The permeability properties of the plasmalemma of oat mesophyll protoplasts during the application of an electric field pulse were studied. As a measure, the intracellular fluorescence resulting from the uptake of DNA and RNA staining dyes (ethidium bromide, berberine hemisulfate), showing a very low rate of permeation across the plasmalemma of intact protoplasts, were determined microphotometrically.The results show that membrane breakdown, caused by supercritical field strengths, leads to an uptake of the charged dyes only via those membrane sites oriented toward the positive electrode. Mechanisms possibly underlying this asymmetrical uptake as well as its practical application are discussed.

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By variation of physical parameters (field strength, pulse duration) which result in electrofusion and electroporation, properties of the plasma membrane of different types of plant cell protoplasts were analyzed. The lower threshold for that field pulse intensity at which membrane breakdown occurred (recorded as fusion event) depended on pulse duration, protoplast size, and protoplast type (tobacco, oat; vacuolated, evacuolated). This fusion characteristic of plant protoplasts can also be taken as a measure of the charging process of the membrane and allows thus a non-invasive determination of the time constant and the specific membrane capacitance. Although the fusion yield was comparable at pulse duration/field strength couples of, e.g., 10 μs/1.5 kV*cm(-1) and 200 μs/0.5 kV*cm(-1), hybrid viability was not. Rates of cell wall regeneration and cell division of tobacco mesophyll protoplasts were not affected but may have been increased at short pulse duration/high field strength. Plating efficiency, in contrast, was significantly decreased with longer pulse duration at low field strengths.

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