ABSTRACT
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, KAT1En-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 KAT1En-1 plants. This study demonstrates that multiple K(+) channel transcripts exist in guard cells and that KAT1 is not essential for stomatal action.
Subject(s)
Arabidopsis/physiology , Potassium Channels, Inwardly Rectifying , Potassium Channels/physiology , Arabidopsis Proteins , Base Sequence , DNA Primers , DNA Transposable Elements , Mutation , Patch-Clamp Techniques , Plant Proteins , Potassium Channels/geneticsABSTRACT
Bactericidal/permeability-increasing protein [BPI] is a cationic antimicrobial protein from neutrophils that specifically binds to the surfaces of Gram-negative bacteria via the lipid A component of lipopolysaccharide. To obtain information about the responses of Salmonella typhimurium to cell-surface damage by BPI, two-dimensional gel electrophoresis and N-terminal microsequencing were used to identify proteins that were induced or repressed following BPI treatment. The majority of the affected proteins are involved in central metabolic processes. Upon addition of BPI, the beta-subunit of the F1 portion of Escherichia coli ATP synthase was repressed threefold whereas six proteins were induced up to 11-fold. Three of the latter were identified as lipoamide dehydrogenase, enoyl-acyl carrier protein reductase, and the heat-shock protein HtpG. Additionally, a novel protein, BipA, was identified that is induced over sevenfold by BPI; sequence analysis suggests that it belongs to the GTPase superfamily and interacts with ribosomes. A conserved direct-repeat motif is present in the regulatory regions of several BPI-inducible genes, including the bipA gene. Only one of the BPI-responsive proteins was induced when cells were treated with polymyxin B, which also binds to lipid A. We therefore conclude that BPI and polymyxin B affect different global regulatory networks in S. typhimurium even though they bind with high affinity to the same cell-surface component.
