To elucidate the role of electrical signaling in the phloem of maize the tips of attached leaves were stimulated by chilling and wounding. Two different signals were detected in the phloem at the middle of the leaf using the aphid stylet technique: (1) action potentials (AP) arose in the phloem after chilling; and (2) variation potentials (VPs) were evoked after wounding the leaf tip. Combined electric potential and gas exchange measurements showed that while the wound-induced VP moved rapidly towards the middle of the leaf to induce a reduction in both the net-CO2 uptake rate and the stomatal conductance, there was no response in the gas exchange to the cold-induced AP. To determine if electrical signaling had any impact on assimilate transport the middle of the leaf was exposed to 14CO2. Autoradiography of labeled assimilates provided evidence that phloem and intercellular transport of assimilates from mesophyll to bundle sheath cells was strongly reduced while the cold-induced AP moved through. In contrast, wound-induced VP did not inhibit assimilate translocation but did reduce the amount of the labeled assimilate in phloem and bundle sheath cells. Biochemical analysis revealed that callose content increased significantly in chilled leaves while starch increased in chilled but decreased in wounded leaves. The results led to the conclusion that different stimulation types incite characteristic phloem-transmitted electrical signals, each with a specific influence on gas exchange and assimilate transport.
Keywords: action potential, assimilate translocation, callose, gas exchange, phloem, plasmodesmata, variation potential
Citation: Fromm J, Hajirezaei M-R, Becker VK and Lautner S (2013) Electrical signaling along the phloem and its physiological responses in the maize leaf. Front. Plant Sci. 4:239. doi: 10.3389/fpls.2013.00239
Received: 14 March 2013; Accepted: 16 June 2013;
Published online: 04 July 2013.
Edited by:Aart Van Bel, Justus-Liebig-University Giessen, Germany
Reviewed by:Jens B. Hafke, Justus -Liebig-Universität, Germany
Copyright © 2013 Fromm, Hajirezaei, Becker and Lautner. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc.
*Correspondence: Jörg Fromm, Institute for Wood Biology, Universität Hamburg, Leuschnerstrasse 91d, 21031 Hamburg, Germany e-mail: firstname.lastname@example.org