Characterization of Paraquat Resistance inSolanum americanumMill. I. Paraquat Uptake, Translocation, and Compartmentalization

Studies were conducted to probe the nature of paraquat resistance inSolanum americanum(American black nightshade). This initial characterization was focused on the comparative examination of paraquat uptake, translocation, and compartmentalization of a paraquat-resistant (R) biotype and a paraquat-sensitive (S) biotype. Uptake of paraquat by whole plants of both biotypes was equivalent. No paraquat was translocated out of the treated leaf of the S biotype. However, the R biotype translocated paraquat both acropetally and basipetally. As for whole plants, paraquat uptake by leaf discs did not differ with biotype. Paraquat efflux from leaf discs of both biotypes was biphasic with the rapid phase occurring during the first 10 min. Paraquat efflux occurred more rapidly in the S biotype. A compartmentalization study showed that 37 and 22% of the absorbed paraquat was located in an unbound state in the apoplast of the S and R biotypes, respectively. Although the R biotype adsorbed 15% of the paraquat compared with 12% in the S biotype, rapid sequestration of paraquat by apoplastic adsorption is not a plausible explanation of resistance inS. americanumsince there was no biotypic difference in the percentage of paraquat found in the cytoplasm. Paraquat stimulated greater ethane production in the S biotype. These results support a primary mechanism of paraquat resistance inS. americanumthat is located within the protoplast.