羧基化多壁碳纳米管与铅镉对蚕豆幼苗叶片的氧化损伤

Oxidative Damages of Carboxylated Multi-Walled Carbon Nanotubes,Lead and Cadmium in the Leaves of Vicia faba Seedlings

蚕豆幼苗悬浮培养于含有羧基化多壁碳纳米管MWCNTs-COOH(0、2.5、5.0和10.0 mg·L^(-1))、20.0μmol·L^(-1)Pb+5.0μmol·L^(-1)Cd(简称Pb+Cd),以及MWCNTs-COOH与Pb+Cd的复合溶液中,15 d后检测叶片生理生化指标的变化,以期为MWCNTs与Pb、Cd复合污染的植物毒性和生态风险性评价提供科学依据。结果表明,随着MWCNTs-COOH浓度的增加,与对照组比较,MWCNTs-COOH单一或与Pb+Cd的复合溶液均诱导了叶片O_2^(·-)和H_2O_2产物的明显积累,并伴随着超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、抗坏血酸过氧化物酶(APX)及愈创木酚过氧化物酶(POD)同工酶及其酶活性的升高。2.5 mg·L^(-1)MWCNTs-COOH单一或与Pb+Cd的复合显著诱导CAT酶活性,10.0 mg·L^(-1)MWCNTs-COOH与Pb+Cd的复合导致CAT酶活性降低至对照组以下,CAT酶可作为早期诊断MWCNTs-COOH或MWCNTs-COOH复合重金属环境污染的敏感的生物标志物。MWCNTsCOOH还诱导了蛋白羰基化、热休克蛋白70(HSP70)、非蛋白巯基(NPT)产物和内肽酶(EP)同工酶活性的增加,与Pb+Cd复合后HSP70产物趋于降低,而蛋白羰基化和NPT产物以及EP酶活性显著升高。叶片抗氧化酶和EP酶活性的升高、HSP70和NPT产物的增加缓解了上述氧化胁迫与损伤,是蚕豆幼苗重要的防御机制。综上,MWCNTs-COOH诱导了蚕豆叶片的氧化胁迫和应激响应,与Pb+Cd复合后则加剧了叶片的氧化损伤与蛋白降解。

Vicia faba seedlings were hydroponically cultivated in different concentrations of carboxylated multi-walled carbon nanotubes（ MWCNTs-COOH）（ 0,2. 5,5. 0,and 10 mg·L-1）,20. 0 μmol·L-1 Pb＋ 5. 0 μmol·L-1 Cd（ shortened as Pb＋Cd）,and Pb＋Cd＋MWCNTs-COOH for 15 days respectively,and several related physiological and biochemical parameters were assayed to evaluate the ecotoxicological risks of MWCNTs-COOH and its joint exposure with Pb＋Cd in the leaves. The results show that the reactive oxygen species（ ROS） such as superoxide radical（ O2^（·-）） and hydrogen peroxide（ H2O2） were overproduced in response to MWCNTs-COOH exposure or combination with Pb＋Cd compared with the control,accompanied by enhanced patterns of isozymes and total activities of superoxide dismutase（ SOD）,catalase（ CAT）,ascorbate peroxidase（ APX） and guaiacol peroxidase（ POD）. The activities of CAT were activated significantly under 2. 5 mg·L-1 of MWCNTs-COOH or combined with Pb＋Cd,however,it decreased significantly under 10. 0 mg·L-1 Pb＋Cd＋MWCNTs-COOH. Thus,CAT activities can be used as a sensitive biomarker for early warning of MWCNTsCOOH exposure or combination with heavy metals in the contaminated environment. MWCNTs-COOH exposure resulted in the accumulation of carbonylated proteins,heat shock protein 70（ HSP70）,and non-protein thiol（ NPT）,as well as activated the activities of endopeptidase（ EP） isozymes enhancing. After combination with Pb＋Cd,the production of carbonylated proteins and NPT,and the activities of EP isozymes were significantly enhanced,whereas HSP70 presented in a declined state,The increased activities of antioxidant enzymes and EPs,and the overproduction of HSP70 and NPT should be the crucial defense mechanisms in the Vicia faba seedlings to alleviate the oxidative stress and damage under MWCNTs-COOH exposure or combined with Pb＋Cd. It can be concluded that MWCNTs-COOH caused oxidative stress and defense responses in the leaves of Vicia faba seedlings,and the joint exposure with Pb＋Cd aggravated the oxidative damages and protein degradation.