Acifluorfen Research Articles

Amphiphilic Cationic Carbon Dots for Efficient Delivery of Light-Dependent Herbicide.

The inefficient delivery of herbicides causes unpleasant side effects on the ecological environment. Protoporphyrinogen oxidase (PPO)-inhibiting herbicides rely on the presence of external light to exert the activities and thus their performance in the field is extremely susceptible to the light environment. Here, taking acifluorfen (ACI) as a model PPO-inhibiting herbicide to enhance efficacy by boosting the utilization rate of sunlight, amphiphilic cationic CDs (CPC-CDs) from cetylpyridinium chloride (CPC) as a precursor, is first prepared as a supplementary light source generator, and subsequently co-assembled with ACI through non-covalent bond interactions to obtain the stable fluorescent nanoparticles (ACI@CPC-CDs). ACI@CPC-CDs with fascinating physicochemical properties can penetrate the leaves of weeds through the stomata and undergo a long-distance transport in the cell intervals. Under low light intensity, CPC-CDs can be applied as the internal light source to promote the formation of more singlet oxygen to damage the leaf cell membrane, consequently improving the herbicidal activity of ACI. Moreover, the safety evaluation of ACI@CPC-CDs demonstrates no risk to non-target organisms and the environment. Therefore, this work offers a promising strategy for the efficient delivery of light-dependent PPO-inhibiting herbicides and opens new insights into the application of CDs in the development of sustainable agriculture.

Design, Synthesis, and Herbicidal Evaluation of Pyrrolidinone-Containing 2-Phenylpyridine Derivatives as Novel Protoporphyrinogen Oxidase Inhibitors.

In this work, a series of pyrrolidinone-containing 2-phenylpyridine derivatives were synthesized and evaluated as novel protoporphyrinogen IX oxidase (PPO, EC 1.3.3.4) inhibitors for herbicide development. At 150 g ai/ha, compounds 4d, 4f, and 4l can inhibit the grassy weeds of Echinochloa crus-galli (EC), Digitaria sanguinalis (DS), and Lolium perenne (LP) with a range of 60 to 90%. Remarkably, at 9.375 g ai/ha, these compounds showed 100% inhibition effects against broadleaf weeds of Amaranthus retroflexus (AR) and Abutilon theophrasti (AT), which were comparable to the performance of the commercial herbicides flumioxazin (FLU) and saflufenacil (SAF) and better than that of acifluorfen (ACI). Molecular docking analyses revealed significant hydrogen bonding and π-π stacking interactions between compounds 4d and 4l with Arg98, Asn67, and Phe392, respectively. Additionally, representative compounds were chosen for in vivo assessment of PPO inhibitory activity, with compounds 4d, 4f, and 4l demonstrating excellent inhibitory effects. Notably, compounds 4d and 4l induced the accumulation of reactive oxygen species (ROS) and a reduction in the chlorophyll (Chl) content. Consequently, compounds 4d, 4f, and 4l are promising lead candidates for the development of novel PPO herbicides.

Stable Fluorescent Nanoparticles Based on Co-assembly of Acifluorfen and Poly(salicylic acid) for Enhancing Herbicidal Activity and Reducing Environmental Risks.

Herbicides are widely used in modern agricultural production for their advantages of high efficiency, convenience, and speed. However, there have been many problems caused by herbicide formulations, such as volatilization, leaching, and rain-washing loss in the process of agricultural application. Self-assembled nanotechnology is a promising strategy to solve these existing problems due to the environmentally friendly preparation process and high delivery efficiency. In this study, the stable fluorescent nanoparticles (AP NPs) based on co-assembly of acifluorfen (ACI) and poly(salicylic acid) (PSA) are constructed by using non-covalent bond interactions. The results indicate that the obtained nanoparticles with a stable fluorescence characteristic show improved physiochemical properties, such as uniform morphology, good thermal stability, low surface tension, and high retention on plants. The co-assembly can produce singlet oxygen to enhance the herbicidal activity under irradiation of light and reduce the leaching property of ACI to minimize the adverse impact on the aquatic environment. The safety evaluation of soybean seedlings indicates that AP NPs have no damage to non-target plants. In summary, the co-assembled herbicidal nano-formulation composed of ACI and PSA has high bioactivity and low environmental risks, which can be widely used in agricultural production.

