Fig. 2.

Simultaneous recordings of the cytoplasmic free [Ca²⁺] and ABA-induced anion currents. (A) ABA responses of a V. faba guard cell in an intact plant, recorded at a holding potential of –100 mV before and after injection of FURA-2. (Left) Response to ABA before loading. (Right) ABA response after loading of FURA-2. The upper trace shows the FURA-2 F₃₄₅/F₃₉₀ fluorescent ratio. (B) Guard cell stimulated with voltage pulses and ABA. A FURA-2 loaded guard cell was clamped to a holding potential of –100 mV and to test potentials of 0 and –180 mV (lower trace). Hyperpolarization, but not depolarization, evoked an increase in cytoplasmic free [Ca²⁺] (upper trace), followed by an increase in inward current (arrow, middle trace). Subsequent application of ABA (black bar) induced an inward current without a change in cytoplasmic free [Ca²⁺]. (C) Average change in cytoplasmic free [Ca²⁺] (upper trace) of six guard cells displaying typical ABA-induced anion currents (lower trace). Note that ABA did not affect the cytoplasmic free [Ca²⁺]. Error bars represent SE. (D) Average change in cytoplasmic free [Ca²⁺] (upper trace) of 11 guard cells clamped to –275 mV for 1 s, starting after 20 s, from a holding potential of –100 mV. Note that strong hyperpolarizations triggered large changes in the cytoplasmic free [Ca²⁺] and were followed by a transient increase in inward current. Error bars represent SE.