Toxic Effects Of Heavy Metal Cu On The Thallus And Conchocelis Of Porphyral Haitanensis

Heavy metals pollution is becoming more and more serious in marine environment due to heavy human activities, and more attention has been paid to the effects of heavy metals on algae during recent years. In this paper, the chronic(Low concentration: 0.1mg/L, 0.5mg/L, 1mg/L, 10mg/L and 20mg/L; Time: 3d, 7d, 10d) and acute (High concentration:0.1mg/L, 0.5mg/L, 1mg/L, 10mg/L and 20mg/L;Time:12h, 24h, 48h and 72h) toxic effects of copper (Cu²⁺) on different life stages (thallus and free conchocelis) of Porphyra haitanensis were investigated, and physiological and biochemical parameters included relative growth rate (RGR), the contents of photosynthetic pigments, phycoerythrin (PE),phycocyanin (PC), the activities of super oxide dismutase (SOD), catalase (CAT) and the content of malondiald- ehyde (MDA) .The toxic concentration and exposure time were delineated from this study,and the results will be helpful for breeding of Porphyra haitanensis and deciphering the toxic mechanism on Porphyra haitanensis under stress of Cu²⁺ contamination. In detail, the findings from this study included:(1) Growth. When Cu²⁺≤0.01mg / L, it promoted the growth of the thallus of Porphyra haitanensis. When 0.01mg / L <Cu²⁺ <0.1mg / L, no significant growth in hibition on the thallus was found at the beginning of exposure, but significant inhibition was recorded with the increase of exposure duration.When Cu²⁺≥0.1mg / L, the growth of thallus of Porphyra haitanensis was significantly inhibited immediately, and thallus stopped growing or even started to decay with the increase in exposure duration. Free conchocelis was found to be more sensitive to Cu²⁺ stress, and the toxic experiment showed that growth was significantly inhibited immediately and started to decay even at the low concentration.(2) Chlorophyll, carotenoids, phycoerythrin and phycocyanin. For the thallus of Porphyra haitanensis, chlorophyll content increased significantly when Cu²⁺ <0.1mg / L, but it declined significantly with exposure duration when Cu²⁺≥1mg / L . For the free conchocelis, the higher concentration of Cu²⁺≥0.1mg / L was found to depressed the chlorophyll content in a short time. Under acute conditions, the low concentration of Cu²⁺ can enhance the carotenoids content of thallus to a certain extent, but high concentrations significantly depressed the carotenoids content. Under the conditions of chronic low concentrations, carotenoids content of thallus increased at first and then decreased with the exposure duration. For PE and PC in both thallus and free conchocelis, they changed more sharply than Chla and Car. High concentrations of Cu²⁺ stress under acute condition depressed PE and PC significantly and sharply, and low concentrations of Cu²⁺ treatment increased PE and PC significantly and sharply..(3) Oxidative stress. For thallus of Porphyra haitanensis, the low concentration (chronic conditions)had no significant impact on MDA content, SOD and CAT activities , but with the high concentration of Cu²⁺ asignificantly enhanced MDA contents, SOD and CAT activities for all exposure periods.. In the free conchocelis, both MDA content and SOD activities increased significantly for all exposure periods, but SOD activities were found to decreased significantly at high concentrations treatment. The antioxidant system of the thallus of Porphyra haitanensis may has stronger resilience than that of the free conchocelis: high concentrations of Cu²⁺ in acute conditions, SOD activity in thallus has been an upward trend, while the SOD activity conchocelis first rise, the final sharp decline, indicating that copper ions on the enzyme system conchocelis have significant impact; from the experimental results of acute toxicity tests in the free conchocelis, SOD activity began to appear significantly differences in the 1mg / L, 48h, and it was 2 times compared to the control group. Free conchocelis in the 1mg / L, 24h significant differences began to appear, 72h, SOD activity value is 2.68 times than the control group.(4)Conchosαore releasing. The numbers of released conchospore performed a good dose - response relationship with the stress of Cu²⁺. Under low concentrations of Cu²⁺, the released conchospore number was not affected, while they were significantly inhibited at the high concentration treatment.(5)IC50。The thallus of Porphyra haitanensis at 24h, 48h, 72h IC50 concentrations were 17.77mg / L, 12.76mg / L, 0.997mg / L( probable value), the safe concentration was 0.0997- mg / L( probable value); The free conchocelis in the 24h, 48h , 72h IC50 concentrations were: 3.298 mg / L, 0.625 mg / L, 0.171mg / L ( probable value), safe concentration was 0.0171 mg / L( probable value).