Altered regulation of porphyrin biosynthesis and protective responses to acifluorfen-induced photodynamic stress in transgenic rice expressing Bradyrhizobium japonicum Fe-chelatase

We examined the molecular regulation of porphyrin biosynthesis and protective responses in transgenic rice (Oryza sativa) expressing Bradyrhizobium japonicum Fe-chelatase (BjFeCh) after treatment with acifluorfen (AF). During the photodynamic stress imposed by AF, transcript levels of BjFeCh in transgenic plants increased greatly; moreover, transcript levels of OsFeCh2 remained almost constant, whereas in wild type (WT) plants they were considerably down-regulated. In the heme branch, transgenic plants exhibited greater levels of OsFC and HO transcripts than WT plants in the untreated stems as well as in the AF-treated leaves and stems. Both WT and transgenic plants treated with AF substantially decreased transcript levels for all the genes in the chlorophyll branch, with less decline in transgenic plants. After AF treatment, ascorbate (Asc) content and the redox Asc state greatly decreased in leaves of WT plants; however, in transgenic plants both parameters remained constant in leaves and the Asc redox state increased by 20% in stems. In response to AF, the leaves of WT plants greatly up-regulated CatA, CatB, and GST compared to those of transgenic plants, whereas, in the stems, transgenic plants showed higher levels of CatA, CatC, APXb, BCH, and VDE. Photochemical quenching, qP, was considerably dropped by 31% and 18% in WT and transgenic plants, respectively in response to AF, whereas non-radiative energy dissipation through non-photochemical quenching increased by 77% and 38% in WT and transgenic plants, respectively. Transgenic plants treated with AF exhibited higher transcript levels of nucleus-encoded photosynthetic genes, Lhcb1 and Lhcb6, as well as levels of Lhcb6 protein compared to those of WT plants. Our study demonstrates that expression of BjFeCh in transgenic plants influences not only the regulation of porphyrin biosynthesis through maintaining higher levels of gene expression in the heme branch, but also the Asc redox function during photodynamic stress caused by AF.

β-catenin Mutations Are Not Involved in Early-stage Hepatocarcinogenesis Induced by Protoporphyrinogen Oxidase Inhibitors in Mice.

We previously reported the contribution of constitutive androstane receptor (CAR) in cytotoxicity-related hepatocarcinogenesis induced by oxadiazon (OX) or acifluorfen (ACI), two pesticides categorized as protoporphyrinogen oxidase (PROTOX) inhibitors. The molecular characteristics of preneoplastic and neoplastic lesions induced by OX and ACI were immunohistochemically compared to those by phenobarbital (PB), a typical CAR activator, in wild-type (WT) and CAR knockout (CARKO) mice after diethylnitrosamine initiation. We focused on changes in β-catenin and its transcriptional product glutamine synthetase (GS). In PB-promoted foci and adenomas, nuclear accumulation of mutated β-catenin was increased with high frequency. PB treatment also increased the multiplicity and area of GS-positive foci and adenomas in WT mice. No foci and adenomas showed nuclear accumulation of β-catenin and expression of GS in CARKO mice, similar to both genotypes of mice treated with OX and ACI. Interestingly, hepatocellular carcinoma induced in ACI-treated WT mice showed nuclear accumulation of β-catenin and was positive for GS. Our results indicated that β-catenin mutations were not involved in early-stage hepatocarcinogenesis induced by PROTOX inhibitors in mice, although activation of β-catenin and CAR is important in PB-induced tumorigenesis. The significant differences in molecular profiles suggested involvements of multiple mode of actions for hepatocarcinogenesis induced by PROTOX inhibitors.

