镉在五节芒(Miscanthus floridulus)不同种群细胞中的分布及化学形态

Subcellular distribution and chemical forms of Cd in two Miscanthus floridulus populations

通过营养液培养,以种子分别来自粤北大宝山矿区和惠州博罗非矿区的2个五节芒种群为试验材料,并采用差速离心技术和化学试剂逐步提取法,比较研究了Cd在2个种群根、茎和叶片中的亚细胞分布及化学形态。结果表明,五节芒2种群各部位的Cd主要富集在细胞壁和以液泡为主的可溶组分,在叶绿体、细胞核和线粒体中的分布较少;2种群根、茎、叶的亚细胞各组分Cd含量由高到低的次序均为:细胞壁组分(F1),可溶组分(F4),细胞核和叶绿体组分(F2),线粒体组分(F3)。Cd在五节芒矿区种群根、茎、叶中的含量均显著高于非矿区种群。提高Cd处理质量浓度,对于非矿区种群,Cd在细胞壁(F1)和可溶组分(F4)的分配比例下降,在细胞核和叶绿体组分(F2)与线粒体组分(F3)的分配比例上升;而对于矿区种群,Cd在细胞壁(F1)的分配比例上升,在可溶组分(F4)、细胞核和叶绿体组分(F2)与线粒体组分(F3)的分配比例下降,细胞壁对Cd的固持作用增强。五节芒2种群根中Cd的化学形态存在着明显差异:低Cd(5mg·L-1)处理下,矿区种群根中的Cd以水提取态、氯化钠提取态和醋酸提取态为主,各占36.41%、28.15%和17.04%,其它形态所占比例较少;而非矿区种群根中的Cd以氯化钠提取态、水提取态和醋酸提取态所占比例较大,各占31.58%、23.15%和20.85%。提高Cd处理质量浓度,矿区种群根中的氯化钠提取态为优势形态,所占比例提高到41.29%,水提取态所占比例也提高到38.25%,其他提取态所占比例均有不同幅度下降;而非矿区种群根中氯化钠提取态Cd含量比例下降到21.45%,各化学形态的在分配比例上表现为平均化趋势。因此,细胞壁固持、可溶组分的液泡区隔化和向活性较弱的结合形态转移可能是五节芒矿区种群耐Cd的主要机制。

Using differential centrifugation technique and sequential chemical extraction methods, the subcellular distribution and the chemical forms of Cd in the roots, stems and leaves of two Miscanthusfloridulus populations, one population from Boluo an uncon- taminated site,and another population from Dabaoshan a mine site, under nutrient solution culture were studied in green house. The results showed that, 65% - 90% of total Cd were bound to cell wall and soluble fraction in both populations,and only a small quantity of Cd distributed in chloroplast, karyon and mitochondrion, which suggested that cell wall and soluble fraction in the plant were the major storage sites for Cd. The subcelluar Cd distribution in the roots, stems and leaves of both populations were as follows： cell wall（F 1） 〉 soluble fraction（F4） 〉 karyon and chloroplast（F2） 〉 mitochondria（F3）. The addition of Cd generally reduced the percent- age of Cd in the cell wall（F1） and in the soluble fraction of the non-mine population,but increased the percentage of Cd in the cell wall（F 1） and reduced it in the soluble fraction of the mine population, suggesting that cell wall binding has been strengthened. As to the chemical forms, at 5 mg＇Lt Cd, H2O -extractable, NaCI-extractable, and HAc-extractable Cd were dominant in roots of the mine population, and the proportion of them are 36.41%, 28.15%, 17.04%, respectivesly. But for the non-mine population, NaCI-extractable, H20 -extractable and HAc-extractable Cd were dominant in roots. NaCI-extractable Cd in roots decreased to 21.45% for the non-mine population but increased to 41.29% for the mine population with increasing Cd level to 40 mg.L-1. The results mentioned above indicate that cell wall binding, vacuolar compartmentalization in the soluble fraction and transferring to lower active chemical forms are the main tolerance mechanisms for Cd in the mine population.