The Distribution of Electromotive Forces in the Neighbourhood of Apical Meristems

Abstract

1. A research is described using different methods of experiment on two contrasted types of apical meristems with the object of measuring the permanent electrical field inside and outside the plant in the neighbourhood of the apical meristem under conditions of specified control. 2. Most of the experiments were performed on 3-5-day-old maize seedling roots and turnip seedling hypocotyls. The conditions of measurement were such as to produce minimum stimulation of the plant. The general results were checked by experiments with other plants. 3. The measured p.d. is a result of e.m.f.'s which are unchanged when supplying current of the order of 10-8 amp. through external conductors. Both turnip hypocotyls and sections of couch grass stems generate power of the order of 10-9 W. without polarizing (see text). In these experiments the equivalent resistance of the plant materials obeyed Ohm's law. 4. The average potential gradient along the surface of thirty-four turnip hypocotyls in the neighbourhood of the apical meristems was found to be 7.1±3.8 mV./mm. (over 6-8 mm.). The surface of the meristematic region is positive to that of older tissue. The corresponding average for twenty-five maize roots was 5.7±2.4 mV./mm. (over 6-8 mm.). 5. There are transverse e.m.f.'s between the outside and inside of the plants distributed radially from the stele to the root exodermis and hypocotyl epidermis. The inside is always negative with respect to the outside. The radial e.m.f. is larger in the meristematic region than elsewhere: In turnip hypocotyls, the radial e.m.f. at the meristematic region varies between 44 and 103 mV.; 5-10 mm. from the apex it is 17-60 mV. In maize roots, the corresponding figures are 17-77 and 6-33 mV. There is a small but possibly not significant potential change along the axis in both the organs considered, possibly 1 mV./mm. Under the conditions of the experiment, the interior of the meristem was found to be negative with respect to the rest of the axis. Points 4 and 5 are summarized in Fig. 4A. 6. The theory that the interior of a mass of meristematic tissue is electrically negative to older tissue is discussed in the light of the experimental evidence and with regard to the limitations of the technique used.