Casparian strip

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

The Casparian strip blocks the passage of dissolved minerals, water and gases through the cell walls and intercellular spaces in the central cylinder. Transport in the apoplastic space - between the Endodermiszellen through - will stop it. In this way, minerals must travel through the passage cells of the endodermis and consequently the control and selection of the symplastic space exposed.

In the primary condition of the Caspary Strip few microns wide and consists mainly of lignin and from Endodermin, a substance similar to suberin, which is located any Endodermiszelle inside. In the secondary state, most cells attach as secondary cell wall on Suberinlamellen. Recent studies have shown that, in spite of secondary and tertiary Auflagerung in Endodermiszellen, water passes relatively unhindered through the apoplastic pathway in the central cylinder. Be prevented especially in water solutes such as ions and organic compounds. The main task, which belongs to these apoplastic barriers is to prevent above all things that actively pumped into the xylem ions can flow back into the root cortex .. The thus constructed negative water potential allows water to continue to flow passively into the xylem. Root pressure thus constructed provides a permanent water supply. Especially in monocots is additionally supported on the outer and lateral cell walls lignified cellulose. This condition is called tertiary endodermis.

Nutrient salts that are already in the symplast, pass through the Endodermiszellen in the central cylinder. The xylem transports water and now the nutrient salts upward into the shoot system.