Accumulation of Protoporphyrinogen IX prior to Protoporphyrin IX in Intact Plants Treated with Protoporphyrinogen IX Oxidase-Inhibiting Herbicides

Abstract

A combination of two conventional methods of porphyrins analysis revealed a significant accumulation of protoporphyrinogen IX (Protogen) prior to protoporphyrin IX (Proto IX) in cucumber (Cucumis sativus L.) cotyledons immediately after the foliar application of a protoporphyrinogen IX oxidase (Protox)-inhibiting herbicide, pyraflufen-ethyl. The accumulation of Protogen peaked at 4 to 7 hr and then decreased with the increase of Proto IX. Although a similar time-course of Protogen accumulation was observed in cucumber cotyledons treated with another Protox-inhibiting herbicide, acifluorfen, the amount of Proto IX accumulated was 2 to 3 times lower than that after the pyraflufen-ethyl treatment. Furthermore, a foliar application of pyraflufen-ethyl caused a significant accumulation of Protogen rather than Proto IX in cleavers (Galium aparine L.) after 7 hr, while little accumulation of Protogen and Proto IX took place in wheat (Triticum aestivum L.).

Close Link between Protoporphyrin IX Accumulation and Developmental Toxicity Induced by N‐Phenylimide Herbicides in Rats

“…Once PPIX is liberated into cytoplasm, it cannot reach the active site of ferrochelatase through the substrate channel. Recently, accumulation of protoporphyrinogen before PPIX in intact plants treated with PPO inhibitors was reported (Murata et al., ).…”

Identification of a gene essential for protoporphyrinogen IX oxidase activity in the cyanobacterium Synechocystis sp. PCC6803

“…These herbicides act as competitive inhibitors of the hemY-encoded Protox (13), resulting in the accumulation of Protogen IX within the chloroplast. Protogen IX leaks out of the chloroplast into the cytoplasm, where it is rapidly oxidized to Proto IX by nonspecific peroxidases and auto-oxidation (14). Proto IX is a potent photosensitizer, thus causing rapid oxidation of various molecules in cells, ultimately leading to cell death (5,13).…”