Systemic signalling in barley through action potentials

Abstract

Using apoplastic voltage- and ion selective microprobes, in barley leaves action potentials (APs) have been measured, which propagate acropetally as well as basipetally from leaf to leaf or from root to leaf following the application of mild salt stress (e.g. 30-50 mM KCl or NH(4)Cl) or amino acids (e.g. 1 mM glutamic acid or 5 mM GABA). Voltage changes were biphasic, followed an 'all-or-none' characteristic, and propagated at 20-30 cm min(-1) irrespective of the direction. With the salt-induced APs, a strong initial depolarization is the main AP-releasing factor that first causes Ca(2+) influx and then anion efflux. Ca(2+) influx coincides with an initial slower depolarization, the rapid anion efflux causes the typical voltage 'break-through'. Subsequently, K(+)-efflux starts after the depolarizing voltage has passed the K(+) equilibrium potential (inversion of the K(+) driving force). Glutamic acid and GABA induce APs not through membrane depolarization, but presumably by binding to a putative receptor or to ligand-gated Ca(2+)-conducting channels, respectively, followed by Ca(2+) induced activation of anion efflux. APs are accompanied by transient apoplastic pH increase (about 1 unit), and by cytoplasmic pH decrease (about 0.5 units). The apoplastic pH change is interpreted as an indicator of stress, the cytoplasmic pH change as a prerequisite for defence related gene activation. Since APs are released by agents added in a moderate concentration range, it is suggested that they may serve as first and fast systemic signals following attack from pathogens.

Variation potential in higher plants: Mechanisms of generation and propagation

“…AP generation is mainly based on passive Ca 2C , Cl ¡ and K C fluxes, 35 but transient H C -ATPase inactivation also participates in this process. 36 VP generation is still under investigation 7,[11][12][13] and it has been difficult to determine its precise functional role.…”

Recognition of Herbivory-Associated Molecular Patterns

“…; Felle and Zimmermann, 2007). However, other electrical signals, such as variation potentials, might be involved as well.…”

A ROS-Assisted Calcium Wave Dependent on the AtRBOHD NADPH Oxidase and TPC1 Cation Channel Propagates the Systemic Response to Salt Stress

“…Examples include wounding (Miller et al, 2009), pathogen attack (Dempsey and Klessig, 2012), and osmotic shock (Christmann et al, 2007). The system(s) involved in the plant-wide propagation of these signals has been proposed to be mediated by a diverse set of molecular regulators, including changes in membrane potential and ion fluxes (Felle and Zimmermann, 2007;Zimmermann et al, 2009;Mousavi et al, 2013), hydraulics in the vasculature (Christmann et al, 2007;Farmer et al, 2014), and reactive oxygen species (ROS; Miller et al, 2009). A novel addition to this suite of systemic signals was described by Choi et al (2014), in which a wave-like propagation of increased cytoplasmic Ca 2+ moved throughout the plant in response to localized salt stress.…”