Physiological Roles of Nonselective Cation Channels in the Plasma Membrane of Higher Plants - Communication in Plants: Neuronal Aspects of Plant Life - page 240

dependent), blocked by lanthanides, insensitive to Ca 2+ and K + channel
inhibitors (such as nifedipine, verapamil and tetraethylammonium), and
showed fast activation kinetics (in the millisecond range).
In addition to permeating constitutive NSCC, Na + can also perme-
ate a membrane through glutamate-activated conductance, as was re-
cently characterised in Arabidopsis root epidermis (Demidchik et al. 2004).
Glutamate-induced Na + influx currents were present in a low proportion
of protoplasts (about one tenth of the protoplasts at 0.1 mM and about one
third at 3 mM glutamate), were weakly voltage dependent, permeable to
K + ,Cs + and Ca 2+ and rapidly activating. However, the role of Na + influx

through glutamate-activated channels is obscure because 44 Na + was only

slightly affected by glutamate (Demidchik et al. 2004).
ROS-activated NSCC are permeable to Na + ( P K

/ 0. 7) (Demidchik

et al. 2003). NaCl was shown to stimulate the production of extracellular
ROS (Demidchik et al. 2003). I suggest that NaCl-induced ROS produc-
tion can activate Na + uptake through ROS-activated cation channels. This
mechanism can potentially be very important for toxic Na +

P Na ≈

influx under

salinity.
Welch (1995) suggested that “nonspecific” cation channels are involved
in the plant uptake of cation micronutrients and toxic metals, and since
then a number of reports have been published about the NSCC-mediated
influx of different metals in plants (Demidchik et al. 2002, 2003; Reid and
Liu, 2004). The uptake of micronutrients, toxic and trace elements could
be an important physiological function of NSCC. This function is based on
NSCC domination in divalent cation influx at resting membrane voltages
(Demidchik et al. 2002). Constitutive NSCC were shown to conduct large
influx currents of Zn 2+ / 0. 51) (Demidchik et al. 2002). ROS-

activated NSCC were also permeable to this cation (Foreman et al. 2003).
Experimental evidence supporting the involvement of cyclic nucleotide-
gated channels (CNGC) in transport of Ni 2+ and Pb 2+ has recently been
reported for tobacco plants (Arazi et al. 1999; Sunkar et al. 2000). Reid
and Liu (2004) have demonstrated that when extracellular radio-labelled
Co 2+ concentrations were between 1 and 10 µM this micronutrient was
taken up into plants exclusively by NSCC. NSCC also play a crucial role in
an accumulation of Chernobyl pollutant 37 Cs + (White and Broadley 2000;
Broadley et al. 2001; Demidchik et al. 2002).

( P Ca P Zn ≈

16.5
The Role of NSCC in Plant Signalling

Figure 16.1 shows a model of possible NSCC involvement in plant sig-
nalling and communication processes. These processes are necessary for