeleton weed (Chondrilla juncea L.)

Abstract

These studies relate to the translocation of orthoarsenic acid and 2,4-D from the above-ground parts of skeleton weed, usually the leaves, to the roots. Poor translocation of orthoarsenic acid is to be attributed to some factor other than poor oxygenation of the soil, possibly unfavourable source-sink relationships. The apparently anomalous unimpaired translocation of both herbicides after old plants were subjected to darkness for 4 days is related to a sustained high carbohydrate content of the leaves. Other factors also affect translocation. Orthophosphate, 0.25M at pH 3.0, significantly increased translocation of radioactive 2,4-D in comparison with equimolar citrate or glycine. Phosphate metabolism, perhaps ATP content, is regarded as influencing translocation. Maximum radioactivity in the roots was found some 7 days after labelled 2,4-D was applied to the leaves, which showed that absorption and translocation were prolonged. Radioactivity within treated young plants progressively lessened from the petioles to the roots, there being no focal point of concentration limiting translocation. At first proportional radioactivity, then total radioactivity found in the roots, decreased as the concentration of labelled 2,4-D applied to the leaves was increased. Injury to the leaf tissue or the phloem, or both, is regarded as a major factor limiting the translocation of such poisons to the roots.