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