Electrophysiology and Phototropism - Communication in Plants: Neuronal Aspects of Plant Life - page 359

Fig. 24.3. Action potentials in soybean induced by irradiation at 450 nm in direction B as
shown in Fig. 24.1. The irradiance was 8.5 µE m 2 s. The distance between the electrodes was

5 cm. The soil was preliminarily treated with water every day. The volume of soil was 0.5 L.
The frequency of scanning was 50,000 samples/s

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(Figs. 24.3-24.5) depending on the wavelength of light irradiation. Irradi-
ation at wavelengths 400−500 nm induces fast action potentials in soybean
with a duration time of about 0.3 ms; conversely, the irradiation of soybean
in direction B at wavelengths between 500 and 600 nm fails to generate
action potentials. The action spectrum of light-induced action potentials
is illustrated in Fig. 24.6. Irradiation between 500 and 700 nm does not
induce phototropism. Irradiation of soybean by blue light induces positive
phototropism (Fig. 24.7).
The sensitive membranes in phloem cells facilitate the passage of elec-
trical excitations in the form of action potentials. The action potential has
a stereotypical form and an essentially fixed amplitude - an “all-or-none”
response to a stimulus. Each impulse is followed by the absolute refractory