Selective Action Mechanism of Fenclorim on Rice and Echinochloa crusgalli Is Associated with the Inducibility of Detoxifying Enzyme Activities and Antioxidative Defense

Fenclorim (Fen) is a safener developed for pretilachlor (Pre) that can protect rice from injury caused by Pre but does not lower the weed control effects of Pre. Unfortunately, the mechanism of selective action of Fen between rice and weeds, such as Echinochloa crusgalli (barnyard grass), has not been clarified. In this study, the differences in physiology, biochemistry, and gene transcription between rice and E. crusgalli response to Fen were compared. Comparing the protection effects of Fen on plant growth, it was found that Fen significantly protected rice from Pre, but did not protect E. crusgalli. The detection of malondialdehyde (MDA) content and activities of antioxidant enzymes showed that Pre induced significant oxidative damage both in rice and E. crusgalli; however, Fen reduced oxidative damage in rice but not in E. crusgalli. Transcriptome analysis revealed that Fen induced more genes related to herbicide metabolism in rice than in E. crusgalli, especially the glutathione-S-transferase (GST) genes, with six upregulated in rice but no genes upregulated in E. crusgalli. Accordingly, the GST activity analysis showed that Fen increased the activity of rice instead of E. crusgalli. These results indicate that the elevation of detoxifying enzyme activities and antioxidative defense may be the mechanism of selective action of Fen in rice but not in E. crusgalli.

氟草胺（Fenclorim，简称Fen）是一种专为丙草胺（Pretilachlor，简称Pre）开发的除草剂安全剂，可保护水稻免受丙草胺药害，且不会降低丙草胺的除草效果。遗憾的是，氟草胺在水稻与稗草（Echinochloa crusgalli，barnyard grass）等杂草间的选择性作用机制尚未阐明。本研究对比了水稻与稗草在响应氟草胺时的生理、生化及基因转录差异。通过对比氟草胺对植物生长的保护效果，发现氟草胺可显著保护水稻免受丙草胺药害，但无法对稗草起到保护作用。对丙二醛（malondialdehyde，MDA）含量与抗氧化酶活性的检测结果显示，丙草胺会在水稻与稗草体内均诱发显著氧化损伤；然而氟草胺仅能减轻水稻体内的氧化损伤，对稗草则无此效果。转录组分析表明，氟草胺在水稻体内诱导的除草剂代谢相关基因数量多于稗草，其中谷胱甘肽S-转移酶（glutathione-S-transferase，GST）基因尤为突出：水稻体内有6个该类基因被上调表达，而稗草体内则无此类基因出现上调。与之相符的是，谷胱甘肽S-转移酶活性分析显示，氟草胺仅能提升水稻体内的该酶活性，对稗草则无此作用。上述结果表明，解毒酶活性提升与抗氧化防御系统激活，或许是氟草胺对水稻产生选择性保护作用、而对稗草无此效果的作用机制。