| The ABA-regulated and G-proein-regulated cell sigal transductions are two important cell signal transduction systems in plant cell. It has been reported that ABA is one of the important phytohormes in the regulation of in ward-rectify potassium (K+in) channels thus control the stomatal movements. G protein coupled receptor is one of important elements in G protein signal transduction pathway. It plays many important roles in mammalian cells, but seldom was studied in plant cells.The guard cell is a model system for studying cell sigal transduction in plants. In order to study the relationship between the two sigal transduction pathways and find out if the K+in channel of guard cells in mutants displayed the different manners with wild type plants to the extracellular ABA or if the GCR2 was involved in the ABA signal transduction process, the techniques as stomatal eperture measurment and patch clamping method were employed, the Arabidopsis thaliana plant mutants of the the GCR2 as gcr2-l and 35S..GCR2 were tested in this work as well as the wild type.Results of stomatal aperture assay showed that gcr2-l stomata exhibit hyposensitivety relative to wild type, however 35S::GCR2 shows hyper-sensitivity to extracellular 50 [imol/L ABA.By application of patch clamp technique, the voltage-dependent inward-rectify potassium currents were recorded and characterized. The K+in current of the guard cells of the wild plants was inhibited by 50 u.mol/L extracellular ABA for about 38% at the voltage -180 mV, but the inhibition of ABA was abolished in the current of gcr2-l guard cells.The K+in current of the mutant as 35S::GCR2 was also tested, and the results showed that from the current traces and the I/V curves of the 35S::GCR2 and wild type guard cells, there is no significant difference between the two materials under the test of extracelluar ABA.It is concluded that putative G-protein coupled receptor, GCR2, is somehow involved in the process of ABA regulated guard cell inward...
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