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PubMedDate not supplied

Comparative investigation of antipyrine half-life and induction of cytochrome P-450 dependent monooxygenases in rats treated with phenylurea herbicides.

The short-term effect of three substituted phenylurea herbicides has been investigated on antipyrine plasma half-life in rats. Isoproturon was ineffective, while chlortoluron and diuron decreased the half-life significantly. There was a close correlation between antipyrine half-lives and induction of hepatic cytochrome P-450 dependent benzo(a)pyrene monooxygenase, 7-ethoxycoumarin O-deethylase and 7-ethoxyresorufin O-deethylase.

Animals↗
PubMedDate not supplied

Multiresidue method for determining substituted urea herbicides in foods by liquid chromatography.

A method is described for determining substituted urea herbicides in foods. The residues are extracted from the product with methanol, and the food coextractives are removed by using solvent partitioning and Florisil column chromatography. The extract is analyzed using liquid chromatography with postcolumn photodegradation, chemical derivatization with orthophthalaldehyde, and spectrofluorometry. Recoveries were determined by spiking 8 different food products with 6 phenylureas--chlorbromuron, chloroxuron, diuron, fluometuron, linuron, and metobromuron--at 0.05 and 0.5 ppm. Three determinations were made at each level for each product. Average recovery at 0.05 ppm was 95% (with a standard deviation of 7.9%), and at 0.5 ppm, 98% (with a standard deviation of 6.9%).

Chromatography, Liquid↗
PubMed1985

Differentiation and development of bundle sheath and mesophyll thylakoids in maize. Thylakoid polypeptide composition, phosphorylation, and organization of photosystem II.

Photosynthetic electron flow, polypeptide pattern, presence of chlorophyll-protein complexes, and phosphorylation of thylakoid polypeptides have been investigated in differentiated mesophyll (M) and bundle sheath (B) thylakoids of the C4 plant Zea mays. The polypeptide pattern of M thylakoids and their photosynthetic electron flow are comparable to those of other green plants. B thylakoids exhibit only photosystem I (PSI) activity, contain only traces of the PSII light harvesting (LHCII) polypeptide, do not bind [3H] diuron, and lack polypeptides of the water-oxidation complex of PSII and the herbicide binding 32-kDa polypeptide, as detected by specific antibodies. However, B thylakoids possess a partially active PSII reaction center, as demonstrated by light-dependent reduction of silicomolybdate with 1,5-diphenylcarbazide (DPC) as an electron donor, and the presence of the PSII reaction center polypeptides of 44-47 kDa. Only one chlorophyll a-protein complex, corresponding to the PSI reaction center-core antenna, was detectable in B thylakoids, as opposed to chlorophyll a and chlorophyll a,b-protein complexes present in M thylakoids. The light-dependent, membrane-bound kinase activity present in M thylakoids could not be detected in B thylakoids which, nevertheless, contain a protein kinase able to phosphorylate casein. A total of 19 differences between the electrophoretic pattern of B and M thylakoid polypeptides were observed. The mRNA coding for the LHCII polypeptide is primarily, if not exclusively, localized in M cells. The development of PSII complex precedes that of PSI during the differentiation of B and M chloroplasts in expanding leaves of light-grown plants and during the greening of dark-grown etiolated seedlings. The differentiation of the maize leaf into cells programmed to form B or M chloroplasts does not require light. In light-grown plants, the differentiation of B and M thylakoids occurred progressively from the base of the leaf and was completed at 4-5 cm from the leaf base.

Cell Differentiation↗
PubMedDate not supplied

Herbicidal treatments for control of Cannabis sativa L.

