Effect of heavy metal stress on emerging plants community constructions in wetland.

In this paper, we report the effects of heavy metals (HMs) (cadmium and mercury) on seed germination and seedling growth of Phragmites australis and Triarrhena sacchariflora, which are the two main typical emerging plants in Hongze Lake wetland. The results showed that there was a reduction in germination percentage, germination index and seedling length as HM concentration in the growing media increased for both treatments. The effect of HMs toxicity on seed germination and seedling growth of T. sacchariflora was more obvious than of P. australis. At the stage of seed germination, P. australis and T. sacchariflora were sensitive to Hg(2 + ) and Cd(2 + ), respectively, and Hg(2 + ) was more toxic than Cd(2 + ) at the stage of seedling growth. The effect of HMs toxicity is not invariable during plant growth. Compared to the stage of seedling growth, P. australis and T. sacchariflora are more susceptible to HMs at the stage of seed germination. In addition, we calculated the ecological thresholds of P. australis to Cd and Hg are 19.32 and 1.08 mg kg(-1), and that of T. sacchariflora to Cd is 4.62 mg kg(-1) based on the lab simulation. The results also indicated that the species of P. australis is more tolerant than T. sacchariflora to the HMs and is a better candidate for restoration in Hongze Lake wetland ecosystem.

Evolution of structure in gamma-class carbonic anhydrase and structurally related proteins.

Protein structure contains evolutionary information and it is more highly conserved than sequence. The evolution of structure in gamma-class carbonic anhydrase (gamma-CA) and its structurally related proteins (gammaCASRPs) were discussed. To obtain a reliable analysis, we defined a subset that contains all specificities and organisms as the nonredundant set using QR factorization based on the multiple structural alignment of the known crystallographic structures of gammaCASRPs with Q(H) as the structural homology measure. Then, we applied unweighted pair group method with arithmetic averages (UPGMA) to reconstruct structural phylogeny. We found that gamma-CA most likely arose through duplication events; the domain of gamma-CA underwent a process of alpha-helical content from amino-terminal end to carboxyl-terminal end of the left-handed beta-helix (LbetaH); the capacity of gamma-CA to bind Zn occurred early in evolution and only later included the ability to catalyze the reversible hydration of CO(2) efficiently for the occurrence of two loops involving Glu 62 and Glu 84, respectively, and a long helix at the carboxyl-terminal end of the LbetaH. In addition, the main conserved regions in these structures are in the structurally constrained residues of LbetaH domain, and the topology of the structural dendrogram can be rather easily understood in terms of functional diversification.