Casparian strip
/kæˈspɛriən strɪp/
Definition
Casparian strip is a band of waterproof material, mainly lignin, in the radial and transverse walls of endodermal cells in roots. This plant structure blocks water and dissolved minerals from moving between cells through cell walls, forcing them to cross cell membranes instead. By regulating this pathway into the vascular tissue, the casparian strip helps plants control nutrient uptake and limit the entry of harmful substances.
Function in Plants
- Selective uptake at the root: In roots, the casparian strip forces water and dissolved minerals to cross cell membranes before entering the vascular system. That checkpoint helps the plant regulate which ions move inward.
- Barrier against backflow: Once materials reach the stele, the casparian strip helps limit leakage back into outer root tissues. This supports efficient transport toward stems and leaves.
- Protection from harmful solutes: By blocking the free apoplastic route, the casparian strip can reduce uncontrolled entry of excess salts and some toxic substances. Its effectiveness depends on root age, species, and growing conditions.
- Part of root maturation: The casparian strip forms as root tissues develop, especially in the endodermis. It works alongside later wall changes, such as suberin deposition, that further strengthen the root's internal barrier system.
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