Higher plants exhibit an oscillation of electrical potential near the surface along the root. The oscillation was studied with the aid of both the usual intracellular microelectrode technique and the extracellular multielectrode technique, the latter making it possible to measure simultaneously electrical potentials along the root. It was found that the oscillation of extracellular surface potential showed the largest amplitude in the elongation region, and the phase of the oscillation in this region differed by 180 degrees from that in the mature region, where the oscillation appeared coherent. The measurement of the intracellular electrical potential suggested the existence of oscillatory components localized to the parenchyma/xylem interface in the elongation region. A theoretical analysis based on an electrical circuit network described the above-mentioned behavior. It was shown that the oscillation was propagated along the root over several centimeters without substantial decay in the mature region.
Extracellular and intracellular electric potentials in bean roots are known to show electric oscillations along the longitudinal axis with a period of several minutes. The relationship between growth and the electric oscillations was studied using roots of adzuki (Phaseolus chrysanthos). We measured surface electric potentials with a multielectrode apparatus while simultaneously measuring elongation using a CCD camera and monitor. Roots having an electric oscillation grew faster than roots with no oscillation. Furthermore, elongation rate was higher in roots with higher oscillation frequency. Oscillation frequency had a strong dependence on temperature; i.e. 010 was estimated at 1.7. These results suggest a correlation between electric oscillation and elongation.A periodic electrical pattern is formed near the surface of the internodal cell of Characean species (13). Electric current patterns appear along the surfaces of roots (1,4,20,25). Oscillations of surface electric potential also occur (7,8,16,19,22). Bean roots show spontaneously electric oscillations without a stimulus along the root surface with about 5 min period, which continues constant for over a few hours (16,19). The amplitude of the oscillation is maximal in the elongation region and the phase of the oscillation in that region differs by 1800 from that in the mature region. It is noticeable that the oscillation appears consistent (or coherent) in the mature region over several centimeters, because the phase and also the period are the same at any position (16,19,22). Resonance of oscillation occurs in such a way that the phase of osmotic pressure variation sets the phase of electric oscillation when an oscillation of osmotic pressure is applied to a root (7,8).In a previous paper (22), the membrane potential within the root was measured with a microelectrode technique (2) while the surface electric potential was measured using a multielectrode measuring method (4,19,20). In the elongation region, the membrane potential of epidermal cells oscillated with the same period and the same phase as the surface potential. In the mature region, on the other hand, the membrane potential did not oscillate, although the surface potential oscillated. It was concluded from a theoretical analysis using an equivalent electrical circuit that the source ofsurfacepotential oscillations existed in the membrane at the xylem/ parenchyma interface in the elongation region and the oscillation was propagated to the mature region inside the parenchyma. A mechanism for the oscillations has not, however, been elucidated especially from the viewpoint of a relation to growth.The purpose ofthe present paper is to study the relationship between growth and electric oscillation in roots. The surface electric potentials were measured together with a measurement of elongation. MATERIALS AND METHODS Plant MaterialExperiments were done using roots of adzuki bean (Phaseolus chrysanthos) seedlings which were 4 to 5 d old. Seeds were soaked in water at 40 ± 1°C for 3 h and were ...
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