Different cytoplasmic calcium contents among three species of Characeae

Internodal cells of three species of Characeae, Nitella flexilis, Nitella axilliformis and Chara corallina, were analyzed for the contents of Ca(2+ )and Mg(2+) in the cytoplasm. To avoid contamination of Ca(2+) from the cell wall and vacuole, the vacuolar sap was replaced with a sorbitol solution containing Sr(2+) by the vacuolar perfusion method after the cell had been treated with Sr(2+). No significant difference in the cytoplasmic content of Mg(2+) was found among three species of Characeae, but significant differences in the cytoplasmic content of Ca(2+) were observed among them. The cytoplasmic Ca(2+) content of N. flexilis was 2.0 times that of N. axilliformis and 3.3 times that of C. corallina. The cytoplasmic drop was furthermore separated into two fractions: a chloroplast-free fraction and a chloroplast fraction. In the chloroplast-free fraction the Ca(2+) content of N. flexilis was 2.3 times that of C. corallina and 2.0 times that of N. axilliformis, while the Mg(2+) content was the same among the three species. In the chloroplast fraction N. flexilis contained about seven times more Ca(2+) and about two times more Mg(2+) than C. corallina. The difference in the cytoplasmic Ca(2+ )content was discussed in relation to the difference in the capacity for the hydration-induced Ca(2+) release existing among the three species.