Some Cytological Changes accompanying the Regeneration of Meristematic Activity at the Apex of Decapitated Roots of Vicia faba L.

The changes that took place in mitotic index (MI), labelling index (LI) and the relative proportions of interphase nuclei with different amounts of DNA have been investigated during the regeneration of meristematic activity at the apex of roots of Vicia faba over the 144 h period following removal of the cap and apical mm of the meristem. Measurements were also made of the corresponding changes that took place as cells were displaced basally along the root from the apex over the experimental period. In both parts of the root, MI and the relative proportions of nuclei with different DNA contents changed from levels similar to those at the apex of the controls at the start and end of the experiment to levels resembling those found in more mature parts of the root at 24 and 48 h. In contrast to these results, LI declined over the experimental period. These cytological changes were aresult of the development of lateral root primordia in both the apical 2 mm of the decapitated roots and as cells were displaced out of the meristem into more basal parts of the root. It was concluded that the events leading to the regeneration of meristematic activity at the apex of roots from which the cap and apical mm of the meristem were removed, are no different from those which result in lateral formation as cells are displaced basally along the primary root from the apex, and they take place over the same time interval in both systems.