Abstract: Potamogeton crispus Linn.was cultivated in solution with different Zinc gradient concentration for 5 days for studying the effect of Zn excess on plants. Changes of SOD, POD, CAT and other indicators were analyzed and ultra structural damage was observed using electron microscope. The conclusion showed that:None toxic effect was caused by low Zn concentration (< 20mg/L), all in indicators had an increment tendency. Activity of SOD and CAT reached maximum at 50mg/L, while the other four indicators decreased, but activity of POD and chlorophyll content remain higher than that of the control, soluble protein content was lower than that of the control. All indicators decreased obviously at 100mg/L. Meanwhile ultra structural damage was caused by on excess of Zn. Such as disrupted chloroplast membrane, disintegration of chloroplasts;swelling of cristae of mitochondria and vesiculation of mitochondria at last;disrupted nuclear membrane, break of nucleolus into several small nucleoli and eventually cell death. So we could come to the conclusion that serious injury was caused by on excess of Zn.

Key words: Zinc, potamogeton crispus Linn., antioxidant enzyme, ultra structure, damage