Metribuzin metabolism

Falb, L.N. and A.E. Smith Jr. (1984). Metribuzin metabolism in soybeans Characterization of the intraspecific differential tolerance. J. Agric. Food Chem., 32 1425-1428. 

Frear, D.S., E.R. Mansager, H.R. Swanson, and F.S. Tanaka (1982). Metribuzin metabolism in tomato Isolation and identification of N-glucoside conjugates. Preprint. Miles Ag. Div. Report Number 82481.2... 

Smith, A.E., S.C. Phatak, and D.A. Emmatty (1989). Metribuzin metabolism by tomato cultivars with low, medium, and high levels of tolerance to metribuzin. Pestic. Biochem. Physiol., 35 284-290. 

Gawronski, S.W., L.C. Haderlie, and J.C. Stark (1987). Metribuzin metabolism as the basis for tolerance in barley (Hordeum vulgare L.). 

Plant. Metribuzin is metabolized in soybean plants to a deaminated diketo derivative which is nonphytoxic (Duke et al., 1991). 

The triazine herbicides can be divided into four different structural classes chlorotriazines, methylthiotriazines, methoxytriazines, and atypical or asymmetrical triazines. The chlorotriazine group includes atrazine, simazine, pro-pazine, terbuthylazine, and cyanazine. The methylthiotriazine group includes ametryn, prometryn, and terbutryn. The methoxytriazine group will include prometon and secbumeton. Hexazinone and metribuzin were chosen to represent the atypical triazine group. The plant metabolism of the most researched member of each triazine group will be discussed in detail to cover all major biological and chemical transformations reported in the literature. 

Metribuzin is a member of the substituted as-triazinone group of herbicides. Activity is due to interference with photosystem II electron transport in plant chloroplasts (Dodge, 1983). The metabolism of metribuzin in plants has been the subject of many short-term and long-term studies dating back to the early 1970s. 

The short-term metabolism of metribuzin may involve two major nonconjugative pathways, two major conjugative pathways, and/or production of nonextractable residues. 

Figure 7.14 Metabolism of metribuzin to deaminated diketo metribuzin in various plants.

The long-term metabolism of metribuzin is very complex. Given the extended length of these experiments, identifying the individual metabolic pathways has been very challenging. Also, some degradation of metribuzin occurs in the treated soil before plant uptake occurs (Schumacher, 1974 Prestel et al, 1976). 

Figure 7.18 The short-term metabolism of metribuzin in soybean.

In long-term plant metabolism studies (Gronberg et al, 1971 Morgan, 1972, 1973, 1974 Church and Flint, 1973 Hilton et al, 1974,1976 Stanley and Flint, 1974 Lenz et al, 1987 Schocken et al, 1987) very little free metribuzin, DA, or DK were detected (0.1-15%). The majority of the organosoluble material was DADK (2-35%). 

Abusteit, E.O., F.T. Corbin, D.P. Schmitt, J.W. Burton, A.D. Worsham, and L. Thompson Jr. (1985). Absorption, translocation, and metabolism of metribuzin in diploid and tetraploid soybean (Glycine max) plants and cell cultures. Weed Sci., 33 618-628. 

Davis, D.G., P.A. Olson, H.R. Swanson, and D.S. Frear (1991). Metabolism of the herbicide metribuzin by an V-glucosylIrans(erase from tomato cell cultures. Plant Sci., 74 73-80. 

Devlin, D.L., D.R. Gealy, and L.A. Morrow (1987). Differential metabolism of metribuzin by downy brome (Bromus tectorum) and winter wheat (Triticum aestivum). Weed Sci., 35 741-745. 

Saeman, M.C. (1984). Chemical and Metabolic Oxidation of the Herbicide Metribuzin [Dissertation], Berkeley, CA University of California, p. 94. 

Saeman, M.C., M.T. Smith, and J.E. Casida (1985). Metabolism and toxicity of metribuzin in mouse liver. Pestic. Biochem. Physiol., 23 123-130. 

Schumacher, R.W. (1974). Metabolism of Metribuzin in Soybeans and Soil [Dissertation], Lexington, KY University of Kentucky, p. 91. 

Smith, A.E. and R.E. Wilkinson (1974). Differential absorption, translocation and metabolism of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] by soybean cultivars. Physiol. Plant., 32 253-257. 

Figure 9.2 Metabolism of metribuzin in plants. aGlu = glucose. bMal = malonyl Mal-Glu, malonyl glucose.

Several processes may play a role in the environmental dissipation of -triazine herbicides. Dissipation processes can include microbial or chemical degradation in soil metabolism or conjugation in plants photodegradation in air, water, and on soil and plant surfaces and volatilization and transport mechanisms. This chapter will address photolytic degradation and abiotic hydrolysis of the currently used triazine herbicides, the triazinone herbicides (metribuzin and metamitron), and the triazinedione herbicide hexazinone. 

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