pericycle

The pericycle is a plant tissue that forms the outermost layer of the root stele, lying just inside the endodermis and surrounding the vascular tissue. It typically consists of one to several layers of parenchyma-like cells that can become sclerenchymatous with age. The pericycle originates from provascular tissue during embryogenesis and remains meristematic in many roots, retaining the capacity to divide in mature tissue.

The primary function of the pericycle is to initiate lateral roots. Lateral root primordia arise from pericycle cells that re-enter the cell cycle, proliferate, and push through the endodermis and cortex to emerge as new roots. In addition to this role, the pericycle can contribute to secondary growth by giving rise to lateral meristems such as the vascular cambium, and in some species also the cork cambium, thereby supporting thickening of the root.

Relation to surrounding tissues: The pericycle is enclosed by the endodermis, which contains Casparian strips, and forms a boundary around the vascular cylinder. It is distinct from the cortex and its activity is influenced by hormonal signals, particularly auxin, which promotes lateral root initiation.

Significance: The pericycle plays a crucial role in root architecture by enabling branching and, in many plants, participating in the formation of vascular cambia that contribute to secondary growth. Its meristematic potential allows it to respond to developmental and environmental cues to adapt the root system.