Reactivation of Cytoplasmic Streaming in a Tonoplast-Permeabilized Cell Model of Acetabularia

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To find whether cytoplasmic streaming in Acetubularia is controlled by Ca^<2+>, a tonoplast-permeabilized cell model was prepared using a vacuolar perfusion technique. The cytoplasmic streaming remained almost normal after perfusion with EGTA medium (10mM EGTA, 40mM PIPES, 5mM MgCl_2 and 800mM sorbitol, pH 6.9), but stopped within 10 min when saponin medium (EGTA medium plus 50μg/ml saponin, 50μg/ml hexokinase and 5mM glucose) was perfused. This model system was reactivated with a solution containing 0. mM ATP and different concentrations of Ca^<2+> (reactivation medium). With the reactivation medium at pCa 6-5, the resumed streaming lasted for about 10min before the cytoplasm aggregated. At pCa 4-3, the streaming was observed only for a few minutes because the cytoplasm aggregated quickly. At pCa 7, no reactivated movement was observed. Reactivation was not induced in an ATP- or Mg^<2+>_deficient medium even in the presence of an adequate concentration of Ca^<2+>, and was inhibited by 50μg/ml cytochalasin B or 1mM N-ethylmaleimide. We concluded from these observations that the cytoplasmic streaming in Acetabularia is very likely to be driven by the actomyosin system in the presence of Mg-ATP and Ca^<2+> at pCa 6-5.
日本植物生理学会の論文