Dominant Negative Guard Cell K(+) Channel Mutants Reduce Inward-Rectifying K(+) Currents and Light-Induced Stomatal Opening in Arabidopsis

Inward-rectifying potassium (K(+)(in)) channels in guard cells have been suggested to provide a pathway for K(+) uptake into guard cells during stomatal opening. To test the proposed role of guard cell K(+)(in) channels in light-induced stomatal opening, transgenic Arabidopsis plants were generated that expressed dominant negative point mutations in the K(+)(in) channel subunit KAT1. Patch-clamp analyses with transgenic guard cells from independent lines showed that K(+)(in) current magnitudes were reduced by approximately 75% compared with vector-transformed controls at −180 mV, which resulted in reduction in light-induced stomatal opening by 38% to 45% compared with vector-transformed controls. Analyses of intracellular K(+) content using both sodium hexanitrocobaltate (III) and elemental x-ray microanalyses showed that light-induced K(+) uptake was also significantly reduced in guard cells of K(+)(in) channel depressor lines. These findings support the model that K(+)(in) channels contribute to K(+) uptake during light-induced stomatal opening. Furthermore, transpirational water loss from leaves was reduced in the K(+)(in) channel depressor lines. Comparisons of guard cell K(+)(in) current magnitudes among four different transgenic lines with different K(+)(in) current magnitudes show the range of activities of K(+)(in) channels required for guard cell K(+) uptake during light-induced stomatal opening.