Potassium and carrot embryogenesis: are K+ channels necessary for development?

The expression pattern of the KDC1 gene, coding for an inwardly-rectifying K(+) channel of Daucus carota , is described in several embryo stages and seedling tissues. Relative quantitative RT-PCR experiments indicated that, during (somatic) embryonic development, the KDC1 transcript appears as early as the globular stage and that the transcript level remains constant throughout the successive heart and torpedo stages. Thereafter, the KDC1 transcript is preferentially expressed in plant roots, but is also present in other tissues, and in particular, in the shoot apical meristem. In situ hybridisation experiments showed that in embryos KDC1 mRNA is detectable preferentially in protoderm cells with a stage dependent expression pattern. At later times, the hybridisation signal is particularly evident in root hairs, root epidermis and endodermis, but is also observed in single cell layers corresponding to L1 of the shoot apical meristem and leaf primordia. Promoter studies with the beta -glucuronidase reporter gene confirm preferential expression of KDC1 in embryo protoderm cells and in plant root epidermis and root hairs. Western blot analysis of embryonic proteins and immunolocalisation experiments on somatic embryos sections revealed the presence of KDC1 during embryo development. Consistent with these observations, patch-clamp experiments performed on protoplasts isolated from embryos at the torpedo stage demonstrated the presence of functional inward rectifying K(+) channels. This is the first report on the expression of a plant ion channel during embryo development.