Comparative Absorption, Translocation, and Metabolism of Foliar-Applied Oxyfluorfen in Wheat and Barley

Wheat is known to be relatively tolerant to diphenyl ether herbicides. The absorption, translocation, and metabolism of foliarapplied oxyfluorfen in wheat were examined in comparison with those of oxyfluorfen-susceptible barley. Epicuticular wax contents in the first fully expanded leaves were similar in wheat and barley, but the wheat leaves had a 1.74-fold higher cuticle content than the barely leaves. Absorption of [14C]oxyfluorfen, as estimated by the amount of [14C]oxyfluorfen penetrating the cuticle, appeared to be similar in the leaves of both species, although most of the radioactivity remained in the epicuticular wax. Little translocation of the herbicide out of the treated leaf was observed in either species, but slightly more translocation of [14C]oxyfluorfen to shoots other than the treated leaf or to roots was found in barley than in wheat leaves. Autoradiographs of the [14C]oxyfluorfen-treated leaves of both species also showed that the radioactivity was distributed mainly in the treated site. Thin-layer chromatographic analysis of leaf extracts revealed that oxyfluorfen metabolism did not occur in intact leaves of either species. The binding constants for the herbicide were estimated as 44.2 and 191 nM, respectively, for wheat and barley etioplasts, showing that the herbicide had higher affinity to barley than to wheat etioplasts. These results indicate that the differential susceptibilities of wheat and barley to oxyfluorfen are not due to the differential absorption, translocation, and metabolism of the herbicide, but to the differential affinity of the herbicide.