Activation of embryo during rape (Brassica napus L.) seed germination II. Transversal organisation of radicle apical meristem

Abstract

Series of microtome cross sections of the root apical meristem were investigated in the mature embryo and young seedling of rape. The cell patterns are described in 3 layers of promeristem. Radial sectors of the root cap and protoderm, formed by common dermatocalyptrogen initials, and radial sectors of the cortex, produced by periblem initials were identified on all cross sections of the root. Between these sectors 4 segmentation boundaries of proembryo quadrants were distinguished, running across the whole root proper. The boundaries between the 4 sectors of connecting cells arising from the upper hypophysis derivative and the boundaries between the 4 sectors of the columella originating from the lower hypophysis derivative do not follow the same course and are not identical with the boundaries of the proembryo quadrants. Therefore during the whole embryogenesis, the central connecting cells, considered generally as cortex initials (iec), take no part in the development of the cortex but they form the quiescent centre of the radicle. Neither do the columella initial cells participate in the development of the lateral parts of the root cap.