海州香薷根细胞壁对铜的吸附固定机制研究

Mechanism of fixation and adsorption of copper on root cell wall of Elsholtzia splendens

海州香薷是铜耐性植物,细胞壁是其吸收积累铜的重要场所.本文利用细胞壁化学改性结合吸附动力学试验和红外光谱学研究了海州香薷根细胞壁及其组分对Cu2+的吸附动力学特征,以及它们吸附固定Cu2+的功能基团.吸附动力学试验表明,海州香薷根细胞壁对Cu2+吸附300 min后,吸附量已接近饱和水平,达到最大吸附量的90%左右;500 min时达到吸附饱和,饱和吸附量为5.85 mg·g-1.当细胞壁进行化学改性后,如氨水处理细胞壁使果胶变成低酯化的酰胺类果胶或者去除细胞壁中的纤维素,根细胞壁对铜的吸附量会显著降低.果胶和纤维素分别吸附了19.85%和25.48%的Cu2+,是细胞壁吸附固定Cu2+的两大主要组分.红外光谱研究也表明,在海州香薷根细胞壁吸附Cu2+的过程中,羟基、羧基和氨基是Cu2+的主要结合位点.其中,果胶为Cu2+的结合提供了羟基官能团,纤维素和半纤维素为Cu2+的结合提供了羧基官能团,而细胞壁蛋白提供了氨基官能团等结合位点.由此可见,根细胞壁及其各个组分对Cu2+具有较高的吸附固定能力,是海州香薷根系Cu耐性的重要机制.

Elsholtzia splendens is a copper-tolerant plant species. The cell wall of the plant root was found to be the most important part of Cu localization. Chemical modification of cell wall, adsorption dynamic experiments and the FTIR spectroscopy analysis were combined to explore adsorption kinetic characteristics and the functional groups of the cell wall and its components under copper stress. The adsorption dynamic experiments showed that the copper content adsorbed by the root cell wall was close to its saturation level after 300 minutes, which was about 90% of the maximum adsorption capacity. We obtained a saturated adsorption capacity of copper after 500 minutes, with 5.85 mg·g^-1. The proportion of copper adsorption by pectin and cellulose in the root cell wall were 19.85% and 25.48% , respectively. The copper adsorption by the root cell wall had been significantly reduced by the ammonia and cellulose treatments on the cell wall. The FTIR spectra also revealed that hydroxyl, carboxyl and amino group are the main binding sites of Cu2 ＋ by the root cell wall in the adsorption process. Cellulose and hemicellulose provide a combination of Cu2 ＋ with earboxyl functional groups, pectin offers carboxyl groups, while the cell wall proteins provide amino functional groups for binding sites. The results showed that the root cell wall has high adsorption capacity for copper, which may be an important mechanism of the high copper tolerance by E splendens.