Casparian strip

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Endodermis with Caspary stripes (in Equisetum giganteum )

The Casparian strip or Caspary strip (after the botanist Robert Caspary or Robert Caspari) is located in the cell walls of the endodermis and hypodermis cells of the roots . A hypodermis that is equipped with a Caspary strip is called an exodermis .

The Casparian strip blocks the passage of dissolved minerals , water and gases through the cell walls and intercellular spaces into the central cylinder . The transport in the apoplastic space - between the endodermis cells - is thereby stopped. In this way, minerals have to migrate through the passage cells of the endodermis and are consequently exposed to the control and selection of the symplastic space .

In the primary state, the Caspary strip is a few µm wide and consists mainly of lignin and endodermin, a substance similar to suberin , which is located in the interior of every endodermis cell. In the secondary state, most of the cells accumulate suberine lamellae as a secondary cell wall. The latest studies have shown that, despite secondary and tertiary deposits in the endodermis cells, water reaches the central cylinder relatively unhindered via the apoplastic route. Substances dissolved in the water, such as ions and organic compounds, are particularly hindered. The main task of these apoplastic barriers is above all to prevent ions actively pumped into the xylem from flowing back into the root cortex. The negative water potential built up in this way allows water to flow passively into the xylem. The root pressure built up in this way ensures a permanent water supply. Especially with monocots , lignified cellulose is deposited on the outer and side cell walls . This condition is called tertiary endodermis.

Nutrient salts that are already in the symplast get through the endodermis cells into the central cylinder. The xylem now transports the water and the nutrient salts upwards into the shoot system.

Individual evidence

  1. ↑ Lukas Schreiber, Rochus B. Franke: Endodermis and Exodermis in Roots . eLS. John Wiley & Sons, Chichester., Bonn 2011, doi : 10.1002 / 9780470015902.a0002086.pub2 .
  2. ↑ Elmar Weiler , Lutz Nover; Founded by Wilhelm Nultsch : General and molecular botany . Thieme, Stuttgart 2008, ISBN 978-3-13-147661-6 , p. 120-121 .