In order to test herbicides for the destruction of illicit stands of cannabis (Cannabis sativa L.) a series of commercially available herbicides were sprayed on glasshouse-grown plants having 2 to 6 leaves. The following herbicides caused complete kill or severe injury to cannabis plants: (a) herbicides with root and foliage activity--ametryn, atrazine, metribuzin, prometryn, terbutryne, diuron, fluometuron, linuron, methabenzthiazuron, phenobenzuron, ethofumesate, karbutilate, methazole and oxadiazon; and (b) foliar-acting herbicides with brief or no soil persistence--amitrole, bentazon, 2,4-D, diquat + paraquat, glyphosate and phenmedipham. In field experiments herbicides of the latter group, and ioxynil, metribuzin, and a MSMA-cacodylate mixture, caused death or severe damage to young cannabis plants. Glyphosate, ioxynil and bentazon destroyed developed cannabis plants. In glasshouse and field experiments the following herbicides applied to young cannabis plants caused marked deformations of stems, leaves and/or inflorescences: barban, butralin, dalapon, difenzoquat, dinitramine, diphenamid, IPC, napropamide, penoxalin, triffuralin, and U-27267.

Cannabis↗
PubMed1980

Herbicidal treatments for control of Papaver somniferum L.

Fifty-five commercially available herbicides were evaluated for possible use to destroy illicit opium poppy crops (Papaver somniferum). In the first stage, herbicides were sprayed on poppy plants grown in containers. The following compounds killed poppy plants: (a) herbicides with typical foliar activity--amitrole, bromoxynil, 2,4-D, glyphosate, ioxynil and paraquat; and (b) herbicides with root and foliar activity--the triazines ametryn, atrazine, metribuzin, prometryn, simazine and terbutryn; the substituted ureas benzthiazuron, chloroxuron, diuron, fluometuron, linuron, methabenzthiazuron, neburon and phenobenzuron; and the miscellaneous compounds karbutilate, methazole, oxadiazon and pyrazon. Severe but sublethal injury was caused by cycloate, EPTC, molinate, pobulate, cacodylate + MSMA, ethofumesate, perfluidone and phenmedipham. Abnormal development of vegetative or reproductive parts of the plant was induced by benefin, butralin, dinitramine, pendimethalin, trifluralin, diphenamid, napropamide, dalapon and propham. Efficient herbicides with negligible persistence in soil at the doses applied were evaluated on poppy plants in the field at various stages of growth. Small plants were severely injured by 2,4-D, killed rapidly by bromoxynil, ioxynil, paraquat (in mixture + diquat), and more slowly by glyphosate and metribuzin. The resistance to herbicides increased with the age of the poppy plant. Severe damage with partial kill of developed plants was obtained with bromoxynil, ioxynil, glyphosate, and paraquat + diquat; the last treatment produced the fastest effect.

Drug and Narcotic Control↗
PubMed1982

General occurrence and structural similarity of the rapidly synthesized, 32,000-dalton protein of the chloroplast membrane.

A rapidly metabolized membrane protein from Spirodela, with an apparent molecular weight of 32,000, has been implicated in allosterically regulating electron transport and mediating diuron herbicide sensitivity in the chloroplast (Mattoo, A. K., Pick, U., Hoffman-Falk, H., and Edelman, M. (1981) Proc. Natl. Acad. Sci. U. S. A. 78, 1572-1576). Rapid synthesis of a 32,000-dalton plastid membrane protein is demonstrated for several diverse angiosperms and the alga, Chlamydomonas. Comparative partial proteolytic mapping of the polypeptide showed similar patterns for all species tested. In some cases, a 33,500-dalton precursor polypeptide was identified which also displayed interspecific structural homologies. Lastly, in situ analysis of the surface-exposed 32,000-dalton membrane protein yielded a common trypsinization pattern for the organisms studied. These findings point toward a broad distribution and phylogenetic similarity of the 32,000-dalton thylakoid protein of the chloroplast at levels of precursor maturation, membrane orientation, and primary structure.

Chloroplasts↗
PubMed1976

High-pressure liquid chromatographic analysis of urea herbicides in foods.

