The effect of trifluralin on the ultrastructure of dividing cells of the root meristem of cotton (Gossypium hirsutum L. ‘acala 4-42’)

ABSTRACT Ultrastructural studies of trifluralin-treated cells in lateral root meristems of cotton (Gossy-pium hirsutum L.) revealed that mitotic disruptions were due to the absence of microtubules. The extent of disruption varied between individual roots and correlated with the presence or absence of microtubules. Where microtubules were absent, cells began division with a normal prophase chromosome cycle. The chromosomes did not line up along a metaphase plate, but coalesced in the cell. If cell division had begun prior to microtubule disappearance the mitotic process was arrested at the stage that had been reached when the disappearance occurred. In some cell divisions randomly oriented microtubules were noted, with mitosis apparently arrested at those stages. Nuclear envelope reformation yielded cells that were polyploid, polymorphonucleate, binucleate, or occasionally multinucleate. If microtubules were present and if their orientation were normal, all stages of mitosis occurred. The range of mitotic disruption observed can be explained by the threshold concentration for microtubule disappearance being very near aqueous saturation of trifluralin.