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 foliar-applied oxyfluorfen in wheat were examined in comparison with those of oxyfluorfen-susceptible bar ley. Epicuticular wax contents in the first fully expanded leaves were simi lar in wheat and barley, but the wheat leaves had a 1.74-fold higher cuticl e content than the barely leaves. Absorption of [C-14]oxyfluorfen, as estim ated by the amount of [C-14]oxyfluorfen penetrating the cuticle, appeared t o be similar in the leaves of both species, although most of the radioactiv ity 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 [C-14]oxyfluorfen to shoots other than the treated leaf or to roots was found in barley than in wheat Leaves. Autoradiographs of the [C-14]oxyfluorfen-treated leaves of both species also showed that the radio activity was distributed mainly in the treated site. Thin-layer chromatogra phic analysis of leaf extracts revealed that oxyfluorfen metabolism did nor occur in intact leaves of either species. The binding constants for the he rbicide were estimated as 44.2 and 191 nM, respectively, for wheat and barl ey etioplasts, showing that the herbicide had higher affinity to barley tha n to wheat etioplasts. These results indicate that the differential suscept ibilities of wheat and barley to oxyfluorfen are not due to the differentia l absorption, translocation, and metabolism of the herbicide, but to the di fferential affinity of the herbicide. (C) 2001 Academic Press.