Pb uptake, accumulation, subcellular distribution in a Pb-accumulating ecotype of Sedum alfredii (Hance)

Lead concentrations in roots, stems and leaves of accumulating and non accumulating ecotypes of Sedum alfredii (Hance) were studied through a hydroponic experiment with different Pb concentrations supplied as Pb(NO(3))(2). Lead concentrations in leaves and stems of the accumulating ecotype were 4 - 9 times and 3 - 5 times those of the non-accumulating ecotype, and Pb accumulated amounts in stems and leaves of the accumulating ecotype were 4 - 9 times and 8 - 11 times higher than those of the non-accumulating ecotype, respectively. The results indicated that the accumulating ecotype had better ability to transport Pb from roots to shoots. The subcellular distributions of Pb in the root, stem and leaf tissues were studied using sucrose differential centrifugation. Approximately 50% of Pb contents was found to be associated with the cell wall fraction in stems of the accumulating ecotype and the percentage increased to 80% both in roots and leaves, no matter when plants were grown with different levels of Pb. The results indicated that the distribution of Pb on cell walls of the accumulating ecotype could mainly account for the high tolerance to Pb.