Institute for Biological Research "Siniša Stanković", Department for Plant Physiology, Bulevar despota Stefana 142, University of Belgrade, 11000 Belgrade, Serbia.
Dose Response. 2012 Sep 29;11(3):344-60. doi: 10.2203/dose-response.12-039.Simonovic. eCollection 2012.
Herbicide phosphinothricin (PPT) inhibits glutamine synthetase (GS), a key enzyme in nitrogen assimilation, thus causing ammonia accumulation, glutamine depletion and eventually plant death. However, the growth response of Lotus corniculatus L. plants immersed in solutions with a broad range of PPT concentrations is biphasic, with pronounced stimulating effect on biomass production at concentrations ≤ 50 μM and growth inhibition at higher concentrations. The growth stimulation at low PPT concentrations is a result of activation of chloroplastic isoform GS2, while the growth suppression is caused by inhibition of both cytosolic GS1 and GS2 at higher PPT concentrations. Since the results are obtained in cell-free system (e.g. protein extracts), to which the principles of homeostasis are not applicable, this PPT effect is an unambiguous example of direct stimulation hormesis. A detailed molecular mechanism of concentration-dependent interaction of both PPT and a related GS inhibitor, methionine sulfoximine, with GS holoenzymes is proposed. The mechanism is in concurrence with all experimental and literature data.
除草剂草丁膦（PPT）抑制谷氨酰胺合成酶（GS），这是氮同化的关键酶，从而导致氨积累、谷氨酰胺耗竭，最终导致植物死亡。然而，浸泡在广泛浓度范围的 PPT 溶液中的百脉根植物的生长反应呈双峰型，在浓度≤50μM 时对生物量生产有明显的刺激作用，而在较高浓度时则抑制生长。低 PPT 浓度下的生长刺激是由于质体同工型 GS2 的激活，而较高 PPT 浓度下的生长抑制是由于胞质 GS1 和 GS2 的抑制。由于这些结果是在无细胞系统（例如蛋白质提取物）中获得的，而内稳态的原则不适用于该系统，因此这种 PPT 效应是直接刺激兴奋作用的明确例子。提出了 PPT 和相关的 GS 抑制剂甲硫氨酸亚砜亚胺与 GS 全酶的浓度依赖性相互作用的详细分子机制。该机制与所有实验和文献数据一致。
