Physiological responses of Porphyra haitanensis (Rhodophyta) to copper and cadmium exposure

The aim of the present work was to evaluate the effects of copper (Cu) and cadmium (Cd) on the physiology of the red macroalga Porphyra haitanensis Chang and Zheng. The alga was cultured in media with different Cu or Cd concentrations for 7 days. The relative growth rate was significantly reduced at Cu concentrations of 0.10 mg l(-1) and above or at Cd concentrations of 4 mg l(-1) and above. Chlorophyll a (Chl a), carotenoids (Car), phycoerythrin (PE) and phycocyanin (PC) contents decreased at high Cu or Cd concentrations, and PE content increased at 0.10 mg l (-1) Cu or 4-8 mg l (-1) Cd. Moreover, the optimal quantum yield, maximum net photosynthetic rate (P-m) and apparent photosynthetic efficiency (a) were significantly reduced at high Cu or Cd concentrations. In contrast, malondialdehyde (MDA) content and superoxide dismutase (SOD) activity increased in response to Cu or Cd treatment. Catalase activity increased at 2-8 mg l (-1) Cd and significantly declined at 0.50 mg l (-1) Cu or 10 mg l (-1) Cd. Nitrate reductase (NR) activity declined at high Cu or Cd concentrations. Consequently, both Cu and Cd were physiological stressors for P. haitanensis, with Cu being more toxic than Cd. This work has generated valuable knowledge about the toxic effects of Cu and Cd on macroalgae.