Researchers at the University of Tokyo and Aberdeen University have identified the master switch for formation of the Casparian strip, a special structure in the root that plays an important role in nutrient uptake. The Casparian strip is made of lignin, the main component of wood, deposited in a particular location the anticlinal cell wall in between endodermal cells in the root. By filling the gap between cells, the Casparian strip prevents harmful materials from entering into plants and also prevents leakage of nutrient from roots.
Casparian strip CS is an impregnation of endodermal cell wall, forming an apoplastic diffusion barrier which forces the symplastic and selective transport of nutrients across endodermis. This extracellular structure can be found in the roots of all higher plants and is thought to provide the protection of vascular tissues. In Arabidopsisa genetic toolbox regulating the formation of Casparian strips has emerged recently.
In a growing plant root, the inner vascular system is sealed off by an epithelium, the endodermis. The space between all of the cells in the endodermal layer is filled with an impermeable mass called the Casparian strip, which closes the spaces between cells in the endodermal layer. The role of the Casparian strip has been proposed to prevent backflow of water and nutrients into the soil, but as mutant plants lacking the Casparian strip only have weak phenotypes, the view that it serves an essential function in plants has been challenged.
The Casparian strip, which is specific to roots, was studied in the epicotyls of dark-grown seedlings of pea Pisum sativum L. In dark-grown seedlings, the distance between the upper-most position of the Casparian strip and the bending point of the hook about 37 mm did not change during growth of the seedlings. In the uppermost 0. The development of the Casparian strip continued for about 42 h after dark-grown seedlings were transferred to the light, indicating that i the cells that have been determined to form the Casparian strip in darkness form the strip in the light, and that ii it takes about 42 h for the cells to complete formation of the strip.
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Casparian strip A band of suberinan impermeable substance, found in the endodermal cell walls of plant roots; it was named after R. Movement of water through the apoplast pathway is diverted from the cell wall to the cytoplasm, where it then follows the symplast pathway. The endodermal cells actively secrete salts into the vascular tissue.
Lignification and suberization of Casparian strips occurred simultaneously during the development of Cunninghamia lanceolata primary roots. The Casparian strips in the cell walls of vascular plant root endodermis and exodermis cells are vital for the exclusion of salts and pathogens, selective nutrient uptake, and other processes related to the transport and assimilates of water. Despite the importance of Casparian strips, their chemical composition and its relevance to their diffusion barrier functions remain a matter of debate, especially in woody plants.