Different cytoplasmic calcium contents among three species of Characeae

Abstract

Internodal cells of three species of Characeae, Nitella flexilis, Nitella axilliformis and Chara corallina, were analyzed for the contents of Ca2+ and Mg2+ in the cytoplasm. To avoid contamination of Ca2+ from the cell wall and vacuole, the vacuolar sap was replaced with a sorbitol solution containing Sr2+ by the vacuolar perfusion method after the cell had been treated with Sr2+. No significant difference in the cytoplasmic content of Mg2+ was found among three species of Characeae, but significant differences in the cytoplasmic content of Ca2+ were observed among them. The cytoplasmic Ca2+ 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 Ca2+ content of N. flexilis was 2.3 times that of C. corallina and 2.0 times that of N. axilliformis, while the Mg2+ content was the same among the three species. In the chloroplast fraction N. flexilis contained about seven times more Ca2+ and about two times more Mg2+ than C. corallina. The difference in the cytoplasmic Ca2+ content was discussed in relation to the difference in the capacity for the hydration-induced Ca2+ release existing among the three species.