Relif Effects Of Rare Earth Elements To The Damage Of High Aquatic Plants Under The Stress Of Heavy Metals

The relif effects of the rare earth ions La3+ and Ce3+ to the damage of high aquatic phants Myriophyllum verticillatum Linn., Hydrocharis dubia B L. Backer and Potamogeton crispus Linn, produced by heavy metals Cr3+, Cr6+, Ni3+, Cd2+ and Hg2+ were measured by physiological and biochemical indexes, concentration of elements as well as observations of electron microscopy. We also evaluate the effects of single treatment by La3+ to the physiological indexes of Hydrocharis dubia B L. Backer and Potamogeton crispus Linn. The results showed obvious damage to the photosynthetic systems, protective enzyme systems and membrane systems by all the selected heavy metal ions. Resistance ability from endogenous protective enzyme systems in the plants was enhanced by heavy metal stress inducement in restricted range, while defence reaction crippled as the aggravation of the damage. La3+and Ce3+ could stabilise the structure and fuction of the membrane, thus promote the growth of aquatic plants. The submerged macrophyte was more sensitive to La3+ than the floating plants. After adding La3+ and Ce3+, the enhancement of relative membrane penetration (RMP) by heavy metal stress was reduced, the peroxidation of membrane lipids was alleviated and to some degree protected the membrane from injury by heavy metal ions, thus utimately promote the tolerance ability of plants to heavy metal stress. Mesurement of element consentration by ICP-MS method showed that rare earths could decrease the accumulation of heavy metal ions in the plants through competition effect. The chances of heavy metal into the plant cell were reduced and stress alleviated. Ultrastructural Observation of leaf cells of Myriophyllum verticillatum Linn, showed that La3+ coule alleviate the injury of cell structure produced by Cr6+. La3+ has greater ability of relieving the toxic effect of Ni3+ to Hydrocharis dubia B L. Backer than that of Ce3+. However, the relif ability of rare earth to the stress of heavy metal was limited. As the increase of damage produced by heavy metal to the plants, the relieving ability of rare earth reduced. Under the extremely high concentration of heavy metal ions treatment, rare earth elements could aggrevate the damage to the plant cells by cooperating with heavy metal. In this case, rare earth element has the same effect on plant as heavy metal did.