References

25 Hydro-Electrochemical Integration of the Higher Plant 371
Fig.25.1. Experimental setup. Measuring device for long-term recording of changes in
electric surface membrane potential, leaf movements (LM) and stem elongation rate (SER).
Video imaging at 950 nm for continuous monitoring of LMs in light–dark cycles. Linear
voltage differential transformers (LVDTs)hookedtotheplantstemwithaspring-loaded
constant pull of 1.5 g. Platinum electrodes are used together with a commercial contact
gel for measuring and stimulation. Additional sensors monitor electromagnetic noise,
temperature, light intensity and humidity
down the stem axis to the lowest still growing pair of leaves. The rhythmic
LMs reflect rhythmic changes in hydraulics. Such changes in hydraulics are
also obvious at the basal end of the plant from a circadian rhythm in root
exudation (Fig. 25.2).
Controlofcellvolumeandwaterrelationsattheplasmamembranemost
likely involves stretch-activated ion channels (Kloda and Martinac 2002;
Lang and Waldegger 1997). Securing the integrity of the plasma membrane
therefore seems imperative. Maintaining integrity of the plasma membrane
might be the basis of hydro-electrochemical activity reflected in action
potentials as discussed by Goldsworthy (1983).
Membrane potentials, being ubiquitous in all living cells, with the inside
of the cell about 100 mV negative compared with the outside, are maintained
by the activity of electrogenic ion pumps providing the energy for
the active transport of many substances across the membrane. Depolarisation
of cells leads to action potentials. Goldsworthy (1983) proposed that
action potentials might have evolved as a mechanism for rapidly switching