A method is described for the direct analysis of the urea herbicides linuron, monuron, diuron, chlorbromuron, fluometuron, chloroxuron, and fenuron in cabbage, corn, potatoes, turnip, and wheat at 0.01-1.0 ppm. The samples are extracted with acetone; the filtrate is partitioned with hexane-methylene chloride (1+1) followed by 2 other extractions with methylene chloride. The organic phases are dried and concentrated for column chromatographic cleanup on 2% deactivated Florisil. The column fractions are evaporated just to dryness and redissolved in 10 ml isooctane for high-pressure liquid chromatography on a 25 cm silica gel (5 mum) column. Isopropanol in isooctane is the mobile phase, and compounds are measured by ultraviolet absorption at 254 nm. Recoveries are greater than 80% in most cases. These results are confirmed by alkylation with sodium hydride-methyl iodide in dimethyl sulfoxide to form the methyl products which are analyzed by the same chromatographic system or by gas-liquid chromatography.

Chromatography, High Pressure Liquid↗
PubMedDate not supplied

Determination of phenylurea herbicide residues in vegetables by liquid chromatography after gel permeation chromatography and Florisil cartridge cleanup.

A liquid chromatographic method for quantitative determination of 9 phenylurea herbicide residues (metoxuron, metobromuron, monolinuron, chlortoluron, isoproturon, diuron, linuron, chloroxuron, and neburon) in potatoes, carrots, and mixed vegetables is described. Samples are extracted with acetone, partitioned with ethyl acetate-cyclohexane (50 + 50, v/v) and cleaned up by gel permeation chromatography with ethyl acetate-cyclohexane (50 + 50, v/v) as eluant. A small column (1 cm id) packed with Biobeads SX3 resin is used to reduce solvent consumption and analytical time. After solid-phase extraction on a Florisil cartridge, herbicide residues are successfully separated on a C18 column by gradient elution and determined by UV detection at 242 nm. Average recoveries of 9 compounds from different samples range from 70 to 98% at 0.010 and 0.100 mg/kg fortification levels. Quantitation limits are 0.010 mg/kg.

Chromatography, Gel↗
PubMed1998

Effect of nitrite on primary photosynthetic processes in isolated chloroplasts of wheat grown under various conditions of nitrogen supply.

In wheat chloroplasts, NO2- (5 mM) inhibited non-cyclic phosphorylation coupled to the linear electron flow through both photosystems but stimulated cyclic phosphorylation with phenazine methosulfate (plus diuron) and electron flux from an artificial electron donor through PSI and methylviologen to oxygen. During light energization of chloroplasts, NO2- increased the F740/F695 ratio in the low-temperature fluorescence spectra, thus suggesting that the energy of absorbed quanta is redistributed in favor of PSI. Nitrite also stimulated the activity of Mg2+-dependent H+-ATPase. Changes in the slow component of the induction curve of delayed fluorescence also suggest that NO2- affects energy transformation processes that are coupled to electron transport in the chloroplasts. Nitrite had no effect on these functional characteristics of thylakoids and chloroplasts isolated from plants grown under nitrogen deficiency in the medium.

Chloroplasts↗
PubMed1999

Electrically driven microseparation methods for pesticides and metabolites. II: on-line and off-line preconcentration of urea herbicides in capillary electrochromatography.

