Comparative Study On Cytochrome P450 From Mesosulfuron-sensitive And Mesosulfuron-tolerant Wheat Cultivars

Mesosulfuron is a new sulfonylurea herbicide, which is safe to wheat and high efficiency to control the grasses in wheat field. Up to now, the selectivity mechanism of mesosulfuron is still not fully understood. In this paper, we mensured the sensitivity of two wheat cultivars to mesosulfuron and evaluated the function of cytochrome P450 contributing to the selectivity mechanism of mesosulfuron.There was a marked difference in sensitivity to mesosulfuron between R-6# and S-18# wheat cultivars, and the tolerance to mesosulfuron of R-6# was 5.27-fold higher than that of S-18# wheat.Tissue age affected cytochrome P450 contents. As the age and length of wheat seedling tissues increased, cytochrome P450 contents were decreased. Cytochrome P450 contents of the two wheat cultivars were highest in the seedlings grown in the dark for 96h, and the cytochrome P450 content of R-6# was 1.49-fold higher than that of S-18#. Cytochrome P450 contents were increased after the two wheat cultivars treated by mefenpyr-diethyl, fenchlorazole-ethyl and 1,8-naplithalic anhydride (NA). Mefenpyr-diethyl was more effective than fenchlorazole-ethyl and NA as inducers of cytochrome P450 content, and NA did not affect cytochrome P450 content to any significant extent.Cytochrome P450 contents of the two wheat cultivars were highest in wheat microsome, intermediate in mitochondria supernatant and lowest in microsomal supernatant. Cytochrome P450 was easily transformed to cytochrome P420 when the wheat microsomal preparations deposited at room temperature a long time, and the half life of cytochrome P450 from R-6# might be longer than that of cytochrome P450 from S-18#. The binding spectra of cytochrome P450 with mesosulfuron, piperonyl butoxide, and 1-aminobenzotriazole were all type I spectra, however, the binding spectra of R-6# was stronger than those of S-18#, and the binding spectra with PBO of R-6# and S-18# were all stronger than that with mesosulfuron.Cytochrome P450s from the two wheat cultivars all could metabolize mesosulfuron in vitro, and the half lives of mesosulfuron metabolism by cytochrome P450s from R-6# and S-18# were 7.56~14.22h, 11.32~18.91h, respectively. A more rapid rate of metabolism by cytochrome P450 from R-6#, in comparison with that of S-18#, most likely account for different sensitivities to mesosulfuron between R-6# and S-18# wheat cultivars and the selectivity mechanism of mesosulfuron.