Depolymerization of microtubule arrays in root tip cells by oryzalin and their recovery with modified nucleation patterns

Immunofluorescence microscopy with anti-tubulin has been used to study the effects of the dinitroaniline herbicide, oryzalin, on microtubule arrays in root tip cells of a number of species of plants. All species of grasses that were examined showed rapid microtubule depolymerization, as did the nongrass Potamogeton. All other nongrass monocotyledons and dicotyledons tested required much longer treatment times to achieve microtubule depolymerization in the majority of root tip cells. Correlated immunofluorescence and electron microscopy have been used to obtain details of depolymerization and repolymerization of microtubules during treatment and recovery in a resistant plant, Zinnia elegans, and in a sensitive plant, Lolium rigidum. Although rates of disruption differ, both plants displayed similar patterns of microtubule depolymerization and repolymerization. The microtubules that comprise the different categories of array in the root tip cells were differentially sensitive to oryzalin. In order of increasing stability they were as follows: polar microtubules in mitotic cells < interphase arrays < preprophase bands ≤ phragmoplasts [Formula: see text] kinetochore microtubules. During recovery, microtubules are nucleated in the cell cortex in interphase and at the kinetochores during mitosis. The cells are able to reinstate cortical interphase arrays, preprophase bands, and phragmoplasts of apparently normal organization, but not normal, functional spindles. Our results provide basic information on the use of oryzalin in studying the organization and dynamics of microtubule arrays in higher plant cells.