Capillary electrochromatography (CEC) was introduced to the separation of nine important urea herbicides using octadecyl-silica (ODS) capillary columns that were specially designed to allow the realization of a relatively strong electroosmotic flow (EOF) and, in turn, fast separations. The ODS stationary phase was intentionally prepared to have a low surface coverage in octadecyl ligands in order to ensure a strong EOF. This ODS stationary phase of low surface coverage exhibited the usual reversed-phase chromatographic behavior as was manifested by the linearity of plots of log kappa versus the percent organic modifier in the mobile phase. The nature of the organic modifier of the mobile phase influenced the order of elution as well as the separation efficiency of the nine urea herbicides. Mobile phases containing acetonitrile yielded higher separation efficiency (by a factor of 1.5) than methanol-containing mobile phases. This was attributed to the higher mass transfer resistances of the solute in and out of the pores in the presence of the more viscous methanol-containing mobile phases. Due to the relatively strong affinity of the urea herbicides to the ODS stationary phase, on-line preconcentration consisting of prolonged injections allowed the determination of 10(-5) M urea herbicide samples using a UV detector without sacrificing separation efficiency. This was further decreased to 10(-7) M when the prolonged injection was preceded by the injection of a plug of water. The plug of water (the more retentive mobile phase) brought about an enhanced accumulation of the dilute samples into a narrow band at the inlet of the CEC column. When this on-column sample enrichment approach was combined with an off-line sample preconcentration step, which consisted of a solid-phase extraction process, ultra dilute samples of 10(-10) M (0.1 ppb) could be detected.

Chromatography, High Pressure Liquid↗
PubMed1987

Gas chromatography mass spectrometry of some thermally labile urea pesticides.

The application of gas chromatography/mass spectrometry to three thermally labile phenylurea pesticides is reported. Using alcohols as solvents the decomposition of the pesticides is followed by a reaction in which esters of N-(3,4-dichlorophenyl)carbamic acid are formed. As these reactions occur during the gas chromatographic analysis, it is the esters which are identified in the mass spectrometer. The methyl ester is itself a pesticide so an erroneous conclusion about the original pesticide could be reached when methanol is the solvent.

Diuron↗
PubMed1995

Electron transport regulates exchange of two forms of photosystem II D1 protein in the cyanobacterium Synechococcus.

Synechococcus sp. PCC 7942 modulates photosynthetic function by transiently replacing the constitutive D1 photosystem II protein, D1:1, with an alternate form, D1:2, to help counteract photoinhibition under excess light. We show that a temperature drop from 37 to 25 degrees C also drives D1:1/D1:2 exchange under constant, moderate light. Chilling or light-induced D1 exchange results from rapid loss of psbAI message coding for D1:1 and accumulation of psbAII and psbAIII messages coding for D1:2. During chilling, a large pool of a novel form, D1:2*, transiently accumulates, distinguishable from normal D1 by an increase in apparent molecular mass. D1:2* is not phosphorylated and is probably a functionally inactive, incompletely processed precursor. After acclimation to 25 degrees C, D1:2* disappears and D1:1 again predominates, although substantial D1:2 remains. Partial inhibition of electron transport under constant, moderate light also triggers the D1 exchange process. These treatments all increase excitation pressure on photosystem II relative to electron transport. Therefore, information from photosynthetic electron transport regulates D1 exchange without any requirement for a change in light intensity or quality, possibly via a redox sensing mechanism proximal to photosystem II.

Antioxidants↗
PubMed1983

Isolation of PS II reaction centre and its relationship to the minor chlorophyll-protein complexes.

Evidence is presented for the identification of the chlorophyll- protein complex CPa-1 (CP 47) as the reaction centre of photosystem II (PS II). We have developed a simple, rapid method using octyl glucoside solubilization to obtain preparations from spinach and barley that are highly enriched in PS II reaction centre activity (measured as the light-driven reduction of diphenylcarbazide by 2,6-dichlorophenolindophenol). These preparations contain only the two minor chlorophyll-protein complexes CPa-1 and CPa-2. During centrifugation on a sucrose density gradient, there is a partial separation of the two CPa complexes from each other, and a complete separation from other chlorophyll-protein complexes. The PS II activity comigrates with CPa-1 but not CPa-2, strongly suggesting that the former is the reaction centre complex of PS II. Reaction centre preparations are sensitive to the herbicide 3(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), but only at much higher concentrations than those required to inhibit intact thylakoid membranes. A model of PS II incorporating our current knowledge of the chlorophyll-protein complexes is presented. It is proposed that CPa-2 and the chlorophyll a + b complex CP 29 may function as internal antenna complexes surrounding the reaction centre, with the addition of variable amounts of the major chlorophyll a + b light-harvesting complex.

