Abstract
Respiratory and photosynthetic electron transports share plastoquinone (PQ) pool in cyanobacteria, and PQ pool is either reduced by NADH dehydrogenase (NDH) complex or by photosystem II. Here we analyzed the photosynthetic characteristics of the disruption mutant of ndhF1, a gene encoding a subunit of NDH complex, in order to reveal the effect of respiratory electron transport on photosynthesis. The effective quantum yield of photosynthetic electron transport in the ndhF1 disruptant of Synechocystis sp. PCC 6803 is higher than that in the wild type, when measured by PAM fluorometer under growth light condition (20μmol/m2/s). However, electron transfer rates determined by oxygen electrode under saturating light showed little difference between the two strains. Chlorophyll emission spectra determined at 77 K revealed that the wild type was in state 2 in the dark while the ndhF1 mutant was fixed in state 1, which was canceled by the addition of KCN, an inhibitor of the terminal oxidase in respiratory chain. These results indicate that suppressed state transition due to more oxidized PQ pool is the cause of high photosynthetic quantum yield in the ndhF1 disruption mutant.
