“…In this respect, at least three hypotheses have been formulated: (1) the inhibition of hydrogenase by O 2 produced by water photolysis (Ghirardi et al, 1997;Cohen et al, 2005), (2) the competition between ferredoxin-NADP + oxidoreductase (FNR) and hydrogenase activity for reduced FDX (Yacoby et al, 2011), and (3) the inhibition of electron supply to hydrogenases by the proton gradient generated by another AEF, the cyclic electron flow around PSI (PSI-CEF; Tolleter et al, 2011). First described by Arnon (1955), PSI-CEF consists in a reinjection of electrons from reduced FDX or NADPH pool in the plastoquinone (PQ) pool.…”