Electrical signaling along the phloem and its physiological responses in the maize leaf

Abstract

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.

Beyond APs and VPs: evidences of chaos and self-organized criticality in electrical signals in plants

“…Distinction between APs and VPs in plants based solely upon their kinetic characteristics might be doubtful because VPs often mimic AP kinetics, and they often overlap each other 14,44 , arising a spatial and temporal complex web of electrical signaling 4 . Additionally, the well known complexity of calcium waves underlying plant electrical signaling 13,42 , and the network of neurotransmitters signaling, acting on development, communication and stress responses 5,17 can explain, at least in part, the temporal complexity in the electrical transmission of significant (not random) physiological information through the plant body, which is not properly congregated by single VPs or APs signals 14 .…”

“…19, 2016; Despite of different induction mechanisms, the electrical signals are able to inform distant cells about local stimuli, triggering proper physiological responses to a multitude of environmental stimuli 6 . As far as we know, the studies linking electrical signaling with physiological responses to environmental cues are based on the analysis of APs or VPs waves, taking into account only parameters as frequency, amplitude, distance of propagation and time frame 6,8,12,13 . However, quite often mixed electrical potential waves (EPWs) are recorded, for instance, as result of overlapping APs and VPs, which impedes proper signal analysis 14 .…”

ROS, Calcium, and Electric Signals: Key Mediators of Rapid Systemic Signaling in Plants

“…Following wounding the hydrostatic pressure in xylem vessels changes, leading to turgor changes in the adjacent parenchyma cells that cause membrane potential changes potentially via mechano-sensors (Stahlberg et al, 2006; for review, see Farmer et al, 2014;van Bel et al, 2014). Transmission of the signal between mesophyll and phloem is thought to be mediated by bundle-sheath cells (Szechy nska-Hebda et al, 2010;Fromm et al, 2013). Such electrical signal propagation along the vascular tissue in the leaves of Helianthus annuus was recently shown by spatio-temporal surface recording (Zhao et al, 2014).…”

Use of plant woody species electrical potential for irrigation scheduling

“…[20][21][22] Phloematic tissue is the main route of electrical signal transmission over long distances, similar to a simple neural network, allowing physiological information transfer between tissues and organs. 10,19,23,24 Evidence of this electrical transport over long distances in plants have been documented by Fromm and Fei,25 who first reported the occurrence of stomata closure prior to a decrease in leaf turgor in Zea mays. Fromm and Lautner, 26 indicated that leaf stomata apparently receive direct information related to soil water status, irrespective of leaf water potential.…”

“…[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] Differential plant electrical responses have been measured for water status variations. [20][21][22] Phloematic tissue is the main route of electrical signal transmission over long distances, similar to a simple neural network, allowing physiological information transfer between tissues and organs.…”