Endodermisen

Endodermisen, known in English as the endodermis, is a plant tissue that surrounds the vascular cylinder (stele) in the roots and, in some plant species, in the stems. It forms a single layer of compact cells that encircle the stele and lie between the cortex and the central vascular tissues. The mature endodermal cells typically display thickened walls due to suberin and sometimes lignin, especially in the radial walls where the Casparian strip is located. The Casparian strip is a band of cell wall impregnated with suberin and lignin that blocks the apoplastic flow of water and solutes, forcing them to cross cell membranes via the symplastic route through the endodermal cytoplasm and plasmodesmata.

The endodermis acts as a selective barrier, regulating the uptake of minerals and water from the soil into the vascular tissue, preventing the uncontrolled loss of nutrients back into the soil. It contributes to ion homeostasis and helps the plant respond to varying soil conditions, including salinity and drought.

Endodermal cells derive from the ground meristem. The Casparian strip forms as cells differentiate, sealing the radial walls; in some roots there are exodermal or passage cells that modify the barrier properties. In aging roots, suberin deposition can increase, tightening the barrier.

In animals, endoderm refers to a germ layer; the plant endodermis is unrelated, despite the similar name. The term endodermisen is sometimes used in Finnish or related languages to denote this structure.