镉胁迫对紫花苜蓿幼苗生理特性和镉富集的影响

Effects of Cd stress on physiological characteristics of alfalfa and its Cd enrichment

关键词:  镉胁迫, 紫花苜蓿, 生理特性, 镉富集, 镉污染

Key words:  Cd stress, alfalfa, physiological characteristics, Cd enrichment, Cd pollution

摘要:

以“甘农三号”紫花苜蓿幼苗为材料,在水培条件下,探究了在10 d内不同浓度(0～2.0 mmol·L^-1)镉(Cd)胁迫对其根长、茎长、生物量、叶绿素和丙二醛(MDA)含量、超氧化物歧化酶(SOD)和过氧化物酶(POD)活性、Cd富集及其亚细胞分布的影响。结果表明:低浓度(0.125 mmol·L^-1)Cd能促进幼苗根和茎的生长,增加叶片叶绿素含量,较高浓度(0.5～2.0 mmol·L^-1)Cd显著抑制幼苗根和茎的生长,叶绿素及生物量显著降低; Cd胁迫使MDA含量显著增加,而SOD和POD活性显著增强,其中Cd胁迫浓度为0.5 mmol·L^-1时, SOD和POD活性达到最大值,这可能是植物对环境胁迫的一种应激保护反应; Cd在各亚细胞组分中的含量依次为细胞壁>细胞质>线粒体>叶绿体,且均随Cd胁迫浓度的升高而增加。当Cd胁迫浓度为0.125 mmol·L^-1时,水培10 d的紫花苜蓿幼苗单株地上部对Cd的净化率最高可达0.214%,而整盆植株在单位体积内对Cd的净化率最高可达15.5%; 当Cd胁迫浓度为2.0 mmol·L^-1时,紫花苜蓿幼苗地上部Cd含量达89.36 μg·g^-1。这些结果表明紫花苜蓿对Cd具有很强的富集能力,虽未达到Cd超富集植物的临界标准,但从植株生物量、耐Cd能力、富集Cd量及对Cd的净化率等方面综合考虑,紫花苜蓿在Cd污染土壤的植物修复中具备良好的应用价值。

Abstract:

Taking seedlings of alfalfa variety ‘Medicago sativa cv. Gannong No. 3', we studied the effects of Cd stress on the length of stem and root, biomass, the contents of chlorophyll and malonyldialdehyde(MDA), the activities of superoxide dismutase(SOD)and peroxide enzyme(POD), Cd enrichment and Cd subcellular distribution in leaf of alfalfa seedlings under Cd stress with concentration between 0 to 20 mol·L^-1 for 10 d. The results showed that length of stem and root, chlorophyll content increased under lower Cd concentration(0.125 mmol·L^-1)stress. However, lower length of stem and root, biomass and chlorophyll content were observed under the higher Cd concentration(0.5～2.0 mmol·L^-1)stress. Accumulation of reactive oxygen species(ROS)in alfalfa seedlings under Cd stress caused membrane lipid system peroxidation, MDA content increased significantly, while the activity of SOD and POD was significantly enhanced. When the concentration of Cd stress was 0.5 mmol·L^-1, the activity of SOD and POD reached the maximum, which may be a protective reaction of plants to environmental stress, antioxidant enzyme system was started up to remove ROS accumulated during Cd stress and to mitigate membrane lipid peroxidation damage caused by Cd stress. Subcellular distribution of Cd in leaf was in the order of cell wall, cytoplasm, mitochondria, chloroplast, and the content of Cd in each subcellular fraction increased with the concentration increase of Cd stress. When the concentration of Cd was 0.125 mmol·L^-1, purification rate of Cd in the shoots of individual plants grown in nutrient solution for 10 d up to 0.214%, and the purification rate of Cd for whole pot plant per unit volume up to 15.5%. When the concentration of Cd was 2.0 mmol·L^-1, the content of Cd in the aboveground part of alfalfa seedlings was 89.36 μg·g^-1. Those results suggest that alfalfa has a very strong enrichment ability for Cd, although it does not meet the critical criteria for Cd-rich plants. However, alfalfa has a good application value in the phytoremediation of Cd-contaminated soil, considering the plant biomass, Cd tolerance, Cd enrichment, and purification rate of Cd.