Ion-mediated increase in the xylem hydraulic conductivity of Laurel stems: role of pits and consequences for the impact of cavitation on water transport

Changes in hydraulic conductivity (Kh) were measured in stems of Laurus nobilis L. during perfusion with KCl, NaCl or sucrose solutions. Ionic solutes induced marked increase of Kh with respect to deionized water but sucrose had no effect. The kinetics of KCl-induced Kh increase was measured together with changes in [K+] of the perfused solution. Kh increases were paralleled by increases in the [K+]out/[K+]in ratio. Samples of different lengths or with increasing percentage loss of conductivity (PLC) due to xylem cavitation were tested, with the aim of increasing radial flow through intervessel pits. KCl solutions enhanced the Kh of 12-cm-long samples with a concentration-dependent effect up to 100 mm KCl. ΔKh increased from 3 to 30% in 1.5- and 12-cm-long samples, respectively and remained constant for longer samples. Increasing PLC induced an exponential increase in ΔKh.