Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 3/15/2000
Publication Date: N/A
Technical Abstract: Approximately one quarter of all of the marketed herbicides are classified in the mitotic disrupter herbicide group, including the widely used dinitroaniline and carbamate herbicides. Most of the herbicides in this grouping are used commercially to control grasses and other small-seeded weed species in larger-seeded dicot crop species. Grass morphology of the seedlings after treatment with mitotic disrupter herbicides is distinctly club shaped or swollen, compared to the uniformly tapered roots found in untreated controls, and are similar to those effects noted for the classical microtubule disrupter colchicine. Microscopic examination of herbicide-treated roots reveals concentration dependent loss of microtubules, with phragmoplast and spindle arrays being the ones affected at lowest concentrations and cortical and kinetochore microtubules being the least affected. The loss of these microtubule arrays results in the production of irregular cell walls, C-metaphase figures, and lobed nuclei. Loss of the cortical microtubule array results in isodiametric growth, which leads to the root clubbing the zone of root elongation. Limited biochemical analysis indicates that the herbicides oryzalin and pronamide (propyzamide) bind directly to tubulin and that the carbamates and phosphoric amides can inhibit in vitro polymerization, indirectly, confirming this site of action for these herbicides as well. A possible non-tubulin site has been suggested for the herbicide dithiopyr, although the effects induced by this herbicide are identical to other members of this group. Data from both resistant mutants and molecular modeling analysis indicates that the dinitroanilines and phosphoric amides bind to a similar site.