Bio-electric Potentials of Intact Green Plants: I. MEASUREMENT OF THE BIO-ELECTRIC POTENTIALS OF COLEOPTILES OFAVENA SATIV AL.,VAR. ‘BARNWELL’

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Abstract
The following article first reviews the possible types of electrodes that may be used in the measurement of the bio-electric potentials of plants. Zinc/zinc sulphate electrodes were chosen for this research on the grounds of their relative insensitivity to light, their ability to undergo positional changes, and their infrequent needs of maintenance; they therefore fulfil the requirements for the measurement of photo- and geo-electric potentials. A detailed description of the construction of such an electrode is given; due to its assembly within a nylon hypodermic syringe it is of an extremely robust form. Some of the problems involved in making contact with the plant are then discussed and two contact systems to overcome these are described. These make use of the continuous circulation of fresh aqueous contact medium through a liquid dorp in contact with the plant tissue. The effects of changes in the growth and contact media on the bio-electric potentils of Avena sativa coleoptiles are then described. These results show that we are measuring diffusion potentials in their broadest sense, and that bio-electric potential maps of plants are of little value, referring as they do to one particular combination of growth and contact medium. The relevance of the results to theories of electrophretic transport of auxin is discussed and it is concluded that the potentials can be in no way responsible.