Influence of Cytoplasmic Streaming and Turgor Pressure Gradient on the Transnodal Transport of Rubidium and Electrical Conductance in Chara corallina

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In order to study the transnodal transport of Rb^+ in internodal cells of Chara corallina, a low-temperature loading system was established to separate the loading process from the transport process. Tandem cells, consisting of internode-node-internode, were isolated from algal plants. Treatment of a single internode with 100 mM RbCl at 5℃ for 30 min caused an accumulation of 43 mM Rb^+ in the cytoplasm of this cell (= source cell), but no Rb^+ was found in the other internode (= sink cell) of the tandem cells. In 40 min after a return to 25℃, about 12% of the Rb^+ loaded in the source cell was transported into the sink cell. The apparent transnodal permeability of Rb^+ was calculated to be 4.6 × 10^<-7> m・s^<-1>. Under the assumption that the total cross-sectional area of plasmodesmata occupies 10% of the nodal area, the diffusion coefficient of RbCl through plasmodesmata was calculated to be 2.3 × 10^<-11> m^2・s^<-1> which is about 1% of the free diffusion coefficient in water (2 × 10^<-9> m^2・s^<-1>). The transnodal transport of Rb^+ was intimately correlated with the rate of cytoplasmic streaming. The rate of streaming in both the source and sink cells was varied either by treating the cells with cytochalasin B (CB) or by lowering the temperature. The transport rate correlated with the streaming rate irrespective of the method used. Since the level of ATP was not influenced by CB or low temperature, the transnodal transport is assumed to be the result of passive diffusion process through plasmodesmata. A turgor pressure gradient across the node decreased both the nodal electrical conductance and the transnodal transport of Rb^+. By contrast, the exposure of both internodal cells to a solution of sorbitol had no effect on either of them. A turgor pressure gradient of 240 mOsm decreased the transport of Rb^+ in the first hour to 3% of the control, while it decreased the nodal conductance to about 50%. The increase in the electrical resistance occurred on the junction side between the node and the internode that was treated with sorbitol. Cytochalasin E had no effect on the nodal electrical resistance. It is assumed that plasmodesmata are equipped with a valve-like mechanism which is sensitive to the gradient of turgor pressure across the node and is not regulated by an actomyosin system.
日本植物生理学会の論文

Influence of Cytoplasmic Streaming and Turgor Pressure Gradient on the Transnodal Transport of Rubidium and Electrical Conductance in Chara corallina

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