Effects Of Temperature And Salinity Variations On The Growth And MAPK Gene Expression Of Two Strains Of Karenia Mikimotoi (Dinophyceae)

As one of the most basic and important environmental factors in the marine environment,temperature and salinity are important onthe growth of marine phytoplankton.Mitogen-activated protein kinase?MAPK?is a key molecule of the signal transduction pathway and exists extensively in eukaryotic organisms.It plays an important role in the physiological regulation of plant growth and stress response.In this study,two strains of Karenia mikimotoi,one of the most common harmful algal species in coastal area of China,were studied.MAPK gene was selected to evaluate molecular response of Karenia mikimotoi to temperature and salinity variations.The Fujian and Huizhou strains of Karenia mikimotoi were cultured in the condition that temperature and salinity gradually change.The temperature varies from 15 to 33?,and the salinity varies from 15 to 38.The growth rate,chlorophyll a concentration,maximum potential photosynthetic capacity and Mitogen-activated protein kinase sequence of the two strains of K.mikimotoi were measured.The major research results are as follows:The preference temperature for the K.mikimotoi Fujian strain was ranging from 15 to 30?,and the preference salinity was ranging from 20 to 37.The optimal temperature and salinity wereranging from 24 to 28? and 23 to 37 respectively.For the K.mikimotoi Huizhou strain,the preference temperature was ranging from 15 to 33?,and the preference salinity was ranging from 20 to 37.The optimal temperature and salinity were ranging from 24 to 30? and 26 to 32 respectively.In the temperature change experiment,the maximum growth rates of the strains of Fujian and Huizhou were recorded at 28 ?(0.37d^-1)and 26 ?(0.31d^-1),respectively.In the salinity change experiment,the maximum growth rates of the two strains of Fujian and Huizhou were recorded at 23(0.34d^-1)and 26(0.20d^-1),respectively.The chlorophyll a concentration was positively correlated with the algal celldensity.For the Fujian strain,the Fv/ Fm value of the algae was inhibited at the temperatures ?30?,and at the salinities ? 37 or ? 20.For the Huizhou strain,the Fv/ Fm value of the algae was inhibited at the temperatures ? 28? or ? 20?,and at the salinities ? 38 or ? 17.The MAPK gene of the K.mikimotoi Huizhou strain was significantly upregulated at 22 and 26?,and was significantly down-regulated at 20 and 28?.The MAPK gene of the Karenia mikimotoi Fujian strain was down-regulated at 15 and 33?,and was up-regulated at 20,26,28 and 30?.The MAPK gene of the Huizhou strain was significantly down-regulated at the salinity of 30³7,and was significantly upregulated at the salinity 17 and 20.The MAPK gene of the Fujian strain was significantly up-regulated at the salinity of 23,26,30 and 32,and was significantly down-regulated at the 34 and 37.The results showed that MAPK gene was associated with the regulation of temperature and salinity variations in Karenia mikimotoi,indicating that MAPK gene was involved in the transduction signals of temperature and salinity.