Study On The Functional Mechanism That Absence Of NdhO Delays Cyanobacterial Cell Death Under High Temperature Conditions

Cyanobacterial NDH-1 is localized in the thylakoid membrane and participates in a variety of bioenergetic reactions,including respiration,CO2 uptake and cyclic electron transport around photosystem I.The complex transfers electrons from electron donor to quinone,and hence generating a transmembrane proton motive force used for ATP synthesis,which plays an important physiological role in resisting environmental stress.However,the functional role of NDH-1 in resisting high temperature stress is poorly understood,and the relationship between its activity and cell death is not clear.In this study,the wild-type,ndhO gene deletion mutant and ndhO overexpression strain of Synechocystis sp.strain PCC 6803 were treated with high temperature(45°C).By analyzing the physiological indicators of chlorophyll bleaching rate,cell death rate and cell viability,we found that the deletion of NdhO delayed the cell death caused by high temperature,but overexpression of NdhO increased the cell death caused by high temperature.The accumulation of reactive oxygen species in the cells detected by physiological means showed that the total reactive oxygen species and H2O2 contents in the cells were positively correlated with the expression of NdhO.In order to further explore the causes of reactive oxygen species in ?ndhO,WT and OX-ndh O cells,we found that the deletion of NdhO was beneficial to maintain high carbon assimilation by analyzing the carbon assimilation efficiency of the cells,but overexpression of NdhO significantly reduced the activity.The results of the above experiments showed that the deletion of NdhO increased the activity of NDH-1,which was beneficial to protecting the carbon assimilation efficiency under high temperature,thus reducing the accumulation of reactive oxygen species in the cells and finally delaying the cell death and improving cell viability,and vice versa.In conclusion,this study first revealed that deletion of NdhO could optimize photosynthesis and reduce ROS production,thereby delaying cyanobacterial cell death under high temperature conditions.It also first revealed that NDH-1 had the physiological function in delaying cyanobacterial cell death,and increased the understanding of the regulation mechanism on NDH-1 involving in cell death in cyanobacteria.In addition,this study further supported our previous findings: deletion of NdhO in cyanobacteria could increase NDH-1 activity.