盐胁迫下3种杨树的抗氧化能力与耐盐性研究

以抗盐性不同的胡杨、群众杨和I-214杨3种杨树为材料，对NaCl胁迫下叶片中的盐离子含量、超氧化物歧化酶（SOD）、过氧化物酶（POD）活性以及丙二醛（MDA）含量和电解质外渗率的动态变化进行分析和对比，探讨3种杨树抗氧化能力的差异及其与抗盐性的关系．结果显示，在长期且不断提高的盐胁迫下，群众杨叶片中Na+、Cl－离子浓度不断升高，特别是在盐处理后的第28 d，叶片中的盐离子含量达到最高时，SOD和POD的活性大幅度下降，叶片中MDA的含量和电解质外渗率随之大幅度上升，叶片出现了严重的盐害症状．与群众杨相比，I-214杨叶片中Na＋、Cl－浓度也有相同的变化趋势，但其MDA和电解质外渗率增加幅度较小，盐害症状也较轻. 与前两种杨树明显不同，胡杨在轻度盐胁迫下（土壤NaCl浓度58.5 mmol/L），叶片中SOD和POD的活性就显著上升，并且在盐胁迫期间，胡杨叶片中盐离子含量、MDA的含量和电解质外渗率都没有明显的变化．因此，在长期盐胁迫条件下，群众杨和I-214杨叶片中电解质外渗率的增加与盐离子的大量积累有关，而叶片电解质外渗主要是膜脂过氧化的结果．活性氧清除酶（SOD、POD）活性的下降，是导致这两种杨树膜脂过氧化和电解质外渗率增加的主要原因．而胡杨在盐胁迫初始阶段就能大幅度上调SOD、POD活性，以避免活性氧对膜的伤害．在长期不断提高的盐胁迫条件下，胡杨的排盐性强，降低了盐诱导的膜脂过氧化，最终减少了电解质外渗率，从而提高了抗盐性． 

Genotypic differences in antioxidative ability and salt tolerance of three poplars under sact stress

In order to evaluate genotypic difference in antioxidative ability and salt tolerance in poplars，the authors investigated the effects of increasing soil NaCl content on salt concentration in leaves，superoxide dismutase (SOD)，peroxidase (POD) activities，malondialdehyde(MDA) content and membrane permeability in Populus euphratica Oliv． and P．popularis ‘35-44’ and P．× euramericana cv．I-214．Na^＋and Cl^－concentrations in leaves of P.popularis markedly increased over the increase of the duration of exposure to salinity，and culminated after 28 d of salt stress．SOD and POD activities declined correspondingly，followed by significant increases of MDA and membrane permeability，and leaf injury was eventually observed．Leaf Na^＋ and Cl^－in P．×euramericana cv． I-214 exhibited a trend similar to P．popularis，but a lower salt_induced increase of MDA and permeability was observed and lighter leaf necrosis occurred，compared with P．popularis．In contrast to P．popularis and P．×euramericana cv．I-214，leaf SOD and POD activities in P．euphratica increased rapidly at the beginning of salt stress with a light soil NaCl concentration of 58.5 mmol/L．Furthermore，salt ion concentration，MDA content and membrane permeability in leaves of P．euphratica did not significantly increase during 28 d of increasing salt stress．Therefore， the increase of membrane permeability in P．popularis and P．×euramericana cv．I-214 was related with a salt buildup in leaves under increasing salt stress．Salt_induced declines of SOD and POD activity might accelerate lipid peroxide and consequently resulted in ion leakage．P．euphratica rapidly activated antioxidant enzymes after the onset of salt stress，which might reduce reactive oxygen species (ROS) accumulation and the subsequent acceleration of lipid peroxide．P．euphratica leaves exhibited a higher capacity to exclude salt in a longer term of increasing salinity，thus limited salt_induced lipid peroxide and membrane permeability，which contributed to membrane integrity maintenance and salt tolerance of P．euphratica．