基于叶片质外体相关成分和酶活性响应的龙葵耐Cd机理研究

为探讨龙葵(Solanum nigrum L.)耐镉(Cd)机理,采用基质培养法,研究了50 μmol·L^-1 Cd(CdCl₂·2.5H₂O)处理120 d对其生长和叶片细胞壁果胶、木质素含量、多聚半乳糖醛酸酶(PG)、纤维素酶(Cx)、NADH-过氧化物酶(NADH-POD)、愈创木酚过氧化物酶(GPOD)和松柏醇过氧化物酶(CAPX)活性以及质外体汁液中过氧化氢(H₂O₂)含量和GPOD、过氧化氢酶(CAT)、抗坏血酸过氧化物酶(APX)和超氧化物歧化酶(SOD)活性的影响。结果表明,与对照相比,Cd处理显著抑制了龙葵地上和地下部的伸长生长、降低了根的干物质积累(P<0.05),但茎的分枝增多,叶面积、叶绿素含量、净光合速率和胞间CO₂浓度无显著变化(P>0.05);细胞壁结合酶NADH-POD、GPOD和CAPX活性以及果胶含量显著增高(P<0.05),而PG活性显著下降(P<0.05),Cx活性和木质素含量无显著变化(P>0.05);质外体汁液中H₂O₂含量显著增加(P<0.05),GPOD和SOD同工酶谱及活性无显著变化(P>0.05);CAT同工酶谱带增宽,APX同工酶谱带数增加,二者活性均显著升高(P<0.05)。说明50 μmol·L^-1 Cd较长时间处理龙葵植株,其地上部分生长仍处于良好状态,表现出对Cd毒害的耐性,这与Cd处理后叶片细胞壁果胶含量和结合酶GPOD以及质外体汁液中APX、CAT活性升高有关,推测这是龙葵耐Cd的一种机理。

Cadmium tolerance mechanism of Solanum nigrum L. based on components and enzyme activity changes in apoplast

To investigate the cadmium tolerance mechanism of Solanum nigrum L., a substrate culture experiment was conducted to study the effects of 50 μmol·L^-1 Cd (CdCl₂·2.5H₂O) treatment on the contents of pectin and lignin, the activities of polygalacturonase (PG), cellulase (Cx), NADH-peroxidase (NADH-POD), guaiacol peroxidase (GPOD) and coniferylalcohol peroxidase (CAPX) in cell wall, and the content of hydrogen peroxide (H₂O₂) and the activities of superoxide dismutase (SOD), catalase (CAT), ascorbic acid oxidase (APX) in apoplast sap. The results showed that after 50 μmol·L^-1 Cd treatment for 120 days, compared with the control, the length of shoot and root were inhibited, and the biomass of root was decreased (P<0.05), but the leaf area, chlorophyll content (SPAD), net photosynthetic rate (P_n) and intercellular CO₂ concentration (C_i) showed no significant difference (P>0.05). In the cell wall of leaves, the activity of NADH-POD, GPOD and CAPX and the pectin content were all significantly increased (P<0.05), the PG activity was decreased (P<0.05), and Cx activity and lignin content showed no significant difference (P>0.05). In the apoplast sap of leaves, H₂O₂ content increased significantly (P<0.05), and the activity and isozyme band of GPOD and SOD weren't significantly influenced (P>0.05), but the activities of APX and CAT increased (P<0.05) with more isozyme band number and enhanced isozyme band, respectively. In conclusion, the pectin, H₂O₂-producing NADH-POD and H₂O₂-consuming GPOD in cell wall, and H₂O₂-consuming APX and CAT in apoplast sap might play major roles in Cd tolerance of Solanum nigrum L.