title: Dynamics of ionic activities in the apoplast of the sub-stomatal cavity of intact Vicia faba leaves during stomatal closure evoked by ABA and darkness.
abstract: Stomatal movement is accomplished by changes in the ionic content within guard cells as well as in the cell wall of the surrounding stomatal pore. In this study, the sub-stomatal apoplastic activities of K+, Cl-, Ca2+ and H+ were continuously monitored by inserting ion-selective micro-electrodes through the open stomata of intact Vicia faba leaves. In light-adapted leaves, the mean activities were 2.59 mM (K+), 1.26 mM (Cl-), 64 microM (Ca2+) and 89 microM (H+). Stomatal closure was investigated through exposure to abscisic acid (ABA), sudden darkness or both. Feeding the leaves with ABA through the cut petiole initially resulted in peaks after 9-10 min, in which Ca2+ and H+ activities transiently decreased, and Cl- and K+ activities transiently increased. Thereafter, Ca2+, H+ and Cl- activities completely recovered, while K+ activity approached an elevated level of around 10 mM within 20 min. Similar responses were observed following sudden darkness, with the difference that Cl- and Ca2+ activities recovered more slowly. Addition of ABA to dark-adapted leaves evoked responses of Cl- and Ca2+ similar to those observed in the light. K+ activity, starting from its elevated level, responded to ABA with a transient increase peaking around 16 mM, but then returned to its dark level. During stomatal closure, membrane potential changes in mesophyll cells showed no correlation with the K+ kinetics in the sub-stomatal cavity. We thus conclude that the increase in K+ activity mainly resulted from K+ release by the guard cells, indicating apoplastic compartmentation. Based on the close correlation between Cl- and Ca2+ changes, we suggest that anion channels are activated by a rise in cytosolic free Ca2+, a process which activates depolarization-activated K+ release channels.
authors.affiliation: Botanisches Institut I, Universität Giessen, Senckenbergstrasse 17, D-35390 Giessen, Germany. Hubert.Felle@bio.uni-giessen.de
authors.forename: H H
authors.initials: HH
authors.lastname: Felle
authors.forename: S
authors.initials: S
authors.lastname: Hanstein
authors.forename: R
authors.initials: R
authors.lastname: Steinmeyer
authors.forename: R
authors.initials: R
authors.lastname: Hedrich
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D003624:Darkness; D007887:Fabaceae / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism; D017136:Ion Transport / Q000187:drug effects; D008564:Membrane Potentials; D018515:Plant Leaves / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D010946:Plants, Medicinal; D011188:Potassium / Q000378:metabolism
chemical_list: D007473:Ion Channels; D000040:Abscisic Acid; D011188:Potassium; D002118:Calcium