Plant pesticide metabolism

Because of the Importance of GSH conjugation In pesticide metabolism and the diversity of the plant kingdom. It seemed desirable to study the catabolism of another GSH conjugate In several plant species. Pentachloronltrobenzene-UL- C,... 

Shimabukuro, R. H. Lamoureux, G. L. Frear, D. S. Pesticide Metabolism in Plants Reactions and Mechanisms, Proceedings of the US-India Seminar on Biodegradable Pesticides, April 16-19, 1979, Lucknow, India. 

This paper is the only one in the liquid chromatography portion of this symposium which will attempt to deal with chromatography specifically from the viewpoint of the pesticide metabolism chemist. A residue analyst knows what compound he must analyze for, and develops his method with the properties of that substance in mind. On the other hand, the pesticide metabolism chemist has a different problem. At the conclusion of the treatment, exposure, and harvest phases of a radiolabeled metabolism study, he divides his material into appropriate samples, and extracts each sample with selected solvents to obtain the radioactive materials in soluble form. Typically these extracts consist of low levels (ppm) of carbon-14 labeled metabolites in a complicated mixture of normal natural products from the plant, animal, or soil source. The identity of each metabolite is unknown, and each must be isolated from the natural background and from other labeled metabolites in sufficient quantity and in adequate purity for identification studies, usually by mass spectrometry. The situation is rather like looking for the proverbial "needle in the haystack" when one does not know the size, shape,or composition of the needle, or even how many needles there are in the stack. At this point a separation technique must be selected with certain important requirements in mind. 

Cooper et al. [86] analyzed environmental matrices derived from soil, plant, and animal extracts to study an insecticide, a fungicide, and their metabolites. The clean-up steps consisted simply of removal of the solid debris by centrifugation and filtration. The authors recognized that while retention time reproducibility was satisfactory for a study of pesticides metabolism, in order to achieve the sensitivity required for this type of analysis a sample preconcentration step was required before the CEC separation. 

In this volume of Annual Plant Reviews, we have tried to provide an up-to-date survey of the biochemistry and physiology of plant secondary metabolism. A companion volume - M. Wink (ed.) Functions of Plant Secondary Metabolites and Biotechnology - published simultaneously provides overviews of the modes of action of bioactive SMs and their use in pharmacology as molecular probes, in medicine as therapeutic agents and in agriculture as biorational pesticides. 

The study of xenobiotic metabolism has developed rapidly during the past few decades. These studies have been fundamental in the assessment of drug efficacy, safety, and design of dosage regimens in the development of food additives and the assessment of potential hazards of contaminants in the evaluation of toxic chemicals and in the development of pesticides and herbicides and their metabolic fate in insects, other animals, and plants. The metabolism of many xenobiotics is fundamental to many toxic processes such as carcinogenesis, teratogenesis, and tissue necrosis. Often the same enzymes involved in... 

Use of Plant Cell Cultures in Pesticide Metabolism Studies... 

The use of plant cell cultures in pesticide metabolism studies has a history of only about 20 years, but pioneers of the technique have laid the groundwork for an increasing number of researchers interested in the advantages the cell culture systems offer. Host have chosen to use suspension cultures, because of the ease with which they can be manipulated, and the increased possibility for standardization of conditions from laboratory to laboratory. As an adjunct to whole plant studies cell cultures provide information as to the changes that structural modifications of a basic molecule may have on phytotoxicity, especially in detecting the inherent toxicity of a molecule that fails to penetrate or translocate in a whole plant. 

All of the comparative metabolism studies have shown that qualitatively there is little difference in pesticide metabolism in plants and cell cultures. Quantitative differences, either in the rate of conversion to a single product or relative inportance of one pathway over another, do occur. Some of these differences may be of biological significance and would require the use of whole plants or plant parts to confirm the quantitative aspects of metd)olism. 

Pioneers in the use of plant cell systems for studies of xeno-biotic phytotoxicity and metabolism have laid the groundwork for an increasing number of researchers interested in the advantages the cell systems offer (4 6-9). Greater emphasis on the identification of pesticide metabolites formed in whole plants and cell cultures has made evaluation of both systems more meaningful. Although the literature is nearly devoid of studies concerning diaracterization of enzyme systems from plant cell cultures that may be responsible for pesticide metabolism reference to the cell cultures as a convenient source has been made (10). 

Much of the literature on the use of plant cell cultures in pesticide research concerns herbicide metabolism and it will be emphasized here. However the comparative metsbolism of other classes of pesticides in plants and plant cell cultures will also be reviewed. The advantages and disadvantages of plant cell cultures in pesticide metabolism studies will be presented and a prognosis of the future attempted. 

Comparative Pesticide Metabolism in Plants and Plant Cell Cultures... 

In general, studies of pesticide metabolism in cell cultures have shown that metabolism is qualitatively similar to that of the whole plant, but quantitative differences do exist. Whole plants or plant parts need to be used to confirm the quantitative aspects of pesticide metabolism observed in plant cell cultures. However, cell cultures can be used to estimate the phytotoxicity and metabolic fate of chemicals that exhibit poor uptake and mobility in whole plants. Thus, they provide an inq>ortant adjunct to whole plant studies. In addition, higher yields of minor or transitory metabolites can usually be achieved in cell cultures, allowing the determination of a sequence of metabolic steps in a reaction. 

We must always recognize that pesticide metabolism studies cannot be considered as an end in themselves but rather, they are a means toward an end. For the ultimate value of a metabolism study, be it in microorganisms, plants, birds, laboratory mammals, or v atever, is its yield of data valuable toward further assessment of the toxicological significance of the pesticide in question to lower organisms (i.e., its environmental impact) or, more importantly, to assess toxicological significance to man himself. 

An important specialized use of TLC involves the separation, identification, and measurement of radioisotopes. The principal methods used are autoradiography, liquid scintillation counting, and direct scanning using a radiation detector interfaced with a computer for data collection. Radiolabeled compounds are used in radiotracer methods to follow the course of chemical and biochemical reactions, e.g., the study of pesticide metabolism in plants and animals (205), and drugs in humans. 

This review will focus on similarities and differences of pesticide metabolism by plants and prokaryotic organisms. Examples of pesticide biotransformations will be used to illustrate how these metabolic processes can affect efficacy, environmental fate, and persistence. 

Physiological Processes in Plants and Prokaryotes and Potential for Pesticide Metabolism... 

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