Root pressure and beyond : energetically uphill water transport into xylem vessels?

The thermodynamics of root pressure remains an enigma up to the present day. Water is transported radially into xylem vessels, under some conditions even when the xylem sap is more dilute than the ambient medium (soil solution). It is suggested here that water secretion across the plasma membrane of...

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Publié dans:Journal of experimental botany. - 1985. - 65(2014), 2 vom: 01. Feb., Seite 381-93
Auteur principal: Wegner, Lars H (Auteur)
Format: Article en ligne
Langue:English
Publié: 2014
Accès à la collection:Journal of experimental botany
Sujets:Journal Article Aquaporin CCC transporters cohesion–tension (CT) theory embolism repair reflection coefficient root pressure water ascent water co-transport hypothesis xylem refilling. plus... Aquaporins Water 059QF0KO0R
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520 |a The thermodynamics of root pressure remains an enigma up to the present day. Water is transported radially into xylem vessels, under some conditions even when the xylem sap is more dilute than the ambient medium (soil solution). It is suggested here that water secretion across the plasma membrane of xylem parenchyma cells is driven by a co-transport of water and solutes as previously shown for mammalian epithelia (Zeuthen T. 2010. Water-transporting proteins. Journal of Membrane Biology 234, 57-73.). This process could drive volume flow 'energetically uphill', against the free energy gradient of water. According to the model, solutes released by xylem parenchyma cells are subsequently retrieved from the sap at the expense of metabolic energy to maintain the concentration gradient that drives the water secretion. Transporters of the CCC type known to mediate water secretion in mammalian cells have also been found in Arabidopsis and in rice. The mechanism proposed here for root pressure could also explain refilling of embolized vessels. Moreover, it could contribute to long-distance water transport in trees when the cohesion-tension mechanism of water ascent fails. This is discussed with respect to the old and the more recent literature on these subjects 
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