Protox Inhibition Research Articles

Soybean (Glycine max) cultivar differences in response to sulfentrazone

Greenhouse-grown soybean cultivars varied in their tolerance to preemergence application of sulfentrazone. The cultivars Ransom, Hutcheson, Kato, Gasoy 17, and Cobb exhibited relatively low tolerance to 0.5 kg ai ha−1 sulfentrazone with 38, 41, 46, 50, and 58% height reduction compared to respective controls. The growth of tolerant cultivars Centennial, Edison, and Hartz 5164 was not affected by this treatment. However, the growth of all cultivars was reduced at the excessive rate of 2.0 kg ha−1 preemergence application of sulfentrazone. No differences in root uptake or translocation of [14C] sulfentrazone were observed between the relatively tolerant and less tolerant cultivars tested. Centennial and Hutcheson cultivars rapidly metabolized sulfentrazone via oxidative degradation of the 3-methyl group on the triazolinone ring of the herbicide. Only 4.7 and 4.9% of the active ingredient remained in the foliage of Hutcheson and Centennial 24 h after treatment, respectively. While there were no differences in Protox inhibition or Proto IX accumulation between the two cultivars, Hutcheson was more sensitive than Centennial to peroxidative stresses induced by either Proto IX accumulation or rose bengal. Therefore, tolerance to sulfentrazone is due to rapid metabolism of the herbicide; however, the intraspecific difference in response to sulfentrazone appears to be due to intrinsic differential tolerance to the herbicide-induced peroxidative stress.

3D-QSARs of Herbicidal 2-N-Phenylisoindolin-1-one Analogues as a New Class of Potent Inhibitors of Protox

3D-QSARs for the inhibition activities against protox by herbicidal 2-N-phenylisoindolin-1-one derivatives were studied quantitatively using CoMFA and CoMSIA methods. The result of the statistical quality of optimized CoMSIA model 2 (<TEX>$FF:\;{r^2}_{cv.};\;0.973\;&\;{r^2}_{ncv.};\;0.612$</TEX>) was higher than that of CoMFA model 1 (<TEX>$AF:\;{r^2}_{cv.};\;0.414\;&\;{r^2}_{ncv.};\;0.909$</TEX>). Also, the relative contribution of the optimized CoMSIA model 2 showed the steric (24.6%), electrostatic (31.0%), hydrophobic (ClogP, 23.4%) and H-bond acceptor field (21.0%), respectively. From the results of the contour maps, the protox inhibition activities are expected to increase when steric favor and H-bond acceptor favor groups are substituted on <TEX>$R_2$</TEX> position and positive favor group are substituted on <TEX>$C_2,\;C_3,\;and\;C_5$</TEX> atom in phenyl ring of <TEX>$R_2$</TEX> position. And the inhibition activities are expected to increase when hydrophobic favor group is substituted on <TEX>$C_1,\;C_3$</TEX> atom in phenyl ring of <TEX>$R_2$</TEX> position and <TEX>$C_1$</TEX> atom of <TEX>$R_2$</TEX> position and hydrophilic favor groups are substituted on <TEX>$C_4$</TEX> atom in phenyl ring of <TEX>$R_1$</TEX> position and the terminal group of <TEX>$R_1$</TEX> position.

Enzymatic Activity of Protoporphyrinogen-IX Oxidase from Various Plant Species

Enzyme activity of protoporphyrinogen-IX oxidase (Protox) prepared from 34 kinds of plant sources, containing 18 monocotyledons and 16 dicotyledons was evaluated. Protox(es) originated in monocotyledonous plants such as Zea mays cv. Anjou and DK212, Lolium perenne and Poa annua exhibited high enzyme activity, and Protox(es) in dicotyledonous plants such as Agrostemma githago and Arabidopsis thaliana showed a little higher enzyme activity than that of the above monocotyledonous plants. Highly active Protox(es) obtained from Zea mays cv. Anjou, Lolium perenne, Agrostemma githago and Arabidopsis thaliana were selected for the Protox inhibitory assay of peroxidizing herbicides. Echinochloa utilis was also selected for control. Protox inhibition by six peroxidizing herbicides such as oxyfluorfen, chlorophthalim, BW-91, pyraflufen-ethyl, DLH-1777 and LS-82556 was investigated using highly active Protox from the above monocotyledons and dicotyledons. As a result, six peroxidizing herbicides exhibited high inhibitory activity to Protox. Pyraflufen-ethyl showed the highest inhibition. The order of Protox inhibitory activity was pyraflufen-ethyl > oxyfluorfen > BW-91 > chlorophthalim > DLH-1777 > LS-82556, in experiment using four Protox(es) such as Zea mays cv. Anjou, Echinochloa utilis, Agrostemma githago and Arabidopsis thaliana except Lolium perenne. Oxyfluorfen exhibited the highest inhibitory activity to Protox of Lolium perenne. On the other hand, DLH-1777 showed a little less activity to Protox of Zea mays than that of other four weeds. DLH-1777 may become a model compound to find out new selective herbicides. Protox from four weeds will be used for peroxidizing herbicides assay, since the Protox showed high sensitivity to structually different peroxidizers.

