Drugs with Colchicine‐like Effects that Specifically Disassemble Plant but Not Animal Microtubulesa

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Abstract
Mitosis is arrested in Haemanthus endosperm by amiprophos-methyl and oryzalin at a concentration of 100 nM, and anaphase chromosome movements are modified at 10 nM. Prolonged exposure to these drugs results in a classical c-mitosis. Anaphase chromosome movement is arrested within less than 30 seconds without any detectable change of MT arrangement, as shown by the immunogold staining method. In the next phase of amiprophos-methyl and oryzalin action, however, all non-kinetochore MTs, and especially those most sensitive to these drugs, polar microtubules, which form abundantly during anaphase, disassemble. Kinetochore microtubules form tight bundles that are very resistant to further drug action and often elongate before they finally disassemble. Because these drugs inhibit MT assembly in vitro in a concentration-dependent manner, we conclude that MT assembly is required for chromosome movements in anaphase and that the elongation of polar MTs is necessary for the progress of anaphase. No effect of the drugs on mitosis was detected, even at the saturated level, in the tissue culture of the frog Xenopus.