Effects of calcium on content of calmodulin, activity of Ca^{2 +}-ATPase and their gene expressions in apple (Malus pumila Mill.) fruits

Effects of calcium on calmodulin (CaM) content, Ca2 +-ATPase activity and their gene expressions in apple (Malus pumila) fruits were investigated under the hydroponic condition with 0，1，10 mmo1/L CaCl2 and 5 mmo1/L EGTA. CaM and Ca2 +-ATPase gene were isolated by homologous cloning and their expression patterns were analyzed by realtime PCR. Addition of 10 mmo1/LCaCl2 to the culture solutions with 12 h exposure significantly increased soluble Ca2 + and CaM contents in apple fruits. With the CaM content increasing, plasma and tonoplast membrane Ca2 +-ATPase activities were enhanced after 12 and 24 h Ca exposure respectively,resulting in the decrease in the soluble Ca2 + content after 48 h Ca exposure. In molecular level, the abundances of CaM and Ca2 +- ATPase genes were up-regulated after 6 h and 12 h Ca exposure, respectively, in accordance with change of the CaM content and plasma membrane Ca2 +-ATPaseactivity. Addition of 5 mmo1/L EGTA to the culture solutions induced up-regulated the expression of the CaM gene, however, did not markedly change the expression of the Ca2 +-ATPase gene. It was concluded that external calcium might increase soluble Ca2 + and CaM contents and the expression of theCaM gene to stimulate an intracellular Ca2 +/calmodulin signaling system. Plasma and tonoplast membrane Ca2 +-ATPase are of major physiological importance to expel Ca2 + from eukaryotic cells and to maintain overall Ca2 + homoeostasis by enhancing their activities and gene expression.