CORRELATION OF PROTOPORPHYRINOGEN OXIDASE INHIBITION BY O-PHENYL PYRROLIDINO-CARBAMATES AND PIPERIDINO-CARBAMATES WITH THEIR HERBICIDAL EFFECTS

Phenopylate (2,4-dichlorophenyl 1-pyrrolidinecarboxylate) and 13 of its O-phenyl pyrrolidino- and piperidino-carbamate analogues were tested for their capacity to inhibit protoporphyrinogen oxidase (Protox), to cause accumulation of protoporphyrin IX (Proto IX), and to cause herbicidal injury. All 14 compounds inhibited Protox of barley etioplast preparations. The I50 values ranged from 21 nm to 4 mm. Highly significant correlations were found between Protox I50 values and herbicidal activity of the more active of the compounds on greenhouse-grown weeds (pitted morningglory, barnyardgrass, prickly sida, and velvetleaf), pre- and/or post-emergence, and on cucumber cotyledon discs or barley leaf sections in cellular leakage bioassays. Proto IX accumulation in barley leaf sections treated with any of the 14 compounds correlated well with both the I50 values for Protox inhibition and with herbicidal damage to the tissue sections. These data indicate most or all of the herbicidal damage caused by these compounds is due to inhibition of Protox.