Cellular Localization of Protoporphyrinogen-Oxidizing Activities of Etiolated Barley (Hordeum vulgare L.) Leaves (Relationship to Mechanism of Action of Protoporphyrinogen Oxidase-Inhibiting Herbicides)

Abstract

Seven-day-old, etiolated barley (Hordeum vulgare 1. var Post) leaves were fractionated into crude and purified etioplast, microsomal, and plasma membrane (PM) fractions. Protoporphyrinogen oxidase (Protox) specific activities of crude etioplast, purified etio- reduced the Protox activity of all fractions, except that microsomal Protox activity was slightly stimulated by NADPH. Ascorbate, CSH, or a combination of the two reductants enhanced Protox inhibition by AFM, and AFM inhibition of Protox was greatest in all fractions with DTT. NADPH enhanced AFM inhibition significantly only in etioplast fractions. Uroporphyrinogen I (Urogen I) and coproporphyrinogen I (Coprogen I) oxidase activities were found in all fractions; however, etioplast fractions had significantly more substrate specificity for protoporphyrinogen IX (Protogen IX) than the other fractions. Urogen I and Coprogen I oxidase activities were unaffected by AFM in all fractions, and 2 mM DTT almost completely inhibited these activities from all fractions. Diethyldithiocarbamate inhibited PM Protox activity by 62% but had less effect on microsome and little or no effect on etioplast Protox. juglone and duroquinone stimulated microsomal and PM Protox activity, whereas the lesser effect of these quinones on etioplast Protox activity was judged to be due to PM and/or microsomal contaminants. These data indicate that there are microsomal and PM Protogen IX-oxidizing activities that are not the same as those associated with the etioplast and that these activities are not inhibited i n vivo by AFM. In summary, these data support the view that the primary source of high protoporphyrin IX concentrations in AFM-treated plant tissues is from Protogen IX exported by plastids and oxidized by AFM-resistant extraorganellar oxidases.

ArabidopsisACCELERATED CELL DEATH2 Modulates Programmed Cell Death

“…The diphenyl ether herbicide oxyfluorfen inhibits protoporphyrinogen oxidase; the accumulated protoporphyrinogen IX leaks form the plastid and then is converted to PPIX by herbicide-insensitive enzymes in the cytoplasm. This mode of action of oxyfluorfen was confirmed in a series of experiments (Jacobs and Jacobs, 1993;Lee et al, 1993;Matsumoto et al, 1999). Paraquat blocks the electron transport chain during photosynthesis in chloroplasts, causing the production of O 2 ÿ (Bus et al, 1974;Murgia et al, 2004).…”

Level of protoporphyrinogen oxidase activity tightly correlates with photodynamic and defense responses in oxyfluorfen-treated transgenic rice

“…[4][5][6][7] The acute toxicity of oxyfluorfen is a result of the accumulation of Protogen IX, which is oxidized in the cytoplasm to Proto IX by a nonspecific plasma membrane-bound peroxidase. 8,9) Proto IX in the cytoplasm is not metabolized by the porphyrin biosynthetic pathway because Mg-chelatase and Fe-chelatase, which use Proto IX as a substrate, are located in chloroplasts and mitochondria. Cytoplasmic Proto(gen) IX, a potent photosensitizer, absorbs light that is used in detrimental reactions.…”

Application of Sulfentrazone in Stages of Germination of IAC 90 Cassava Cuttings in Clay Soils and Sandy

“…The inhibition of PROTOX causes a reduction in synthesis of the photosynthetic pigments (chlorophyll and carotenoids) and oxidative stress, leading to cell death (Jacobs et al, 1991;Lee et al, 1993;Dayan & Weete, 1996;Szmigielski et al, 2009). …”