Whole-plant studies, advantage

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. 

The biosynthetic sequence of alkaloid production in M. cordata was also determined by means of HC using both whole plants and root pieces. It is advantageous in the HC study of metabolic sequences in plants to feed small amounts of compounds (2 mg in 5 ml of solution in this experiment) and stable isotopically labeled compounds instead of radioisotopes. 

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). 

The main advantages of immobilizing whole cells over the isolated enzymes are (i) cells are more resistant to changes in pH or temperature and (ii) a single cell can contain all the enzymes and cofactors needed for bioconversion of the analyte [82], Most of the whole cell-based optical biosensors used in toxicity or bioremediation studies [83,84] employ microorganisms [85— 87], animal [88], plant tissues [89,90] or cell receptors [91] as biorecognition elements. 

Stable isotopes studies. Numerous researchers have taken advantage of the difference in carbon isotope fractionation during photosynthesis of plants with C3 and C4 photosynthetic pathways as a natural tracer to study soil carbon dynamics (Balesdent et al., 1987). If a C3 forest is converted to a C4 pasture or C4 agricultural field, the whole soil carbon turnover time (t) can be calculated as... 

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