褪黑素对镉胁迫下蒿柳抗氧化系统及叶肉细胞超微结构的影响

Effects of Melatonin on Antioxidant System and Mesophyll Cell Ultra-microstructure in Salix viminalis Under Cadmium Stress

短轮伐期木本植物蒿柳(Salix viminalis)具有镉(Cd)污染修复潜力,但对高浓度Cd耐性低,改善其生长状态是提高Cd污染植物修复效率的关键。研究褪黑素(MEL)对高浓度Cd条件下蒿柳抗氧化系统的调控机制,有助于揭示MEL对木本植物抗氧化系统响应Cd胁迫的生理调控模式,为MEL在植物修复技术中的应用提供实践指导。以同一无性系蒿柳扦插苗为试验材料,设定4个处理,空白对照(BT)、叶施MEL(MT)、Cd胁迫(CT)及叶施MEL后Cd胁迫(MCT)。研究MEL对Cd胁迫下蒿柳活性氧水平、脂质过氧化程度及抗氧化系统的调控模式,探讨MEL对叶肉细胞超微结构的保护作用。在处理后第7天,Cd胁迫下蒿柳根过氧化氢及丙二醛(MDA)含量提高69%和28%,过氧化氢酶(CAT)活性降低49%。叶施MEL后叶CAT、谷胱甘肽还原酶(GR)和单脱氢抗坏血酸还原酶(MDHAR)活性分别提高120%、33%和23%,根超氧化物歧化酶(SOD)和GR活性提高60%和36%。在处理后第21天,Cd胁迫下蒿柳叶超氧阴离子和MDA含量提高70%和81%,MDHAR活性降低47%,叶肉细胞器消失;根过氧化氢和MDA含量提高124%和69%,MDHAR活性降低36%。叶施MEL后叶超氧阴离子和MDA含量降低25%和36%,SOD、过氧化物酶(POD)、CAT、GR和MDHAR活性分别提高26%、34%、22%、27%和141%,叶肉细胞结构完整;根过氧化氢和MDA含量降低35%和40%,POD、GR和谷胱甘肽S-转移酶(GST)活性提高25%、33%和10%。MEL通过提高过氧化物酶、根超氧化物歧化酶及叶过氧化氢酶活性提升镉胁迫下蒿柳的抗氧化能力,通过提高单脱氢抗坏血酸还原酶活性增加抗坏血酸含量,通过提高谷胱甘肽还原酶和根谷胱甘肽S-转移酶活性增加谷胱甘肽含量,以促进其抗坏血酸谷胱甘肽循环。这些过程稳定了镉胁迫下蒿柳地上及地下部的活性氧水平,减轻脂质过氧化程度并降低膜透性。从而保护镉胁迫下蒿柳叶肉细胞及叶绿体结构完整。

As a woody plant with short rotation,Salix viminalis demonstrates the potential remediation capacity of cadmium(Cd)pollution,but it has poor tolerance for high concentration Cd.Improving its growth status becomes the key for increasing Cd pollution remediation efficiency.This study aimed to investigate the effects of melatonin(MEL)on antioxidant system of S.viminalis exposed to high concentration Cd,which helps to further reveal the physiological mechanism of MEL regulation on antioxidant system in woody plants exposed to Cd,to provide practical guidance for MEL application in phytoremediation.Cutting seedlings of S.viminalis with the same clone were taken as experimental materials.Four treatments were set:blank(BT),foliar application with MEL(MT),Cd stress(CT),and foliar application with MEL followed by Cd stress(MCT)to examine the regulatory mechanism of MEL on reactive oxygen species level,lipid peroxidation degree,and antioxidant system in S.viminalis under Cd stress,and to investigate the protect effect of MEL on mesophyll cell ultra-microstructure.The root hydrogen peroxide and malondialdehyde(MDA)contents of S.viminalis exposed to Cd decreased by 69%and 28%,catalase(CAT)activity decreased by 49%on the 7th day after treatment;while by using MEL,CAT,glutathione reductase(GR),monodehydroascorbate reductase(MDHAR)activity of the leaf increased by 120%,33%,and 23%respectively,root superoxide dismutase(SOD)and GR activity increased by 60%and 36%.The superoxide anion and MDA contents in the leaf exposed to Cd increased by 70%and 81%,leaf MDHAR activity decreased by 47%,and mesophyll organelles disappeared;the hydrogen peroxide and MDA contents in root increased by 124%and 69%,MDHAR activity decreased by 36%on the 21st day after treatment.By using MEL,superoxide anion and MDA contents of the leaf decreased 25%and 36%,SOD,peroxidase(POD),CAT,GR,and MDHAR activity in the leaf increased by 26%,34%,22%,27%,and 141%,respectively,mesophyll cell structure was intact;the hydrogen peroxide and MDA contents of the root decreased 35%and 40%,POD,GR,and glutathione S-transferase(GST)activity in root increased by 25%,33%,and 10%,respectively.It is inferred that MEL improves antioxidant capacity of S.viminalis exposed to Cd by increasing peroxidase,root superoxide dismutase,and leaf catalase activity;by enhancing monodehydroascorbate reductase activity to increase ascorbic acid content;by increasing glutathione content to enhance the activity of glutathione reductase and glutathione S-transferase and promote the AsA-GSH cycle.These processes stabilize reactive oxygen species level,alleviate lipid peroxidation degree,and decrease membrane permeability to further protect the intactness structure in mesophyll cell and chloroplast of S.viminalis exposed to Cd.