Hemicellulose modification promotes cadmium hyperaccumulation by decreasing its retention on roots in Sedum alfredii

Aims As a vital polysaccharide related to mechanisms of plant resistance to trace metal in the root cell wall, the role of hemicellulose in cadmium (Cd) accumulation in hyperaccumulators is still unknown. We investigated hemicellulose modification in response to Cd in two populations of Sedum alfredii. Methods Nonhyperaccumulating population (NHP) and hyperaccumulating population (HP) of S. alfredii were grown in nutrient solutions with or without 25 mu M Cd for 15 d. Monosaccharide composition of root cell wall hemicellulose and its remolding mechanisms (e.g. enzyme activity and gene expression) were analyzed by using gas chromatography-mass spectrometer (GC-MS), fourier transform infrared spectrometer (FTIR), nuclear magnetic resonance (NMR) and quantitative real-time PCR techniques. Results In 25 mu M Cd treatment, root cell wall hemicellulose in the NHP significantly (P < 0.05) increased and its hemicellulose-bound Cd was nearly 2.5-fold higher than that of HP. In the presence of Cd, xylose and glucose, proved to be the main component of hemicellulose, were higher in the NHP than in the HP owing to the up-regulation of XET/XEH and encoding gene (XTH 31). Cd-113-NMR and FTIR results indicated that hemicellulose with hydroxyl and carboxyl groups of HP retained less Cd than that of NHP. Conclusion Hemicellulose modification decreased the Cd-binding capacity of the root cell wall and increased the entry of Cd in the shoot of HP S. alfredii.