Background ion channel activities in Arabidopsis guard cells and review of ion channel regulation by protein phosphorylation events
In this paper, results on background conductances in Arabidopsis guard cells are presented and recent advances pointing to a central role of protein phosphorylation/dephosphorylation events during stomatal signalling are reviewed. Recently, patch clamp studies of Arabidopsis guard cells were developed to characterize early abscisic acid signalling. It is reported here that whole-cell recordings from Arabidopsis guard cells showed three types of background conductances: two large single channel conductances activated by depolarization and hyperpolarization, respectively, and another instantaneous conductance. The reversal potentials of depolarization-activated single channel currents were in the range of -7 mV and were independent of the CsCl gradient, even at an 86-fold imposed gradient. These data suggest that depolarization-activated single channel currents in Arabidopsis guard cells represent non-selective channels. The instantaneous background currents disappeared when the impermeable anions, acetate or glutamate, were loaded into the cytosol of guard cells via the patch electrode. These data and reversal potentials suggest that the small instantaneous background conductance represents a basal activity of anion currents in guard cells. Possible physiological functions of the single channel currents and background anion conductances are discussed. Furthermore, recently reported guard cell ion channel regulation mechanisms are reviewed in the discussion and brought in context of stomatal movement studies.
Pei, ZM; Schroeder, JI; Schwarz, M
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