| By imitating different concentration of Cd2+ Cu2+ Cr3+ Cr6+and Zn2+polluted water environment,we mainly studied their toxic effects on aquatic piants by means of measurement of physiologicai indexes and electron microscopy observation as well as the relieving to Cu2+ injury of antioxidase enzyme system in Lemna minor L. and Vallisneria asiatica Miki in this paper by throwing Ce.the experimental results showed that Cd2+ Cu2+ Cr3+ Cr6+ and Zn2+ might injure photosynthetic systems, protective enzyme system, substance metabolism systems and cell ultrastructure of the plant.The four species of ions could increase reactive oxygen species (ROS)content of the plant.At the same time,the protective systems (antioxidant enzyme system mainly)reacted on it.The activities of superoxide dismutase (SOD),peroxidase(POD)and catalase (CAT)were induced in high level to eliminate and resolve ROS in order to maintain stability of member system, With more serious damages,the defenses of cells could not protect cells,So the activities of protective enzyme decreased, malondialdehyde (MDA)content increased,and integrality of cell member was destroyed.The more injuries of the heavy metals to the plant were brought under this situation.Ultrastructural observation showed that there was a great deal of damage by Cd2+ pollution:The thylakoids of chloroplast and cristae of mitochondria became swollen or vesiculate and disintegrated finally;The nucleus were distorted and the nuclear membrance was disrupted.The chromatin was polymerized and concentrated and the nucleolus was dispersed.The changes of some biochemical and physiological indexes were in accordance with the destroy of cell ultrastructure and all indexes showed an evident correlation between the dose and effect.There was some difference between Lemna minor L. which is in the same category but different genus to stress caused by Cu . The more stronger the variety' antioxidant enzyme action,the more lower the decreasing degree ofchlorophyll ,soluble protein content and O2- generation rate. This also validated exaction of reactive oxygen system theory. And there was difference between root and leave which is in the same category to stress caused by the same heavy metal ion.Although the antioxidant enzyme action of root was more stronger than that of leaf, the poisonous degree of root was more serious than that of leaf. So the comparison of resistance of different organ of the same plant didn't be judged only by antioxidant enzyme action.So the difference of the resist mechanism of different organ should be considered. The aquatic plants also had some different reaction to the same heavy metal which is in different valence condition. Valence condition and existent morphology influenced the poison to plant. This was also reflected from some physiological index.Rare earth has obvious relieving effect to heavy metal stress.That was represented as follows:It could slow reduction of antioxidant enzyme action and antioxidant substance content,so improving ROS scavenging abilities and chastening production of ROS,reducing membrance lipid peroxidation substance.Although La itself had certain toxic effect to plant, the toxicity of La+Zn to plant is smaller than that of another when La was threw into Zn solution. This phenomenon may be connected with their alternate relieving action.Calcium played an important role in plant' growth as well as response and adaptation to environment. Ca2+concentration in singular Cu treatment group was usually higher than that in composite group by using localization of Ca2+ antimonite precipitation technique,.And distributing of Ca2+ in composite group.has no obvious difference from control group. Only having high condensation in minor cells.Ce might improve the activity of Ca2+-ATPase,which sustain equilibrium of Ca2+ and combine with CAM to exert messager action and to induce plant to improve resistance by enhancing antioxidant enzyme action (SOD,POD etal) and antioxidant substance content (AsA, GSH, Pro) . |
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