Guangdong Provincial Key Laboratory of Plant Molecular Breeding, Guangdong Sub-center of National Center for Soybean Improvement, College of Agriculture, South China Agricultural University, Guangzhou, 510642, Guangdong, China.
Department of Plant Nutrition,College of Resources and Environmental Sciences, China Agricultural University, 2 Yuan-Ming-Yuan Xilu, Beijing, 100193, China.
Environ Sci Pollut Res Int. 2018 Oct;25(29):29705-29714. doi: 10.1007/s11356-018-2956-4. Epub 2018 Aug 25.
The plant root cell wall (CW) is the first structure that comes into contact with extracellular cadmium (Cd), and it plays an important role in the absorption, immobilization, and translocation of Cd in the roots. However, the differences in the cell wall components between Cd-tolerant and Cd-sensitive cultivars are unclear. A hydroponic experiment was carried out to investigate the differences in the concentrations of Cd, total sugars, and uronic acid in pectin, hemicellulose 1, hemicellulose 2, cellulose, and lignin, as well as pectin methylesterase enzyme activity (PME) in the roots of two soybean cultivars that differ with respect to Cd tolerance exposed to 0 and 23 μM Cd treatments. The bound forms of Cd in the roots were found to differ between the two soybean genotypes; 50.2% of the Cd in the root cell wall accumulates in the pectin in the highly Cd-tolerant and low Cd-accumulating cultivar HX3, while 50.6% of the root cell wall Cd accumulates in cellulose in the Cd-sensitive and high Cd-accumulating cultivar BX10. The total sugar and uronic acid concentrations of the cell wall components increased in response to Cd stress, while the concentrations of total sugars and uronic acid in BX10 were higher than in HX3 (except for hemicellulose 1). Increased demethylation of pectin may be the main reason that Cd is mainly concentrated in the primary wall in HX3, because the PME activity was higher in HX3 than it was in BX10 under Cd treatment. Furthermore, BX10 had a higher lignin concentration after Cd treatment, and showed the same change in cellulose. Cd in the root cell wall of BX10 was fixed in the secondary cell wall, which may be a result of the coupling to cellulose and lignin. In conclusion, root cell walls in soybean cultivars that differ in Cd tolerance may possess different mechanisms to prevent Cd from entering cells, and the sequestration of Cd in different cell wall components may determine the differences in Cd tolerance between the two genotypes.
植物根细胞壁（CW）是与细胞外镉（Cd）最先接触的结构，它在根中 Cd 的吸收、固定和迁移中起着重要作用。然而，耐 Cd 和 Cd 敏感品种之间细胞壁成分的差异尚不清楚。通过水培实验研究了在 0 和 23 μM Cd 处理下，两种大豆品种根中 Cd、总糖和果胶中的半乳糖醛酸、半纤维素 1、半纤维素 2、纤维素和木质素的浓度以及果胶甲酯酶（PME）活性的差异。结果发现，两种大豆基因型的根中 Cd 结合形式不同；在高 Cd 耐性和低 Cd 积累品种 HX3 中，50.2%的根细胞壁 Cd 积累在果胶中，而在 Cd 敏感和高 Cd 积累品种 BX10 中，50.6%的根细胞壁 Cd 积累在纤维素中。细胞壁成分的总糖和半乳糖醛酸浓度随着 Cd 胁迫的增加而增加，而 BX10 中的总糖和半乳糖醛酸浓度高于 HX3（除半纤维素 1 外）。果胶的去甲基化增加可能是 Cd 主要集中在 HX3 初生壁中的主要原因，因为在 Cd 处理下，HX3 中的 PME 活性高于 BX10。此外，BX10 在 Cd 处理后木质素浓度较高，纤维素也发生了同样的变化。BX10 根细胞壁中的 Cd 被固定在次生细胞壁中，这可能是与纤维素和木质素结合的结果。综上所述，耐 Cd 能力不同的大豆品种根细胞壁可能具有不同的机制来防止 Cd 进入细胞，不同细胞壁成分对 Cd 的固定可能决定了两个基因型之间 Cd 耐性的差异。
