Plant Physiol.
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First published online October 15, 2002; 10.1104/pp.005769

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Plant Physiol, November 2002, Vol. 130, pp. 1386-1395

The Voltage-Independent Cation Channel in the Plasma Membrane of Wheat Roots Is Permeable to Divalent Cations and May Be Involved in Cytosolic Ca2+ Homeostasis1

Philip J. White* and Romola J. Davenport

Department of Plant Genetics and Biotechnology, Horticulture Research International, Wellesbourne, Warwick CV35 9EF, United Kingdom (P.J.W.); and Department of Plant Sciences, Downing Street, Cambridge CB2 3EA, United Kingdom (R.J.D.)

A voltage-independent cation (VIC) channel has been identified in the plasma membrane of wheat (Triticum aestivum) root cells (P.J. White [1999] Trends Plant Sci 4: 245-246). Several physiological functions have been proposed for this channel, including roles in cation nutrition, osmotic adjustment, and charge compensation. Here, we observe that Ca2+ permeates this VIC channel when assayed in artificial, planar lipid bilayers, and, using an energy barrier model to describe cation fluxes, predict that it catalyzes Ca2+ influx under physiological ionic conditions. Thus, this channel could participate in Ca2+ signaling or cytosolic Ca2+ homeostasis. The pharmacology of 45Ca2+ influx to excised wheat roots and inward cation currents through the VIC channel are similar: Both are insensitive to 20 µM verapamil or 1 mM tetraethylammonium, but inhibited by 0.5 mM Ba2+ or 0.5 mM Gd3+. The weak voltage dependency of the VIC channel (and its lack of modulation by physiological effectors) suggest that it will provide perpetual Ca2+ influx to root cells. Thus, it may effect cytosolic Ca2+ homeostasis by contributing to the basal Ca2+ influx required to balance Ca2+ efflux from the cytoplasm through ATP- and proton-coupled Ca2+ transporters under steady-state conditions.


1 This work was supported by the Biotechnology and Biological Sciences Research Council (to P.J.W.) and by a UK Commonwealth Scholarship (to R.J.D.).

* Corresponding author; e-mail philip-j.white{at}hri.ac.uk; fax 01789-470552.

© 2002 American Society of Plant Biologists






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