Roles of Calcium and Cadmium on Cd-Containing Intra- and Extracellular Formation of Ca Crystals in Tobacco

Growth was severely inhibited when tobacco plants were exposed to toxic levels of cadmium (0.2 mM). However, when this treatment was combined with a high concentration of calcium (30 mM), the Cd-induced damage was strongly alleviated. Under these enhanced conditions, i.e., 30 mM Ca and 0.2 mM Cd, Ca crystals not only were heavily deposited in the leaves but were also actively excreted from the trichomes. The X-ray spectrum from our Energy Dispersive analysis revealed that both intra- and extracellular Ca crystals contained detectable amounts of Cd.