A role for preprophase bands of microtubules in maturation of new cell walls, and a general proposal on the function of preprophase band sites in cell division in higher plants

Abstract

Time-lapse video microscopy of dividing Tradescantia stamen hair cells that are undergoing cytokinesis has revealed that the maturation of the new cell wall is aided by factors at the site where the preprophase band of microtubules forms before mitosis. The wall changes from being fluid and wrinkled before it is inserted into the parental wall at the end of cytokinesis, to being stiff and flat by about 20 min after the time of attachment. This change occurs only if the new wall is inserted at the site formerly occupied by the preprophase band. The cell plate does not flatten when it is caused to insert elsewhere by drug treatments or by centrifugal displacement. If insertion at the correct site is delayed locally by centrifugation against the direction of expansion of the cell plate, then flattening is delayed at the same locality. In combination with a number of points from the literature of plant cell division, some of them very long-standing, our observations lead to a general proposal regarding the nature of the preprophase band site, its mode of action and timing of its operations, and how its role in spatial regulation of histogenesis is achieved.