Electric Characteristics and Cytoplasmic Streaming of Characeae Cells Lacking Tonoplast

Abstract

The tonoplast of Characeae internode was removed by replacing the cell sap with solution containing a Ca2+-chelating agent EGTA [Cethyleneglycol-bis-(β-aminoethyl ether) N, N'-tetraacetic acid]. After replacement, small endoplasmic granules and endoplasmic drops without clear outline were observed in the vacuole. These observations confirmed the disappearance of the tonoplast. Chloroplasts in the endoplasmic drop were often observed to rotate. The endoplasm remaining on the cortical gel flowed actively at nearly the same rate as endoplasm in cytoplasmic streaming of normal cells for at least several hours. ATP and Mg2+ were indispensable for cytoplasmic streaming in tonoplast-free cells. The tonoplast-free cells had very high membrane resistance. The current-voltage relationship showed that the membrane rectifying action was strengthened by removing the tonoplast. The cells elicited prolonged action potentials of rectangular shape. Cessation of cytoplasmic streaming accompanied with the action potential was never observed in tonoplast-free cells although this is generally observed in normal cells. These phenomena on tonoplast-free cells occurred only when the concentration of free Ca2+ in the perfusion medium was less than 10-6 M. The calcium concentration in the protoplasm was analyzed to estimate the free Ca2+ concentration in the cell after disintegration of the tonoplast and dispersion of the cytoplasm-bound Ca into the entire cell space.