Schoenoplectiella juncoides is a noxious sedge weed in rice paddy fields that has evolved resistance to sulfonylurea (SU) herbicides. The molecular basis of resistance is amino acid substitutions at Pro₁₉₇, Trp₅₇₄ or Asp₃₇₆ in the acetolactate synthase (ALS) enzyme, which is the target of SUs. Schoenoplectiella juncoides has two ALS genes and resistant plants have point mutations that cause amino acid substitutions in either encoded protein. Single‐nucleotide substitutions at the codon for Pro₁₉₇ in the ALS genes can cause six types of amino acid substitutions and all of these substitutions have been found in both ALS genes among Japanese SU‐resistant biotypes. Whole‐plant herbicide responses differ among the amino acid substitution types. Furthermore, analyses of ALS activity in plant extracts show that the extracts’ responses to herbicides differ, depending on which ALS gene is mutated. The activity responses of the ALS extracts to the SU, imazosulfuron, showed double‐sigmoid curves with plateaus of ~30% inhibition for Pro₁₉₇ substitutions in ALS1 and ~70% for Pro₁₉₇ substitutions in ALS2. This indicates that ALS1 and ALS2 contribute to the responses with a proportion of 7:3. The double‐sigmoid curves can be reconstructed to show the responses of the resistant and susceptible enzymes separately by regression analysis. The resistance levels of the separate ALS1 or ALS2 mutated enzyme are highly correlated with the whole‐plant responses, with a relationship that the former is the square of the latter. This could provide a quantitative insight into the physiological basis of resistance.

中文翻译：

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日本稻田中的有毒莎草菌（Schoenoplectiella juncoides）对磺酰脲类抗药性的生物学和机制

Schoenoplectiella juncoides是稻田中的一种有害莎草杂草，已逐渐对磺酰脲类（SU）除草剂产生抗性。抗性的分子基础是乙酰乳酸合酶（ALS）酶中Pro ₁₉₇，Trp ₅₇₄或Asp _376的氨基酸取代，而后者是SUs的目标。乳杆菌（Schoenoplectiella juncoides）具有两个ALS基因，抗性植物的点突变会导致任一编码蛋白的氨基酸置换。Pro ₁₉₇密码子的单核苷酸取代ALS基因中的ALS可以引起六种氨基酸取代，并且在日本SU抗性生物型的两种ALS基因中都发现了所有这些取代。全植物除草剂的响应在氨基酸取代类型之间有所不同。此外，对植物提取物中ALS活性的分析表明，提取物对除草剂的反应不同，这取决于哪个ALS基因发生了突变。的ALS提取物的SU，咪唑磺隆的活性响应，呈现双S形曲线与为Pro〜30％抑制的高原_197个在ALS1替换和〜70％的Pro ₁₉₇ALS2中的取代。这表明ALS1和ALS2以7：3的比例参与响应。可以通过回归分析重建双S型曲线，以分别显示抗性酶和易感酶的响应。单独的ALS1或ALS2突变酶的抗性水平与整个植物的反应高度相关，前者是后者的平方。这可以提供对耐药性生理基础的定量见解。