title: Kinetic analyses of state transitions of the cyanobacterium Synechococcus sp. PCC 7002 and its mutant strains impaired in electron transport.
abstract: The state transitions of the cyanobacterium Synechococcus sp. PCC 7002 and of three mutant strains, which were impaired in PsaE-dependent cyclic electron transport (psaE(-)), respiratory electron transport (ndhF(-)) and both activities (psaE(-)ndhF(-)), were analyzed. Dark incubation of the wild type and psaE(-) cells led to a transition to state 2, while the ndhF(-) strains remained in state 1 after dark incubation. The ndhF(-) cells adapted to state 2 when the cells were incubated under anaerobic conditions or in the presence of potassium cyanide; these results suggest that the ndhF(-) cells were inefficient in performing state 1 to state 2 transitions in the dark unless cytochrome oxidase activity was inhibited. In the state 2 to state 1 transition of wild-type cells induced by light in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), there was still a significant reduction of the interphotosystem electron carriers by both respiration and cyclic electron flow around PSI. Kinetic analysis of the state 2 to state 1 transition shows that, in the absence of PSII activity, the relative contribution to the reduced state of the interphotosystem electron carriers by respiratory and cyclic electron transfer is about 72% and 28%, respectively. The state 2 to state 1 transition was prevented by the cytochrome b(6)f inhibitor 2,5-dibromo-3-methyl-6-isopropylbenzoquinone (DBMIB). On the other hand, the state 1 to state 2 transition was induced by DBMIB with half times of approximately 8 s in all strains. The externally added electron acceptor 2,5-dimethyl-benzoquinone (DMBQ) induced a state 2 to state 1 transition in the dark and this transition could be prevented by DBMIB. The light-induced oxidation of P700 showed that approximately 50% of PSI could be excited by 630-nm light absorbed by phycobilisomes (PBS) under state 2 conditions. P700 oxidation measurements with light absorbed by PBS also showed that the dark-induced state 1 to state 2 transition occurred in wild-type cells but not in the ndhF(-) cells. The possible mechanism for sensing an imbalanced light regime in cyanobacterial state transitions is discussed.
authors.affiliation: State Key Labaratory of Protein and Plant Genetic Engineering, College of Life Sciences, Peking University, Beijing 100871, China.
authors.forename: Chenhui
authors.initials: C
authors.lastname: Huang
authors.forename: Xiaolin
authors.initials: X
authors.lastname: Yuan
authors.forename: Jindong
authors.initials: J
authors.lastname: Zhao
authors.forename: Donald A
authors.initials: DA
authors.lastname: Bryant
mesh_terms: D001426:Bacterial Proteins; D002734:Chlorophyll / Q000502:physiology; D000458:Cyanobacteria / Q000235:genetics / Q000502:physiology*; D004579:Electron Transport / Q000235:genetics / Q000502:physiology; D007700:Kinetics; D009154:Mutation; D009245:NADH Dehydrogenase / Q000235:genetics / Q000502:physiology*; D013050:Spectrometry, Fluorescence
chemical_list: D001426:Bacterial Proteins; D002734:Chlorophyll; C001785:chlorophyll P 700; C081468:NdhF protein, bacteria; D009245:NADH Dehydrogenase