Changes of pH of solutions during perfusion through stem segments: Further evidence for hydrogel regulation of xylem hydraulic properties?

Abstract

Changes in hydraulic conductivity (Kh) and pH were measured in stem segments of laurel (Laurus nobilis L.) during perfusion with iso-osmotic solutions of KCl, NaCl and sucrose. Sucrose had no effect on Kh while 100 mM NaCl or KCl induced up to 22 and 35 % increase of Kh with respect to deionized water, respectively. Increases in Kh were accompanied by a sharp drop in pH from 6.0 (inlet solution) to 5.0 (outlet solution). The same effect was observed with both KCl and NaCl solutions but not in the case of sucrose. Also, similar changes of Kh and pH were observed for stems killed after immersion in hot water. Our results might provide further evidence for ion-mediated regulation of xylem hydraulic conductivity based on the hydrogel properties of pectins at the pit membrane level. © 2008 Springer Science+Business Media B.V.