Ion flux interaction with cytoplasmic streaming in branchlets of Chara australis

Both parts of the actin-myosin complex involved in cytoplasmic streaming could be regulated by mineral ions. The main goal of this study was to find a relationship between cyclosis and ion transport across the cell wall and plasma membrane. The transport of K+ and Ca2+ along pH bands in Chara branchlet internodal cells was characterized by using the MIFE system for non-invasive microelectrode measurement of ion fluxes. Branchlets formed acidic and alkaline bands with the pH ranging from 5 to 8. Different pH patterns were observed for different sides of the branchlets. Sides with cyclosis streaming acropetally generally showed greater variation in the profiles of pH and H + fluxes. Although a high correlation was not found between pH bands and Ca2+ or K+ fluxes, there was a positive correlation between Ca2+ and K+ fluxes themselves for both sides of the branchlets. Application of cytochalasin D, an inhibitor of cyclosis, had no immediate effect on pH and ion fluxes, however, the time of cyclosis cessation corresponded with a dramatic change in Ca2+ and K+ fluxes; pH profiles and H+ fluxes were affected within 2 h. The evidence suggests that, in Chara branchlets, pH band formation and Gd3+- insensitive Ca2+ transport systems are linked to the cyclosis machinery: (i) the pH band amplitude for the acropetally streaming side was larger than that for the basipetally streaming side; (ii) cessation of cytoplasmic streaming after cytochalasin D application resulted in changed pH banding profiles and H+, Ca2+ and K+ fluxes; and (iii) the application of GdCl3 or incubation in GdCl3 solutions did not lead to the cessation of cytoplasmic streaming, although external Ca2+ fluxes changed.