Dissection of heat-induced systemic signals: superiority of ion fluxes to voltage changes in substomatal cavities.
Using non-invasive ion-selective microprobes, that were placed in substomatal cavities, long-distance signalling has been investigated in intact Hordeum vulgare and Vicia faba seedlings. Heat (flame), applied to one leaf (S-leaf), triggers apoplastic ion activity (pH, pCa, pCl) transients in a distant leaf (T-leaf), all largely independent of simultaneously occurring action potential-like voltage changes. While apoplastic pCa and pH increase (Ca(2+)-, H(+)-activities decrease), pCl decreases (Cl(-)-activity increases). As the signal transfer from the S- to the T-leaf is too fast to account for mass flow, the heat-induced pressure change is primarily responsible for changes in voltage (H(+) pump deactivation) as well as for the ion fluxes. The pCa transient precedes the pCl- and pH responses, but not the voltage change. Since the apoplastic pCl decrease (Cl(-) increase) occurs after the pCa increase (Ca(2+) decrease) and after the depolarization, we argue that the Cl(-) efflux is a consequence of the Ca(2+) response, but has no part in the depolarization. Kinetic analysis reveals that pH- and pCl changes are interrelated, indicated by the action of the anion channel antagonist NPPB, which inhibits both pCl- and pH changes. It is suggested that efflux of organic anions into the apoplast causes the pH increase rather than the deactivation of the plasma membrane H(+) pump. Since there is considerably more information in ion activity changes than in a single action- or variation potential and heat-induced ion fluxes occur more reliably than voltage changes, released by milder stimuli, they are considered systemic signalling components superior to voltage.
Zimmermann
Mathias R
MR
Botanisches Institut I, Justus-Liebig-Universität, Senckenbergstrasse 17, 35390, Giessen, Germany.
Felle
Hubert H
HH
D020013:Calcium Signaling; D002713:Chlorine / Q000378:metabolism; D004553:Electric Conductivity; D018869:Heat-Shock Response / Q000502:physiology*; D001467:Hordeum / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport; D008839:Microelectrodes; D011522:Protons; D015398:Signal Transduction; D031307:Vicia faba / Q000378:metabolism*
D011522:Protons; D002713:Chlorine