The Research Of Ultrastructure And Gene Expression Of Symbiotic Zooxanthellae In The Coral Under Thermal Stress

Zooxanthellae is a kind of tawny algae which widely symbiosis with marineinvertebrates.This article employs Molecular identification, ultrastructural observation.gene expression analyse and isolated cultivation of Galaxea astreata zooxanthellae.Themain results were presented as follows:1.The nSSU rDNA of zooxanthellae digested by Sau3（AI）and Taq I,then weobtained enzyme fragment are850bp,500bp and900bp,700bp,respectively. The resultsshowed that zooxanthellae belong to sub-clade C1; The ITS-2sequence homology analysisalso indicated it is C1clade..2. The ultrastructure of zooxanthellae was investigated by TEM under the thermalstress process. We found that there was no effect on zooxanthellae at the initial stage ofthermal stress, the cells become abnormal until32℃for72h.and at32℃for168h, mostcells start to occurrence apoptosis,and noly a few cells become necrocytosis.Then reduction of temperature to28℃for120h, the zooxanthellae morphologyalmost recovery to normal state, yet the ultrastructure were not be completely normal until28℃for216h.It suggest that ultrastructure recovery rate slower than morphology.3. The SAM gene was used as reference gene to study the Hsp70, Hsp90,psaA andpsbA mRNA relative gene expression under thermal stress of zooxanthellae by usingreal-time PCR technique.The results showed that the expression level of Hsp70and Hsp90gene were highest at32℃for216h, while the lowest abundance after28℃for120h. Theexpression level of psaA and psbA gene present different patterns, the highest expressionlevel of psaA and psbA were at32℃for24h and32℃for24h, respectively. It indicatedthat they were play different roles under thermal stress.4.By in vitro culture of zooxanthellae,we found that the algae which isolated fromGalaxea astreata can survive in ASP-8A medium for13days,and9days in f/2medium.And when we improve the concentration of Fe3+to1.8*10-5M in ASP-8A medium,thezooxanthellae can alive for15days.The results showed that Fe3+play an important role inzooxanthellae cultivation.