Mechanism of Atrazine Resistance in Lambsquarters and Pigweed

Studies were conducted to determine the effect on absorption and metabolism of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] by atrazine-susceptible (S) and -resistant (R) biotypes of common lambsquarters (Chenopodium albumL.) and redroot pigweed (Amaranthus retroflexusL.). The response of isolated chloroplasts of susceptible and resistant biotypes of each species was also studied. In both species the two biotypes absorbed atrazine equally well and were unable to differentially metabolize the herbicide. The photochemical activity of R chloroplasts isolated from each species was not inhibited by atrazine but S chloroplasts were severely inhibited.