Detoxification of Herbicide

This strategy has led to commercial development of herbicide resistance for glu-fosinate, glyphosate and bromoxynil. Glufosinate and glyphosate resistance will be discussed in detail in later sections of this chapter (see also Chapter 6.2). Bro-moxynil s herbicide activity is due to inhibition of electron transport in photosystem II. Crops engineered with bromoxynil nitrilase metabolize the herbicide to a non-phytotoxic compound [5]. 

Detoxification has also been utilized to engineer resistance against several other herbicides, including various auxins such as 2,4-D and dicamba, diphenyl ethers (DPEs) such as oxyfluorfen and acifluoren, pyridines such as thiazopyr, and chloroacetanilides such as alachlor. To date, none of these have been developed into commercial products [3]. 

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In crop protection as well, understanding plant metabolism is of paramount importance to increase selectivity and to address resistance of chemical compounds. Moreover, dissipation of a compound in the aquatic ecosystem is very similar to the excretion phenomena of the bodies. An extensive amount of evidence has been accumulated to support the involvement of CYPs in the metabolism and detoxification of herbicides, fungicides and insecticides. The understanding of their biotransformations at the molecular level may be extremely helpful for herbicide- or insecticide-synergistic development. 

DETOXIFICATION OF HERBICIDES. Almost all herbicides are metabolized to some extent by higher plants. The selective use of herbicides is often possible because the rates and the mechanisms by which plants detoxify herbicides differ... 

Enhancing Biodegradation for Detoxification of Herbicide Waste in Soil... 

Isol. from wheat, in which it is present mainly as glucoside. Appears to be a natural aphicide and fungicide. Involved in the in vivo detoxification of herbicides, e.g. Simazine. Pink needles. Mp 156-157° dec. 

The biochemistry of crop selectivity has been well studied, but it is really only in the past decade, and with the advent of molecular tools, that we have started to obtain an understanding of the complexities involved. Detoxification of herbicides in plants is often a multi-step process and has more similarities to plant secondary metabolism than it has to plant tolerance to toxic compounds in the environment. The current understanding of the various processes involved in herbicide detoxification is summarized in Figure 1 (2,3). 

As indicated in Figure 1, a number of different enzymes participate in the detoxification of herbicides in plants. Some herbicides are acted on by only a single enzyme, whereas for others several modifications occur in sequence. Not surprisingly, the same enzymes that are responsible for selectivity of herbicides in crops are also responsible for herbicide resistance in weeds. 

Figure 6. Effect of inducers on detoxification of herbicides in wheat (M), herbicide susceptible L rigidum ( ) and herbicide-resistant L rigidum (M), Bars are the mean amount ( SE) of herbicide remaining 24 h after treatment The CYP inducers naphthalic anhydride (NA, I mM), 2,4-D (500 juM), phenobarbital (PB, 1 mM) and ethanol (EtOH, 3%) were applied in hydroponic culture 24 h prior to the addition of herbicides (Preston, C. unpublished data).

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