基于细胞壁吸附固定特性的小飞蓬耐Cd机制研究

Cadmium tolerance mechanism of Conyza canadensis based on cell wall adsorption and fixation characteristics

为探究小飞蓬根、叶细胞壁在Cd吸收过程中发挥的作用,以小飞蓬为供试植物,扫描电镜(SEM)观察Cd在小飞蓬组织中的分布及受损情况,通过细胞壁化学改性,利用吸附动力学和傅里叶红外光谱技术(FTIR)对小飞蓬根、叶细胞壁的Cd吸附固定特性进行了研究。扫描电镜结果显示,Cd胁迫下小飞蓬根、叶组织结构排列不规则,并出现晶体堵塞导管的现象,皮层组织是小飞蓬吸附固定Cd的重要部位;经酯化改性、氨基甲基化改性和果胶酶改性后,吸附动力学试验表明根细胞壁对Cd的累积吸附量分别相对降低了49.1%、38.5%和26.1%,叶细胞壁分别相对降低了39.47%、20.14%和30.23%。根细胞壁上的羧基和氨基在Cd吸附中的贡献作用较大,而叶细胞壁上的羧基和果胶在Cd吸附中的作用较明显。利用FTIR表征了小飞蓬根、叶细胞壁上Cd吸附位点的官能团信息后表明,在小飞蓬根、叶细胞壁吸附Cd的过程中,羟基、羧基和氨基是Cd的主要结合位点。其中,果胶为Cd的结合提供羟基官能团,纤维素和半纤维素为Cd的结合提供羧基官能团,而细胞壁蛋白提供了氨基官能团等结合位点。由此可见,细胞壁各组分中的羟基、羧基和氨基提供Cd结合位点,使细胞壁对Cd具有较高的吸附固定能力,是小飞蓬耐Cd的一种重要机制。

We examined the distribution and damage incurred by the tissues of Conyza canadensis due to Cd stress using scanning electron microscopy(SEM). The adsorption and fixation characteristics of Cd in the root and leaf cell wall were studied by chemical modification,adsorption kinetics, and Fourier transform infrared spectroscopy(FTIR). The results of SEM showed that under Cd stress, the structure of root and leaf tissues was irregularly arranged, and crystals blocked the vessels. The cortical tissue of C. canadensis was an important site for the adsorption and fixation of Cd. The adsorption kinetics test showed that the cumulative adsorptive capacity of the root cell walls for Cd was reduced by 49.1%, 38.5%, and 26.1% after esterification, aminomethylation, and pectinase modification, respectively. That of the leaf cell walls was also reduced, by 39.47%, 20.14%, and 30.23%, respectively. Carboxyl and amino groups in the root cell wall contributed greatly to Cd adsorption, while carboxyl and pectin in the leaf cell wall played a significant role. The functional group information of Cd adsorption sites on the root and leaf cell wall was characterized by FTIR, and the results showed that hydroxyl, carboxyl, and amino groups were the main binding sites. During this process, pectin provided the hydroxyl functional groups for the binding of Cd, cellulose and hemi cellulose provided the carboxyl functional groups, and cell wall proteins provided the amino functional groups and other binding sites. It can be concluded that hydroxyl, carboxyl, and amino groups are the main binding sites of Cd, which results in the cell wall showing a higher adsorption and fixation ability for Cd, and is an important mechanism of Cd tolerance in C. canadensis.