Biochemical and physiological effects of benzheterocycles and related compounds

The biochemical and physiological effects of 18 benzheterocycles and 1 tetrahydrophthalimide-substituted indolin-2(3H)-one were investigated. Eighteen of the compounds were inhibitors of protoporphyrinogen oxidase (Protox) in vitro, with I 50 values ranging from 25 to 650 nM. There was a good correlation between the activity of these compounds as in vitro Protox inhibitors and their in vivo effects on protoporphyrin IX (Proto IX) accumulation. There was also a good correlation between the amount of Proto IX caused to accumulate and the light-induced cellular damage. However, several of the compounds had phytotoxic activity in darkness, indicating that they have mechanisms of action in addition to inhibition of Protox. Greenhouse results generally agreed with laboratory results. The structure/activity relationships for inhibition of Protox are discussed.

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

Seven-day-old, etiolated barley (Hordeum vulgare L. 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 etioplast, microsome, and PM fractions were approximately 29, 26, 23, and 12 nmol h-1 mg-1 of protein, respectively. The herbicide acifluorfen-methyl (AFM), at 1 [mu]M, inhibited Protox activity from crude etioplasts, purified etioplasts, microsomes, and PM by 58, 59, 23, and 0% in the absence of reductants. Reductants (ascorbate, glutathione [GSH], dithiothreitol [DTT], and NADPH) individually reduced the Protox activity of all fractions, except that microsomal Protox activity was slightly stimulated by NADPH. Ascorbate, GSH, 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 in 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.

Correlation of protoporphyrinogen oxidase inhibition by O‐phenyl pyrrolidino‐ and piperidino‐carbamates with their herbicidal effects

AbstractPhenopylatePhenopylate is not a BSI/ISO‐approved common name. (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.

Protoporphyrinogen Oxidase-Inhibiting Herbicides

Several commercial and experimental herbicides such asp-nitrodiphenyl ethers, oxadiazoles, and cyclic imides inhibit protoporphyrinogen IX oxidase (Protox), the enzyme that converts protoporphyrinogen IX to protoporphyrin IX (Proto). This leads to uncontrolled autooxidation of the substrate and results in accumulation of Proto. Blockage of the porphyrin pathway at this site inhibits synthesis of both chlorophylls and heme. Heme is a feedback regulator of the porphyrin pathway. Thus, inhibition of Protox also deregulates the pathway, causing increased carbon flow to the accumulating pool of Proto. Proto is a potent photosensitizer that generates high levels of singlet oxygen in the presence of molecular oxygen and light. In plants treated with these herbicides, damage is light dependent and closely correlated with the level of Proto that accumulates. Proto accumulation is apparently largely extraplastidic, resulting in rapid photodynamic damage to the plasmalemma and tonoplast. After high levels of Proto accumulate in response to these herbicides, protochlorophyllide (PChlide) levels can increase also; however, Proto appears to be the primary photodynamic pigment responsible for the herbicidal activity.

Pyrazole phenyl ether herbicides inhibit protoporphyrinogen oxidase

Two isomeric pairs of pyrazole phenyl ether herbicides [AH 2.429, 4-chloro-1-methyl-5-(4-nitrophenoxy)-3-(trifluoromethyl)-1 H-pyrazole; AH 2.430, 4-chloro-1-methyl-3-(4-nitrophenoxy)-5-(trifluoromethyl)-1 H-pyrazole; AH 2.431, 5-((4-chloro-1-methyl-5-(trifluoromethyl)-1 H-pyrazol-3-yl)oxy)-2-nitrobenzoic acid; and AH 2.432, 5-((4-chloro-1-methyl-3-(trifluoromethyl)-1 H-pyrazol-5-yl)oxy)-2-nitrobenzoic acid were evaluated for herbicidal activity in both intact plants and in tissue sections. Their capacity to induce accumulation of porphyrins in tissue sections and to inhibit protoporphyrinogen oxidase (Protox) in vitro were determined. In whole plant tests, the order of herbicidal activity was AH 2.430 ⪢ AH 2.431 > AH 2.429 > AH 2.432. AH 2.430 consistently caused light-dependent membrane leakage in both green and far-red light grown cucumber cotyledon and barley primary leaf tissue sections after incubation for 20 hr in darkness in 0.1 m M solutions. The same treatment caused marked increases in protoporphyrin IX (PPIX) content during the 20-hr dark incubation. AH 2.429 and 2.431 were less effective and not effective in all tissues in causing herbicidal damage and PPIX accumulation. AH 2.432 was ineffective in tissue section assays. Mg-PPIX levels were not significantly affected by any of the compounds. Protochlorophyllide levels were decreased by AH 2.430 and 2.431 in barley and increased by AH 2.429, 2.431, and 2.432 in cucumber. A positive relationship was found between herbicidal activity and the amount of PPIX that was caused to accumulate by each compound. All of the compounds inhibited Protox activity. Positive correlations were found between herbicidal activity in planta over a 300-fold range and in vitro Protox inhibition and the amount of PPIX caused to accumulate in vivo. These data support the view that the pyrazole phenyl ethers exert their herbicidal activity entirely through inhibition of Protox.