Abstract
Potassium channels were resolved in Vicia faba guard cell protoplasts by patch voltage-clamp. Whole-cell currents and single K + channels had linear instantaneous current-voltage relations, reversing at the calculated Nernst potential for K +. Whole cell K + currents activated exponentially during step depolarizations, with half-activation times of 400–450 msec at +80 mV and 90–110 msec at +150 mV. Single K + channel conductance was 65 ± 5 pS with a mean open time of 1.25 ± 0.30 msec at 150 mV. Potassium channels were blocked by internal Cs + and by external TEA +, but they were insensitive to external 4-aminopyridine. Application of 10 uM abscisic acid increased mean open time and caused long-lasting bursts of channel openings. Since internal and external composition can be controlled, patch-clamped protoplasts are ideal systems for studying the role of ion channels in plant physiology.
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