(1) Temporary falls of the resting potential (maximum c.a. 100mV) observed in the seed embryo of
Vigna sesquipedalis are supposed to belong to the category of the general excitation phenomenon, because they can be brought about by stimuli of various nature in the some manner, although their processes are some 10
3-10
4 times as slow as those in animal tissues.
(2) Applying rectangluar current pulses (1-60V) on the hypocotyl of the plant by means of two accessed stimulating electrodes, the presence of a polarity in parallel with the growth axis was confirmed concerning the excitability; fairly distinguishable two types of the electric responses (I & II) were detected, each corresponding to the positive (acropetal) and negative (basipetal) direction of the stimulating current applied. In this case one of the measuring electrodes (M
+) was placed in the middle of the two stimulating electrodes and another one (M
0) on the boundary of hypocotyl and radicle as counter electrode.
(3) A double propagation of excitation with velocity of 0.2-0.5mm per minute along the growth axis was also observed.
(4) Quantitative relations between intensity as well as length of stimulus and excitation were investigated. Excitation of the type I takes place complying with the Weber-Fechner's low, while that of the type II has its maximum at a certain strength of stimuli.
(5) Further expriments, where M
+ was placed on the same position as either of the stimulating electrodes, proved the existence of one more polarity in the radial direction of hypocotyl, namely, out flux of the stimulating current from the surface of the organ causes the excitation of the type I while influx of the stimulating current causes the excitation of the type II, irrespective of the direction of current along the growth axis.
(6) Thus the polarity along the growth axis reveals itself in the deviation of the “neutral point” towards root tip concerning the excitation types. The nature of the radial polarity was discussed on the basis of the movement of ions through stressed protoplasmic membranes.
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