The Breakdown of 2,4-Dichlorophenoxyacetic Acid in Shoots and Roots

Abstract

Measurements have been made of the rate of evolution of labelled oarbon dioxide from shoots and from roots of tick beans whioh have been treated on one leaflet with a small dose of labelled 2,4-diohlorophenoxyaoetio aoid (2,4-D). The corresponding breakdown of 2,4-D in root and shoot has been oaloulated. The carbon dioxide evolved from the roots was oonsistently more radioaotive than that from the shoot suggesting that 2,4-D is more rapidly broken down in the former and the total loss of labelled oarbon in 4 days corresponded to about 5 per oent. of the applied dose of growth substanoe. 2,4-D was not readily extraotable from the roots at the conolusion of the respiration run and the labelled oarbon was shown to be present there in many compounds that were not 2,4-D. It is ooncluded that though part of the side-chain was rapidly lost from the plant as oarbon dioxide from the roots. this is not a main pathway involved in the inaotivation of this growth substance. The evidence from intact plants points strongly to most of the breakdown occurring in the roots. With out tissue, similar radioaotive assays and bioassays did not reveal a greater intrinsic capacity of the roots for 2,4-D breakdown.