Abstract: The symptoms of the young leaves and ultrastructural changes of mesophyll cells of Brasenia schreberis winter buds when induced by poisoning of Hg^2+ pollution are reported in this paper. When winter buds were treated with a concentration of Hg 2+ in 5mg/L solution within 15 days, the leaves gradually lost their green color; glandular hairs contracted and twisted and mucilagenous material of the leaves was greatly reduced. The ultrastructural changes of the mesophyll cell showed the disappearance of Golgi apparatus and reduction of ribosomes with integration of mitochondria. Increasing of Hg2+ concentration on the same days of treatment as above, caused changes in the ultrastucture of the cells. It showed contraction of plasmalemma and snap of plasmodesmata, nucleolus broke into several parts, chloroplasts swelled and thylakoids disinte-grated. When winter buds were treated with concentration of Hg2+ increased to 15mg/L, the nucleus of cell broke down and cells died. According to our observation, the lethal concentration of Hg2+ to the winter bud of B. schreberi ranges from 2.5 to 5mg/L.

Key words: Brasenia schreberi