College of Biological and Environmental Engineering, Zhejiang University of Technology, Hangzhou, People's Republic of China.
PLoS One. 2011 May 6;6(5):e19451. doi: 10.1371/journal.pone.0019451.
The enantiomers of a chiral compound possess different biological activities, and one of the enantiomers usually shows a higher level of toxicity. Therefore, the exploration of the causative mechanism of enantioselective toxicity is regarded as one of primary goals of biological chemistry. Imazethapyr (IM) is an acetolactate synthase (ALS)-inhibiting chiral herbicide that has been widely used in recent years with racemate. We investigated the enantioselectivity between R- and S-IM to form reactive oxygen species (ROS) and to regulate antioxidant gene transcription and enzyme activity.
Dramatic differences between the enantiomers were observed: the enantiomer of R-IM powerfully induced ROS formation, yet drastically reduced antioxidant gene transcription and enzyme activity, which led to an oxidative stress. The mechanism by which IM affects carbohydrate metabolism in chloroplasts has long remained a mystery. Here we report evidence that enantioselectivity also exists in starch metabolism. The enantiomer of R-IM resulted in the accumulation of glucose, maltose and sucrose in the cytoplasm or the chloroplast and disturbed carbohydrates utilization.
The study suggests that R-IM more strongly retarded plant growth than S-IM not only by acting on ALS, but also by causing an imbalance in the antioxidant system and the disturbance of carbohydrate metabolism with enantioselective manner.
手性化合物的对映异构体具有不同的生物活性，其中一种对映异构体通常表现出更高的毒性水平。因此，探索对映选择性毒性的致病机制被视为生物化学的主要目标之一。咪草烟（IM）是一种近年来广泛使用的乙酰乳酸合成酶（ALS）抑制剂手性除草剂。我们研究了 R-和 S-IM 之间形成活性氧（ROS）以及调节抗氧化基因转录和酶活性的对映选择性。
观察到对映异构体之间存在显著差异：R-IM 对映异构体强烈诱导 ROS 形成，但大大降低抗氧化基因转录和酶活性，导致氧化应激。IM 影响叶绿体中碳水化合物代谢的机制长期以来一直是个谜。在这里，我们报告证据表明，对映选择性也存在于淀粉代谢中。R-IM 对映异构体导致细胞质或叶绿体中葡萄糖、麦芽糖和蔗糖的积累，并扰乱碳水化合物的利用。
该研究表明，R-IM 比 S-IM 更强烈地抑制植物生长，不仅通过作用于 ALS，而且通过以对映选择性方式引起抗氧化系统失衡和碳水化合物代谢紊乱。
