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Differential expression and regulation of K + channels in the maize coleoptile: molecular and biophysical analysis of cells isolated from cortex and vasculature
Author(s) -
Bauer Claudia S.,
Hoth Stefan,
Haga Ken,
Philippar Katrin,
Aoki Naohiro,
Hedrich Rainer
Publication year - 2000
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1046/j.1365-313x.2000.00844.x
Subject(s) - coleoptile , xenopus , biophysics , extracellular , patch clamp , biology , cortex (anatomy) , chemistry , microbiology and biotechnology , biochemistry , electrophysiology , gene , neuroscience
Summary Recently, two K + channel genes, ZMK1 and ZMK2 , were isolated from maize coleoptiles. They are expressed in the cortex and vasculature, respectively. Expression in Xenopus oocytes characterized ZMK1 as an inwardly rectifying K + channel activated by external acidification, while ZMK2 mediates voltage‐independent and proton‐inhibited K + currents. In search of the related gene products in planta , we applied the patch–clamp technique to protoplasts isolated from the cortex and vasculature of Zea mays coleoptiles and mesocotyls. In the cortex, a 6–8 pS K + channel gave rise to inwardly rectifying K + currents. Like ZMK1, this channel was activated by apoplastic acidification. In contrast, protoplasts from vascular tissue expressing the sucrose transporter ZmSUT1 were dominated by largely voltage‐independent K + currents with a single‐channel conductance of 22 pS. The pronounced sensitivity to the extracellular protons Ca 2+ , Cs + and Ba 2+ is reminiscent of ZMK2 properties in oocytes. Thus, the dominant K + channels in cortex and vasculature most likely represent the gene products of ZMK1 and ZMK2 . Our studies on the ZMK2‐like channels represent the first in planta analysis of a K + channel that shares properties with the AKT3 K + channel family. Keywords: K + channel, voltage‐independent, proton block, maize coleoptile.