Date of Award

Spring 1982

Project Type

Dissertation

Program or Major

Botany and Plant Pathology Electrophysiology

Degree Name

Doctor of Philosophy

Abstract

Although membrane potentials have been measured in algal cells and in large cells of some higher plants, this investigation is the first to include such measurements in mesophyll cells of elm (Ulmus americana) leaves. The inquiry entailed the development of the technique for measuring elm leaf cell membrane potentials, the determination of membrane potentials expected of healthy, greenhouse elms, and the effects of various physical and chemical factors on the membrane potentials of elm leaf cells.

The membrane potential of a specific cell, was measured by amplifying the potential difference between a microelectrode inserted in the cell and a reference electrode located in the solution bathing the cell. The potential difference was then visible on an oscilloscope screen and on a strip chart recorder. Changes in the potential difference with time or in response to a stimulus were recorded by the strip chart recorder and could then be compared to measurements taken from other cells. Random electrical radiations were shielded from the measurement system by a Faraday cage. Chemical test factors, such as pH, were tested by flushing the test solution through a perfusion chamber in which the cell being measured was located. Physical factors such as light and temperature were tested with the aid of filters and solutions of various temperature, respectively.

The studies provided an electrophysiological picture of the elm inclusive of healthy and stimulus related effects on membrane potential. Also, an equation was developed which combines several criteria from membrane potential traces to facilitate the comparison of the electrical nature of various cells. The equation also can serve as an internal standard for a particular cell, while simultaneously making a statement about the electrical stability of a cell. Although the equation was only tested for elm, it may be useful in interpreting the electrophysiological nature of other species.

This comprehensive investigation on the electrophysiology of elm has provided elm leaf membrane potential expected for healthy elm and for effects on elm of various physicochemical stimuli. The results suggest that electrophysiological methods have potential for use in pathology and breeding programs for elm.

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