References

22 Electrical signaling via the phloem 329
demonstrated to follow the arrival of an action potential in the leaves. These
results therefore strongly support the view that phloem-transmitted electrical
signalling plays an important role in the root-to-shoot communication
of entire plants.
22.7
Conclusions and Future Perspectives
Although we cannot as yet fully image the genetic and metabolic complexity
of plants we have managed to gain first insights into their multidimensional
electrical communication system. Obviously, the signalling
network responds to a variety of environmental factors which may be biotic
or abiotic. Stimuli perceived in one part of the symplasm can be rapidly
transmitted via electrical signals to other cells, tissues and plant organs. At
the short-distance level, electrical coupling via plasmodesmata is a wellestablished
phenomenon (van Bel and Ehlers 2005) and was demonstrated
in a variety of tissues and species by conventional electrophysiology. After
moving laterally through plasmodesmata, electrical signals are capable
of entering the phloem network to effect fast communication over long
distances (Fig. 22.1). The signals prefer to make their way through the
low-resistance, longitudinally arranged sieve tubes.
Numerous examples exist with regard to the physiological or ecological
functions of electrical signalling. Mimosa leaves look dead and unappealing
to herbivores once the plant is touched. Insectivorous plants obtain their
nitrogen by capturing and digesting insects. In ordinary plants that do not
possess motor activity evidence was provided that action potentials may
regulate a wide variety of physiological responses, including elongation
growth (Shiina and Tazawa 1986), respiration (Dziubinska et al. 1989),
water uptake (Davies et al. 1991), activation of PI genes (Wildon et al.
1992; Stankovic and Davies 1997), phloem transport (Fromm and Bauer
1994), gas exchange (Fromm and Fei 1998) and photosynthesis (Koziolek
et al. 2004). For a better understanding of the complexity of electrical
communication in plants, further studies involving novel methods with
improved resolution will have to be conducted in the future.
References
Ache P, Becker D, Deeken R, Dreyer I, Weber H, Fromm J, Hedrich R (2001) VFK1, a Vicia
faba K + channel involved in phloem unloading. Plant J 27:571–580
Bauer CS, Hoth S, Haga K, Philippar K, Aoki K, Hedrich R (2000) Differential expression and
regulation of K + channels in the maize coleoptile: molecular and biophysical analysis
of cells isolated from cortex and vasculature. Plant J 24:139–145