Photosynthetic electrons transfer in Thalassiosira pseudonana in anoxic condition

Photosynthetic activity of Thalassiosira pseudonana in anoxic condition
Berne Nicolas, Pierre Cardol.
Diatoms are responsible for a large part of oceanic primary production. This ecological success suggests that they have developed a range of strategies to cope with various biotic and abiotic stress factors. In this respect, several diatoms can experience more or less prolonged periods in hypoxia or anoxia. In similar environmental conditions, several green algae express hydrogenase that is connected to photosynthesis and is able to oxidize reduced ferredoxin. Together with photosynthetic cyclic electron flow around PS1 (CEF), this hydrogenase allows the Calvin-Benson Cycle (CBB) reactivation by increasing the ATP/NADPH ratio (Godaux et al, 2015)
In this work, we show that in the centric diatom Thalassiosira pseudonana the availability of photosynthetic electron acceptors decreases during the two first hours of dark anoxic acclimation and reaches a steady state (up to 48h). The existence of some metabolic pathways that oxidized photosynthetic cofactors in anoxia is discussed in the light of the recent report on the putative presence of several fermentative pathways in T. pseudonana (Atteia et al, 2013). We also show that photosynthetic reactivation after prolonged periods of dark anoxic acclimation relies on high and transient CEF. This last result contrasts with the absence of high CEF in oxic condition in diatoms (Bailleul et al, 2015). Altogether our results point to peculiar regulatory mechanisms (CEF and fermentation) that might contribute to sustain photosynthetic capacity in diatoms in hypoxic / anoxic environments.
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Atteia A, et al, 2013. Biochim Biophys Acta - Bioenerg 1827: 210–223