Abstract
Ferredoxin (Fd): NADPH oxidoreductase (FNR) catalyzes reduction of NADP+, in the final step of linear photosynthetic electron transport, and is also implicated in cyclic electron flow. We have identified leaf FNR isoenzymes in maize (ZmLFNR1, ZmLFNR2, ZmLFNR3) and Arabidopsis (AtLFNR1, AtLFNR2). They are differentially localized between the thylakoid membrane and stroma, particularly in maize, where ZmLFNR3 is exclusively soluble, ZmLFNR1 is only found at the thylakoid membrane and ZmLFNR2 has a dual distribution. Thylakoidal isozymes are found to associate with the cyt b6f complex. Although Fd reduction ability of LFNR isoenzymes showed no significant difference, their Fd interactions, which depend on specific salt bridges, vary in a pH dependent manner, indicating that photosynthetic status may determine the ratio of electron flux through different isoenzymes. We are currently characterizing Arabidopsis plants lacking AtLFNR1. These combined results are discussed in terms of the effect of functional differentiation of LFNRs on electron partitioning.