Involvement of Mouse Constitutive Androstane Receptor in Acifluorfen-Induced Liver Injury and Subsequent Tumor Development

Acifluorfen (ACI), a protoporphyrinogen oxidase (PROTOX) inhibitor herbicide, promotes the accumulation of protoporphyrin IX (PPIX), and induces tumors in the rodent liver. Porphyria is a risk factor for liver tumors in humans; however, the specific mechanisms through which ACI induces hepatocarcinogenesis in rodents are unclear. Here, we investigated the mode of action of ACI-induced hepatocarcinogenesis, focusing on constitutive androstane receptor (CAR, NR1I3), which is essential for the development of rodent liver tumors in response to certain cytochrome P450 (CYP) 2B inducers. Dietary treatment with 2500 ppm ACI for up to 13 weeks increased Cyp2b10 expression in the livers of wild-type (WT) mice, but not in CAR-knockout (CARKO) mice. Microscopically, ACI treatment-induced cytotoxic changes, including hepatocellular necrosis and inflammation, and caused regenerative changes accompanied by prolonged increases in the numbers of proliferating cell nuclear antigen-positive hepatocytes in WT mice. In contrast, these cytotoxic and regenerative changes in hepatocytes were significantly attenuated, but still observed, in CARKO mice. ACI treatment also increased liver PPIX levels similarly in both genotypes; however, no morphological evidence of porphyrin deposition was found in hepatocytes from either genotype. Treatment with 2500 ppm ACI for 26 weeks after initiation with diethylnitrosamine increased the incidence and multiplicities of altered foci and adenomas in hepatocytes from WT mice; these effects were significantly reduced in CARKO mice. These results indicated that prolonged cytotoxicity in the liver was a key factor for ACI-induced hepatocarcinogenesis, and that CAR played an important role in ACI-induced liver injury and tumor development in mice.

Increased expression of Fe-chelatase leads to increased metabolic flux into heme and confers protection against photodynamically induced oxidative stress

Fe-chelatase (FeCh, EC 4.99.1.1) inserts Fe(2+) into protoporphyrin IX (Proto IX) to form heme, which influences the flux through the tetrapyrrole biosynthetic pathway as well as fundamental cellular processes. In transgenic rice (Oryza sativa), the ectopic expression of Bradyrhizobium japonicum FeCh protein in cytosol results in a substantial increase of FeCh activity compared to wild-type (WT) rice and an increasing level of heme. Interestingly, the transgenic rice plants showed resistance to oxidative stress caused not only by the peroxidizing herbicide acifluorfen (AF) as indicated by a reduced formation of leaf necrosis, a lower conductivity, lower malondialdehyde and H2O2 contents as well as sustained Fv/Fm compared to WT plants, but also by norflurazon, paraquat, salt, and polyethylene glycol. Moreover, the transgenic plants responded to AF treatment with markedly increasing FeCh activity. The accompanying increases in heme content and heme oxygenase activity demonstrate that increased heme metabolism attenuates effects of oxidative stress caused by accumulating porphyrins. These findings suggest that increases in heme levels and porphyrin scavenging capacity support a detoxification mechanism serving against porphyrin-induced oxidative stress. This study also implicates heme as possibly being a positive signal in plant stress responses.

