Cd2+胁迫下浮萍叶细胞核超微结构、nDNA损伤及抗氧化酶系的变化

Changes of nuclear ultrastructure,nDNA and antioxidant enzymes in leaves of Lemna minor induced by Cd2+

关键词:  Cd²⁺  浮萍  超微结构  nDNA损伤  抗氧化酶  TUNEL

Key words:  Cd²⁺  Lemna minor  ultrastructure  nDNA damage  antioxidant enzymes  TUNEL

摘要:

以不同浓度Cd²⁺处理6 d的浮萍为材料,从细胞核超微结构损伤、nDNA一级结构变化及抗氧化酶系活性改变等方面分析重金属的植物毒理学效应。透射电镜观察发现,5～7 mg/L Cd²⁺处理的细胞核膜完整,染色质凝聚并趋边化; 10 mg/L Cd²⁺处理后则核仁解体,且DNA原位末端标记(TUNEL)检测发现DNA的3'-OH断端可被特异标记,表现出典型的凋亡细胞特征。而20 mg/L Cd²⁺已导致细胞坏死。同时,较低浓度的Cd²⁺胁迫可刺激抗氧化酶(SOD,POD,CAT)活性升高,以清除体内活性氧,而随金属浓度的进一步增高,三种抗氧化酶活性都急速下降。研究发现,活性氧和抗氧化酶系密切参与了重金属Cd²⁺诱导的浮萍体细胞凋亡过程。

Abstract:

Damage to nuclear DNA and ultrastructure and changes of antioxidant enzymes in leaves of Lemna minor grown in different Cd²⁺ concentration gradient for 6 days were investigated to clarify the phytotoxicity of heavy metals in aquatic plants. The condensation and marginations of chromatin were observed under the electron microscope when the Cd²⁺concentration was from 5-7 mg/L; nucleolus break up when the Cd²⁺ concentration was 10 mg/L. TdT-mediated dUTP nick end labeling(TUNEL)analysis of cells revealed that the nuclear DNA strand breaks could be identified by labeling free 3'-OH termini,which was the typical feature of the cell apoptosis process. And necrotic injury occurred in 20 mg/L Cd²⁺ group. The activities of antioxidant enzymes could be stimulated exposing to low Cd²⁺ concentration to clean up the active oxygen,and the cell apoptosis happened when their activities declined rapidly at higher Cd²⁺ concentrations. The results also indicated that reactive oxygen species(ROS)and antioxidant enzymes were involved in the apoptosis process.