Ultrastructural Study of The Toxic Effect of Different Content of Zn2+ on Hepatopancreas in The Larvae of Chinese Crab,Eriocheir sinensis

The impact of different concentrations of Zn2+ on the ultrastucture of hepatopancreas in larval (zoea Ⅳ) of Chinese crab,Eriocheir sinensis was studied after being exposed for 96 h by using transmission electronic microscope.The result demonstrated that significant ultrastructural changes,which occurred in hepatopancreas cells,were found after exposed above 200 μg/L Zn2+.When compared with control group (31.8 μg/L Zn2+).B cells have numerous vacuoles or a large vacuole with a number of insoluble Zn electronic dense granules (EDG) in membrane-lined types.When the mature B cells are extruded from the epithelium of the hepatopancreas tubules,these EDGs in vacuole will be released as the vacuoles which have burst.The EDGs will be found in the lumen.The production of EDGs in the lumen and the vacuole of B cell have been correlated directly with the ambient concentration of Zn2+.The EDGs in lumen then may be removed via the gut and excreted directly to outside and they are insoluble.The cytoplasm of R cells are often disoganized,vacuolized and form large vacuoles.The R cell are seriously damaged.The cytoplasm of E cell have large amount of vacuoles,which may be resulted from the degeneration of swollen mitochondrion.This shows that the E cells have lost their ability to differentiate to other cells.When the concentration of Zn2+ is high (1031.8 μg/L Zn2+),the structure of hepatopancreas will be seriously destroyed and no cell structure can be found. This observation suggested that formation of EDG in B cells was an important cellular detoxifying mechanism,in which Zn2+ or other heavy metal were incorporated into intracellular insoluble form (may be metal-protein complexes).These are harmless to the tissue and cell.Pathological effects occur in tissues when the rate of influx of a toxicant,such as Zn2+,exceeds rate of detoxification and excretion.In this experiment,the effect was found to be the damage of R and E cell,even the all cells in hepatopancreas.