Hexahydrophthalimide–benzothiazole hybrids as a new class of protoporphyrinogen oxidase inhibitors: synthesis, structure–activity relationship, and DFT calculations

Protoporphyrinogen oxidase (PPO, EC 1.3.3.4) has attracted continuous interest during the last few decades not only because of its unique biochemical characteristics but also because of its biomedical significance. As a continuation of our research work on the development of new PPO inhibitors, N-(benzothiazol-5-yl)-hexahydro-2H-isoindole-1,3-dithione (1a–j) and N-(benzothiazol-5-yl)-octahydro-3-thioxoisoindol-1-one derivatives (2a–i) were designed and synthesized. These newly prepared compounds were characterized by elemental analyses, 1H NMR and ESI-MS spectroscopy. The in vitro assay indicated that these compounds displayed good inhibition activity against human PPO (hPPO) with Ki values ranging from 0.38 μM to 6.83 μM. Notably, most of the monothionated products (1a–j) displayed a higher or comparable PPO-inhibition activity compared with the commercial control sulfentrazone. The comparison of the dihedral angles of the representative compound with that of acifluorfen (ACF) complexed with hPPO clearly indicated that the dihedral angle between the thionyl amide or carbonyl amide ring and the benzothiazole ring was closely related to the variation of the PPO inhibition activity of different types of inhibitors.

Structural insight into unique properties of protoporphyrinogen oxidase from Bacillus subtilis

Protoporphyrinogen IX oxidase (PPO) converts protoporphyrinogen IX to protoporphyrin IX, playing an important part in the heme/chlorophyll biosynthetic pathway. Bacillus subtilis PPO (bsPPO) is unique among PPO family members in that it is a soluble monomer, is inefficiently inhibited by the herbicide acifluorfen (AF) and has broader substrate specificity than other PPO enzymes. Here, we present the crystal structure of bsPPO bound to AF. Our structure shows that the AF molecule binds to a new site outside the previously identified inhibitor binding pocket. Most importantly, the benzene ring of the 2-nitrobenzoic acid moiety of AF lies parallel to the isoalloxazine ring of FAD at a distance of less than 3.5A, providing a framework for the interaction of FAD with the substrate protoporphyrinogen IX. Furthermore, our structure reveals that the larger substrate binding chamber and predominantly positively charged chamber surface of bsPPO are more favorable for the binding of coproporphyrinogen-III. These crystallographic findings uncover biochemically unique properties of bsPPO, providing important information for further understanding the enzymatic mechanism.

Collection of Arabidopsis thaliana mutants with altered sensitivity to oxidative stress inductors

Selective systems for screening Arabidopsis thaliana (L.) Heynh. mutants with altered sensitivity to the oxidative stress (OS) inductors norflurazon (NF), acifluorfen (AF), and plumbagin (PB) were developed and a collection of 28 mutants was obtained. Dwarf and necrotic forms predominated among the NF-tolerant mutants, while pigment mutants and those with changed root morphology prevailed among the AF-tolerant and PB-sensitive mutants, respectively. Genetic and biochemical analysis of certain mutants was performed; quantitative and qualitative changes in the content of superoxide dismutase and peroxidase isoforms have been revealed. These data, complemented by the data on the cross-tolerance (sensitivity) of the mutants to paraquat, indicate a correlation between tolerance to the OS inductors and the functions of antioxidant systems.

Polyclonal and monoclonal antibodies for the specific detection of the herbicide acifluorfen and related compounds

Polyclonal and monoclonal antibodies reactive with acifluorfen (AF) were prepared by the immunization of, respectively, rabbits and mice with AF-bovine serum albumin conjugates. The reactivities of polyclonal antibody and three monoclonal antibodies (AF 9-1, AF 51-5 and AF 75-144) were examined in an indirect competitive enzyme-linked immunosorbent assay (C-ELISA). The polyclonal antibody reacted with AF at concentrations of 1·5 to 800 μg litre-1, while the monoclonal antibodies reacted with AF at concentrations of 3 to 24 μg litre-1 for AF 9-1, 1·5 to 12 μg litre-1 for AF 51-5 and 12 to 48 μg litre-1 for AF 75-144. In the presence of up to 40% methanol in C-ELISA, the monoclonal antibodies, particularly AF 75-144, were less affected in their reactivities with AF than was the polyclonal antibody. Moreover AF 9-1 and AF 51-5 specifically reacted with acifluorfen-methyl and oxyfluorfen, while AF 75-144 reacted with chlornitrofen which did not react with the other antibodies. These results indicated that the antibodies are useful for the assay of AF and its related compounds. © 1997 SCI.

