Cell proliferation during the development of lateral root primordia

Abstract

Outside the apieal meristem, the most prominent group of proliferating cells in roots are those representing stages in the development of lateral root primordia. Thus, of the 231 500 cells in meristems, excluding the pericycle, in the apical 9.8 cm of roots of intact plants of Zea mays, 125 000 are confined to the apical meristem of the primary [3] and 106 500 to developing lateral root primordia [data derived from 18]. Unlike the single apical meristem, however, lateral root anlagen occur as numerous groups of initial cells along the primary and not as one discrete cluster. Moreover, lateral root primordia form a different type of meristematic system to that found at the root apex. Thus, root apical meristems are open systems, in the sense that cells are continuously lost at their proximal and distal margins. Also, once established, they do not fluctuate in cell number [23]. In contrast, since no cells are lost from developing lateral root primordia, they increase in cell number from the time of their initiation until secondary root emergence.