Absence Of OCP Results In A More High-light-sensitive Growth Phenotype In Cyclic Electron Flow-impaired Mutant Of Synechocystis Sp. PCC6803

Light has two sides. One is that a modeate intensity of light can provide energy forcyanobacterial growth and the other is that excess light results in significantphotodamage. To adapt high light environments, a variety of photoprotectivemechanisms were developed during the cyanobacterial evolution, including cyclicelectron transport around photosystem I and thermal dissipation. In higher plant, these2photoprotective mechanisms influence each other. For example, cyclic electrontransport induced by high light can create a more acidic environment in the lumenside of thylakoid membrane, which can enhance the levels of thermal dissipation. Incyanobacteria, however, the relationship of these2mechanisms remains elusive.The aim of this thesis is to study this relationship of cyclic electron flow andthermal dissipation during high light treatment. First, we constructed and successfullyobtained the thermal dissipation mutant Δocp, cyclic electron flow mutant ΔndhS/pgr5,and their double mutant ΔndhS/pgr5/ocp by using molecular biology method. Next,we observe the growth phenotypes of these mutants under high light conditions. Ourresults indicated that absence of OCP did not influence the growth but impairment ofcyclic electron flow resulted in a slow growth phenotype; this slow growth phenotypewas significantly strengthened in their double mutants when compared with thewild-type (WT). Finally, we analyzed the relationship of cyclic electron flow andthermal dissipation. Absence of thermial dissipation protein OCP did not affect theactivity of cyclic electron flow and absence of cyclic electron flow did not alsoinfluence the expression and activity of OCP. In cyanobacteria, therefore, cyclic electron flow and thermal dissipation mechanisms work independently, but absence ofthermal dissipation protein OCP resulted in a more high-light-sensitive growthphenotype in cyclic electron flow-impaired mutant of Synechocystis sp. PCC6803.This will help in understanding the relationship of various photoprotectivemechanisms under high light conditions.