Meristemos

Meristemos, also called meristems in English, are plant tissues consisting of undifferentiated cells with the capacity to divide and give rise to all major tissue types. They enable indeterminate growth and the ongoing formation of new organs such as leaves, stems, and roots. Meristematic cells are typically small, with dense cytoplasm and large nuclei, and they retain the ability to divide; their derivatives differentiate into epidermal, ground, and vascular tissues.

Meristems are grouped by position and function. Apical meristems occur at the tips of shoots and roots and are responsible for primary growth, lengthening the plant. Lateral meristems, including the vascular cambium and cork cambium, promote secondary growth and thickening. Intercalary meristems, found in many monocots, lie between mature tissue and contribute to growth in leaf blades or stem bases. The shoot apical meristem (SAM) produces new leaves and nodes, while the root apical meristem (RAM) generates root tissues and the root cap.

Meristem organization varies, but many share a stem cell niche with organizing centers and zones of proliferation and differentiation. In the SAM, a population of initial cells is maintained by signaling gradients and gene networks; in the RAM, initials give rise to most root tissues via a developmental program.

Hormonal regulation plays a central role. Auxin and cytokinin balance activity and organ formation; genetic regulators such as WUSCHEL and CLAVATA control stem cell maintenance in the SAM, while analogous circuits exist in other meristems.

Applications include plant propagation and biotechnology. Meristematic tissue, especially shoot tip meristems, is used in micropropagation to produce virus-free clones and to regenerate plants in tissue culture.