Chlorophyll↗
PubMed1986

Effect of tryptophan on 2,4-dichlorophenoxyacetic acid toxicity in the nitrogen-fixing-cyanobacterium Nostoc linckia.

The combined effect of a hormone weed killer 2,4-dichlorophenoxyacetic acid (2,4-D) and an amino acid (tryptophan) has been studied on growth and heterocyst differentiation in the cyanobacterium Nostoc linckia. 2.4-D at 100 micrograms/ml stimulated growth and heterocyst frequency in combined nitrogen-free medium while its higher concentrations inhibited both. Tryptophan under similar conditions promoted much growth yield with 3-4 fold enhanced heterocyst frequency than the control. Such heterocysts were immature and showed germination under in situ condition. The concentrations of 2,4-D (100 micrograms/ml) and tryptophan (50 micrograms/ml), stimulatory to growth and heterocyst formation, caused additive effect while herbicide inhibition of nitrogen-fixing growth at higher doses was partially relieved by tryptophan but tryptophan-induced heterocyst frequency was completely suppressed under this condition. The possible role of interaction of these two chemicals on growth and heterocyst formation has been discussed.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1996

Modeling of the D1/D2 proteins and cofactors of the photosystem II reaction center: implications for herbicide and bicarbonate binding.

A three-dimensional model of the photosystem II (PSII) reaction center from the cyanobacterium Synechocystis sp. PCC 6803 was generated based on homology with the anoxygenic purple bacterial photosynthetic reaction centers of Rhodobacter sphaeroides and Rhodopseudomonas viridis, for which the X-ray crystallographic structures are available. The model was constructed with an alignment of D1 and D2 sequences with the L and M subunits of the bacterial reaction center, respectively, and by using as a scaffold the structurally conserved regions (SCRs) from bacterial templates. The structurally variant regions were built using a novel sequence-specific approach of searching for the best-matched protein segments in the Protein Data Bank with the "basic local alignment search tool" (Altschul SF, Gish W, Miller W, Myers EW, Lipman DJ, 1990, J Mol Biol 215:403-410), and imposing the matching conformational preference on the corresponding D1 and D2 regions. The structure thus obtained was refined by energy minimization. The modeled D1 and D2 proteins contain five transmembrane alpha-helices each, with cofactors (4 chlorophylls, 2 pheophytins, 2 plastoquinones, and a non-heme iron) essential for PSII primary photochemistry embedded in them. A beta-carotene, considered important for PSII photoprotection, was also included in the model. Four different possible conformations of the primary electron donor P680 chlorophylls were proposed, one based on the homology with the bacterial template and the other three on existing experimental suggestions in literature. The P680 conformation based on homology was preferred because it has the lowest energy. Redox active tyrosine residues important for P680+ reduction as well as residues important for PSII cofactor binding were analyzed. Residues involved in interprotein interactions in the model were also identified. Herbicide 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) was also modeled in the plastoquinone QB binding niche using the structural information available from a DCMU-binding bacterial reaction center. A bicarbonate anion, known to play a role in PSII, but not in anoxygenic photosynthetic bacteria, was modeled in the non-heme iron site, providing a bidentate ligand to the iron. By modifying the previous hypothesis of Blubaugh and Govindjee (1988, Photosyn Res 19:85-128), we modeled a second bicarbonate and a water molecule in the QB site and we proposed a hypothesis to explain the mechanism of QB protonation mediated by bicarbonate and water. The bicarbonate, stabilized by D1-R257, donates a proton to QB2- through the intermediate of D1-H252; and a water molecule donates another proton to QB2-. Based on the discovery of a "water transport channel" in the bacterial reaction center, an analogous channel for transporting water and bicarbonate is proposed in our PSII model. The putative channel appears to be primarily positively charged near QB and the non-heme iron, in contrast to the polarity distribution in the bacterial water transport channel. The constructed model has been found to be consistent with most existing data.

