Turgor Regulation in a Brackish Charophyte, Lamprothamnium succinctum : II. Changes in K^+, Na^+ and Cl^- Concentrations, Membrane Potential and Membrane Resistance during Turgor Regulation

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A brackish Characeae, Lamprothamnium succinctum, regulates intracellular osmotic pressure in response to changes in the external salinity and keeps the turgor pressure constant. The osmotic pressure of the vacuole was found to be mostly due to K^+, Na^+ and Cl^-. But in the cytoplasm, the sum of their concentrations was much lower than the cellular osmotic pressure. Electroneutrality was maintained among the analyzed inorganic ions in the vacuole but a strong anion deficiency was detected in the cytoplasm, supporting the existence of organic anions to balance excess positive charges. During turgor regulation, concentrations of inorganic ions in the vacuole changed just enough to accommodate the osmotic pressure change, while those in the cytoplasm remained almost constant. Since the cytoplasmic volume was almost constant during turgor regulation, some organic molecule(s) may have contributed to the osmoregulation of the cytoplasm. The membrane potential and resistance at steady state under different salinities were almost constant. Hypotonic treatment caused a sudden depolarization of the membrane potential and a drastic decrease in membrane resistance. Hypertonic treatment caused a slow hyperpolization of membrane potential but did not significantly affect the membrane resistance. The energetics ofK^+and Cl^- movements across the plasma membrane is discussed based upon the electrochemical potential gradients.
日本植物生理学会の論文