Dependency of Cytoplasmic Streaming on Intracellular ATP and Mg2+ Concentrations

Abstract

The rate of cytoplasmic streaming (v) was measured with reference to intracellular ATP and Mg2+ concentrations in tonoplast-free cells prepared by replacing the cell sap with EGTA[glycoletherdiamine-N-N-N''-N''-tetraacetic acid]-containing medium. The relation of v vs. [ATP]i was a rectangular hyperbola. The ATP concentration for half saturation of v was 0.08 mM in Nitella axillaris and 0.06 mM in Chara corallina. ATP is apparently saturated for cytoplasmic streaming in normal cells, since the ATP concentration in the normal cytoplasm is about 0.5 mM. The relation between [Mg2+]i and v differed from that between [ATP]i and v. Stable cytoplasmic streaming was observed only when [Mg2+]i was equal to or higher than [ATP]i. The inhibition of cytoplasmic streaming by depletion of ATP was completely reversible but that by depletion of Mg2+ was irreversible. ADP supported streaming. This may be explained by assuming that ATP was synthesized from ADP by the action of adenyl kinase in the cell.