Depolarization of cell membranes in leaves of Lycopersicon by extract containing Ricca's factor

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Abstract
Extract containing Ricca''s factor depolarized the membrane potential of at least 3 types of cells in Lycopersicon leaves: mesophyll, midrib parenchyma and midrib epidermis. The depolarization was studied in some detail for the epidermal cells, in which depolarization began without a lag and was completed within 60-90 s. The maximum rate of depolarization was typically about 3 mV/s. No changes in resistivity, capacivity or intercellular electrical coupling were detected during the depolarization. Extract from 0.5 mg fresh leaf tissue in 1 ml of water at pH 6.6 caused threshold depolarization in many experiments, and a concentration only 40 times greater was usually saturating. Raising the pH increased the concentration of factor required for saturation. With subsaturating concentrations of factor the potential recovered somewhat after depolarization. When factor-free medium was washed over the tissue the potential depolarized briefly before returning to its baseline value. With saturating concentrations of factor the potential depolarized to an essentially stable level and no transient depolarization occurred when the factor was washed out. The potential remaining after application of a saturating concentration of factor was independent of the initial baseline potential but depended on the concentration of K+ in the equilibration medium and in the extract. The saturation level of depolarization was in the range of the Nernstian potential for K+, but whether it was precisely equal to the Nernstian potential for K+ was not established. The occurrence and influence of Ricca''s factor should be taken into account in all electrophysiological studies of shoot tissue since the factor appeared to be released whenever cells were wounded and may be released during other kinds of stress as well.

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