Figure 7.

Graphic summary of the cellular organization and division dynamics in the Ceratopteris richardii first stem-borne root. (A) Roots are divided in three zones: meristematic, elongation, and differentiation zone. Ceratopteris root presents two main zones: meristematic and elongation/differentiation zones. The roots of Azolla and Arabidopsis are represented for comparison purposes. (B) In a longitudinal section, the boundary between meristematic and elongation/differentiation zones is established where the cell length begins to expand. For Azolla and Ceratopteris, the outer cortex layer has a reliable morphology. The size of root apical meristem varies considerably among the three species depicted here. (C) Radial organization changes along the longitudinal axis in a shootward manner. The different tissues would mature according to the position and differentiation stage of the merophytes, from one undifferentiated cell to lineage-specific cells: (Left) The RAC and its merophytes are surrounded by root cap cells. (Middle) Cell transitions from merophytes to specific layer initials. (Right) Differentiated tissues with specific traits. (D) Different cell types of the RAM have different cell cycle activity, based on EdU incorporation analysis. The RAC has a higher activity compared to its derivatives.