| Sensitivity of six wheat cultivars to sulfonylurea herbicide mesosulfuron was studied in the greenhouse. Biochemical differences between the mesosulfuron-tolerance (r-6) and mesosulfuron -sensitive (s-18) cultivars was also examined.Mesosulfuron (at 16.0g-ha"') plus safener AE F107892 (at 600ml-ha"1) reduced the shoot height of the wheat cultivars accordingly. R-6 was the most tolerant and s-18 was the most sensitive to mesosulfuron. The mesosulfuron concentration required to reduce shoot length by 50 percentage compared with the control was about 5-fold higher. Wheat cultivars of Iongchun015, minhe853, xuzhou87633 and yangl 1 were all moderately tolerance to mesosulfuron.In vitro studies, acetolactate synthase (ALS), the target enzyme of sulfonylurea herbicides was extracted from r-6 and s-18, and the specific activity was assayed with pyruvate as substrate. ALS level of r-6 was the most highest and s-18 was the lowest. The specific activity of ALS in r-6 with control was 2.5-fold higher than that of s-18. The latter ALS sensitivity to mesosulfuron was 5-fold higher than that of the former. It is hypothesized that differential sensitivity to mesosulfuon in wheat is mostly due to a less sensitive ALS.The effects of safener on the growth and ALS activity were also examined. It showed that low concentration of AE F107892 could stimulate the growth of s-18 cultivars, but had little effect on the r-6 cultivars. High concentration of AE F107892 could inhibit the growth of both of the two cultivars. After treated with 400|imol/L AE F107892 ALS activities of r-6 and s-18 were increased to 150% and 25% respectively. The GSH level was not affected by the safener. The GST activity in r-6 and s-18 was increased to 83% and 102% after treated with 400u.mol/L AE F107892.It can be concluded that the different responses of wheat cultivars to mesosulfuron may be partly due to the target site sensitivity. Safener increased the ALS activity and it also increased the GST activity of the two cultivars, which may enhance the metabolism of the herbicide, thus increased the tolerance to mesosulfuron. |
