Polar-localised poplar K+ channel capable of controlling electrical properties of wood-forming cells

In previous studies, we have shown that annual expression profiles of cambial and wood tissue with respect to the Shaker K⁺ channel PTORK correlate with cambial activity. To follow PTORK-gene activity on the cellular level, we isolated the respective promoter regions and generated transgenic Arabidopsis plants expressing the GUS gene under the control of the PTORK promoter. Cross-sections of petioles showed PTORK-driven signals predominantly in the xylem parenchyma surrounding the vessels and in the phloem. Antibodies raised against a unique N-terminal region of PTORK in histo-immunochemical analyses recognised this K⁺-release channel in growth-active poplar plants only. PTORK labelling was found in differentiating xylem cells (young fibres) and mature xylem (vessel-associated cells of the ray parenchyma). Patch-clamp measurements on fibre cell protoplasts, derived from young poplar twigs, identified outward-rectifying K⁺ channels as the major K⁺ conductance of this cell type, which resembled the biophysical properties of PTORK when expressed in Xenopus oocytes.Electronic Supplementary Material Supplementary material is available for this article at Matthias Arend and Andrea Stinzing contributed equally to this work