Premitotic stages of experimentally induced vascular differentiation were investigated by confocal laser scanning-fluorescence and electron microscopy. Activation of former quiescent and highly vacuolated cortex cells, observed in living and in fixed tissue, involves a centripetal movement of the nucleus along newly-formed, thick cytoplasmic strands. These traverse the large vacuoles with angles different from the former polar axis, thereby anticipating the orientation of later developing phragmosomes, future divisions, and the course of wound-vascular elements.

A premitotic increase in cellular activity is reflected by the number of mitochondria, rough ER-cisternae, active dictyosomes and dense cytoplasm as well as by shape of nuclei and development of “nucleolar vacuoles”. Microtubules occur in parallel arrays running through the transvacuolar strands and radiating from the nucleus towards the cell wall. They might be responsible for the centripetal movement of the nucleus through the vacuole and/or might participate on the orientation of the plane of a future division. Preprophase bands were not detected in cortex cells of the investigated root region, which prior to wounding were already fully elongated.