汞胁迫对桉树3个保护酶活性及基因表达的影响

以广林9号桉（GL9）3月龄幼苗为材料,用0、25、50、75 μmol/L HgCl₂溶液（对应对照、低、中、高浓度）连续浇灌处理15 d后,测量株高,检测叶片叶绿素和丙二醛（MDA）含量、测定过氧化物酶（class Ⅲ peroxidases,POD）、过氧化氢酶（catalase,CAT）和谷胱甘肽过氧化物酶（glutathione peroxidase,GPX）的活性,分析9个保护酶基因的转录变化,探讨汞胁迫对保护酶活性及基因表达的影响。处理后各组间的株高、叶绿素含量无显著性差异。高浓度Hg²⁺处理使MDA含量升高到对照的3.35倍,达27.88 nmol/g。与对照相比,Hg²⁺处理后GPX活性降低,POD和CAT活性在25 μmol/L Hg²⁺处理下最高。从3类保护酶基因中的酶类选出3个基因进行qPCR分析。Hg²⁺处理后POD3、CAT2、GPX1的转录上调且低浓度处理上调更显著,其他6个基因的转录则呈下调趋势。设对照中基因的相对表达量为1,低浓度Hg²⁺处理后这3个基因的相对表达量分别为6.81、4.58和2.56,高浓度Hg²⁺处理后的相对表达量分别为2.31、2.02和1.08。结果表明,Hg²⁺胁迫影响保护酶活性使膜脂过氧化加剧,低浓度的Hg²⁺诱导POD3、CAT2和GPX1基因转录上调,增强桉树对汞胁迫的适应性。

Effects of Mercury Stress on Enzyme Activities and Gene Expression of Three Protective Enzymes in Eucalyptus

Using three-month-old seedlings of Eucalyptus GL9 (Eucalyptus grandis×Eucalyptus urophylla) as materials,the effects of mercury stress on seedling growth,protective enzyme activities and gene expression were evaluated by irrigating with mercury chloride solutions for 15 days with the concentrations of 0 (control),25 (low),50 (medium),and 75 μmol/L (high concentration).Then,the plant height was measured.The leaves were used to evaluate the contents of chlorophyll and malondialdehyde (MDA) and detect the activities of POD (class Ⅲ peroxidases),CAT (catalase) and GPX (glutathione peroxidase).The transcriptional levels of 9 enzymatic genes were analyzed by real-time quantitative PCR.There were no significant differences in plant height and chlorophyll content among the four treatments.The MDA content was 27.88 nmol/g in high concentration treatment,3.35 times higher than that in the control.Compared with the control,the activity of GPX decreased after Hg²⁺ treatment.The activities of POD and CAT arrived at the climax at 25 μmol/L Hg²⁺ concentration.Nine genes were selected from the three types of protective enzyme genes for qPCR analysis.The transcriptional levels of POD3,CAT2 and GPX1 were all up-regulated at different Hg²⁺ concentrations.And the up-regulation at low concentration was more significant than at high concentration.The other six genes showed an overall down regulation trend on Hg²⁺ stress.Setting the relative transcriptional level of the same genes in control normalized to one,the relative transcriptional levels of POD3,CAT2 and GPX1 were 6.81,4.58,2.56,respectively,at low concentration,and 2.31,2.02,1.08,respectively,at high concentration.However,the results implied that mercury stress had effect on protective enzyme activities and aggravated the membrane lipid peroxidation.Low concentration of Hg²⁺ induced the expression upregulation of POD3,CAT2 and GPX1 genes and enhanced the adaptability of eucalyptus to mercury stress.