Comparison of the Bleaching Activity of Norflurazon and Oxyfluorfen

The bleaching effects of norflurazon [4-chloro-5-(methylamino)-2-( α , α , α -trifluoro- m -tolyl)-3 (2 H )-pyridazinone] and of oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl) benzene] were compared using the intact microalga Scenedesmus acutus and the fungus Phycomyces blakesleeanus. Under the influence of oxyfluorfen, but not of norflurazon, pigments and membranes were degraded. This activity is typical for oxyfluorfen. Norflurazon prevented carotene synthesis, but did not cause degradation of carotenoids, chlorophylls, or 35 S-sulfolipid, a marker of photosynthetic membranes. Furthermore, light-induced ethane evolution by Scenedesmus is substantial with oxyfluorfen, but not with norflurazon present. Oxyfluorfen apparently causes radical-initiated peroxidation of polyunsaturated fatty acids.