Extractable and Nonextractable (Bound) Residues of Acifluorfen in an Organic Soil

Acifluorfen (AC), 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid, was applied to an organic soil at 220 mg kg-1 in a laboratory incubation study. A conventional extraction method with solvents and supercritical fluid extraction (SFE) were used to evaluate extractable and nonextractable (bound) residues of AC and its metabolites in the soil. Over an incubation period of 7 months, the soil contained 22% AC of the initially applied herbicide and the residues were almost completely extracted with aqueous methanol. Only 0.8% AC was found in the bound form. Seventy-five percent AC applied was degraded to aminoacifluorfen (AAC) (due to reduction of nitro group to amino group) of which 60% was extracted by aqueous methanol, and 15% was in the bound form, mainly associated with the humin fraction of the soil organic matter. No further transformation of AAC to other metabolites was observed. Keywords: Acifluorfen; bound residues; soil; SFE

Chemical and Biological Inducers of Systemic Resistance to Pathogens Protect Cucumber and Tobacco Plants from Damage Caused by Paraquat and Cupric Chloride

Oxidative damage has been implicated in the necrotization of plant tissues by incompatible pathogens, including those that induce systemic acquired resistance (SAR). In this study, prooxidant chemicals were employed to evaluate the hypotheses that i) localized oxidative damage that culminates in necrosis can induce SAR and ii) SAR can protect tissues from oxidative damage. Paraquat (PQ), acifluorfen (AF), and sodium chlorate (SC) induced SAR to colletotrichum lagenarium in cucumber. PQ and SC, but not AF, also induced SAR to tobacco mosaic virus (local lesions) and Peronospora tabacina in tobacco. Pathogens and chemicals that triggered SAR to pathogens also systemically enhanced resistance to damage by PQ and CuCl 2 . Local protection from PQ was afforded by salicylate and a synthetic cytokinin known to induce local resistance to pathogens.

Binding Affinities of Peroxidizing Herbicides to Protoporphyrinogen Oxidase from Corn

The binding of the 14C-labeled herbicide thidiazimin (SN 124 085) to membrane-bound protoporphyrinogen oxidase (protox) from corn ( Zea mays) and its displacement by the diphenyl ethers acifluorfen (AF), acifluorfen methyl, and oxyfluorfen were examined and compared to their inhibitory activity on protox. SN 124 085 is a potent inhibitor of protox comparable to oxyfluorfen and acifluorfen methyl, all with I 50 values in the nanomolar range. SN 124 085 is a competitive inhibitor with respect to the substrate protoporphyrinogen having an inhibition constant ( K i) of 0.25 n M. Using 14C-labeled SN 124 085, a binding constant K b of 0.26 n M was obtained. The ability of acifluorfen, acifluorfen methyl, and oxyfluorfen to strictly compete with SN 124 085 was used to examine the binding affinity of the diphenyl ether-type herbicides to protox. All three inhibitors displaced SN 124 085 competitively, acifluorfen methyl being most effective. Secondary plots of the binding of SN 124 085 with different concentrations of the competing nonlabeled inhibitor present yielded the binding constant of the latter. While the potent herbicides acifluorfen methyl and oxyfluorfen showed K b constants below 1 n M, the binding affinity of AF was found to be 10-fold lower, according to its lower inhibitory activity. Binding constants of all inhibitors were found to be similar to their inhibition constant, demonstrating displacement studies as a reliable technique to determine the binding affinity of protox inhibitors.

