Hrvoje FULGOSI Resolving electron partitioning in oxygenic

In photosynthesis, final electron transfer from ferredoxin (Fd) to NADP+ is accomplished by the flavo enzyme ferredoxin:NADP+ oxidoreductase (FNR). FNR is recruited to thylakoid membranes via recently discovered integral membrane thylakoid rodanase-like protein TROL. I will address the fate of electrons downstream of photosystem I (PSI) when TROL is absent. We have employed electron paramagnetic resonance (EPR) to quantify free radical formation and electron partitioning in TROL-depleted chloroplasts. Trol plants grown in different light regimes and measured in both dark and light conditions, consistently exhibited diminished O2¯-accumulation. Propagation of other oxygen radicals was elevated in trol plants in all tested conditions, except for the plants adapted to high-light. These findings implicate that in the absence of the specific FNR membrane attachment, photogenerated electrons do not preferentially spill over to O2, as it could be expected from the present models of photosynthetic electron transport, or the O2¯ is efficiently scavenged.

We can conclude that TROL-mediated sequestration of FNR to thylakoid membranes is important for electron partitioning between electron-conserving and -dissipating pathways of photosynthesis.