Electrical Signals in Long-Distance Communication in Plants - Communication in Plants: Neuronal Aspects of Plant Life - page 281

E/mV

-50

membrane potential

-100

-150

-200

pCa

2+

Ca activity

6.5

7.0

5 min

7.5

Fig. 19.2. Membrane potential changes ( upper traces )andcytoplasmicCa 2+ activity ( lower
traces )measuredin Conocephalum conicum by ordinary and ion-selective microelectrodes,
respectively. Arrows indicate electrical stimulation. White and black bars denote light and
darkness, respectively (After Trebacz et al. 1994)

observed after application of Ca 2+ or anion channel inhibitors (Trebacz et
al. 1989). These findings were confirmed after employing ion-selective mi-
croelectrodes. It was found that during the AP [Ca 2+ ] cyt increases from
resting 231 to 477 nM (Fig. 19.2) while Cl − and K + activities in the cytosol
decrease (Trebacz et al. 1994).
Application of A-9-C, an anion channel inhibitor, together with tetraethy-
lammonium (TEA) discloses voltage transients (VTs) evoked by light or
cold stimuli, which no longer have all-or-none character (Fig. 19.3). Their
amplitude depends on the stimulus strength and the period preceding
stimulation. There is evidence that VTs represent a calcium component of
APs (Trebacz et al. 1997; Krol and Trebacz 1999; Krol at al. 2003). In the
absence of A-9-C and TEA, the VT is short-circuited by a high membrane
conductance caused by the opening of anion and potassium channels dur-
ing the AP. A VT is a suitable tool to investigate the sources of [Ca 2+ ] cyt
increase. Reduction of the VT amplitude by impermeable lanthanides and
its dependence on external Ca 2+ concentration points to the apoplast as
asourceofCa 2+ . On the other hand, suppression of the VT by neomycin, an
inhibitor of phospholipase C catalyzing IP 3 production, and magnification
of the VT by Sr 2+ ,whichisknowntoliberateCa 2+ from internal stores, is
evidence that those Ca 2+ sources play a role in the ion mechanism of the
AP (Krol et al. 2003).