Comparison in copper accumulation and physiological responses of Gracilaria lemaneiformis and G. lichenoides (Rhodophyceae)

Heavy metal pollution has become a worldwide problem in aquaculture. We studied copper (Cu²⁺) accumulation and physiological responses of two red algae Gracilaria lemaneiformis and Gracilaria lichenoides from China under Cu²⁺ exposure of 0–500 μg/L in concentration. Compared with G. lemaneiformis, G. lichenoides was more capable in accumulating Cu²⁺, specifically, more Cu²⁺ on extracellular side (cell wall) than on intracellular side (cytoplasm) and in cell organelles (especially chloroplast, cell nucleus, mitochondria, and ribosome). In addition, G. lichenoides contained more insoluble polysaccharide in cell wall, which might promote the extracellular Cu²⁺-binding as an efficient barrier against metal toxicity. Conversely, G. lemaneiformis was more vulnerable than G. lichenoides to Cu²⁺ toxin for decreases in growth, pigment (chlorophyll a, chlorophyll b, phycobiliprotein, and β-carotene) content, and photosynthetic activity. Moreover, more serious oxidative damages in G. lemaneiformis than in G. lichenoides, in accumulation of reactive oxidative species and malondialdehyde, and in electrolyte leakage, because of lower antioxidant enzyme (superoxide dismutase and glutathione reductase) activities. Therefore, G. lichenoides was less susceptible to Cu²⁺ stress than G. lemaneiformis.