Photosynthetic and molecular responses of the marine diatom Thalassiosira pseudonana to triphenyltin exposure

This study aimed to investigate the responses of the marine diatom Thalassiosira pseudonana upon waterborne exposure to triphenyltin chloride (TPTCI) through determining their photosynthetic response, growth performance, and expressions of genes and proteins. Based on the growth inhibition test, the 96-h IC50 (i.e., median inhibition concentration) was found to be 1.09 mu g/L (95% confidence interval (CI): 0.89-1.34 mu g/L. According to photosynthetic parameters, the 96-h EC(50)s (i.e., median effect concentrations) were estimated at 1.54 mu g/L (95% CI: 1.40-1.69 mu g/L) and 1.51 mu g/L (95% Cl: 1.44-1.58 mu g/L) for the maximum quantum yield of photosystem II (PSII) photochemistry (Phi(po)) and the effective quantum yield of photochemical energy conversion in PSII (Phi(2)), respectively. Non-photochemical quenching in the algae was increased at low concentrations of TPTCI (0.5-1.0 mu g/L) but it decreased gradually when the TPTCI concentration further increased from 1.0 to 205 mu g/L. Results of gene expressions showed that lipid metabolism related genes were not influenced by TPTCI at 0.5 or 1.0 mu g/L, while silica shell formation genes were down-regulated at 0.5 mu g/L. Photosynthesis related genes were up-regulated at 0.5 mu g/L TPTCI but were down-regulated at 1.0 mu g/L TPTCI. Proteomics analysis revealed that relatively less proteins could be detected after exposure to 1.0 mu g/L TPTCI (only about 50-60 spots) compared with that observed in the 0.5 mu g/L TPTCI treatment and two control groups (each with about 290-300 protein spots). At 0.5 mu g/L TPTCI, five proteins were differentially expressed when compared with the seawater control and solvent control, and most of these proteins are involved in defence function to protect the biological systems from reactive oxygen species that generated by TPTCI. These proteins include oxygen-evolving enhancer protein 1 precursor, fucoxanthin chlorophyll a/c protein - LI818 clade, and mitochondrial manganese superoxide dismutase, which can function to maintain the capacity of PSII and stabilize the photosynthesis efficiency as reflected by the unchanged Phi(po) and Phi(2) values at 0.5 mu g/L TPTCI. In contrast, the excess toxicity that caused by TPTCI at the high concentration (1.0 mu g/L TPTCI) might directly damage the proteins, inhibit their expression, and/or cause the suppression of metabolism as indicated by the down-regulation of most studied proteins and genes, which could ultimately inhibit the photosynthesis and growth of the algae. Overall, this study comprehensively elucidated the toxicity effects of TN' on T. pseudonana, and partially revealed the molecular toxic mechanisms and corresponding defence responses in this model algal species. (C) 2014 Elsevier B.V. All rights reserved.