Gas Chromatographic/Electron Capture Detection Method for Determination of Chlorinated Acids in Water: Collaborative Study

A U.S. Environmental Protection Agency (USEPA) interlaboratory method validation study was conducted on USEPA Method 515.1, "Determination of Chlorinated Acids in Water by Gas Chromatography with an Electron Capture Detector." This method is one of the 6 pesticide methods developed for the USEPA National Pesticide Survey (NPS). Method recovery and precision for analyses of sub-ppb to low-ppb concentrations of chlorinated acids were determined in reagent water and finished drinking waters. The analytes evaluated in the study included the 12 pesticides that were quantitatively measured in the National Pesticide Survey (bentazon, 2,4-D, 2,4-DB, 3,5-dichlorobenzoic acid, DCPA-diacid, dicamba, dichlorprop. 5-hydroxydicamba, pentachlorophenol, picloram, 2,4,5-T, and 2,4,5-TP) and 5 pesticides (acifluorfen, chloramben, dalapon, dinoseb, and 4-nitrophenol) that were only qualitatively assessed in the National Pesticide Survey because of recognized method imprecision. The study design was based on Youden's nonreplicate plan for collaborative tests of analytical methods. The waters were spiked with 17 chlorinated acids, each at 6 concentration levels, prepared as 3 Youden pairs. Eight laboratories extracted the spiked test waters at pH < 2 with ethyl ether, performed a solvent exchange with methyl tert-butyl ether, prepared methyl esters of the extracted acids using diazomethane, and analyzed an aliquot of each derivatized extract by gas chromatography with electron capture detection. The submitted data were analyzed using a USEPA computer program, which measured recovery and precision for each of the 17 compounds and compared the performance of the method between water types. Method 515.1 was judged acceptable for the 12 NPS analytes recovered quantitatively; mean percent recoveries at 10-15 times the method detection limits ranged from 79 to 105% in reagent water and from 75 to 123% in finished drinking water. In reagent water, overall precision (reproducibility relative standard deviation, RSDR) ranged from 9.6 to 34.2% and in finished drinking water, the RSDR ranged from 11.9 to 37.0%. Single-analyst precision (RSD for repeatability, RSDr) ranged from 5.8 to 17.7% in reagent water and from 4.6 to 27.9% in drinking water. Results for the 5 other NPS analytes were too inaccurate or imprecise and, for these compounds, supported use of the method for qualitative measurements only; the 5 compounds are not included in the adopted method. The method has been adopted first action by AOAC INTERNATIONAL for determination of residues of 12 chlorinated acids in finished drinking water.

HPLC and in vivo Spectrophotometric Detection of Porphyrins in Plant Tissues Treated with Porphyrinogenic Herbicides

Abstract Protoporphyrinogen oxidase (Protox) inhibitors and other compounds which block or stimulate the porphyrin pathway can cause sufficient levels of porphyrins to accumulate in plant tissues for severe photo dynamic damage to occur. The gross symptomology for all of these por­phyrinogenic herbicides is similar. Porphyrin accumulation induced by three porphyrinogenic herbicides acifluorfen (AF), δ-aminolevulinic acid (ALA), and 2,2′-dipyridyl (DY) was determined by in vivo spectrophotometry and HPLC methods. The averaged in vivo difference spec­tra between untreated and AF-treated (30 μᴍ for 20 h in darkness) yellow cucumber cotyledon discs approximated the absorption spectra of protoporphyrin IX (Proto IX). There was also an enhanced peak near 503 nm. Treatment of cotyledon discs with ALA alone generated a difference spectrum of protochlorophyllide (PChlide) in combination with Mg -Proto IX or Mg-Proto IX monomethyl ester (Mg-Proto IX ME). With ALA and AF in combination , the PChlide and Mg-Proto IX portions of the difference spectrum were reduced and the Proto IX peak and peak near 503 nm were increased. DY treatment yielded a difference spectrum with peaks approximating those of Proto IX and Mg-Proto IX ME , along with a peak near 503 nm . The presence of all porphyrins detected by in vivo spectrophotometry except for the 503 nm peak was confirmed with HPLC . Proto IX monomethyl ester was found by HPLC to be espe­cially elevated in treatments with AF. The in vivo 503 nm peak and in vitro studies with Protox-containing barley etioplast preparations suggest that p rototetrahydroporphyrin IX (an oxida­tion state intermediate between protoporphyrinogen IX and Proto IX) may accumulate under some conditions. These data demonstrate that rapid in vivo spectrophotometric studies can provide much of the qualitative results of HPLC studies and can confirm that in vitro results correspond with the in vivo situation.

