CHARACTERIZATION OF PARAQUAT RESISTANCE IN SOLANUM-AMERICANUM MILL - I - PARAQUAT UPTAKE, TRANSLOCATION, AND COMPARTMENTALIZATION

Studies were conducted to probe the nature of paraquat resistance in S olanum americanum (American black nightshade). This initial characteri zation was focused on the comparative examination of paraquat uptake, translocation, and compartmentalization of a paraquat-resistant (R) bi otype and a paraquat-sensitive (S) biotype. Uptake of paraquat by whol e plants of both biotypes was equivalent. No paraquat was translocated out of the treated leaf of the S biotype. However, the R biotype tran slocated paraquat both acropetally and basipetally. As for whole plant s, paraquat uptake by leaf discs did not differ with biotype. Paraquat efflux from leaf discs of both biotypes was biphasic with the rapid p hase 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 th e apoplast of the S and R biotypes, respectively. Although the R bioty pe adsorbed 15% of the paraquat compared with 12% in the S biotype, ra pid sequestration of paraquat by apoplastic adsorption is not a plausi ble explanation of resistance in S. americanum since there was no biot ypic 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 in S. ameri canum that is located within the protoplast. (C) 1998 Academic Press.