Electrophysiology and Phototropism - Communication in Plants: Neuronal Aspects of Plant Life - page 351

24 Electrophysiology and Phototropism

Alexander G. Volkov

Abstract Plants continually gather information about their environment. The conduction of
bioelectrochemical excitation is a fundamental property of living organisms. Cells, tissues,
and organs transmit electrochemical signals over short and long distances. The sensitive
membranes in phloem cells facilitate the passage of electrical excitations in the form of
action potentials. We have created a unique electrophysiological workstation that can ef-
fectively register this electrical activity in real time. It allows basic properties of electrical
communication in green plants to be established. Our workstation has very high input
impedance and a resolution of 0.01 ms. Excitation waves in higher plants are possible mech-
anisms for intercellular and intracellular communication in the presence of environmental
changes. Ionic channels, as natural nanodevices, control the plasma membrane potential
and the movement of ions across membranes regulating various biological functions. Some
voltage-gated ion channels work as plasma membrane nanopotentiostats. Blockers of ionic
channels, such as tetraethylammonium chloride and ZnCl 2 , stop the propagation of action
potentials in soybean induced by blue light and inhibit phototropism in soybean plants.
Voltage-gated ionic channels control the plasma membrane potential and the movement of
ions across membranes regulating various biological functions. These biological nanode-
vices play vital roles in signal transduction in higher plants. Tetraethylammonium chloride
and ZnCl 2 block K + and Ca 2+ ionic channels. These blockers inhibit the propagation of
action potentials induced by blue light, and inhibit phototropism in soybean plants. The
irradiation of soybean plants at 450 50 nm induces action potentials with duration times

of about 1 ms and amplitudes around 60 mV. The role of the electrified interface of the
plasma membrane in signal transduction is discussed.

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24.1
Introduction
Plants continually gather information about their environment (Ksenzhek
and Volkov 1998). This conglomerate of information supports the main-
tenance of homeostasis. Environmental changes elicit various biological
responses (Volkov 2000; Volkov and Mwesigwa 2001a,b). Plants synchro-
nize their normal biological functions with their responses to the environ-
ment. The synchronization of internal functions, based on external events,
is linked with the phenomenon of excitability in plant cells. The cells, tis-
sues, and organs of plants possess the ability to become excited under
the influence of environmental factors, referred to as irritants. The extreme
sensitivity of the protoplasm to chemical stimuli is the basis for excitability;
these signals can be monitored.