Adaptation Mechanisms Of Ion Transportation,Photosynthesis,and Anti-oxidant System In Coscinodiscus Centralis Under Salinity Stress

Diatoms can be classified as fresh water species,brackish water species,and marine species according to its adaptability to different types of water.Thus diatoms have a strict salinity adaptation range and they can be good indicators of salinity change.The salinity of estuary region is influenced by regular tide,brackish water diatoms can be inhibited by high salinity sea water periodically.It is extremely important that whether diatom can maintain its intracellular ion balance in high salinity environment,but we still do not understand much about how the diatom cell membrane ion transport system regulate the balance of ion environment inside the cell.Thus,using non-invasive micro-test technique(NMT),the response of ion exchange system in salt stress conditions of one Coscinodiscus centralis strain were revealed.The diatom strain was collected in Fugong,Zhangzhou,Fujian Province.The mechanism of diatom regulate the intracellular ion balance is discussed emphatically in this thesis,we studied the dynamic change of H+,Na+and K+flux,in case to reveal the function of ion transport system in salt-stress environment.At the same time,the photosynthesis ability(Fv/Fm)and antioxidant activity(SOD and CAT)were studied.The main results were showed as follows:1)Under transient and short-term salt stress,the H+and Na+efflux were upregulated(in transient and short-term salt stressed cells' H+flux,P=0,in transient salt stressed cells' Na+flux,P=0.008,in short term-salt stressed cells' Na+flux,P=0),which indicates that under such conditions,the H+-ATPase on Coscinodiscus centralis pumps H+out of the cell and activates Na+/H+antipoter to transport Na+out of and H+into the cell.2)Under long-term high salinity stress,H+began to flow into the cell,while Na+effluxes reached their peak.At the same time,we confirmed that amiloride could inhibit H+influx and Na+efflux.This indicated Na+/H+ antipoters were important for diatom to transport Na+out of the cell under long-term salt-stress3)Under transient salt stress condition,K+influx slowed down compared to control group,but after 1-day,it returned to the normal level.This result was consistent with our Fv/Fm result that Fv/Fm dropped under transient salt stress condition and raised after 1-day of stress,indicating that intracellular K+level had a good sustainability under transient and short-term salt stress,and could adapt well under such short-term stress environments.Under long-term salt stress,K+influx peaked,which indicates that the K+/Na+balance system was activated,letting the cell get rid of excessive Na+.These results showed that the K+/Na+balance might be critical for Coscinodiscus centralis to adapt high salinity environment.4)CAT activity showed no obvious change in transient and short-term salt-stressed cells,it indicated that the synthesis pathway of CAT stayed inactive under transient and short-term salt stress,it further suggested that Coscinodiscus centralis developed a well adaption to short-term salt stress.Antioxidant experiments showed that SOD activity increased as the salt stress continued and CAT activity increased under long term stress condition,this is consistent with Na+efflux increases under salt stress condition.Thus the activated antioxidant activity is also a behavior of diatom adjust to high salinity environment.