Model of possible interactions between linear and cyclic electron transport
pathways. Electrons flowing into a plastoquinone pool from Photosystem II reduce
cytochrome b6 f complexes in the appressed regions of the thylakoid membrane. These
flow via plastocyanin to PSI and from there to ferredoxin. Reduced ferredoxin can
reduce NADP, via FNR or can feed electrons to a plastoquinone pool in the stromal
lamellae via either a PGR5 dependent pathway or an NDH dependent pathway.
Reduced PQ then reduces cytochrome b6 f complexes in non-appressed membrane
regions. This in turn reduces plastocyanin and PSI. Plastoquinone in the stacked and
unstacked regions represent isolated pools due to restricted diffusion in the membrane.
Plastocyanin is able to move more or less freely in the thylakoid lumen and exists in
equilibrium with P700 and cytochrome f. Partitioning of electrons between linear and
cyclic pathways occurs at the step of ferredoxin oxidation only