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 fight-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.