3.4: Apical Meristems

The term apical meristem refers to a group of meristematic cells at the apex of shoot and root that by cell division lay the foundation of the primary plant body. Meristems are composed of stem cells, which perpetuate the meristems, and their derivatives. In the shoot a more intensive meristematic activity is observed at levels where new leaves are initiated, as can be appreciated in the image on the right. The change from apical meristem to adult primary tissues is gradual and involves the intergrading of the phenomena of cell division, cell enlargement, and cell differentiation. While the shoot apical meristem drives the growth of the shoot aboveground, the root apical meristem drives the growth of the roots belowground. Often, the cells that comprise the meristems are small and tightly packed, and their most prominent cytologic features are a large central nucleus, numerous mitochondria, small vacuoles, extensive endomembrane system, and a dense, ribosome-rich cytoplasm. This is expected because these cells are highly metabolically active and are undergoing energy-intensive cell divisions that drive the apical growth of the shoots and roots.