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In order to understand the action mechanism of fluazifop-P-butyl (FB) in bristly starbur (Acanthospermum hispidum D.C.), a susceptible plant, the role of active oxygen species (ROS) in herbicide-induced cell death in shoots was investigated. FB-induced phytotoxicity was not reduced by the antioxidants, 1,4-diazabicyclooctane (dabaco), sodium azide, l-tryptophan, d-tryptophan, hydroquinone and dimethyl pyridine N-oxide (DMPO). The activities of superoxide dismutase (SOD) and catalase (CAT), in bristly starbur seedlings were significantly increased by FB at 12 HAT and 24 HAT, while ascorbate peroxidase (APX) and glutathione reductase (GR) activities increased only at 12 HAT. The contents of H 2 O 2 in FB-treated bristly starbur seedlings were significantly higher to that of control between 8 and 24 HAT. According to the analysis of potassium iodide - starch or 3,3-diaminobenzidine, the accumulation of hydrogen peroxide was observed in the apical growing point, stem, petiole and veins of FB-treated bristly starbur seedlings at 24 HAT. The cell viability of bristly starbur seedlings treated by 10μM FB decreased at 18 HAT. These results suggested that FB-induced cell death in bristly starbur shoots may be caused by ROS (O 2 - and H 2 O 2 ) generation and lipid peroxidation., (Copyright © 2016 Elsevier Inc. All rights reserved.)