Abstract: The properties of plasma membrane Ca2 + -ATPases from wheat ( Triticum aestivum L. cv. Lengchun No. 13) root and leaf were compared, and their different properties were analyzed in association with the differentia of the functions of these two organs and their relevant environments. Root plasma membrane Ca2 + -ATPase showed a high activity in a broad range of pH and an optimum reaction temperature of 45 ℃, while the leaf enzyme activated in a narrow range of pH and an optimum reaction temperature of 50 ℃. Hill coefficient of root plasma membrane Ca2 + -ATPase for ATP was 1.6, revealing an obvious positive cooperativity. In contrast, that of leaf plasma membrane Ca2 +-ATPase was 1.0, being in keeping with Michaelis-Menten dynamics. For Ca2 + activation, Hill coefficient of plasma membrane Ca2 + -ATPases from both organs were less than 1, suggesting that both had negative cooperativity. The enzymes were activated by calmodulin and inhibited by Mg2+.

Key words: Ca2+ -ATpase, Mg2+, Calmedulin, Plasma membrane, Wheat, Root, Leaf