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.