Atrazine resistance in velvetleaf ( Abutilon theophrasti) due to enhanced atrazine detoxification

Abstract

A velvetleaf ( Abutilon theophrasti Medic.) biotype, originally discovered in Maryland, was 10-fold more tolerant of atrazine than a susceptible or “wild type” biotype from Minnesota. The I 50 values for the inhibition of shoot growth in the atrazine-resistant and susceptible biotypes were 3.0 and 0.3 μ M, respectively. Electron transport in chloroplast thylakoids isolated from leaves of both biotypes was equally sensitive to atrazine. Atrazine treatment inhibited whole leaf photosynthesis in both biotypes but the extent of the initial inhibition was less and the rate of recovery was greater in the resistant biotype. Both biotypes accumulated approximately equal amounts of radiolabel during a 3-hr pretreatment with [ 14C]atrazine via hydroponic solution. Both biotypes metabolized atrazine via glutathione conjugation in stem and leaf tissue. However, the resistant biotype did so more rapidly. As measured immediately after the 3-hr pretreatment, the concentration of the glutathione conjugate of atrazine was approximately 9-fold greater in stem tissue and approximately 2-fold greater in leaf tissue of the resistant biotype. The rates of formation of the glutathione conjugate of atrazine were compared in excised leaf discs of both biotypes and the F1 hybrids obtained by reciprocal crosses. As compared to the susceptible biotype, the rate of formation of the glutathione conjugate was approximately 6-fold greater in leaf discs of the resistant biotype. The rate of formation of the glutathione conjugate was equivalent in F1 progeny of reciprocal crosses and intermediate between that of the parents. It is concluded that atrazine resistance in the Maryland biotype is under nuclear control and is due to an enhanced capacity to detoxify atrazine via glutathione conjugation.