Overview of herbicide mechanisms of action. (65/174)

Commercial herbicides exhibit many different mechanisms of action. Several enzymes involved in biosynthesis of amino acids are sites of action for herbicides. A large number of different herbicide classes inhibit photosynthesis by binding to the quinone-binding protein, D-1, to prevent photosynthetic electron transfer. Several different types of herbicides apparently cause accumulation of photodynamic porphyrins by inhibiting protoporphyrinogen oxidase. Bipyridyliums and heteropentalenes cause the production of superoxide radicals by energy diversion from photosystem I of photosynthesis. Lipid synthesis is the site of action of a broad array of herbicides used in controlling monocot weeds. Herbicides of several classes apparently act by inhibiting mitosis through direct interaction with tubulin. Several other molecular sites of herbicide action are known. Despite a growing body of knowledge, the exact molecular sites of action of many herbicides are unknown. Some herbicides are known to have more than one site of action. Virtually all knowledge of herbicide structure-activity relationships is semiempirical. In addition to site of action structure-activity relationships, herbicide structure and chemical properties also strongly influence absorption, translocation, bioactivation, and environmental stability. Considering how little is known about all the potential sites of herbicide action, it is unlikely that during the next decade more than a relatively small number of site-specific herbicide structure-activity relationships will be developed.  (+info)

Isolation and characterization of ilvA, ilvBN, and ilvD mutants of Caulobacter crescentus. (66/174)

Caulobacter crescentus strains requiring isoleucine and valine (ilv) for growth were shown by transduction and pulsed-field gel electrophoresis to contain mutations at one of two unlinked loci, ilvB and ilvD. Other C. crescentus strains containing mutations at a third locus, ilvA, required either isoleucine or methionine for growth. Biochemical assays for threonine deaminase, acetohydroxyacid synthase, and dihydroxyacid dehydratase demonstrated that the ilvA locus encodes threonine deaminase, the ilvB locus encodes acetohydroxyacid synthase, and the ilvD locus encodes dihydroxyacid dehydratase. C. crescentus strains resistant to the herbicide sulfometuron methyl, which is known to inhibit the action of certain acetohydroxyacid synthases in a variety of bacteria and plants, were shown to contain mutations at the ilvB locus, further suggesting that an acetohydroxyacid synthase gene resides at this locus. Two recombinant plasmids isolated in our laboratory, pPLG389 and pJCT200, were capable of complementing strains containing the ilvB and ilvD mutations, respectively. The DNA in these plasmids hybridized to the corresponding genes of Escherichia coli and Serratia marcescens, confirming the presence of ilvB-like and ilvD-like DNA sequences at the ilvB and ilvD loci, respectively. However, no hybridization was observed between any of the other enteric ilv genes and C. crescentus DNA. These results suggest that C. crescentus contains an isoleucine-valine biosynthetic pathway which is similar to the corresponding pathway in enteric bacteria but that only the ilvB and ilvD genes contain sequences which are highly conserved at the DNA level.  (+info)

Cytocidal amino acid starvation of Saccharomyces cerevisiae and Candida albicans acetolactate synthase (ilv2{Delta}) mutants is influenced by the carbon source and rapamycin. (67/174)

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Characterization of enzymes of the branched-chain amino acid biosynthetic pathway in Methanococcus spp. (68/174)

Methanococcus aeolicus, Methanococcus maripaludis, and Methanococcus voltae contain similar levels of four enzymes of branched-chain amino acid biosynthesis: acetohydroxy acid synthase, acetohydroxy acid isomeroreductase, dihydroxy acid dehydratase, and transaminase B. Following growth at low partial pressures of H2-CO2, the levels of these enzymes in extracts of M. voltae are reduced three- to fivefold, which suggests that their synthesis is regulated. The enzymes from M. aeolicus were found to be similar to the eubacterial and eucaryotic enzymes with respect to molecular weights, pH optima, kinetic properties, and sensitivities to O2. The acetohydroxy acid isomeroreductase has a specific requirement for Mg2+, and other divalent cations were inhibitory. It was stimulated threefold by K+ and NH4+ ions and was able to utilize NADH as well as NADPH. The partially purified enzyme was not sensitive to O2. The dihydroxy acid dehydratase is extremely sensitive to O2, and it has a half-life under 5% O2 of 6 min at 25 degrees C. Divalent cations were required for activity, and Mg2+, Mn2+, Ni2+, Co2+, and Fe2+ were nearly equally effective. In conclusion, the archaebacterial enzymes are functionally homologous to the eubacterial and eucaryotic enzymes, which implies that this pathway is very ancient.  (+info)

A composite transcriptional signature differentiates responses towards closely related herbicides in Arabidopsis thaliana and Brassica napus. (69/174)

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Mechanism of de novo branched-chain amino acid synthesis as an alternative electron sink in hypoxic Aspergillus nidulans cells. (70/174)

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Novel method to detect a construct-specific sequence of the acetolactate synthase gene in genetically-modified flax CDC Triffid (FP967). (71/174)

During the fall of 2009, a trace of unauthorized genetically modified (GM) flax (Linum usitatissimum L.) line, CDC Triffid, which is resistant to sulfonylurea herbicides, was detected in many countries including Japan. A method to reliably identify the CDC Triffid line was urgently required. We developed a novel construct-specific real-time polymerase chain reaction (PCR) method to identify the mutant acetolactate synthase gene in the CDC Triffid line. We confirmed that the method can detect 0.001% GM flax in DNA mixing solution. The study shows that the developed method is specific, sensitive and reliable way to monitor a trace of CDC Triffid.  (+info)

Production of a monocot-specific monoclonal antibody against acetohydroxyacid synthase and its use in the purification and characterization of the enzyme. (72/174)

Acetohydroxyacid synthase [AHAS; acetolactate pyruvate-lyase (carboxylating), EC 4.1.3.18], the first enzyme unique to the biosynthesis of valine, leucine, and isoleucine, is a known target for several different chemical classes of herbicides. Antibodies required for immunological characterization of the enzyme have not been generated by the conventional method of antibody production using purified protein. Monoclonal antibodies were raised against AHAS from corn by using as immunogen a synthetic peptide representing this enzyme. This antibody immunoprecipitated the enzyme activity from corn. On a Western blot, a protein band with a molecular weight of 65,000 was detected in crude extracts of corn. Furthermore, a monoclonal antibody immunoaffinity gel was used to isolate a single protein from crude enzyme preparations that migrated at Mr 65,000 in an SDS/polyacrylamide gel. The molecular weight of this protein band is the molecular weight predicted for a plant AHAS from a cloned gene sequence. These results strongly suggest that the Mr 65,000 protein represents AHAS in corn extracts. Interestingly, the monoclonal antibody specifically recognized the enzyme from monocots and did not crossreact with AHAS from any dicot species tested. Identification of this monoclonal antibody that distinguishes monocot and dicot AHAS is significant because of a very high degree of amino acid conservation (85%) between AHAS proteins from different species.  (+info)