Effects of cadmium on calmodulin content and Ca²⁺-ATPase activities of maize（Zea mays）seedling

A hydroponics culture experiment was conducted to examine the effects of cadmium (Cd) stress on calmodulin (CaM) content and Ca2+-ATPase activities in maize (Zea mays) plant. Maize seedlings were treated with 0, 5, 20, and 100 mol/L Cd for periods of 12 to 168 h. Results showed that the content of soluble Ca2+ in plant were increased by cadmium stress. The highest levels of soluble Ca2+ in leaves and roots were found in the plants with 48 h and 24 h exposure to Cd respectively. CaM content in plants was enhanced with increasing Cd concentrations and prolonged Cd treatment. However, CaM content in plants began to decrease after 168 h treatments of 20 mol/L and 100 mol/L Cd. The Ca2+ -ATPase activities of Cd stressed plants were higher than that without Cd addition, but they decreased gradually with higher concentrations of Cd and extended Cd treatment after 48 h (plasma, tonoplast and endoplasmic reticulum membrane) and 24 h (mitochondrial membrane). The decrease of Ca2+-ATPase activities in cell membrane systems showed the following pattern: plasma membranetonoplast membraneendoplasmic reticulum membranemitochondrial membrane. The Ca2+-ATPase activities of the same microsomal were higher in root than in leaf.