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Cadmium adsorption by willow root: the role of cell walls and their subfractions
Authors:Guangcai Chen  Yongqing Liu  Renmin Wang  Jianfeng Zhang  Gary Owens
Institution:1. Research Institute of Subtropical Forestry, Chinese Academy of Forestry, Fuyang, 311400, Zhejiang, China
2. College of Agriculture and Biotechnology, Zhejiang University, Hangzhou, 310029, China
3. Mawson Institute, University of South Australia, Mawson Lakes, SA, 5095, Australia
Abstract:Plant cell walls may play an important role in the uptake and accumulation of heavy metals. This study was undertaken to obtain a better understanding of the role of the root cell walls (RCW) and their subfractions on adsorption of cadmium (Cd) in a promising woody phytoremediation species, Salix jiangsuensis J172. In order to examine how Cd binding was affected by pectin and hemicellulose, RCW were isolated and sequentially fractioned by removing pectin (RCW1), partial removal of hemicellulose (RCW2), and complete removal of hemicellulose (RCW3). The RCW and fractions were characterized by Fourier transform infrared spectroscopy, which suggested decomposition of hemicellulose and a decline in nitrogen content following cell wall isolation and fractionation. The adsorption affinity of Cd increased gradually following the sequential extraction of root cells, suggesting that hemicellulose negatively impacted Cd adsorption, while pectin and cellulose enhanced Cd adsorption. Cd adsorption dynamics and isotherms could be best described by the pseudo-second-order (R?>?0.99) and Freundlich (R?>?0.97) models, respectively. Thermodynamic properties (?G, ?H, and ?S), determined using the van’t Hoff equation, indicated that while Cd adsorption was endothermic, and spontaneous for RCW2 and RCW3, adsorption was not spontaneous for the root, RCW, and RCW1. The results provide evidence for the importance of the root cell walls in the adsorption of Cd by willow roots.
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