文摘
Picloram resistance exhibited by transgenic tobacco (Nicotiana tabacum) plants expressing an anti-picloram single-chain variable fragment (scFv) antibody was investigated through the study ofhomozygous lines expressing the antibody. Dose-response bioassays, using foliar application ofpicloram, showed that these homozygous transgenic plants were resistant to at least 5 g of ai ha-1picloram and grew normally to produce seed, whereas wild-type plants did not survive. Althoughthese lines had improved resistance compared with those previously reported, significant improvementsare still required to achieve field-level resistance. Uptake and translocation studies demonstratedthat [14C]picloram translocation from treated leaves to the apical meristem was reduced in transgenicversus wild-type plants. The presence of [14C]picloram, visualized by autoradiography and quantifiedby liquid scintillation spectrometry, demonstrated the distribution of more picloram in the treated leafand less in the apical meristem of transgenic plants when compared to wild-type plants. No differencesbetween transgenic and wild-type plants were found in the distribution of [14C]clopyralid, a herbicidewith structural similarity to picloram as well as the same mechanism of action. No differences werefound in the metabolism of [14C]picloram. Taken together, these results suggest that reducedtranslocation to the site of action is a major mechanism responsible for picloram resistance in tobaccoplants expressing this anti-picloram antibody.