Impermanency of Initial Cells in Huperzia lucidula (Huperziaceae) Shoot Apices

AbstractStructural changes in apical meristems accompany morphological specialization and adaptation of vascular-plant sporophytes to changing environments. Analysis of cell clones at the shoot apical meristem surface of a representative of the basal vascular plants made it possible to trace the dynamics of initial cells, which are recorded in cell wall arrangements. The cellular pattern at the summit of the Huperzia lucidula (Michx.) Trevisan shoot apical meristem is usually composed of four initial cells, forming a tetrad at the apex center, and their derivative clones. Our data show that the apical initial cells present at a given time in a tetrad often are transient and replaced by new initials in the ontogeny of a given Huperzia apex. Specifically, the process of dichotomous branching leads to extensive cell division, resulting in a pool of potential initial cells from which the new initial centers of the twin axes are selected. The ability to specify newly arisen cells as initials during shoot dicho...