Casparian

Casparian typically refers to the Casparian strip, a key feature of plant root anatomy. The Casparian strip is a band-like region of the endodermal cell walls that is impregnated with suberin and often lignin. This layer forms a continuous ring around the endodermis, creating a selective barrier between the cortex and the central vascular cylinder (the stele). The appearance and degree of suberization can vary among species and along the length of a root, and some endodermal cells have specialized “passage cells” with thinner walls that allow more direct transport.

Functionally, the Casparian strip restricts the apoplastic movement of water and dissolved substances through the cell walls. By blocking this extracellular pathway, minerals and other solutes must cross the plasma membranes of endodermal cells to reach the stele, enabling the plant to regulate uptake and prevent the passive influx of potentially harmful ions. Water movement is also influenced by this barrier, contributing to the control of root hydraulic conductivity.

Development and variation are influenced by developmental stage, environmental conditions, and species. As roots mature, suberization typically increases, strengthening the barrier. Passage cells provide a regulated route for certain substances to bypass the barrier when necessary.

The Casparian strip is a defining feature of the endodermis in vascular plants and is named after the German botanist Caspary, who described the structure in the 19th century. Its presence is central to discussions of plant nutrient uptake and root physiology.