Cd2+处理对菹草叶片保护酶活性和细胞超微结构的毒害影响

以不同浓度Cd^2 处理5d的菹草为实验材料，测定了叶片SOD，POD，CAT等生理生化指标的变化，并用透射电镜观察了Cd^2 对叶细胞超微结构，尤其是对叶绿体，线粒体和细胞核的损伤情况。结果表明：SOD活性，叶绿素含量随Cd^2 处理浓度的增加而下降，而CAT和POD活性都是在1mg／L浓度下达到峰值，而后降低。SOD对Cd^2 毒害最敏感，其次为POD和CAT。电镜观察发现：随Cd^2 浓度的增加，对细胞超微结构的损伤程度也加剧。表现为叶绿体膨大，被膜断裂、消失和叶绿体解体；线粒体变形，脊突膨大和空泡化；细胞核核仁分散，核膜断裂，核空泡化。并探讨了Cd^2 对植物的毒害机制。

TOXIC EFFECT OF Cd2+TREATMENT ON PROTECTIVE ENZYME ACTIVITY AND ULTRASTRUCTRUE IN LEAF CELLS OF POTAMOGETON CRISPUS.

Heavy metals are common pollutants in aquatic ecosystems due to atmospheric sedimentation geological leakage, untreated industrial effluents. Compared to most other pollutants, they are not biodegradable and persistent in the environment for a very long period, Their accumulation in organism and bio magnification through food chain pose the great potential threat to aquatic organisms and to human health. So heavy metal pollution has become one of the most troublesome environmental problems and also received more and more attention. On the other hand, submerged macrophytes are directly exposed to heavy metals in water body and are more easily subjected to their toxicity In the present study, Potamogeton crispus, widespread in watin body in China, is cultivated in nutrition media containing different concentration of Cd 2+ for 5d to investigate the toxic effect of Cd 2+ on macrophtes, including:chlorophyll content, changes of protect enzyme activity(SOD, POD, CAT)and the ultrastructural damages to leaf cells, mainly to chloroplasts, mitochondria and nuclei. The results show that:SOD activity and chlorophyll content decrease nearly linearly with augmentation of Cd 2+ concentration by 26. 44%and 60.55%, respectively, When the concentration was 50mg/L, statistical analysis indicate the changes of both indexes had reached significant levels( r SOD =-0.9766; r chl = -0.9132 ); Both POD and CAT activity reached the peak value at 1mg/L, 101. 70% and 186. 39% higher than that of the control, respectively. When treated with 20mg/L,cd 2+ POD activity declined by 12. 87% and 48. 27% at 50mg/L as compared to the control A lthough the CAT activity began to decline when the treatment concentration rises further it still much higher than that of the control, by 86. 88% over the normal value even at 50mg/L within the exposing concentration range, It illustrated CAT has a quite strong tolerance to Cd 2+ pollution. Among the three enzymes, SOD is the most sensitive, followed by POD and CAT. Transmission electron microscopy observation indicate that the higher the pollutant concentration is, the more serious the damages to the leaf cells is, such as swelling of chloroplasts at 1mg/L metal concentration, disruption and disappearance of chloroplast envelop at 10 and 20mg/L, and 50mg/L see the disintegration of chloroplasts;deforming and vacuolization of mitochondria at 1mg/L and 10mg/L concentration, respectively. The disintegration of nucleolus is found when treated with 10mg/L Cd 2+ , 50mg/L induced the disruption of nuclear membrane and vacuolization of nucleus. Disintegration of chloroplasts, vacuolization of mitochondria and vacuolization of nucleus are irreversible damage to organelles and their normal physiological functions are lost. The changes of leaf cells ultrastructure are consistent with the damage of their membrane systems, which may be caused by the disturbance of protect enzyme activity. It can be inferred that one main toxic mechanism of Cd 2+ is to destroy the structural foundation that the normal metabolism necessarily need.