Light response of hydraulic conductance in bur oak (Quercus macrocarpa) leaves
Mihaela C. Voicu (1), Janusz J. Zwiazek (1, 2) and Melvin T. Tyree (1, 3)
1. Department of Renewable Resources, University of Alberta, 4-42 Earth Sciences Building, Edmonton, AB T6G 2E3, Canada / 2. Corresponding author () / 3. USDA Forest Service, Northern Research Station, 705 Spear Street, S. Burlington, VT 05403, USA / Received May 24, 2007; accepted August 2, 2007; published online May 1, 2008
Summary
A four- to seven-fold enhancement of leaf hydraulic conductance by light has been reported in three temperate tree species.
The enhancement occurs in the liquid-flow pathway between the petiole and the site of water evaporation. The enhancement occurs
within 1 h, and dissipates in darkness over a period of 1 to 10 h depending on species. Here we report light-induced enhancement
of leaf hydraulic conductance in a fourth species, bur oak (Quercus macrocarpa Michx.), the dependence of the effect on light flux and color, its absence in leaves of seedlings, and the impact on the
response of leaf vein severance and several metabolic inhibitors. The light response of leaf hydraulic conductance approached
saturation at a photosynthetic photon flux of 150 μmol m–2 s–1. Hydraulic enhancement was greater in response to blue and green light than to visible radiation of longer wavelengths, although
at the same irradiance, the response to white light was greater than to light of any single color. Atrazine (a photosystem
II inhibitor), fusicoccin (which stimulates plasma membrane-bound H+-ATPase) and HgCl2 (an aquaporin blocker) reduced the light response of leaf lamina hydraulic conductance. When 2-mercaptoethanol was added
following mercury treatment, the light response was totally suppressed. Our results are consistent with the notion that the
effect of light on leaf lamina hydraulic conductance is controlled by factors acting outside the leaf veins, possibly through
light-induced changes in membrane permeability of either mesophyll or bundle sheath cells, or both.
