, Volume 217, Issue 4, pp 639–650 | Cite as

The slow and the quick anion conductance in whole guard cells: their voltage-dependent alternation, and the modulation of their activities by abscisic acid and CO2

Original Article


We explored the functioning of the slowly activating anion conductance, S-type or SLAC, and of the quickly activating anion conductance, R-type or QUAC, in whole guard cells of Vicia faba L.; details of QUAC activity had not previously been demonstrated in guard cells possessing their walls. The discontinuous single-electrode voltage-clamp method was used to record current responses to voltage pulses and voltage ramps as well as the free-running membrane voltage. At all voltages tested between −200 and 60 mV, SLAC activated with two components, one had a time constant similar to 7 s, the other similar to 40 s. The current–voltage relationship resembled that obtained by patch-clamp experiments. In pulse experiments and 1-s ramps, QUAC activity appeared with half-maximum activation near −50 mV and full activation above −10 mV; it inactivated with a half-time of approximately 10 s. Inactivation of QUAC at −40 mV led to the appearance of SLAC. After deactivation of SLAC at −200 mV, QUAC could be activated again. We concluded that voltage-dependent interchanges between SLAC and QUAC had occurred. Frequently, SLAC and QUAC were active simultaneously in the same cell. Abscisic acid (ABA, 20 μM) activated SLAC as well as QUAC. External Ca2+ was not required, but enhanced the activation of QUAC. Rises in the partial pressure of CO2, in the range between 0 and 700 μbar, caused rapid and reversible increases in the activity of SLAC (and outward currents of K+). QUAC also responded to CO2, however in an unpredictable manner (either by increased or by decreased activity). Oscillations in the free-running membrane voltage arose either spontaneously or after changes in CO2. They were correlated with periodic activations and inactivations of QUAC and required the simultaneous activity of an electrogenic pump.


Abscisic acid Anion conductance Carbon dioxide Discontinuous single-electrode voltage-clamp (dSEVC) Guard cell Vicia 



abscisic acid


outwardly directed current of K+


partial pressure of CO2


quickly activating anion conductance, R-type


slowly activating anion conductance, S-type





The adaptation of the discontinuous single-electrode voltage clamp to measurements on guard cells was begun in our laboratory by Holger Sack (now at Friedrich-Schiller-Universität, Jena, Germany), and the first recordings were made by Dr. Haiyun Ren (now at Beijing Normal University, Beijing, P.R. China). We thank both of them for their initiatory work. Thanks go to Michaela Weiberg for performing with engagement and persistence the experiments during the final phase of this work, and to Uwe Wedeneyer for his never tiring effort to provide the required healthy plants. This research was supported by grants to K.R. from the Deutsche Forschungsgemeinschaft (Ra 122/17, SPP 298, "Stoffwechsel und Wachstum der Pflanze unter erhöhter Kohlendioxidkonzentration").


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Copyright information

© Springer-Verlag 2003

Authors and Affiliations

  • Klaus Raschke
    • 1
  • Mahbobeh Shabahang
    • 1
  • Rupert Wolf
    • 1
  1. 1.Albrecht-von-Haller-Institut für PflanzenwissenschaftenGeorg-August-Universität GöttingenGöttingenGermany

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