Abstract
The regulation of the cyclic electron flow around photosystem I (PSI) was investigated in Arabidopsis using a transient increase in chlorophyll fluorescence after cessation of illumination. The fluorescence signal was absent in air in a mutant lacking the NAD(P)H dehydrogenase (NDH) complex (ndhM), indicating that the signal is due to plastoquinone (PQ) reduction by stromal reductants via the NDH complex. In this plant, the signal was detected in CO2-free air containing 2% O2, reflecting ferredoxin (Fd)-dependent electron donation around PSI, which is redundant with NDH-dependent PQ reduction. The post-illumination fluorescence increase was enhanced in a mutant impaired in plastid fructose-1,6-bisphosphate aldolase activity. We showed that the main route for the PSI cyclic electron flow shifts from the NDH-dependent path to the Fd-dependent path in response to sink limitation of linear electron flow.
