Ca2+ and phosphate releases from calcified Chara cell walls in concentrated KCl solution

Ca2+ and P-i (inorganic phosphate) releases from isolated calcified and uncalcified Chara cell walls were measured with a Ca2+-selective electrode and colorimetry, and their ionic relations were analysed on the basis of the electroneutrality rule. The results showed that (1) not only Ca2+ but also P-i can be released from isolated calcified Chara cell walls into pure deionized water and 100 mM KCI solution, and (2) the positive charge due to the Ca2+ released cannot be neutralized only by the negative charge from the simultaneously released P-i. These findings suggest that calcium bands of calcified Chara cell walls are composed of mainly CaCO3 and CaHPO4 and some anions other than P-i should be released simultaneously with the Ca2+ and P-i. More Ca2+ and P-i can be solubilized from isolated Chara cell walls in 100 mM KCI solution than in pure deionized water. The pH value of 100 mM KCl solution in which isolated uncalcified young Chara cell walls have been immersed is a little lower than that of pure deionized water in which the same isolated uncalcified young Chara cell walls have been immersed, suggesting that some acidic substances are solubilized by 100 mM KCI. To explain this from the viewpoint of solution chemistry, the solubilities of pure CaCO3 and pure CaHPO4 in water and 100 mM KCl solution were measured with a Ca2+-selective electrode and their pH values with a glass pH electrode. The conclusion reached was that the Ca2+ release from isolated Chara cell walls is accompanied by the release of P-i, CO32- and acidic substances. This suggests that the so-called calcium bands and/or ionic relations, including ion exchange, in Chara cell walls are chemically or physicochemically more complex than they are currently considered to be.