The Toxic Effects Of Single And Their Combined Pollution Of Heavy Metals On Submerged Macrophytes And Fluoresscence Loealization Observation

In this paper, we studied the toxic effects of Hg2+ , Cd2+ , Cu2+and their combined pollution on Myriophyllum verticillatum Linn., Potamogeton crispus Linn.,and Cabomba caroliniana A.Gray.by means of measurements of physiological indexes,observations of electron microscopy and confocal laser scanning microscopy. Fluorescence localization of Hg2+ was observed as well. The experimental results showed that Hg2+, Cd2+ and Cu2+ might injure photosynthetic systems, protective enzyme systems, substance metabolism systems, and cell structure of Submerged macrophytes. Resistance ability from endogenous protective systems and stability of biological membrane were key to resist heavy metals in plants. Photosynthetic systems of plants were more sensitive. The three species of ions increased reactive oxygen species(ROS) content of plants. The activities of superoxide dismutase (SOD),peroxidase (POD) and catalase (CAT) were induced in high level to eliminate and resolve ROS in order to stand up for stability of membrane systems. With more serious damages, the activities of protective enzymes decreased, the defense systems of cells could not protect cells,malondialdehyde(MDA) content of plant cellular increased, and integrality of cell membrane was destroyed. Ultrastructural observation showed plasmolysis, the polymerized chromatin ,dispersion of nucleolus ,disruption of nuclear membrane, swelling or vesiculation of thylakoids of chloroplast and cristae of mitochondria, and disintegration of mitochondria and chloroplast . The action processes and concentration ranges of the three ion species were different from each other because of different plants , physiological indexes and ions. Sensitivity and resistance of Submerged macrophytes to heavy metals were different too. P. crispus could be used as Cu2+ indicator plant for environmental monitoring and determination. C. caroliniana had higher endurance to Cd2+ andCu2+ , and could be used as resistance plant for biological precaution and harnessing. The interaction of Hg2+ and Cd2+ combined pollution on M. verticillatum and that of Hg2+, Cd2+ and Cu2+ combined pollution on P. crispus were synergy . Fluorescence localization observation showed that Hg2+ accumulated in cell wall of P. crispus leaves and appeared in cytoplasm as well.