| Sargassum thunbergii is a common economic brown seaweed in coastal areas of China,and it is also one of the main seaweed in offshore seaweed beds.Due to its strong absorption capacity of nutrient salts and heavy metals,it plays an important role in reducing offshore eutrophication,repairing damaged marine environments and maintaining the balance of offshore ecosystems.Salicylic acid(SA)has the ability to improve plant stress tolerance.The effects of exogenous salicylic acid on the growth and development of S thunbergia under adversity and the application prospects of salicylic acid in seaweed culture were investigated.In this paper,we investigated the changes of growth,photosynthetic pigments,chlorophyll fluorescence kinetic properties,antioxidant enzymes,StGST and HSP70 gene expression of S thunberga under cadmium stress and high temperature stress by pretreatment with exogenous salicylic acid at four different concentrations of 0,1,5 and 50 mg/L.We found that salicylic acid could effectively alleviate the growth inhibition of S thunberga caused by cadmium and high temperature stress.The results of the experiment are as follows.1.Sequence analysis of the StGST family of genes in S thunberga showed that the sequence of the obtained genes was indeed the StGST sequence of S thunberga and that StGST2 belonged to a different type of glutathione S-transferase(GST)from StGST1 and StGST3;homology and evolutionary analysis of the proteins encoded by the StGST genes led to the conclusion that S thunbergia,StGST1 and StGST3 belong to the Sigma-type GST,while StGST2 may belong to one of the DHAR-type GST family members;finally,the expression analysis of StGST genes under cadmium stress revealed that there were differences in the sensitivity of different genes to cadmium,among which StGST1 was the most sensitive to cadmium.2.Salicylic acid pretreatment significantly increased the growth rate of S thunberga under Cd stress,with 5 mg/L salicylic acid promoting growth most significantly,increasing 154%compared to the Cd stress group;chlorophyll a and carotenoid content both showed a trend of increasing and then decreasing with the increase of salicylic acid concentration,while chlorophyll c continued to increase with the increase of salicylic acid concentration;among the chlorophyll fluorescence parameters,the changes of F_v/F_m and qP The changes in F_V/F_M and q P were not significant before and after Cd stress and salicylic acid treatment,while the NPQ parameters decreased significantly under Cd stress compared to the blank control group;salicylic acid treatment increased the SOD activity and MDA content of S thunberga,and the most significant changes were observed in the5 mg/L treatment group compared to the Cd stress group.The expression of StGST1 gene increased significantly under Cd stress and decreased significantly after salicylic acid treatment;indicating that salicylic acid has some alleviating effect on Cd stress.3.The specific growth rate,chlorophyll a,chlorophyll c and carotenoid content all increased and then decreased with the increase of salicylic acid concentration.5 mg/L salicylic acid promoted the growth most significantly,the specific growth rate increased by 589%compared with the high temperature group,the chlorophyll fluorescence parameter F_v/F_m increased,the NPQ activity increased significantly and the expression of HSP70 gene increased.The expression of HSP70 gene was significantly increased at high temperature.1 mg/L salicylic acid treatment further promoted the expression of HSP70gene,while 5 and 50 mg/L salicylic acid treatment reduced the expression of HSP70 gene at high temperature. |
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