Acifluorfen effects on intermediates of chlorophyll synthesis in green cucumber cotyledon tissues

Photobleaching herbicides like acifluorfen (AF) cause accumulation of protoporphyrin IX (PPIX) due to inhibition of protoporphyrinogen IX oxidase, resulting in deregulation of the porphyrin pathway. Chlorophyll intermediates other than PPIX have been reported to accumulate in response to these herbicides. The effects of AF and other chlorophyll synthesis modulators on the accumulation of PPIX, Mg-PPIX, Mg-PPIX monomethylester (ME), and protochlorophyllide (PChlide) in green cucumber cotyledon tissues were examined. Only PPIX accumulated above control levels in 0.3 to 33 μ M AF treatments. At concentrations of 100 and 333 μ M AF, there was a slight increase in Mg-PPIXME, however, PChlide levels were decreased by these AF concentrations. In δ-aminolevulinic acid (ALA)-treated tissues, PPIX, Mg-PPIX, Mg-PPIXME, and PChlide accumulated above control levels. ALA and 2,2′-dipyridyl (DP) increased AF-enhanced PPIX levels and AF prevented or reduced ALA- or DP-stimulated Mg-PPIX, Mg-PPIXME, and PChlide levels. Herbicidal damage in all treatments correlated best with PPIX caused to accumulate by these chlorophyll synthesis modulators rather than with other chlorophyll intermediates. These data indicate that PPIX is the only chlorophyll intermediate caused to accumulate in AF-treated tissues that plays a significant role in herbicidal activity of AF, and that AF blocks carbon flow to chlorophyll intermediates after PPIX.

Effects of temperature on the activity of the p-nitrosubstituted diphenyl ether herbicide acifluorfen in cucumber ( Cucumis sativus L.)

The influence of temperature on the activity of the herbicide acifluorfen (AF) (2-chloro-4-(trifluoromethyl)phenoxy-2-nitrobenzoate) in cucumber cotyledon disks exposed to light after being loaded with AF in darkness was small; generally > 90% of the 30°C effect at 3°C. The effects of 0.3 to 30 μ M acifluorfen on rapid (5 hr) disruption of the plasmalemma and slower (24 hr) photobleaching of chlorophyll were approximately the same at 3 and 30°C. In similar experiments, the herbicidal activity of rose bengal, a photodynamic dye, was also little affected by temperature. The activity of paraquat, however, was reduced by ca. 75% at 3°C compared to 30°C. Pretreatment with antimycin A during the dark incubation reduced the herbicidal activity of both AF and rose bengal equally well at both 3 and 30°C. Experiments with radiolabeled AF showed that the effect of antimycin A was not on AF uptake during the dark loading period prior to light exposure, suggesting that antimycin A acts as a radical scavanger or that mitochondrial respiration is a requirement for a process that potentiates sensitivity to photodynamic damage. Photosystem II inhibitors (atrazine and DCMU) enhanced the activity of AF at 30°C, but had no effect at 3°C, suggesting that a functional photosynthetic system provides some level of protection from AF by regeneration of antioxidants. These data indicate that there is no metabolic requirement for AF activity after it arrives at its site of action and is associated with its chromophore.

