Rotating condenser method to measure two-dimensional biophysical potentials

Abstract

A new device has been constructed to measure bioelectric potentials in plants. It measures, simultaneously, the electric length potentials along the shoot and the potentials across the shoot. Such potentials arise in plants in response to external physical stimuli. The instrument measures the potentials without touching the plants. The electric fields are detected capacitively by rotating two discs on two sides of the shoots. Each disc has four symmetrical 'vanes'; the discs are fixed and rotated 45 degrees with respect to each other. All vanes are electrically connected. The sensor arrangement will separate the length and the transverse potentials by generating two different frequencies (8 and 4 times the disc rotating frequency). The signal so generated is capacitively coupled to a high input impedance (1013 Omega ) amplifier. Two selective amplifying systems are used to generate feedback voltages and the overall equipment will work as a zero instrument. The equipment has been tested and used to record potentials in plants stimulated for 30 min in horizontal position. Transverse potentials recorded under these circumstances were of the order of 50 mV.