Effects of Different Salinities on the Free Amino Acids Composition in the Gill of Portunus trituberculatus

Abstract:

In this study, we investigated the composition and function of free amino acids (FAAs) in the gill of Portunus trituberculatus under different salinities. In a 5-day experiment, the contents of FAAs were measured under a series of salinities. We found that in seawater-adapted P. trituberculatus, the concentration of taurine (2.54 mg/g) was the highest, followed by alanine (0.65 mg/g), glutamate (0.64 mg/g), arginine (0.58 mg/g), glycine (0.48 mg/g) and proline (0.25 mg/g). The level of total free amino acids (TOFAA) in the gill increased significantly with the rise in salinity (P<0.05). When salinity was 10, 20, 33, 40, and 50, the concentration of TOFAA in the gill was 5.32 mg/g, 7.26 mg/g, 6.34 mg/g, 7.25 mg/g, and 7.90 mg/g respectively. Non-essential amino acids (NEAA) increased significantly as the salinity was elevated from 10 to 50. Essential amino acids (EAA) was not affected by external salinity change (P>0.05). NEAA includes glutamate (Glu), alanine (Ala), glycine (Gly), aspartic acid (Asp), serine (Ser), cysteine (Cys), tyrosine (Tyr), proline (Pro), and Tauine (Tau), and the rest are EAA. TAA include aspartic acid (Asp), glutamate (Glu), glycine (Gly), and alanine (Ala). The concentrations of free Gly, Glu, Ala, Pro in the gill of P. trituberculatus were raised sharply (P<0.05) with the increase in salinity, whereas the concentration of free Arg decreased (P<0.05). The results suggested that FAAs, especially individual Gly, Glu, Ala, and Arg, could play an important role in salinity adaption. During adaptation, the FAAs pool (mainly NEAA) in the gill may be directly associated to osmoregulation. Change in the FAAs pool in the gill after acclimatization suggested that mainly NEAA might be involved in intracellular osmoregulation. It was also demonstrated that the salinity change mainly affected the NEAA content in the gill.