Subcellular distribution and chemical forms of Cd in two Miscanthus floridulus populations

Using differential centrifugation technique and sequential chemical extraction methods, the subcellular distribution and the chemical forms of Cd in the roots, stems and leaves of two Miscanthus floridulus populations, one population from Boluo an uncontaminated site,and another population from Dabaoshan a mine site, under nutrient solution culture were studied in green house. The results showed that, 65%～90% of total Cd were bound to cell wall and soluble fraction in both populations,and only a small quantity of Cd distributed in chloroplast, karyon and mitochondrion, which suggested that cell wall and soluble fraction in the plant were the major storage sites for Cd. The subcelluar Cd distribution in the roots, stems and leaves of both populations were as follows: cell wall(F1) soluble fraction(F4) karyon and chloroplast(F2) mitochondria(F3). The addition of Cd generally reduced the percentage of Cd in the cell wall(F1) and in the soluble fraction of the non-mine population,but increased the percentage of Cd in the cell wall(F1) and reduced it in the soluble fraction of the mine population, suggesting that cell wall binding has been strengthened. As to the chemical forms, at 5 mg·L-1 Cd, H2O -extractable, NaCI-extractable, and HAc-extractable Cd were dominant in roots of the mine population, and the proportion of them are 36.41%, 28.15%, 17.04%, respectivesly. But for the non-mine population, NaCI-extractable, H2O -extractable and HAc-extractable Cd were dominant in roots. NaCI-extractable Cd in roots decreased to 21.45% for the non-mine population but increased to 41.29% for the mine population with increasing Cd level to 40 mg·L-1. The results mentioned above indicate that cell wall binding, vacuolar compartmentalization in the soluble fraction and transferring to lower active chemical forms are the main tolerance mechanisms for Cd in the mine population.