A major goal of pesticide scientists has been to understand the precise mechanisms of action of pesticides. To this end numerous mechanisms of action have been postulated through reactions of fungicides with intact target organisms or interferences with target enzymes at the molecular level. However, in certain cases, it is always difficult to obtain conformity between the said mechanisms. On the other hand, in the past decade many procedures have become available for the isolation and culture of viable protoplasts from fungi or plants. In pesticide science, these procedures may open new prospectives for analyzing interactions between pesticides and target organisms in the minimum unit of living cells and for establishing more conformity between studies done at the intact organism and molecular level. The work which will be presented emphasizes how the techniques of using protoplasts and tissue culture can be applied in mechanism of action studies of pesticides, e.g. as indicated in the following examples: 1) Cytological and biochemical studies on fungicidal mechanisms: Our research has been focused on actions of fungicides on cell wall biogenesis, membrane functions, cell organelles and biosynthesis of cellular macromolecules in fungal protoplasts. Effects of fungicides, Polyoxin D and IBP, on regeneration of cell wall and organelles of Pyricularia oryzae were observed with an electron microscope. Then, effects on development of the microfibrils which are fated to form cell walls were checked by observing the specific bindings of sugars with lectins under a fluorescent microscope. Reactions of fungicides with intact organelles and membrane systems separated from protoplasts after osmotic shock were also analyzed. In biochemical studies, incorporation of radioactive precursors into proteins, nucleic acids, lipids and cell walls were checked using suspension cultures of protoplasts.
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