Abstract
Common reed is widely distributed in the world and tolerant to toxic heavy metals, such as Zn, Cd, and Pb. Cd concentration of stem is 4 fold higher than that of leaves, and 70% of stem Cd are soluble. Stem cell sap from plants grown with 0.1mM of CdCl2 for 7day was fractionated by ultrafiltration, and 60% of Cd were detected in 10k-50kDa fraction. Molecular weight of well-known Cd-binding peptide is smaller than 10kDa, thus a novel Cd-binding molecule may be found in stem of common reed. We examined whether SH groups in 10k-50kDa fraction bind Cd. The SH:Cd molar ratio was 1:5, and Cd was not released when added dithiothreitol, suggesting that Cd was not bound to SH groups in this fraction. To speculate the structure of this Cd-binding molecule, various degrading enzymes were added to stem cell sap. Cd was released only when added alpha-amylase. These results suggest that Cd-binding macromolecule has the alpha-glucan backbone. Moreover 20% of Cd in 10k-50kDa fraction was released when added mercaptoethanol. Taken together, SH groups may not bind Cd on the surface of the macromolecule, but disulfide bonds may be involved in maintenance of the structure which is suitable to bind Cd.
