Heavy metal pollution has become a worldwide problem in aquaculture. We studied copper （Cu^2＋） accumulation and physiological responses of two red algae Gracilaria lemaneiformis and Gracilaria lichenoides from China under Cu^2＋ exposure of 0-500 μg/L in concentration. Compared with G. lemaneiformis, G. lichenoides was more capable in accumulating Cu^2＋, specifically, more Cu〉 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 Cu^2＋-binding as an efficient barrier against metal toxicity. Conversely, G. lemaneiformis was more vulnerable than G. lichenoides to Cu^2＋ toxin for decreases in growth, pigment （chlorophyll a, chlorophyll b, phycobiliprotein, and B-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 Cu〉 stress than G. lemaneiformis.
Comparative studies of absorption spectra of phycobiliproteins of Gracilaria lemaneiformis Greville and its pigmental mutants were conducted in this study. The results showed that the absorption spectra of phycoerythrins ( PE) from different material changed significantly, while those of phycocyanins (PC) and allophycocyanins (APC) were basically similar. In order to disclose the essence of die difference, partial sequences of die subunit genes of PE of Qingdao strain of G. lemaneiformis (qd) and its pigmental mutants were determined. The amino acid sequences were deduced and used to explain spectral shifts of PE from the pigmental mutants. The amino acid sequences of PE resembled each other, and several residues changed among qd and its pigmental mutants. Residue substitutions were found in a region consisting of amino acids which determined are secondary structure and subunits interactions, thus might influence the confirmation and interaction of subunits, and further caused spectral deviation.
Cloning and sequencing of the genes coding for the α and β subunit of phycoerythrin (PE) of a red alga- Gracilaria lemaneiformis (GL) are reported. Alignment of 1084 nucleotides sequenced with three known red algal PE genes, Rhodella violacea (RV), Polysiphonia boldii (PB) and Aglaothamnion neglectum (AN), showed high level of conservation, and similarities of 77.6% (between GL and RV), 77.9% (GL and AN) and 79.0% (GL and PB). The similarities of amino acids were 84.8% (between GL and RV), 85.7% (GL and PB), and 80.6% (AN and GL), higher than those among nucleotides.
