Zawoznik Myriam S, Tomaro María L
Cátedra de Química Biológica Vegetal, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Buenos Aires, Argentina.
Pest Manag Sci. 2005 Oct;61(10):1003-8. doi: 10.1002/ps.1077.
Possible side-effects of the acetolactate synthase (ALS)-inhibiting herbicide chlorimuron-ethyl on Bradyrhizobium japonicum (Kirchner & Jordan) in pure culture and on inoculated soybean plants growing under controlled conditions were investigated. Growth of B japonicum strain E109 was not affected by this herbicide even when exposed to concentrations 150 times higher than recommended field doses. However, nodulation of soybean plants treated 5 days after emergence with chlorimuron-ethyl at standard application rates was impaired: a 38% decrease in the number of nodules per plant was observed four weeks after treatment. Despite nodule number decrease, no changes in shoot nitrogen content could be detected. Total fresh biomass was diminished by 25% in herbicide-treated plants. Leghemoglobin content in nodules did not vary; nevertheless total nodule protein was diminished by 40% in the herbicide-treated group. ALS activity in different soybean tissues and their relative sensitivity to chlorimuron-ethyl were also investigated. Roots and bacteroids had the greatest specific ALS activities. On a fresh weight basis, the bacteroid fraction displayed the highest ALS activity and was also the most tolerant to in vitro chlorimuron addition: 72% of its activity was retained after including 10 microM chlorimuron-ethyl in the reaction mixture. These results indicate that standard application rates of chlorimuron-ethyl will have limited incidence on B japonicum survival, and effects on nodulation may have little long-term consequences on soybean nitrogen fixation potential. The differences found among soybean tissues not only in intrinsic ALS activity but also in their relative sensitivity to this herbicide suggests that, in leguminous plants living in symbiosis with rhizobia, nodules may contribute to an enhanced tolerance to ALS inhibitors.
研究了乙酰乳酸合酶（ALS）抑制型除草剂氯嘧磺隆对纯培养条件下的慢生根瘤菌（基尔希纳和乔丹）以及在可控条件下生长的接种大豆植株的潜在副作用。即使暴露于比推荐田间剂量高150倍的浓度下，慢生根瘤菌菌株E109的生长也不受这种除草剂的影响。然而，在出苗后5天以标准施用量用氯嘧磺隆处理的大豆植株的结瘤受到损害：处理后四周观察到每株植物的根瘤数量减少了38%。尽管根瘤数量减少，但未检测到地上部氮含量的变化。除草剂处理的植株总鲜生物量减少了25%。根瘤中的豆血红蛋白含量没有变化；然而，除草剂处理组的根瘤总蛋白减少了40%。还研究了氯嘧磺隆在不同大豆组织中的活性及其相对敏感性。根和类菌体具有最高的比ALS活性。以鲜重计，类菌体部分显示出最高的ALS活性，并且对体外添加氯嘧磺隆也最耐受：在反应混合物中加入10 microM氯嘧磺隆后，其活性保留了72%。这些结果表明，氯嘧磺隆的标准施用量对慢生根瘤菌存活的影响有限，对结瘤的影响可能对大豆固氮潜力没有长期影响。在大豆组织中发现的差异不仅在于内在的ALS活性，还在于它们对这种除草剂的相对敏感性，这表明在与根瘤菌共生的豆科植物中，根瘤可能有助于提高对ALS抑制剂的耐受性。
