A Major Role for Transcellular Ca^<2+> Ion Currents in Cell Elongation in The Unicellular Green Alga Closterium : GROWTH AND DEVELOPMENT

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In semicells of the unicellular green alga Closterium that are undergoing elongation, transcellular ion currents enter the elongating region of the cell and leave via the non-elongating region of the cell, as in the case of many other tip-growing organisms. The density of the inwardly and outwardly directed currents was 142.5±63.7 nA cm^<-2> (n=42) and 109.3±46.5 nA cm^<-2> (n = 33), respectively, at the respective regions of the cells. Both currents clearly decreased with decreases in the external concentration of Ca^<2+> ions, and they were completely blocked by addition of Ca^<2+>-channel blockers, such as 20 μM LaCl_3, to the external medium. Increases in pH up to 10.2 had no effect on the currents, but a decrease in pH from 7.5 to 5.7 or 4.5 resulted in an explosive increase in the currents. Removal of external K^+ and Cl^- ions induced some increases in the currents, but removal of external Na^+, Mg^<2+> plus SO^<2+>_4 and NO^-_3 ions had little effect on the currents. A major part of the currents may be carried by Ca^<2+> ions, while H^+, K^+ and Cl^- ions may play a minor role as members of the group of ions that carry the currents. Thus, there is a clear relationship between Ca^<2+> ion currents and elongation in Closterium.
日本植物生理学会の論文