References

386 E. Wagner et al.
25.9
Conclusions and Future Perspectives
The hydro-electrochemical communication of the higher plant is intrinsically
linked with and depends on the membrane potential of cells and
organelles, which can be modulated by the light environment (Trebacz and
Sievers 1998). High-frequency (e.g. 24 min) temperature-compensated oscillations
like in NADH oxidase activity of plasma membranes (Morré and
Morré 1998) might be a high-frequency time scale for redox-control on
a circadian scale. Populations of synchronised chloroplasts and mitochondria
might be involved in the generation of proton-conducting structures
like the mitochondrial network in animal cells (Giorgi et al. 2000). The
hydro-electrochemical integration of the whole plant is the control net for
integrating plant and environment in daily and seasonal adaptations using
action potentials in a frequency-coded communication. The most important
questions concern the mechanism of oscillator functioning in the
various plant organs and the mode of coupling of oscillators, not to forget
oscillator generation (Fig. 25.12). The following questions need immediate
attention:
1. Where exactly are the action potentials for the systemic signalling generated?
2. What is the structural basis for stem polarity in the propagation of action
potentials?
3. How does an induced leaf define propagation of action potentials in the
stem?
4. What is the induced state of a leaf on the physiological level?
5. How does the photoperiod, e.g. via phytochrome (cryptochrome), create
the induced state of a leaf?
6. What is common in an induced leaf from a short-day and a long-day
plant?
7. How do circadian rhythmicity and hydro-electrochemical activity integrate
the plant as a whole?
Acknowledgements. We gratefully acknowledge the generous support of
Carl Lücking at the Neurocenter Freiburg.