![]() ![]() These effects indicate that acetic acid permeates through 4 membranes to acidify the thylakoid lumen and induce protonation of LHCSR3 and LHCSR1, the proteins responsible for low pH-sensing in the alga 17, 18, 19, 20, 21. This can be relevant because it has been shown that the addition of weak acids into a suspension of Chlamydomonas reinhardtii cell induces immediate, reversible non-photochemical quenching (NPQ) of chlorophyll fluorescence and a slower reduction of the plastoquinone (PQ) pool 16. ![]() Currently, how these metabolites affect photosynthesis is poorly understood. Under certain stress conditions, the concentration of those acids builds up in the medium to mM-range within an hour of hypoxia 8. Under anaerobic conditions, cells produce various weak acids, such as pyruvate, lactate, formic and acetic acid 15. In phylogenetically distant microalgae such as diatoms or Euglenas, metabolite exchange between aerobic pathways has also been shown 13, 14. Nonetheless, these metabolic processes are inevitably intertwined since their products can passively- and actively cross the cellular membranes 10.Īdditionally, a tight energetic coupling was found between chloroplasts and mitochondria in Chlamydomonas via a redistribution of reducing power 11, 12. The activity of the enzymes participating in the photosynthetic and respiratory metabolism is finely regulated and often separated not only in space but also in time 7, 9. In Chlamydomonas, photosynthesis and aerobic respiration occur in chloroplasts and mitochondria, respectively 7, while fermentation pathways could independently occur in the cytoplasm, mitochondria or chloroplasts 8. For Chlamydomonas reinhardtii ( Chlamydomonas throughout), a model soil-dwelling alga, fermentation has been demonstrated to be important for survival in the weak light environment in the morning and evening 3, 4, 5, and it has been proven to be the preferred metabolic process at night, even when oxygen is not limiting 6. While the former process harvests sunlight and stores its energy in the form of sugars, aerobic and anaerobic respiration (fermentation) oxidizes sugars releasing energy to meet metabolic requirements 1, 2. Photoautotrophic species rely on both photosynthesis and respiration. This likely allows algae to better cope with changing environmental conditions. Since we show that this effect is conserved across photosynthetic phyla, these results indicate that fermentation metabolites exert widespread feedback control over photosynthesis and aerobic respiration. ![]() Physiologically, we propose that under certain conditions, e.g., dim light at dawn, tuning down the photosynthetic light reaction could mitigate the pressure on its electron transport chains, while suppression of respiration could accelerate the net oxygen evolution, thus speeding up the recovery from hypoxia. This effect is mechanistically explained with an “ion trapping” model, in which the lipid bilayer selectively traps protons that effectively acidify subcellular compartments with smaller buffer capacities – such as the thylakoid lumen. Here we report that the weak acids produced during fermentation down-regulate both photosynthesis and aerobic respiration. These processes take place within one cell across several compartments, however it remains largely unexplored how they interact with one another. While photosynthesis transforms sunlight energy into sugar, aerobic and anaerobic respiration (fermentation) catabolizes sugars to fuel cellular activities. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |