Figure 4.

Inward-rectifying K⁺ currents in intact guard cells from wild-type and KAT1 knockout plants. (A) Hyperpolarization-induced K⁺ currents in the presence of 1 mM Ca²⁺ and 50 mM K⁺ in guard cells from wild-type (Left) and KAT1∷En-1 (Right). Cells were clamped from a holding potential of −100 mV to test pulses ranging from −100 mV to −220 mV in 20-mV decrements. (B) Activation of K⁺ channels in wild-type (Left) and KAT1∷En-1 (Right) using the pulse protocol as in A. Currents were recorded in the presence of 20 mM Ca²⁺ and 50 mM K⁺. (C) Steady-state current-voltage relation of K⁺ currents in wild type (filled symbols) and KAT1∷En-1 (open symbols) in the presence of 1 mM (Left) and 20 mM Ca²⁺ (Right). Data points represent mean values ± SEM, n = 8 (wild type, 1 mM Ca²⁺), 7 (KAT1∷En-1, 1 mM Ca²⁺), and 6 (wild type and KAT1∷En-1, 20 mM Ca²⁺). Note the higher Ca²⁺ sensitivity of inward K⁺ channels in KAT1∷En-1 compared with the wild type. Inward K⁺ currents were observed in 20 out of 32 (wild type) and 21 out of 44 measurements (KAT1∷En-1).