KAT1 is not essential for stomatal opening

It is generally accepted that Kf uptake into guard cells via inward-rectify ing K+ channels is required for stomatal opening. To test whether the guard cell K+ channel KAT1 is essential for stomatal opening, a knockout mutant, KAT1::En-1, was isolated from an En-l mutagenized Arabidopsis thaliana pop ulation. Stomatal action and K+ uptake, however, were not impaired in KAT1- deficient plants. Reverse transcription-PCR experiments with isolated guard cell protoplasts showed that in addition to KAT1, the Kf channels AKT1, AK T2/3, AtKC1, and KAT2 were expressed in this cell type. In impalement measu rements, intact guard cells exhibited inward-rectifying Kf currents across the plasma membrane of both wildtype and KAT1::En-1 plants. This study demo nstrates that multiple K+ channel transcripts exist in guard cells and that KAT1 is not essential for stomatal action.