AUTHOR=Gain Gwenaëlle , Berne Nicolas , Feller Tom , Godaux Damien , Cenci Ugo , Cardol Pierre 

TITLE=Induction of photosynthesis under anoxic condition in Thalassiosira pseudonana and Euglena gracilis: interactions between fermentation and photosynthesis

JOURNAL=Frontiers in Plant Science

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2023.1186926

DOI=10.3389/fpls.2023.1186926

ISSN=1664-462X

ABSTRACT=<sec><title>Introduction</title><p>In their natural environment, microalgae can be transiently exposed to hypoxic or anoxic environments. Whereas fermentative pathways and their interactions with photosynthesis are relatively well characterized in the green alga model <italic>Chlamydomonas reinhardtii</italic>, little information is available in other groups of photosynthetic micro-eukaryotes. In <italic>C. reinhardtii</italic> cyclic electron flow (CEF) around photosystem (PS) I, and light-dependent oxygen-sensitive hydrogenase activity both contribute to restoring photosynthetic linear electron flow (LEF) in anoxic conditions.</p></sec><sec><title>Methods</title><p>Here we analyzed photosynthetic electron transfer after incubation in dark anoxic conditions (up to 24 h) in two secondary microalgae: the marine diatom <italic>Thalassiosira pseudonana</italic> and the excavate <italic>Euglena gracilis</italic>.</p></sec><sec><title>Results</title><p>Both species showed sustained abilities to prevent over-reduction of photosynthetic electron carriers and to restore LEF. A high and transient CEF around PSI was also observed specifically in anoxic conditions at light onset in both species. In contrast, at variance with <italic>C. reinhardtii</italic>, no sustained hydrogenase activity was detected in anoxic conditions in both species.</p></sec><sec><title>Discussion</title><p>Altogether our results suggest that another fermentative pathway might contribute, along with CEF around PSI, to restore photosynthetic activity in anoxic conditions in <italic>E. gracilis</italic> and <italic>T. pseudonana</italic>. We discuss the possible implication of the dissimilatory nitrate reduction to ammonium (DNRA) in <italic>T. pseudonana</italic> and the wax ester fermentation in <italic>E. gracilis</italic>.</p></sec>