SPLINE AND FLAGELLAR MICROTUBULES ARE RESISTANT TO MITOTIC DISRUPTER HERBICIDES

Microtubule arrays in developing spermatogenous cells of pteridophytes have unique microtubule organizing centers and post-translation modif ications of tubulin. Sensitivity of these arrays to the microtubule-de stabilizing effects of the mitotic disrupter herbicides was examined b y immunofluorescence, transmission and immunogold electron microscopy. Acetylated, stabilized arrays, such as the spline, and microtubules o f the basal bodies and flagella are formed after the final mitotic div ision and are resistant to these herbicides. Non-acetylated, dynamic a rrays that exist prior to the final mitosis, such as interphase and mi totic arrays, are eliminated by all of these herbicides, with symptomo logy (arrested prometaphase, lobed nuclei, irregular cell plate format ion) similar to that observed in other land plants. The only exception to the instability of these mitotic microtubule arrays are the few mi crotubules that are collected by kinetochores into short tufts. The pr esence of structurally-distinguishable MTOCs, such as the blepharoplas t, did not confer resistance, despite the anchoring of the minus ends of the microtubules. Simultaneous treatment with herbicide and 5-bromo deoxyuridine (BrdU), with subsequent detection with anti-BrdU of cells that had gone through S-phase during the BrdU incubation, reveals tha t only acetylated arrays formed prior to herbicide treatment are resis tant. These data indicate that only actively polymerizing, dynamic mic rotubule arrays are sensitive to the destabilizing effects of the mito tic disrupter herbicides.