The advent of biotechnology-derived, herbicide-resistant crops has revolutionized farming practices in many countries. Facile, highly effective, environmentally sound, and profitable weed control methods have been rapidly adopted by crop producers who value the benefits associated with biotechnology-derived weed management traits. But a rapid rise in the populations of several troublesome weeds that are tolerant or resistant to herbicides currently used in conjunction with herbicide-resistant crops may signify that the useful lifetime of these economically important weed management traits will be cut short. We describe the development of soybean and other broadleaf plant species resistant to dicamba, a widely used, inexpensive, and environmentally safe herbicide. The dicamba resistance technology will augment current herbicide resistance technologies and extend their effective lifetime. Attributes of both nuclear- and chloroplast-encoded dicamba resistance genes that affect the potency and expected durability of the herbicide resistance trait are examined.
Dicamba O-demethylase is a multicomponent enzyme from Pseudomonas maltophilia, strain DI-6, that catalyzes the conversion of the widely used herbicide dicamba (2-methoxy-3,6-dichlorobenzoic acid) to DCSA (3,6-dichlorosalicylic acid). We recently described the biochemical characteristics of the three components of this enzyme (i.e. reductase DIC , ferredoxin DIC , and oxygenase DIC ) and classified the oxygenase component of dicamba O-demethylase as a member of the Rieske nonheme iron family of oxygenases. In the current study, we used N-terminal and internal amino acid sequence information from the purified proteins to clone the genes that encode dicamba O-demethylase. Two reductase genes (ddmA1 and ddmA2) with predicted amino acid sequences of 408 and 409 residues were identified. The open reading frames encode 43.7-and 43.9-kDa proteins that are 99.3% identical to each other and homologous to members of the FAD-dependent pyridine nucleotide reductase family. The ferredoxin coding sequence (ddmB) specifies an 11.4-kDa protein composed of 105 residues with similarity to the adrenodoxin family of [2Fe-2S] bacterial ferredoxins. The oxygenase gene (ddmC) encodes a 37.3-kDa protein composed of 339 amino acids that is homologous to members of the Phthalate family of Rieske non-heme iron oxygenases that function as monooxygenases. Southern analysis localized the oxygenase gene to a megaplasmid in cells of P. maltophilia. Mixtures of the three highly purified recombinant dicamba O-demethylase components overexpressed in Escherichia coli converted dicamba to DCSA with an efficiency similar to that of the native enzyme, suggesting that all of the components required for optimal enzymatic activity have been identified. Computer modeling suggests that oxygenase DIC has strong similarities with the core ␣ subunits of naphthalene 1,2-dioxygenase. Nonetheless, the present studies point to dicamba O-demethylase as an enzyme system with its own unique combination of characteristics.The herbicide dicamba (2-methoxy-3,6-dichlorobenzoic acid) has been used to effectively control broadleaf weeds in crops such as corn and wheat for almost 40 years. Like a number of other chlorinated organic compounds, dicamba does not persist in the soil because it is efficiently metabolized by a consortium of soil bacteria under both aerobic and anaerobic conditions (1-4). Studies with different soil types treated with dicamba have demonstrated that 3,6-dichlorosalicylic acid (DCSA), 1 a compound without herbicidal activity, is a major product of the microbial degradation process (2, 3, 5). Soil samples taken from a single site exposed to dicamba for several years yielded a number of bacterial species capable of utilizing dicamba as a sole carbon source (6). These soil microorganisms could completely mineralize dicamba to carbon dioxide, water, and chloride ion (7). Studies on the metabolism of dicamba in the cells of one of these bacteria, the DI-6 strain of Pseudomonas maltophilia, showed that DCSA is a major degradation product (7,8).We have be...
Terpenes and terpenoids are primary constituents of essential oils of different type of plants and flowers. Some qualitative estimation methods of terpenoids in plant tissue have been previously described but there is no protocol of estimating the same quantitatively till date. In the present study a protocol has been attempted to estimate the total terpenoids concentration of different resin producing plants using a monoterpene, Linalool as standard reagent.
Methionine synthase is an important cellular housekeeping enzyme and is dependent on the cofactor cobalamin, a derivative of vitamin B12, for activity. It functions in two major metabolic pathways including the tetrahydrofolate-dependent one-carbon cycle and the salvage pathway for methionine. Its dysfunction has several physiological ramifications and leads to the development of megaloblastic anemia. In addition, it is suspected to be involved in the pathogenesis of neural tube defects. An issue that is central in weighing therapeutic options for methionine synthase-related disorders is the extent to which the enzyme exists as apoenzyme in vivo and, thus, can be potentially responsive to vitamin B12 therapy. despite the importance of this issue, the extent of holo- versus apoenzyme in mammalian tissue is controversial and unresolved. To address this question, we have developed a convenient anaerobic assay that employs titanium citrate to deliver low potential electron equivalents. The reductive activation of this enzyme is essential under in vitro assay conditions. We find that both the human placental and porcine liver methionine synthases exist predominantly in the holoenzyme form (90-100%) in the crude homogenate. In addition, the activity of the pure enzyme measured in the titanium citrate assay is also independent of exogenous cofactor, revealing that the cobalamin is tightly bound to the active site.
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