Different strategies of Cd tolerance and accumulation in low-Cd-accumulating and high-Cd-accumulating ramie cultivars

Ramie (Boehmeria nivea L.) is an industrial crop for the heavy metal-polluted farmland in south China due to its high tolerance and accumulation ability of heavy metals. To investigate if antioxidation enzymes and heavy metal chelators are synergism defense mechanisms of cadmium, YJ, a low-Cd-accumulating, and DY, a high-Cd-accumulating ramie cultivar, were cultivated with increasing concentrations of cadmium such as 0, 5, 25 and 50 mg/L. The Cd accumulation and distribution, oxidation stress, glutathione (GSH), phytochelatins (PCs) as well as the level of the transcripts that encode glutamate-cysteine ligase (GCL) and phytochelatin synthase (PCS) were determined. After 7 days of Cd exposure, we found that the higher Cd accumulation in DY was associated with higher antioxidative enzyme activities, suggesting that antioxidative enzymes were the crucial factors associated with the diversity in Cd cumulation. YJ suffered less oxidative stress, while higher root activities and soluble protein content, along with higher contents of GSH and PCs were identified in YJ under Cd exposure, particularly under high dose of Cd exposure. Failing to detoxify overmuch Cd owing to GSH and PCs limitation as well as the downregulation of BnGCL1 and BnPCS1 might cause the lower tolerance identified in DY. The results herein reveal that Cd detoxification of the YJ cultivar happened primarily through the regulation of gene expression, increased GSH content, and PCs content, which sequestered Cd in the roots and decreased Cd translocation to the shoots. Furthermore, we infer that the ramie cultivar has evolved different strategies to realize the detoxification of Cd and to tackle the corresponding oxidation stress.