DIFFERENTIAL MOVEMENT OF PARAQUAT IN RESISTANT AND SENSITIVE BIOTYPESOF CONYZA

Previous indirect evidence indicates that paraquat resistance in hairy fleabane (Conyza bonariensis [L.] Cronq.) is correlated with restrict ed movement in the resistant (R) biotype. Experiments were conducted t o further characterize the mobility of paraquat (1,1'-dimethyl-4-4'bip yridinium ion) in R and sensitive (S) biotypes of Conyza. The lateral movement of [C-14]paraquat from the point of application on he adaxial surface of intact leaves incubated in darkness was significantly rest ricted in the R relative to the S biotype. This restricted movement of paraquat may result from a mechanism of sequestration that conveys re sistance to the R biotype. Autoradiographs of treated, intact leaves a s well as leaf disks floated in an aqueous solution containing [C-14]p araquat (dark incubation) revealed a distinctive pattern of black spot s very similar to the density and distribution of unicellular and mult icellular leaf hairs (trichomes). Paraquat accumulated in trichomes on the abaxial surface of leaf disks of both biotypes even though this s urface was not in direct contact with the incubation solution. Microau toradiography and paradermal sectioning studies were conducted followi ng the treatment of the adaxial surface of intact leaves of both bioty pes with [C-14]paraquat for 4 hr in darkness. Analyses of the data ind icated a 10- to 100-fold increase in the amount of paraquat associated with trichomes (relative to other leaf cells) on the adaxial and abax ial leaf surfaces of both biotypes. It is unlikely that the accumulati on of paraquat in abaxial trichomes within 4 hr after treatment can oc cur solely by diffusion. A 20% increase in the density of multicellula r trichomes was observed in leaves of the R biotype. This small increa se may contribute slightly to the 100-fold level of resistance typical ly observed in intact leaves of the R biotype. These data further supp ort the hypothesis that paraquat resistance in Conyza is correlated wi th restricted movement (sequestration) in the R biotype. (C) 1994 Acad emic Press, Inc.