Reduction of hydraulic conductance to the canopy has been shown to result in stomatal responses to limit transpiration. To test for similar responses to perturbations of the hydraulic network in leaves, we simultaneously measured leaf gas exchange with spatially explicit chlorophyll-a fluorescence and leaf temperature to examine the effects of cutting a primary leaf vein in Helianthus annuus. We repeated the leaf treatment at each of three different vapor pressure deficits and monitored the short-term dynamics of gas exchange following the treatment. Immediately after treatment, photosynthesis and stomatal conductance (gs) showed a transient “wrong way” response in which photosynthesis declined despite increased gs. Comparisons of fluorescence and temperature across the leaf showed that both photosynthesis and gs were transiently patchy across the measured leaf area, but that the patchiness of the two processes did not correspond in space or time. This suggests that photosynthesis and gs respond to vein cutting-induced cavitation via different mechanisms. Because the stomatal response varied by vapor pressure difference condition but photosynthesis did not, it is likely that gs, but not photosynthesis, responded to a hydraulic signal. In contrast, we hypothesize that photosynthesis declined due to a wound-induced electrical signal that has recently been shown to transiently decrease mesophyll conductance to CO2. The interaction of epidermal hydraulics and the electrical signal across the leaf likely created a patchy pattern of chlorophyll fluorescence and leaf temperature that cannot be explained through the action of a single signal.
Keywords: stomatal conductance, leaf hydraulic conductance, mesophyll conductance, stomatal patchiness, chlorophyll fluorescence imaging, photosynthesis, transpiration, cavitation
Citation: Hanson DT, Green LE and Pockman WT (2013) Spatio-temporal decoupling of stomatal and mesophyll conductance induced by vein cutting in leaves of Helianthus annuus. Front. Plant Sci. 4:365. doi: 10.3389/fpls.2013.00365
Received: 31 May 2013; Accepted: 27 August 2013;
Published online: 23 September 2013.
Edited by:Peter Jegsen Melcher, Ithaca College, USA
Reviewed by:Lars Hendrik Wegner, Karlsruhe Institute of Technology, Germany
Copyright © 2013 Hanson, Green and Pockman. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: David T. Hanson, Department of Biology, University of New Mexico, MSC03-2020 Biology, Albuquerque, NM 87131, USA e-mail: firstname.lastname@example.org