Shaner D. L., Singh B. K.
American Cyanamid Company, Princeton, New Jersey 08543-0400.
Plant Physiol. 1993 Dec;103(4):1221-1226. doi: 10.1104/pp.103.4.1221.
Acetohydroxyacid synthase (AHAS) is the site of action of herbicides of different chemical classes, such as imidazolinones, sulfonylureas, and triazolopyrimidines. Inhibition of AHAS causes the accumulation of 2-ketobutyrate (2-KB) and 2-aminobutyrate (2-AB) (the transamination product of 2-KB), and it has been proposed that the phytotoxicity of these inhibitors is due to this accumulation. Experiments were done to determine the relationship between accumulation of 2-KB and 2-AB and the phytotoxicity of imazaquin to maize (Zea mays). Imazaquin concentrations that inhibit growth of maize plants also cause the accumulation of 2-KB and 2-AB in the shoots. Supplementation of imazaquin-treated plants with isoleucine reduced the pools of 2-KB and 2-AB in the plant but did not protect plants from the growth inhibitory effects of imazaquin. Conversely, feeding 2-AB to maize plants increased 2-KB and 2-AB pools to much higher levels than those observed in imazaquin-treated plants, yet such high pools of 2-KB and 2-AB in the plant had no significant effect on growth. These results conclusively demonstrate that growth inhibition following imazaquin treatment is not due to accumulation of 2-KB and/or 2-AB in plants. Changes in the amino acid profiles after treatment with imazaquin suggest that starvation for the branched-chain amino acids may be the primary cause of growth retardation of maize.
乙酰羟酸合酶（AHAS）是不同化学类别的除草剂，如咪唑啉酮类、磺酰脲类和三唑并嘧啶类的作用位点。抑制AHAS会导致2-酮丁酸（2-KB）和2-氨基丁酸（2-AB，2-KB的转氨产物）的积累，并且有人提出这些抑制剂的植物毒性是由于这种积累。进行了实验以确定2-KB和2-AB的积累与咪唑喹啉酸对玉米（Zea mays）的植物毒性之间的关系。抑制玉米植株生长的咪唑喹啉酸浓度也会导致2-KB和2-AB在地上部积累。用异亮氨酸补充经咪唑喹啉酸处理的植株会降低植株中2-KB和2-AB的含量，但不能保护植株免受咪唑喹啉酸的生长抑制作用。相反，给玉米植株饲喂2-AB会使2-KB和2-AB的含量增加到比经咪唑喹啉酸处理的植株中观察到的水平高得多的程度，然而植株中如此高的2-KB和2-AB含量对生长没有显著影响。这些结果确凿地证明，咪唑喹啉酸处理后生长受到抑制并非由于植株中2-KB和/或2-AB的积累。用咪唑喹啉酸处理后氨基酸谱的变化表明，对支链氨基酸的饥饿可能是玉米生长迟缓的主要原因。
