Sada Yoshinao, Ikeda Hajime, Yamato Seiji, Kizawa Satoru
Health and Crop Sciences Research Laboratory, Sumitomo Chemical Co., Ltd, Takarazuka, Hyogo, Japan; Crop Protection Division - International, Sumitomo Chemical Co., Ltd, Tokyo, Japan.
Health and Crop Sciences Research Laboratory, Sumitomo Chemical Co., Ltd, Takarazuka, Hyogo, Japan.
Pestic Biochem Physiol. 2013 Sep;107(1):106-11. doi: 10.1016/j.pestbp.2013.05.013. Epub 2013 Jun 1.
Schoenoplectus juncoides, a noxious weed for paddy rice, is known to become resistant to sulfonylurea (SU) herbicides by a target-site mutation in either of the two acetolactate synthase (ALS) genes (ALS1 and ALS2). SU-resistant S. juncoides plants having an Asp376Glu mutation in ALS2 were found from a paddy rice field in Japan, but their resistance profile has not been quantitatively investigated. In this study, dose-response of the SU-resistant accession was compared with that of a SU-susceptible accession at in vivo whole-plant level as well as at in vitro enzymatic level. In whole-plant tests, resistance factors (RFs) based on 50% growth reduction (GR50) for imazosulfuron (ISF), bensulfuron-methyl (BSM), metsulfuron-methyl (MSM), bispyribac-sodium (BPS), and imazaquin (IMQ) were 176, 40, 14, 5.2 and 1.5, respectively. Thus, the accession having an Asp376Glu mutation in ALS2 was highly resistant to the three SU herbicides and moderately resistant to BPS, but was not substantially resistant to IMQ. This is slightly different from the earlier results reported from other weeds with an Asp376Glu mutation, in which the mutation confers resistance to broadly all the chemical classes of ALS-inhibiting herbicides. In enzymatic tests, ALS2 of S. juncoides was expressed in E. coli; the resultant ALS2 was subjected to an in vitro assay. RFs of the mutated ALS2 based on 50% enzymatic inhibition (I50) for ISF, BSM, MSM, BPS, and IMQ were 3699, 2438, 322, 80, and 4.8, respectively. The RFs of ALS2 were highly correlated with those of the whole-plant; this suggests that the Asp376Glu mutation in ALS2 is a molecular basis for the whole-plant resistance. The presence of two ALS genes in S. juncoides can at least partially explain why the whole-plant RFs were less than those of the expressed ALS2 enzymes.
灯心草状荸荠是水稻的一种有害杂草，已知它会通过两个乙酰乳酸合成酶（ALS）基因（ALS1和ALS2）中的任何一个发生靶标位点突变而对磺酰脲（SU）类除草剂产生抗性。在日本的一块稻田中发现了ALS2基因发生Asp376Glu突变的抗SU灯心草状荸荠植株，但它们的抗性特征尚未进行定量研究。在本研究中，在体内全株水平以及体外酶水平上，将抗SU种质与感SU种质的剂量反应进行了比较。在全株试验中，基于50%生长抑制（GR50）的咪唑磺隆（ISF）、苄嘧磺隆（BSM）、甲磺隆（MSM）、双草醚（BPS）和咪唑喹啉酸（IMQ）的抗性因子（RFs）分别为176、40、14、5.2和1.5。因此，ALS2基因发生Asp376Glu突变的种质对三种SU类除草剂具有高抗性，对BPS具有中等抗性，但对IMQ没有显著抗性。这与其他具有Asp376Glu突变的杂草早期报道的结果略有不同，在那些杂草中，该突变赋予了对几乎所有化学类别的ALS抑制除草剂的抗性。在酶试验中，灯心草状荸荠的ALS2在大肠杆菌中表达；将所得的ALS2进行体外测定。基于50%酶抑制（I50）的突变型ALS2对ISF、BSM、MSM、BPS和IMQ的RFs分别为3699、2438、322、80和4.8。ALS2的RFs与全株的RFs高度相关；这表明ALS2中的Asp376Glu突变是全株抗性的分子基础。灯心草状荸荠中两个ALS基因的存在至少可以部分解释为什么全株RFs低于表达的ALS2酶的RFs。
