Selection of tobacco cell lines resistant to photobleaching herbicides

Tobacco cell lines resistant to photobleaching herbicides were selected by subculturing tobacco calli regenerated from protoplasts in the presence of ET-62311 (4-chloro-3-[2,4-dichloro-5-(2-propenyloxy) phenyl]-5-difluorometh oxy-1-methylpyrazole), a derivative of pyraflufen-ethyl [ethyl 2-chloro-5-( 4-chloro-5-difluoromethoxy-1-methylpyrazol-3-yl)-4-fluorophenoxyacetate] (f ormerly known as ET-751). Selected cell lines were more than 240-fold resis tant than normal cells and designated as ETR-056, 245 and 253. The ET-62311 treatment induced Proto IX accumulation in ETR-056, but not in ETR-245 nor 253. Cross-resistance of resistant cell lines to herbicides with various m ode of action was evaluated. Each resistant cell line was cross-resistant t o photobleaching herbicides such as pyraflufen-ethyl. In addition, ETR-056 was cross-resistant to paraquat and ETR-253 was cross-resistant to several herbicides with different modes of action. On the other hand, protoporphyri nogen oxidase (Protox) activity in ETR-245 was almost equivalent to that in normal cells, but more than 100-fold resistant to pyraflufen-ethyl. These results suggested the involvement of radical scavenger in ETR-056, multiple resistance due to a reduced uptake and/or an enhanced metabolism of the he rbicides in ETR-253 and an alteration of Protox from photobleaching herbici de sensitive form to resistant one in ETR-245.