Agriculture Reference
In-Depth Information
16
Physiological Roles of Nonselective
Cation Channels in the Plasma
Membrane of Higher Plants
Vadim Demidchik
Abstract
Nonselective cation channels (NSCC) in the plasma membrane of higher plants
form a large and diverse group of plant cation channels which are permeable for K
+
,Na
+
and Ca
2+
. They include four classes: (1) constitutive NSCC; (2) NSCC activated by reactive
oxygen species (ROS); (3) ligand-activated NSCC; and (4) mechanosensitive NSCC. Our
understanding of physiological functions of NSCC has significantly progressed in the last
few years. NSCC were demonstrated to be involved in nutritional uptake of K
+
,NH
4
,Ca
2+
,
Mg
2+
, micronutrients and trace elements, toxic Na
+
influx, in ROS-, amino acid, purine- and
cyclic nucleotide induced signalling, growth and development. Here, physiological roles of
plant NSCC are reviewed and discussed.
16.1
Introduction
Plant ion channels transporting cations through the plasma membrane
can be divided in to three main groups. The first identified group is K
+
channels that includes two large classes, namely outwardly and inwardly
rectifying K
+
channels (KOR and KIR respectively) (reviewed by Very and
Sentenac 2003). These channels are highly selective for K
+
and NH
4
over
other cations and are involved in K
+
and NH
4
uptake, release and redistri-
bution in plants. The second group of cation channels is Ca
2+
channels. This
group embraces depolarisation-activated (Thuleau et al. 1994; Thion et al.
1996) and hyperpolarisation-activated (Gelli and Blumwald 1997; Kiegle
et al. 2000; Very and Davies 2000; Demidchik et al. 2002) Ca
2+
channels
(DACC and HACC respectively). Cation selectivity of Ca
2+
channels has
been properly tested only in a few studies; therefore, it is unclear whether
these channels are highly selective for Ca
2+
over all other cations (like the
animal Ca
2+
channel) or not. Besides, genes-encoding classic voltage-gated
Ca
2+
channels (known from animal physiology) have not been identified
in plants (White et al. 2002). So, many plant Ca
2+
-permeable channels very
likely belong to nonselective cation channels (NSCC). NSCC form the third
group of plant cation channels with about equal permeability for K
+
and
Na
+
(P
K
/P
Na
<3) and high Ca
2+
permeability (P
Ca
/P
K
> 0.1 - 0.2) (Demid-
chik et al. 2002). The focus of this review is on NSCC with a particular
emphasis on their physiological functions in plants. Our understanding of
the physiological roles of NSCC has improved significantly, but not much
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