Agriculture Reference
In-Depth Information
E/mV
0
AP
VT
-50
2 min
-100
-150
2
3
4
5
10
-200
Fig. 19.3.
AP and voltage transients (
VTs
)elicitedbylightin
C. conicum
.
Numbers
over
black
bars
denote the duration of darkness period preceding illumination (After Trebacz et al.
1997)
Different aspects of ion mechanism of APs were also studied in higher
plants. Special attention was paid to carnivorous plants
Dionaea muscipula
and
Aldrovanda vesiculosa
as well as seismonastic
Mimosa pudica
.In
Al-
drovanda
Ca
2+
influx during the AP was estimated as 8 pmol cm
−2
(Iijima
and Sibaoka 1985), which points to calcium influx as a trigger of subse-
quent ion fluxes. Potassium efflux was much higher - 6,200 pmol cm
−2
.It
was suggested that a charge balancing current was carried by Cl
−
(Iijima
and Sibaoka 1983). The data concerning the ion basis of APs in
D. mus-
cipula
are mostly indirect. The dependence of the AP amplitude on an
external Ca
2+
concentration and its reduction by La
3+
and ethylene glycol
bis(2-aminoethyl ether)tetraacetic acid points to a calcium influx (Hodick
and Sievers 1988). Repetitive electrical stimulation or a blockage of Ca
2+
-
ATPase, both leading to accumulation of Ca
2+
in the cytoplasm, causes
gradual reduction of AP amplitudes (Trebacz et al. 1996). The chloride
component previously questioned (Hodick and Sievers 1988) was recently
demonstrated (Krol et al. 2005).
In a leaf pulvinus of
M. pudica
large asymmetric K
+
and Cl
−
effluxes with
higher amounts of the ions in the lower part were demonstrated (Samejima
and Sibaoka 1982; Kumon and Suda 1984). Ion channels in protoplasts from
M. pudica
pulvini were examined by the patch-clamp technique (Stoeckel
and Takeda 1993). Delayed outward-rectifying potassium channels were
found. Some of the protoplasts showed an N-shaped
I
/
V
curve character-
istic of excitable cells (Stoeckel and Takeda 1993).
The Ion mechanism of APs was also studied in other higher plants
exhibiting no fast movements. Fromm and Spanswick (1993) confirmed
participation of Ca
2+
,Cl
−
and K
+
fluxes during the AP in
Salix viminalis
.
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