The Influence of the Cell Membrane on some Toxicity Effects of Growth Substances inNitella

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Abstract
When cells of Nitella are placed in a solution of some plant growth substances there is a profound increase in the membrane resistance as measured by means of an internal silver/silver chloride micro-electrode. This impedance effect is accompanied by some marked visible changes within the cell cytoplasm, these changes being dependent upon the concentration of undissociated growth substance in the vicinity of the membrane, and upon the pH of the external environment. A detailed study is made of these visible changes and, taking into account the negatively charged membrane, one possible interpretation of the results is that only undissociated molecules of the growth substance may enter the cytoplasm of Nitella from the environment, the diffusion obeying a simple Fick Law relationship. The substances are used in sufficient quantity to kill the Nitella cell, death following the visible effects, and they appear to be unique in that their toxic effect produces a system of high membrane impedance.

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