Abstract
The resistant mechanism of the tobacco cell line ETR-245 to the photobleaching herbicide, pyraflufen-ethyl, was analyzed at the molecular level. Wild-type cDNAs of protoporphyrinogen oxidase (Protox), the target enzyme of photobleaching herbicides, were isolated from tobacco leaves and sequenced by the genetic complementation. Using the sequence information, Protox cDNAs were amplified by RT-PCR from normal and ETR-245 cells. The sensitivities of each Protox gene product to pyraflufen-ethyl were compared. Although mitochondrial Protox gene products showed almost equivalent sensitivities to pyraflufen-ethyl, the chloroplastic Protox gene product encoded by the cDNA from ETR-245 cells was more than 4000-fold resistant than that encoded by the cDNA from normal cells. The nucleotide sequence analysis of these chloroplastic Protox cDNAs revealed single-point mutation in the Protox cDNA from ETR-245, which accompanied with one amino acid substitution. From these results, it was clarified that this mutation was the cause for the resistance in ETR-245.
