How are shoot meristems organized?
There are approximately 100 cells in the SAM of Arabidopsis thaliana. These cells are organized in two ways: cells are organized in radial zones and also in layers. Radial organization: Cells that are at the very top of the meristem divide infrequently. This region is called the central zone. This is the location of the self-renewing undifferentiated stem cells. Surrounding the central zone is the peripheral zone. The rate of cell division in the peripheral zone is higher than that of the central zone. Peripheral zone cells give rise to cells which contribute to the organs of the plant, including leaves, inflorescence meristems, and floral meristems. Below the central zone is another region of rapidly dividing cells, called the rib meristem. Division and elongation of rib meristem cells gives rise to the stem of the plant. Layer organization: The surface layer(s) of cells (L1) divides only by forming anticlinal cell walls – that is, cell division is always perpendicular to the meristem
