KAT1 is not essential for stomatal opening

It is generally accepted that K + uptake into guard cells via inward-rectifying 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-1 mutagenized Arabidopsis thaliana population. 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 K + channels AKT1, AKT2/3, AtKC1, and KAT2 were expressed in this cell type. In impalement measurements, intact guard cells exhibited inward-rectifying K + currents across the plasma membrane of both wild-type and KAT1∷En-1 plants. This study demonstrates that multiple K + channel transcripts exist in guard cells and that KAT1 is not essential for stomatal action.