References

19 Electrical Signals in Long-Distance Communication in Plants 285
The coupling between APs and functioning of digestive glands remains
elusive. The presence of the prey is not necessary to induce the process.
It is possible to evoke an extensive release of a digestive fluid by electrical
stimulation of an immobilized trap (Trebacz, unpublished).
A. vesiculosa,acloserelativeofDionaea,shutsdownitstrapsafterasingle
stimulation of a trigger hair followed by generation of a single AP (Iijima
and Sibaoka 1982). When the trap receives only one stimulus it begins to
open after 1 h. More stimuli make that the trap lobes press tightly against
each other. Thus, in Aldrovanda, the system protecting against accidental
stimulation is somewhat simpler than that in Dionaea. Instagnantwater,
where it grows, such a sophisticated mechanism does not seem necessary.
Iijima and Sibaoka (1983) pointed out that traps of Aldravanda possess
a motor zone consisting of cells located in a central part of the trap between
two epidermal layers. A massive efflux of ions attributed to that zone
causes a loss of turgor and a sudden trap closure.
The physiological significance of AP-regulated movements of leaves and
pinna-rachis in other plant species, like M. pudica, Biophytum dendroides
and Desmodium motorium is a matter of discussion, although the coupling
between the AP and the movement is well documented (Sibaoka 1973;
Antkowiak and Engelmann 1995).
In Mimosa, itwasshownthatnotonlythemovementbutalsoaphotoassimilate
unloading from the phloem occurs following an AP (Fromm
and Eschrich 1988). A similar effect was demonstrated in Zea mays,which
makes it probable that it is common in excitable plants.
APs also play a role in plant pollination and fertilization. The most
spectacular example was described by Sinyukhin and Britikov (1967) in
Incarvillea. Its flowers possess a bilobal stigma which closes upon mechanical
stimulation exerted by a falling pollen grain. The movement which is
mediatedbytheAPleadstopollengrainarrestinsidethestigma.Soon
afterthat,thesecondAPtravelstotheovary,whereitevokesasignificant
increase in respiration long before fertilization. APs evoked by pollination
were also found in Lilium and Hibiscus (Fromm et al. 1995). The large dimensions
of the pistils, which made electrode attachment easy, determined
the selection of these objects. It is possible that the phenomenon is more
general in flowering plants. APs were registered during movement of stamens
in Berberis and Mahonia too (Simons 1981). APs were postulated to
mediate between illumination and guttation in gametophytes of the moss
Bryum pseudotriquetrum (Sinyukhin 1973). Drops of liquid appearing by
guttation enable fertilization.
Excitation also influences gas exchange in plants. The significant increase
of respiration following stimulation of the C. conicum thallus is
well documented (Dziubinska et al. 1989). It was demonstrated that both
damaging (cutting of a thallus edge) and nondamaging electrical stimuli