Dependence of Plasmalemma Conductance and Potential on Intracellular Free Ca^<2+> in Tonoplast-Removed Cells of a Brackish Water Characeae Lamprothamnium

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In response to hypotonic treatment internodal cells of the brackish water Characeae Lamprothamnium regulate turgor pressure by releasing K^+ and Cl^-, accompanying membrane depolarization and a transient increase in membrane electrical conductance (Okazaki et al. 1984b). The hypothesis that a transient increase in cytoplasmic free Ca^<2+> concentration ([Ca^<2+>]_c) caused by hypotonic treatment triggers release of K^+ and Cl^- from the cell (Okazaki and Tazawa 1986a, b, c) was tested using tonoplast-removed cells. These cells did not regulate turgor pressure. The plasmalemma conductance remained almost constant for a change in the intracellular free Ca^<2+> concentration ([Ca^<2+>]_i) from 10^<-6> to 10^<-2> mol・m^<-3>. The results suggest that some cytoplasmic Ca^<2+>-sensitizing soluble components, which work as mediators to activate K^+ and/or Cl^- channels in the plasmalemma and/or the tonoplast, were lost after desintegration of the tonoplast. The plasmalemma potential was depolarized under high [Ca^<2+>]_i. However, no membrane depolarization was observed upon hypotonic treatment. Since membrane depolarization has been suggsted to occur under normal [Ca^<2+>]_c in intact cells (Okazaki and Tazawa 1986a, b), its absence suggests that some cytoplasmic factors, which induce the membrane depolarization in a Ca^<2+>-independent manner, are lost in tonoplast-removed cells.
日本植物生理学会の論文