根细胞壁中镉亚细胞分布对土壤-烟草系统中镉吸收、转运的影响

Effects of subcellular Cd accumulation in root cell wall on Cd transfer and translocation from soil to tobacco cultivars

根细胞壁是植物吸收、转运镉(Cd)的第一道屏障。为了揭示烟草根细胞壁中Cd的亚细胞分布与结合形态对烟草茎叶Cd吸收、转运的影响机理,文中研究了12种不同烟草根、茎、叶对Cd的富集、转运特征,利用活体细胞分离技术分析了根细胞壁中Cd的亚细胞分布及结合形态,在此基础上对根细胞壁Cd的亚细胞分布与烟草Cd吸收、转运的关系进行了研究。结果表明不同烟草根、叶对土壤中Cd的富集系数间存在显著差异(P<0.05):根中Cd含量为3.13~7.10 mg/kg,最大相差2.27倍;烟叶中Cd含量为3.29~9.93mg/kg,最大相差3.0倍;根-叶转运系数为0.50~3.17,最大相差6.34倍。烟草根部Cd主要以醋酸浸提态(FHAC)为主。不同细胞壁组分中Cd含量测定发现,去果胶后细胞壁(CW-P)中Cd含量显著增加,而去半纤维素后细胞壁中Cd含量显著降低。去果胶后细胞壁中Cd含量与根-叶中Cd的转运系数呈显著的负相关,转运系数最低的K346中,CW-P中Cd含量最高,说明半纤维素是烟草根细胞壁蓄积Cd的主要场所,烟草根细胞壁中半纤维素对Cd的束缚降低了Cd通过长距离向地上部分的转运。

Root cell wall is the first barrier to the transfer and translocation of Cd from soil to plants.To understand the mechanism of Cd transfer and translocation by tobacco cultivars affected by subcellular Cd accumulation and binding forms in root cell walls,we investigated the bioconcentration factor(BCF)and transfer factor(TF)of Cd in roots,shoots and leaves of twelve tobacco cultivar species in pot experiments.We determined the subcellular Cd accumulation characteristics and binding forms in root cell walls using in vivo bioseparation technology.We then studied the relationship between Cd uptake and translocation by tobacco plants and subcellular Cd accumulation and binding forms in root cell walls.The results showed significant difference(P<0.05)in BCFs of Cd in roots,shoots and leaves among the tested tobacco cultivars.For example,the Cd concentrations in roots ranged from 3.13 to 7.10 mg/kg,a maximum 2.27 fold variation;the Cd concentrations in tobacco leaves ranged from 3.29 to 9.93 mg/kg,a maximum 3-fold variation.Similarly,the TFs of Cd from root to leaf varied from 0.50 to 3.17,a maximum 6.34 fold change among cultivars.Our analysis indicated that the insoluble forms of Cd,binding to phosphate(Cd(PO4)n)or hemicellulose(FHAC-Cd),were the main binding forms of Cd in plant roots.The results further showed that Cd concentrations in root cell walls increased significantly after removing pectin while decreased sharply after removing hemicelluloses.We found negative correlation(P<0.05)between root-to-leaf TFs and Cd contents of cell walls after removing pectin;e.g.,cultivar K346 had the highest Cd content but lowest rootto-leaf TF among the cultivars.The results implied that hemicelluloses bind most of insoluble forms of Cd in root cell walls,impeding the long distance migration and translocation of Cd from soil through xylem to the above ground parts of tobacco plants.