Response Mechanism Of Three Populations Of Sinonovacula Constricta Under Different Salinity Stress

The razor clam,Sinonovacula constricta,is commonly known as "Chengzi ",which is an important economic marine aquaculture shellfish in China.The maturity of S.constricta artificial nursery technology has promoted the rapid development of aquaculure,with an annual output of more than 800,000 tons.Salinity is one of the important environmental factors of the ocean.Due to the global climate,sudden changes in environmental salinity caused by natural factors such as high temperature,drought and precipitation will affect the biological processes such as the survival and growth of marine life.In this research,three populations of S.constricta are used as experimental materials,including Lianyungang population(LYGSC),the new variety "Shenzhe No.1"(SZSC),and the Ninghai population(NHSC).The acute experiments were performed under different salinity stress using the still water method.The survival,physiological and biochemical indicators,and stress resistance genes were detected.In order to analyze their response mechanism under different salinity stress.The result will provide a theoretical reference for the breeding of resistant varieties.The main findings are as follows:(1)Using three populations(LYGSC,SZSC and NHSC)as experimental materials,acute stress experiments were performed at different salinities(20,25,30,and 35),and their survival rate,oxygen consumption rate,ammonia excretion rate,and O: N ratio were measured.The results showed that LYGSC had the highest survival rate of100%,and NHSC had the lowest survival rate of 94.44%.The oxygen consumption rate,ammonia excretion rate,and O: N ratio increased with the increasing of salinity,and reached the maximum value at 35 salinity.It shows that the clam can resist the stress of the environment by improving their respiratory metabolism ability after salinity stress.In addition,the oxygen consumption rate,ammonia excretion rate,and O: N ratio showed a trend of first increasing and then decreasing with the extension of stress time,showing a certain correlation with the stress time.In this study,the survival rate,oxygen consumption rate and ammonia excretion rate of LYGSC were significantly higher than those of the other two groups(P(27)0.05),indicating thatLYGSC had a higher Stress adaptability is stronger.In addition,after stress of 30 and35 salinity,it was found that SZSC had higher oxygen consumption rate and ammonia excretion rate than NHSC in two different populations in the same area,indicating that SZSC shows a strong ability to adapt to or resist adverse environments under high salt stress.(2)The activities of NKA and immune-related enzymes at different salinities(20,25,30 and 35)were determined.The results show that the activities of NKA,superoxide dismutase(SOD),catalase(CAT)and alkaline phosphatase(AKP)also increased with the increasing of salinity,and reached a maximum values at 35 salinity.It shows that after salinity stress,the body can adapt to or resist adverse environmental stress by increasing enzyme activities.Similarly,the activities of NKA,SOD,CAT,and AKP increased firstly and then decreased with the extension of the stress time.Under salinity stress,there were significant differences in the NKA,SOD,CAT,and AKP activities(P(27)0.05)in the three populations.In this study,under different salinity stresses,LYGSC's four enzyme activities can quickly recover to a stable or initial value after a short up-regulation compared with the population in different regions,indicating that LYGSC has strong adaptability to salinity stress.In addition,under the same conditions,Compared with NHSC in salinity 35 stress,SZSC showed higher activity in the detection of NKA,SOD,CAT and AKP after salinity stress,indicating that SZSC may have a stronger ability to resist or adapt to the adverse environment.(3)The ScHSP90 gene expression of three populations were determined at different salinities(20,25,30,and 35).The full-length c DNA of the ScHSP90 gene was 3 070 bp and encoded 726 amino acids.Real-time quantitative PCR(q RT-PCR)analysis showed that ScHSP90 could express in all examined tissues and the relative higher expression level was observed in siphon and hemolymph.After the acute treatments of different salinity concentration,the expression of ScHSP90 gene in siphon,gills and hepatopancreas significantly increased at salinity 30 or 35(P<0.05),and the expression increased following the salinity concentration increasing.It shows that the ScHSP90 gene could be involved in the process of resisting the adverse environment.Similarly,the ScHSP90 gene expression in different populations of S.constricta was significantly different under different salinity stress(P<0.05).It shows that the ability of each population of S.constricta to respond to salinity stress may be different.This study found that LYGSC has a higher ScHSP90 gene expression level whenpopulations in different regions face salinity 35 stress,indicating that LYGSC shows strong adaptability in high salt stress.In addition,after high salt stress,it was found that the expression of ScHSP90 gene in SZSC was relatively high in two different populations in the same area.indicating that SZSC has a stronger ability to resist or adapt to the adverse environment under high salt stress.