Reduced paraquat transport from the site of application to the site of action in the chloroplast seems a likely mechanism for paraquat resistance in several weed species including Arctotheca calendula. Recently, it has been shown that paraquat translocation in A. calendula is correlated with paraquat-induced injury and is reduced in paraquat-resistant A. calendula. Studies with leaf slices have shown that some polyamines when applied concomitantly with paraquat can reduce the toxic effects of paraquat. This study examined the effects of three polyamines, putrescine, cadaverine, and spermidine, on paraquat translocation to examine the possibility that paraquat translocation in susceptible plants would be reduced in the presence of polyamines due to competition of the polyamines with cellular paraquat uptake. Two polyamines, spermidine and cadaverine were effective in reducing paraquat translocation in susceptible A. calendula inducing these plants to perform more like resistant A. calendula in terms of translocation. Quantification of the polyamine contents of resistant and susceptible A. calendula showed that resistant plants have higher constitutive spermidine levels than susceptible plants, which infers a possible role of either polyamines or a polyamine transporter in paraquat resistance. (C) 2004 Elsevier Inc. All rights reserved.