Tracer Studies by14C-labeled Herbicides, DMSO, and Surfactant

Abstract

Primary leaves of 17-day-old-bean(Phaseolus vulgarisL. ‘Black Valentine’) were treated with14C-labeled dimethylsulfoxide (DMSO), 3,6-dichloro-o-anisic acid (dicamba), 1,1′-dimethyl-4,4′-dipyridinium salt (paraquat), and 2-chloro-4-(ethylamino)-6-(isopropylamino-s-triazine (atrazine). Each herbicide was tested alone, and in combination with 30% DMSO, 0.25% Tween 80 (nonionic surfactant containing polyoxyethylene sorbitan monooleate), or both. DMSO at concentrations of 25% or more caused varying degrees of acute toxicity. However, a small amount of radioactive carbon generally was distributed throughout the plant 5 days after application of DMSO-14C, as determined by autoradiography and counting. Tween 80 enhanced whereas DMSO had little effect on the absorption and translocation of dicamba, a phloem-mobile herbicide. The contact toxicity and apoplastic movement of paraquat was increased with DMSO. Tween 80 enhanced eight-fold and DMSO, two-fold, the foliar uptake and (apoplastic) movement of atrazine within the treated leaves.