Bearded sprangletop (Leptochloa fusca spp. fasicularis) is a problematic weed in California rice (Oryza sativa) production. Historically, bearded sprangletop is controlled with clomazone in California rice fields. The continuous use of clomazone and lack of crop rotation in rice fields resulted in resistance to clomazone in several bearded sprangletop. The objective of this research was to determine the clomazone mechanism of resistance of two bearded sprangletop populations in California rice by investigating clomazone absorption, translocation, and metabolism under controlled environmental conditions in two resistant (CRBS1 and CRBS2) and one susceptible (S) populations. Absorption and translocation of 14C-clomazone were similar in R and S. Clomazone metabolism, as determined by inhibition of cytochrome P450 enzymes with malathion and determining clomazone metabolites profile, was different between S and R 3 days after treatment. Bearded sprangletop pretreated with malathion was 2-fold more sensitive to clomazone than when treated with clomazone alone, suggesting that cytochrome P450-mediated clomazone metabolism might be involved in the mechanism of resistance. An HPLC-MS/MS analysis revealed differences in clomazone metabolism between R and S biotypes. Hydroxymethylclomazone was the most abundant metabolite found in R plants with three and five-fold more abundant in CRBS1 and CRBS2, respectively, when compared to S plants. 5-ketoclomazone, the known toxic metabolite of clomazone, accumulated 2-fold more in S plants than in R plants at 72 h after treatment. This research shows that clomazone is metabolized differently between R and S populations of bearded sprangletop and that P450 monooxidation is likely involved in the mechanism of resistance.

中文翻译：

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Leptochloa fusca spp. 对异恶草酮的抗性机制。异恶草松

Bearded sprangletop (Leptochloa fusca spp. fasicularis) 是加州水稻 (Oryza sativa) 生产中的一种有问题的杂草。历史上，有胡子的 sprangletop 是用加利福尼亚稻田的异恶草酮控制的。在稻田中连续使用异恶草酮和缺乏轮作导致一些有胡须的金花菜对异恶草酮产生抗药性。本研究的目的是通过研究在受控环境条件下在两个抗性（CRBS1 和 CRBS2）和一个易感（S）种群中对异恶草酮的吸收、易位和代谢，确定加利福尼亚水稻中两个有胡须的 sprangletop 种群对异恶草酮的抗性机制。14C-异恶草酮的吸收和易位在 R 和 S 中相似。通过用马拉硫磷抑制细胞色素 P450 酶和确定异恶草酮代谢物谱来确定，处理后 3 天 S 和 R 之间存在差异。用马拉硫磷预处理的有胡子的 sprangletop 对异恶草酮的敏感性比单独使用异恶草酮处理时高 2 倍，这表明细胞色素 P450 介导的异恶草酮代谢可能参与了耐药机制。HPLC-MS/MS 分析揭示了 R 和 S 生物型之间异恶草酮代谢的差异。羟甲基异恶草酮是在 R 植物中发现的最丰富的代谢物，与 S 植物相比，CRBS1 和 CRBS2 中的含量分别高出三倍和五倍。5-ketoclomazone 是广灭灵的已知毒性代谢物，在处理后 72 小时，在 S 植物中的积累量是 R 植物的 2 倍。