Whole plants pesticide metabolism

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). 

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. 

To the pesticide scientist, phytoalexin research should still be of interest in spite of the fact that nothing commercially useful has yet emerged. There are ample indications that a considerable number of novel fungitoxlns remain to be uncovered in plants. These compounds are distinctive from constitutive antifungal substances often a different biosynthetic pathway is induced from those involved in normal secondary metabolism. Relatively few plants have yet been analysed in depth so that we still have a long way to go to understand fully this important disease resistance mechanism in the plant kingdom as a whole. 

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