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To explore the effect of temperature and salinity on the mitochondrial DNA (mtDNA) copy number of Palaemon carinicauda Holthuis, 1950, 5 temperature groups (10, 15, 20, 25 and 30°C) and 6 salinity groups (10, 15, 20, 25, 30 and 35) were set up, respectively. Subsequently, the numbers of copies of mtDNA of samples from all groups were detected by the TaqMan probe method. The results showed that the mtDNA copy number in the temperature samples was 2388, 2366, 4158, 4805 and 6027 at the above-mentioned temperature values, respectively. Obviously, the number of mtDNA copies in the cell tends to increase as temperatures rise. In addition, the mtDNA copy numbers of the salinity samples was 2609, 2593, 3215, 3478, 2618 and 2709, respectively, at the experimental salinities as listed above. This indicates, that the copy numbers of mtDNA tend to increase at first, and then again to decrease as the salinity values rise and pass beyond a threshold.

The p38 mitogen-activated protein kinases (MAPK) are a kind of Ser/Thr protein kinases that convert extracellular stimuli into a wide range of cellular response, appearing to function not only in stress stimuli but also in development. To explore the function of p38 MAPK in Palaemon carinicauda Holthuis, 1950, we cloned and characterized the full-length cDNA sequence (GenBank accession number KX893515) (designated as Pc-p38). The results showed that the open reading frame (ORF) of Pc-p38 was 1098 bp and it encoded a protein of 365 amino acids. Pc-p38 contained the conserved structures of a Thr-Gly-Tyr (TGY) motif and a substrate-binding site, Ala-Thr-Arg-Trp (ATRW), and was shown to have a close phylogenetic relationship to other p38 MAPKs in crustaceans. The tissue distribution patterns showed that Pc-p38 was widely expressed in all tissues, with highest expression in the hepatopancreas and ovary. Quantitative real-time PCR revealed that Pc-p38 was upregulated during ecdysis, reaching a peak at 5 min post-moult, suggesting that Pc-p38 may be involved in muscle remodeling after moulting. In addition, the expression of Pc-p38 increased following exposure to different concentrations of mercury, in a dose- and time-dependent manner. In conclusion, an Pc-p38 gene was cloned and its role determined at different times post-moult and after stress from different concentrations of mercury, to further reveal the possible functions of p38 MAPK in P. carinicauda.