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Articles

Changes in Membrane Potential as a Demonstration of Selective Pore Formation in the Plasmalemma by Poly-L-Lysine Treatment ¹

Department of Botany, Institute of Life Sciences, The Hebrew University of Jerusalem, 91904, Jerusalem, Israel

A technique which allows determination of solute pool concentrations in the cytosol was developed exploiting the interaction between a polycation and the anionic sites of the plasmalemma. It was shown that treatment of Nicotiana tabacum, cv Xanthi, cells in suspension culture with an appropriate concentration of poly-L-lysine induced pore formation selectively in the plasmalemma. The data presented in this paper shows that the plasmalemma of all the cells was affected while the tonoplast remained undamaged. This conclusion is based on the facts that treatment of the cells with the minimum amount of poly-L-lysine which just abolishes the electrogenic potential (similarly to carbonyl cyanide-p-trifluormethoxyphenylhydrazone and NaN₃) induces the leakage of only a small fraction of the K⁺ present in the cells. These effects of poly-L-lysine differ from the effects of polymyxin B which induces total leakage of low molecular weight solutes (R. Weimberg, H. R. Lerner, A. Poljakoff-Mayber 1983 J Exp Bot 34: 1333-1346) and therefore affects also the tonoplast.

Membrane potential was determined using the partition of the lipophilic cation tetraphenylphosphonium. The electrogenic component of the membrane potential was estimated using carbonyl cyanide-p-trifluormethoxyphenylhydrazone and azide. Poly-L-lysine treatment was used to measure K⁺ compartmentation in Nicotiana cells grown in a NaCl-containing medium.

¹ Supported in part by a grant from the United States-Israel Binational Science Foundation, Jerusalem, Israel, and in part by a grant from the United States-Israel (Binational) Agricultural Research and Development Fund.