Amino Acid Sequence↗
PubMed1995

Modeling the quinone-B binding site of the photosystem-II reaction center using notions of complementarity and contact-surface between atoms.

Functional identity and significant similarities in cofactors and sequence exist between the L and M reaction center proteins of the photosynthetic bacteria and the D1 and D2 photosystem-II reaction center proteins of cyanobacteria, algae, and plants. A model of the quinone (QB) binding site of the D1 protein is presented based upon the resolved structure of the QB binding pocket of the L subunit, and introducing novel quantitative notions of complementarity and contact surface between atoms. This model, built without using traditional methods of molecular mechanics and restricted to residues in direct contact with QB, accounts for the experimentally derived functional state of mutants of the D1 protein in the region of QB. It predicts the binding of both the classical and phenol-type PSII herbicides and rationalizes the relative levels of tolerance of mutant phenotypes.

Atrazine↗
PubMed1985

Partial restoration of meiosis in an apomictic strain of Saccharomyces cerevisiae: a model system for investigation of nucleomitochondrial interactions during sporulation.

In an apomictic strain of Saccharomyces cerevisiae (ATCC 4117-H2) which undergoes a single nuclear division during sporulation and consequently forms asci containing two uninucleate diploid spores, a study was undertaken to investigate the effects of cultivation in three presporulation media (YPA; YNB; SMM) on nuclear division and ascosporogenesis in sporulation medium. Comparison of effects of presporulation culture in these media on the number of spores formed per ascus showed that a marked induction (30 +/- 4.3 per cent) of three- and four-spored asci could occur in sporulation medium following cultivation in a defined YNB medium supplemented with a 1 per cent solution of vitamins and containing decreased ammonium sulphate and increased glucose levels. Experiments in which the concentrations of glucose and of ammonium sulphate were varied simultaneously indicated that the initial presporulation carbon to nitrogen source ratio is an important factor in determining tetrad formation in sporulation medium. Nuclear staining demonstrated two classes of asci: binucleate (one- and two-spored) and tetranucleate (three- and four-spored). Genetic evidence and data concerning effects of inclusion in sporulation medium of a meiotic inhibitor (glucose) indicated spores in tetrads were haploid rather than diploid. This ability to condition a significant number of cells for meiotic rather than apomictic differentiation made possible investigation of effects of mitochondrial inhibitors on both developmental processes simultaneously. It was found possible to selectively inhibit meiotic development by inclusion in sporulation medium of appropriate concentrations of specific inhibitors. Moreover, the data suggest meiotic sporulation is more strictly dependent than apomictic sporulation on mitochondrial function.

Acetates↗
PubMed1993

Involvement of acceptor side components of PSII in the regulatory mechanism of Plectonema boryanum grown photoautotrophically under diazotrophic condition.

Alternating peaks of photosynthetic activity (P-phase) and nitrogen fixing activity (N-phase) were shown in Plectonema boryanum grown under diazotrophic condition in continuous light. In N-phase photosystem I activity increased by 35-45% and oxygen evolution decreased by 70-80% which was partially restored to 45-55% in the presence of 2,6-dichloro-p-benzoquinone. Thermoluminescence glow curve in P-phase consists of a major band at 25 degrees C which was shifted to 10 degrees C in N-phase. Both these bands are sensitive to DCMU and tetranitromethane. Flash excitation studies with major thermoluminescence band in P and N-phase showed oscillations with same periodicity of four having maxima at 2nd and 6th flashes. On the basis of these observations it is suggested that photosynthetic electron transport under diazotrophic growth condition is regulated by the redox levels of the secondary quinone acceptor QB.

Benzoquinones↗