Photosynthesis Involvement in the Mechanism of Action of Diphenyl Ether Herbicides

Photosynthesis is not required for the toxicity of diphenyl ether herbicides, nor are chloroplast thylakoids the primary site of diphenyl ether herbicide activity. Isolated spinach (Spinacia oleracea L.) chloroplast fragments produced malonyl dialdehyde, indicating lipid peroxidation, when paraquat (1,1'-dimethyl-4,4'-bipyridinium ion) or diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] were added to the medium, but no malonyl dialdehyde was produced when chloroplast fragments were treated with the methyl ester of acifluorfen (methyl 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid), oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene], or MC15608 (methyl 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-chlorobenzoate). In most cases the toxicity of acifluorfen-methyl, oxyfluorfen, or MC15608 to the unicellular green alga Chlamydomonas eugametos (Moewus) did not decrease after simultaneous treatment with diuron. However, diuron significantly reduced cell death after paraquat treatment at all but the highest paraquat concentration tested (0.1 millimolar). These data indicate electron transport of photosynthesis is not serving the same function for diphenyl ether herbicides as for paraquat. Additional evidence for differential action of paraquat was obtained from the superoxide scavenger copper penicillamine (copper complex of 2-amino-3-mercapto-3-methylbutanoic acid). Copper penicillamine eliminated paraquat toxicity in cucumber (Cucumis sativus L.) cotyledons but did not reduce diphenyl ether herbicide toxicity.

Eficiência e seletividade de herbicidas aplicados em pós-emergência na soja (Glycinemax (L .) Merril )

O experimento foi conduzido, num Latossolo Vermelho Escuro com 53% de argila e 4,5% de matéria orgânica, objetivando-se estudar a eficiência e seletividade de herbicidas pós-emergentes na soja, cv. União. Os herbicidas foram aplicados quando as plantas daninhas estavam com 3 a 5 folhas. Os tratamentos com as respectivas doses, em kg/ha do i.a., foram os seguintes: misturas de tanque de alloxydim - Na a 1,125, e de sethoxydim a 0,221, com bentazon a 0,72; combinação de diclofop-metil a 0,84, com acifluorfen, a 0,224; diclofop-metil a 0,84, sethoxydim a 0,147, 0,184 e 0,221, fluazifop-butil a 0,25 e 0,37, CGA 82725 (éster 2 - propilínico do ácido 2-4 (3,5 - dicloro - 2 - pyridiloxi) - fenoxy - propiônico), a 0,35; todos combinados com bentazon, a 0,72. Utilizou-se ainda os tratamentos oryzalin + metribuzin (1,125 + 0,42), além das testemunhas com capina e sem capina o ciclo todo. Nas combinações, os graminicidas foram aplicados 3 dias depois de acifluorfen ou de bentazon. O controle de papuã (Brachiaria plantaginea (Link) Hitch) e de capim-arroz (Echinochloa crusgalli (L.) Beauv.) foi deficiente apenas nos tratamentos com alloxydim - Na. Milhã (Digitaria sanguinalis (L.) Scop.) não foi controlada pelos tratamentos com diclofop-metil, alloxydim - Na e com as menores doses de sethoxydim. Entre as dicotiledôneas, somente guanxuma (Sida rhombifolia L.) não foi bem controlada por acifluorfen. A mistura de alloxydim - Na + bentazon diminuiu o efeito do graminicida, enquanto que sethoxydim + bentazon não demonstrou este antagonismo. A fitotoxicidade à soja foi mais acentuada no tratamento de diclofop-metil com acifluorfen. A altura e a população de plantas da soja não foram influenciadas pelos herbicidas. Fluazifop - butil na maior dose, com bentazon, apresentou o melhor rendimento (2.416 kg/ha), superando em 5,4% a testemunha capinada (2.292 kg/ha). Foram ainda superiores a esta, os tratamentos oryzalin + metribuzin, as duas maio- res doses de sethoxydim e a sua mistura de tanque com bentazon, bem como fluazifop-butil na menor dose.