Transition zone cells reach G2 phase before initiating elongation in maize root apex

Abstract

Root elongation requires cell divisions in the meristematic zone and cell elongation that occurs in the elongation zone. The boundary between dividing and elongating cells is called transition zone. In the meristem zone, initial cells are continuously dividing, but in the basal side of the meristem, cells exit the meristem through the transition zone and enter in the elongation zone, where they stop division and rapidly elongate. In this journey, cells are accompanied by changes in cell cycle progression. Flow cytometry analysis showed that meristematic cells are in cycle, but they exit the cell cycle when they enter the elongation zone. In addition, the percentage of cells in G2 phase (4C) strongly increased from meristem to elongation zone. However, we did not observe remarkable changes in the percentage of cells in cell cycle phases along the entire elongation zone. These results suggest that meristematic cells in maize root apex stop cell cycle in G2 phase after leaving the meristem.