Lead (Pb)is an important pollution source of heavy metals.Exogenous nitric oxide (NO)is a common sig-nal molecule in biology regulating plant growth and it has been shown that it participate in all kinds of plant responses to Pb stress,Bidens pilosa is an ideal germplasm resource repairing soils contaminated by Pb.The effects of NO on the membrane lipid peroxidation,osmotic regulation substances,antioxidant enzyme activities and active oxygen me-tabolism in leaves,stems and roots of B.pilosa seedlings under Pb (600μmol/L lead nitrate)stress for 3 d were studied by determining relative electrical conductivity (REC ),contents of malondialdehyde (MDA ),hydrogen peroxide (H2 O2 ),superoxide anion (O-2•)generating rate,contents of proline (Pro),soluble protein (SP), carotenoid (Car),activities of ascorbic acid peroxidase (APX),glutathione reductase (GR),peroxidase (POD), catalase (CAT ),superoxide dismutase (SOD)in the leaves,stems and roots of sixty-day-old seedlings of B.pilosa pretreated with different concentrations of sodium nitroprusside (SNP)as an exogenous NO donor to explore the role and mechanism of NO in plant under Pb stress,to enhance B.pilosa resistance to Pb and its better application in phytoremediation of Pb contaminated soil.The results indicated:50-400μmol/L SNP remarkably reduced REC, contents of MDA,H2 O2 and O-2•generating rate,while 500-1 000 μmol/L SNP remarkably increased REC, contents of MDA,H2 O2 and O-2•generating rate,of which protection of the membrane system stability 300μmol/L SNP treatment on B.pilosa seedlings under Pb stress was the most remarkable.Moreover 300μmol/L SNP signifi-cantly promoted the synthesis of Pro,SP and Car.The effects of SNP on activities of antioxidant enzymes in leaves, stems and roots of B.pilosa seedlings was complex.And 200μmol/L SNP significantly enhanced activities of APX in leaves and stems and GR in stems,300μmol/L SNP significantly enhanced activities of POD in leaves,and 1 000μmol/L SNP significantly enhanced activities of CAT in stems and roots and SOD in leaves.It was shown that appro-priate concentration of exogenous NO could increase the contents of osmotic regulation substances and regulate activi-ties of antioxidant enzymes to effectively protect the membrane system stability and alleviate the harm of Pb stress on B.pilosa seedlings.Exogenous nitric oxide could reduce the harm of Pb stress on B.pilosa seedlings because that ni-tric oxide SNP produced could directly react with reactive oxygen species (ROS)B.pilosa seedlings produced under Pb stress to reduce the harm of the membrane system,NO also could indirectly adjust the antioxidant enzyme system to reduce the oxidative damage caused by Pb stress;moreover it was because that the SNP could ease Pb stress of B.pilosa seedlings by increasing contents of osmotic regulation substances which could regulate, protect and scavenge ROS and stimulate the growth of plant.But the effects of exogenous NO had two sides, namely the low concentration eased and the high damaged,of which mitigation effects of 300 μmol/L SNP treatment on B.pilosa seedlings under Pb stress was the most remarkable.Those results suggested that ap-propriate concentration of NO could enhance B.pilosa resistance to Pb and NO had well prospect in phytore-mediation of Pb contaminated soil with B.pilosa seedlings.%铅(Pb)是已知毒性最强的重金属污染源之一,一氧化氮(NO)是一种普遍存在于生物界的信使分子,广泛参与植物对Pb胁迫的应答反应调控,而三叶鬼针草(Bidens pilosa)是修复Pb污染的重要种质资源。为了进一步探明NO在植物Pb胁迫响应中的作用及机理,增强三叶鬼针草对Pb污染土壤的耐性以及更好地应用于Pb污染土壤的修复。该研究以培养60 d的三叶鬼针草幼苗为材料,用不同浓度 NO 供体硝普钠(SNP)预处理,测定600μmol/L硝酸铅胁迫处理第3天三叶鬼针草叶、茎和根的膜质过氧化、抗氧化酶系统和渗透调节物质含量等指标,分析外源NO对铅胁迫下三叶鬼针草活性氧代谢的影响。结果表明：300μmol/L SNP能显著降低铅胁迫下三叶鬼针草相对电导率(REC)、丙二醛(MDA)、过氧化氢(H2 O2)含量以及超氧阴离子(O－2•)产生速率；能显著促进脯氨酸(Pro)、可溶性蛋白(SP)、类胡萝卜素(Car)的合成；和不同浓度 SNP 对三叶鬼针草叶、茎和根中抗氧化酶活性的影响较复杂,其中200μmol/L SNP 能显著增强叶和茎中抗坏血酸氧化酶(APX)活性、茎中谷胱甘肽还原酶(GR)活性,300μmol/L SNP能显著增强叶中过氧化物酶(POD)活性,1000μmol/L SNP能显著增强茎和根中过氧化氢酶(CAT)活性和叶中超氧化物歧化酶(SOD)活性。综上表明,适宜浓度NO可以通过启动抗氧化系统,增加渗透调节物质含量和调节抗氧化酶活性,从而有效保护三叶鬼针草膜系统稳定性,缓解Pb胁迫伤害。因此,适宜浓度NO可以增强三叶鬼针草对Pb污染土壤的耐性,其在三叶鬼针草修复Pb污染土壤中具有较好的应用价值。
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