The Toxic Effects Of Heavy Metal Pollution On Alternanthera Philoxeroides. And The Mechanism Of Relieving To Hg～(2+) Injury By Spraying 6-BA

By imitating different concentration Cr6+, Cr3, Cd2+and Hg2+ polluted water environment, we mainly studied their toxic effects on Alternanthera philoxeroides(Mart.)Griseb by means of measurement of physiological indexes and electron microscopy observation in this paper, and also the relieving to Hg2+ injury of Alternanthera philoxeroides' antioxidant enzyme systems by spraying 6-BA and its mechanism were discussed. The experimental results showed that Cr6+,Cr3+,Cd2+and Hg2+ might injure photosynthetic systems , protective enzyme systems, 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 membrane systems. With more serious damages, the defense systems of cells could not protect cells, the activities of protective enzymes decreased, malondialdehyde(MDA) content increased, and integrality of cell membrane 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 activity of Gogi apparatus became slow and disappeared at last; The thylakoids of chloroplast and cristae of mitochondria became swoln or vesiculate and disintegrated finally; The nucleus were distorted and the nuclear membrane 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: The more Cd2+pollution, the more serious damage. The action processes and concentration ranges of the four ions were different from each other because of different areas and developments of plants, physiological indexes and ions.And the results indicated that various concentrations 6-BA by foliar spraying had different effects on physiological characters of A. philoxeroides under Hg2+ pollution.6-BA could effectively improve the activity of antioxidase and reduce the generation of active oxygen and MDA in vivo. It was proved that the former depends on the increase of the antioxidase content and the activity itself, while the latter mainly depends on that 6-BA could improve the ability of antioxidase to eliminated active oxygen, therefore it indirectly reduced the content of active oxygen. But it was still uncertain whether 6-BA has direct effect on active oxygen, so some further studies were needed. The results showed that different concentration 6-BA had different effects on physiological indexes of A. philoxeroides: 2x10-5mol/L is the best dose of 6-BA for the changes of SOD, MDA and O2-; on the other hand, CAT and POD are significantly affected under 3X10-5mol/L 6-BA. It was also proved that Hg2+ pollution could reduce the activity of antioxidases of the plant in vitro and 6-BA had no effects on the activity of antioxidases of the plant in vitro. So we could draw a conclusion that it did in vivo indirectly. In the further experiment we proved that the increasing of antioxidases' activities relied on the rise of antioxidases' content to a great extent by spraying 6-BA. 6-BA could regulate the express of antioxidase on translation level.