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The endodermis is a single layer of cells that is located between the cortex and the vascular tissues. It is the central, innermost layer of cortex in land plants.

In most of the seeded plants, endodermis is absent from the stems but is present in roots. On the other hand, in many seedless variants, it is a distinctly visible layer of cells immediately outside the vascular tissue layer in roots and shoots.

Its Structure

It is the central, innermost layer of cortex in land plants. It may consist of a single or several layers of compact, barrel-shaped or cylindrical, living, parenchymatous epidermal cells without any intercellular spaces. The radial primary cell walls of these epidermal cells are thickened on four sides and are also impregnated with a hydrophobic waxy substance, suberin. This waxy, water-impermeable substance gets deposited in distinctive bands called Casparian strips, which restrict apoplastic flow of water to the inside. These strips vary in width but are typically smaller than the cell wall on which they are deposited. In older endodermal cells, suberin may be more extensively deposited on all cell wall surfaces and the cells can become lignified, forming a complete waterproof layer. Some plants have a large number of amyloplasts (starch containing organelles) in their endodermal cells, in which case the endodermis may be called a starch sheath.

Function: What Does the Endodermis do

  1. The endodermis prevents water, and any solutes dissolved in the water, from passing through this layer via the apoplast pathway. Water can only pass through the endodermis by crossing the membrane of endodermal cells twice (once to enter and a second time to exit). Water moving into or out of the xylem, which is part of the apoplast, can thereby be regulated since it must enter the symplast in the endodermis. This allows the plant to control to some degree the movement of water and to selectively uptake or prevent the passage of ions or other molecules. Along with water, it also regulates the movement of ions and hormones into and out of the vascular system.
  2. Endodermal cells may contain starch granules in the form of amyloplasts. These may serve as food storage, and perception of gravity.
  3. The endodermis does not allow gas bubbles to enter the xylem and helps prevent embolisms from occurring in the water column.
  4. It forms a waxy seal around a plant’s vascular tissue, preventing the entry of harmful organisms and chemicals into the plant.

Article was last reviewed on Thursday, May 5, 2022

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