Electric Fields in Plants

Abstract

In the past 180 years much has been written on the intimate relationship between electricity and life. Animal and plant materials of many kinds have been found to have electric fields associated with them and to be affected by externally applied fields. The earlier work on plants has been reviewed on a number of occasions (1, 4, 5, 41,51, 53, 54). Since living cells contain aqueous phases which are separated from each other and from the external medium by membranes through which some ions in solution pass more easily than others, it is not surprising that electric fields are produced. The interior of the cell is maintained at a different ionic composition from that of the environment (and in the case of most plant cells at a much higher concentration) by processes requiring the continual expenditure of metabolic energy. These processes are conveniently described in terms of ionic or molecular pumps. Ions diffusing through a membrane establish an electric field which adjusts its magnitude so that the total flux of positive ions through the membrane (as determined by concentration differ­ ences and electric potential difference across the membrane, ion pumps, and possibly bulk water movement) balances the flux of negative ions exactly. Almost always the interior of the cell is more negative in potential than the external solution by 70 to 150 mV. The causes of macroscopic fields in and around bulk tissue will be considered later. Most of the recent investigations of plant electricity have been carried out at the cellular level. Attempts have been made to examine in detail the interrelationships among the electrical properties of the cellular membranes, the potential differences and ion concentration differences across them, and the fluxes of ions through them. Because of the difficulties of working with cells of normal size, most investigators have used the unusually large coeno­ cytic cells of certain fresh water and marine algae. One aim of these studies is to determine which ions cross a membrane passively (their movement being determined by concentration differences and electric potential differ­ ences alone), and which ions are being pumped as well. This information is essential to a fuller understanding of the mechanisms of ion accumulation by cells. Very good accounts of the electrochemical theory of ion movement in plant cells were given by Briggs, Hope & Robertson (3) in 1961 and by