Key Laboratory of Original Agro-Environmental Pollution Prevention and Control, Ministry of Agriculture and Rural Affairs, Tianjin Key Laboratory of Agro-Environment and Agro-Product Safety, Agro-Environmental Protection Institute, Ministry of Agriculture and Rural Affairs, Tianjin, 300191, China.
Key Laboratory of Original Agro-Environmental Pollution Prevention and Control, Ministry of Agriculture and Rural Affairs, Tianjin Key Laboratory of Agro-Environment and Agro-Product Safety, Agro-Environmental Protection Institute, Ministry of Agriculture and Rural Affairs, Tianjin, 300191, China.
Ecotoxicol Environ Saf. 2020 May;194:110369. doi: 10.1016/j.ecoenv.2020.110369. Epub 2020 Mar 2.
Polysaccharides are the main components of plant cell walls in which they make an important contribution to cadmium (Cd) fixation. However, knowledge regarding the role of root cell wall polysaccharides in Cd accumulation in low-Cd cultivars is limited. Here, we compared the differences in root cell wall polysaccharides between two cultivars of Brassica chinensis L. (pakchoi) with different Cd accumulation abilities. A hydroponic experiment was conducted using low- (Huajun 2) and high-Cd (Hanlv) pakchoi cultivars. We investigated Cd subcellular distribution and Cd accumulation in cell wall polysaccharides and examined polysaccharide modifications in root cell walls by Fourier transform infrared spectroscopy. A Cd adsorption kinetics experiment was conducted to examine the connection between Cd-induced polysaccharide modifications and Cd fixation by cell walls. Amounts of Cd were significantly higher and more Cd was bound to cell walls in the roots of Huajun 2 than in those of Hanlv. These results indicated that the greater Cd retention capacity of the root cell wall in Huajun 2 accounted for the low Cd accumulation in the shoot. Up to 79.4% and 32.1% of cell-wall-bound Cd was found in the pectin and hemicellulose 1, respectively, and higher amounts of Cd were found in these cell wall components of Huajun 2 than in those of Hanlv. Exposure to Cd significantly increased amounts of pectin and hemicellulose 1 in both pakchoi cultivars, but the pectin levels were significantly higher in Huajun 2 than in Hanlv. Huajun 2 had higher pectin methylesterase (PME) activity and a lower degree of pectin methyl-esterification (DM) than Hanlv, although Cd treatments resulted in increased PME activity and decreased DM in both cultivars. The higher Cd treatment (44.5 μM) resulted in enhanced Cd-binding capacity in root cell walls of the two cultivars with higher Cd adsorption levels in the root cell wall of Huajun 2. These results indicate that differences in the amount of cell wall polysaccharide and DM play key roles in establishing the genotypic differences underlying Cd accumulation in pakchoi. These findings conduce to a better understanding of the physiological mechanisms underlying low Cd accumulation in pakchoi and the breeding of new, low-Cd pakchoi cultivars.
多糖是植物细胞壁的主要成分，它们对镉（Cd）固定有重要贡献。然而，关于低镉品种根系细胞壁多糖在 Cd 积累中的作用的知识有限。在这里，我们比较了两个镉积累能力不同的白菜（白菜）品种根细胞壁多糖的差异。采用水培实验，选用低镉（华君 2 号）和高镉（汉禄）白菜品种。我们研究了 Cd 的亚细胞分布和细胞壁多糖中的 Cd 积累，并通过傅里叶变换红外光谱法检查了根细胞壁中多糖的修饰。进行了 Cd 吸附动力学实验，以检验细胞壁中 Cd 诱导的多糖修饰与 Cd 固定之间的联系。华君 2 号根中 Cd 的含量明显更高，与细胞壁结合的 Cd 也更多。这些结果表明，华君 2 号根细胞壁对 Cd 的保留能力更强，导致地上部 Cd 积累量较低。果胶和半纤维素 1 中分别有 79.4%和 32.1%的细胞壁结合 Cd，华君 2 号中这两种细胞壁成分中的 Cd 含量明显高于汉禄。暴露于 Cd 显著增加了两个白菜品种的果胶和半纤维素 1 的含量，但华君 2 号中的果胶含量明显高于汉禄。华君 2 号的果胶甲酯酶（PME）活性较高，果胶甲酯化程度（DM）较低，而 Cd 处理后两个品种的 PME 活性均升高，DM 降低。较高的 Cd 处理（44.5 μM）导致两个品种根细胞壁的 Cd 结合能力增强，华君 2 号根细胞壁的 Cd 吸附水平较高。这些结果表明，细胞壁多糖的量和 DM 的差异在建立白菜 Cd 积累的基因型差异方面起着关键作用。这些发现有助于更好地理解白菜低 Cd 积累的生理机制，以及培育新的低 Cd 白菜品种。
