Inhibition of Plant Microtubule Polymerization in vitro by the Phosphoric Amide Herbicide Amiprophos-Methyl

The phosphoric amide herbicide amiprophos-methyl (APM) produced a concentration-dependent inhibition of taxol-induced rose microtubule polymerization in vitro. Parallel studies on taxol-induced assembly of bovine brain microtubules showed no effect of APM at a concentration ten times that required to give complete inhibition of rose microtubule assembly. The data indicate that (i) APM is a specific and potent antimicrotubule drug and (ii) APM directly poisons microtubule dynamics in plant cells, rather than indirectly depolymerizing microtubules through a previously proposed mechanism involving deregulation of intracellular calcium levels.