Accumulation and subcellular distribution of cadmium in ramie (Boehmeria nivea L. Gaud.) planted on elevated soil cadmium contents

The tolerance, accumulation and subcellular distribution characteristics of cadmium (Cd) in ramie (Boehmeria nivea L. Gaud.) were investigated using a 2-year field experiment. The results indicated that ramie has a certain extent of tolerance to soil Cd (<= 20 mg/kg) contamination with no significant decrease in shoot biomass and fibre yield relative to control conditions. Although ramie did not hyperaccumulate Cd, it accumulated considerable amount of Cd in the aboveground parts (approximately 0.19 to 1.09 kg/ha annually). The Cd contents retained in ramie tissues were found in order of roots > stems > leaves. Further, regarding the subcellular distribution of Cd in ramie tissues, 80% of the total Cd was bound to the cell walls of the roots and stems, whereas in leaves the proportion of Cd stored in the cell wall fraction was around 60% and a lesser amount of Cd was stored in the soluble fraction (24.1-25.5%). Our collective results indicated that ramie adapts to Cd stress via the store of a large amount of Cd in cell walls, and suggested potential usefulness of ramie in the phytoremediation of Cd-contaminated farmlands.