An involvement of aquaporin in heat acclimation and cross-tolerance against ammonia stress in black tiger shrimp, Penaeus monodon

The full-length cDNA sequence of an aquaporin gene (PmAQP1) (786-bp open reading frame encoding 261 amino acids) was identified and characterized in Penaeus monodon. Its expression pattern in various tissues was investigated, and quantitative analyses of the expression levels were determined. PmAQP1 transcripts were detected in hepatopancreas, gill, ovaries, testes, intestine, stomach and heart. The level in gill appeared to be greater than in the other tested tissues. Expression of PmAQP1 was not detected in hemocytes, epidermis, lymphoid organs or muscle. Then, the stress tolerance of shrimp was enhanced by heat acclimation (shrimp were transferred from ambient temperature to 35 °C for 2 h and then brought back to the ambient temperature). The expression of PmAQP1 in the gill was significantly upregulated after 6 h of post-heat shock, and cross-protection against ammonia stress was also induced in heat-acclimated shrimp. The expression level of PmAQP1 from gills of shrimp both with and without heat acclimation was significantly higher than that of control shrimp (no heat shock and no ammonia stress) within 24 h and remained high after 48 h of post-ammonia stress (P < 0.05), indicating that ammonia stress can induce PmAQP1. However, particularly in heat-acclimated shrimp, the expression of PmAQP1 was significantly higher than that of shrimp with no heat acclimation. The results from our study suggest that PmAQP1 is heat-inducible and this upregulated PmAQP1 also helps shrimp to resist ammonia stress.